GMN7152_2002

ENGINEERING STANDARDS

Material Specification Metals

GMN7152

Specification and Verification of Tensile and Fatigue Properties in Cast Components

© Copyright October 2001 General Motors Corporation All Rights Reserved

October 2001 Originating Department: North American Engineering Standards, Records and Documentation of 16

1 Scope 1.1 Description. This specification provides pro-cedures for (1) specifying tensile and fatigue prop-erties at designated control locations for aluminum and cast iron parts and (2) verifying that these properties exist as specified. Control locations may be in the part, from co-cast appendages, or from separately cast specimens. This specification may be used in drawings, CTS, VTS, statements of requirements, BOM/BOP/BOD, or other docu-ments.

1.1.1 This specification may also be used to pro-vide requirements for properties other than tensile and fatigue.

1.1.2 Except for Class 1 lot control, procedures specified herein are intended to audit capability of meeting mechanical property requirements.

1.2 Limitations 1.2.1 This specification neither requires nor pro-motes the usage of mechanical property specifica-tions. Further, this specification should not be used if mechanical property control is not needed.

1.2.2 This specification does not designate particu-lar property levels or control locations. These are to be chosen based upon the needs of the part and the availability of an adequate volume of material from which to prepare a test specimen.

1.2.3 This specification specifically applies to prop-erties measured in designated control locations for parts during manufacturing. Once parts have been subjected to environments known to affect me-chanical properties, including normal use, degradation of properties does not constitute an out-of-specification condition.

1.2.4 This specification does not supplant specifi-cations that define a given material and grades by minimum mechanical properties. Further, proper-ties specified for parts should not be derived solely from such specifications for material.

1.2.5 Warranty Disclaimer. Data submitted under this specification does not constitute any express or implied warranty, including without limitation any

warranty of merchantability or fitness for a particu-lar purpose.

1.2.6 General Disclaimer. Use of this specification does not imply that the designated control location represents any other region of the part.

1.2.7 Adherence to this specification does not ab-solve Supplier of the responsibility to provide ac-ceptable product.

2 References Note: Only the latest approved standards are ap-plicable unless otherwise specified.

2.1 Normative ASTM B557M ASTM E8M ASTM E21 ASTM E83 ASTM E466 ASTM E1012 ISO/IEC Guide 25 ISO/IEC Standard 17025 ISO 6892 QS 9000

2.2 GM GP-11 GP-12 GMW3001 GMW3059

2.3 Additional DCT-4627 (Delphi specification)

3 Requirements 3.1 Responsibilities 3.1.1 Supplier shall:

3.1.1.1 Quote parts against this specification with an expectation that, based on experience with similar castings and processes, mechanical prop-erty requirements will be met.

3.1.1.2 Bear all costs required to comply with re-quirements in this specification, including manufac-turing additional parts required for testing. Costs are not to be separately rebilled to Customer.

3.1.1.3 Obtain written agreement from Customer on any deviation from requirements in this specifi-cation.

GMN7152 GM ENGINEERING STANDARDS


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3.1.1.4 Provide qualified personnel to manage all operations obtaining, reporting and reacting to property data. This includes casting sufficient parts to provide required test specimens and ex-pediting long lead-time items such as fatigue test-ing.

3.1.1.5 Develop a process control plan containing procedures to satisfy requirements in this specifi-cation and a PFMEA showing response to insuffi-cient specified requirements.

3.1.1.6 Keep records on test data and statistical calculations available for inspection by Customer, and submit complete reports at required reporting periods.

3.1.1.7 Notify Customer when mechanical test results or statistical calculations fall below speci-fied requirements.

3.1.2 Customer shall:

3.1.2.1 Specify property levels for which a docu-mented need exists, and within the capability of the design of the part and the casting process chosen.

3.1.2.2 Establish lines of communication with Sup-plier on data reporting and notification. The default contact person for Customer is the Design-Responsible Engineer.

3.1.2.3 Designate sufficiently large control loca-tions to meet minimum sample size requirements.

3.2 Classes 3.2.1 One of four Classes in Table 1 is to be speci-fied.

3.2.2 Class 1 requires tensile testing prior to re-lease of individual lots plus statistical analysis of tensile and fatigue data to audit process capability.

3.2.3 Class 2 omits lot control, but requires statisti-cal analysis of tensile and fatigue data to audit process capability.

3.2.4 Class 3 requires statistical analysis to audit tensile property capability in production, omitting both lot control and fatigue studies.

3.2.5 Class 4 requires that tensile property data be submitted at PPAP, but no process auditing in production. Class 4 is particularly applicable to parts where component-level testing is to be used to audit material integrity.

3.3 Reporting Periods 3.3.1 Tables 2A-2D list required actions by report-ing period – properties to be measured, sampling frequency, sample count, and responses to results.

Table 1: Mechanical Property Control Classes Class Definition Examples*

1 For rigorous control of ten-sile and related properties, including fatigue.

Chassis components

2 For control of tensile and related properties, including fatigue, but without contain-ment.

Aluminum bedplates

3 For control of tensile and related properties, excluding fatigue and containment.

Aluminum engine blocks and heads

4

Where supplier qualification is needed, but long term property monitoring is not (may apply if component-level QC is done).

Miscellaneous

*Note: Application of this specification and its classes is not limited to the examples cited.

3.3.2 Prototype. Mechanical property tests are to be performed at prototype to establish capability of process and design in preparation for PPAP. - Lot control testing is required for all Class 1

parts. - Tensile and fatigue studies shall be made with

material, tooling and process representative of production.

- Compliance with property specifications is not required at prototype except for Class 1 tensile testing for lot control.

- By agreement from Customer, previously estab-lished data from similar parts in production may be submitted to comply with prototype testing requirements.

3.3.3 PPAP. Testing listed in Tables 2A-2D applies to the initial PPAP submission. Mechanical properties are not required to be documented in subsequent PPAP submissions for replicate tooling. However: - Following significant process change Customer

has discretion to require additional PPAP sub-missions of mechanical property data.

- All specifications must be met for PPAP submis-sions.

3.3.4 GP-12. Initial production data is sampled at a greater rate than in later production.

3.3.5 Regular Production. In production, a small number of samples are to be taken on a weekly basis (lot-by-lot for Class 1) and reported semi-annually.

GM ENGINEERING STANDARDS GMN7152


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Table 2A: Test Requirements for Class 1 Table 2B: Test Requirements for Class 2

Reporting Period Property

Sample Count/ Sampling Frequency

Data Interpretation & Required

Actions Reporting

Period Property Sample Count/

Sampling Frequency

Data Interpretation & Required

Actions

UTS, YS & % EL

Greater of 1 sample/10 pcs, or 1 sample/lot. One 15-sample tensile study.

UTS, YS & % EL

1 sample/25 pcs. One 15-sample tensile study

GP-11

Prototype (Note 1-2)

Fatigue Strength

One 30-sample Fatigue/SC study

Tensile lot control mins. must be met. Report fatigue data to Cus-tomer.

GP-11


Fatigue Strength

One 30-sample Fatigue/SC study

Report data to Customer

UTS, YS & % EL

One 30-sample tensile property study

UTS, YS & % EL

One 30-sample tensile property study PPAP

(Note 3) Fatigue Strength

One 30-sample Fatigue/OP study

PPAP submissions must meet both min. and statistical specs.

PPAP (Note 3)

Fatigue Strength

One 30-sample fatigue strength study


UTS, YS & % EL

Greater of 1 sample/500 pcs, or 2 samples/lot

UTS, YS & % EL

Greater of 1 sample/1000 pcs, or 2 samples/wk GP-12

Fatigue Strength

Fatigue/OP: 4 samples/mo

GP-12

Fatigue Strength 4 samples /mo

UTS, YS & % EL

Greater of 1 sample/1000 pcs, or 1 sample/lot

UTS, YS & % EL

Greater of 1 sample/5000 pcs, or 1 sample /wk

Regular Production

Fatigue Strength

Fatigue/OP: 2 samples/mo

Semi-annual reporting. Tensile lot control mins. Must be met. If statistical specs are not met monthly, initiate notification procedure

Regular Production

Fatigue Strength

Fatigue/SC: 2 samples /mo

Semi-annual reporting. If statistical specs are not met monthly, initiate notification procedure

Notes: 1. Parts sampled for tensile and fatigue studies are to be made with tooling and process representative of production. 2. By agreement from Customer, for prototype: (a) multiple specimens may be taken from the designated control location in the same

part, (b) data available from similar parts already in production may be used to establish prototype capability. 3. Initial PPAP only. In tooling undergoing PPAP, the 30 samples should be distributed among each available cavity.

3.4 Test Methods 3.4.1 Coding for each property is listed in Table 3 along with standards covering permissible test methods.

3.4.1.1 Requirements in this specification take precedence over Normative and Additional stan-dards referenced herein.

3.4.2 Elongation 3.4.2.1 Where specified minimum elongation is ≤ 3.0%, elongation shall be determined by the extensometer method per ASTM B557M with an extensometer of ASTM E83, Class B2 or better. (see also Appendix A: Definitions.)

3.4.2.2 Where specified minimum elongation > 3.0%, the gage mark method may be used, pro-vided:

- Supplier’s laboratory demonstrates acceptable correlation between results of the extensometer and gage mark methods, per Appendix B.

- Each operator is qualified for each reporting period.

- A spring-loaded fixture (e.g. per ASTM B557M) is used to clamp the specimen halves together prior to measuring the gage length after test.

3.4.2.3 Gage length for elongation measurement shall not be changed after PPAP.



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Table 2C: Test Requirements for Class 3 Table 2D: Test Requirements for Class 4

Reporting Period Property

Sample Count/ Sampling Frequency

Data Interpretation& Required

Actions Reporting

Period PropertySample Count/

Sampling Frequency

Data Interpretation& Required

Actions GP-11


UTS, YS & % EL



GP-11


UTS, YS & % EL



PPAP (Note 3)

UTS, YS & % EL



PPAP (Note 3)

UTS, YS & % EL



GP-12 UTS, YS & % EL

Greater of 1 sample/1000 pcs, or 2 samples/wk

GP-12 UTS, YS & % EL NA

Regular Production

UTS, YS & % EL

Greater of 1 sample/5000 pcs, or 1 sample/wk

Semi-annual reporting. If specs are not met monthly, initi-ate notification procedure

Regular Production

UTS, YS & % EL NA

Not required

Notes: 1. Parts sampled for tensile and fatigue studies are to be made with tooling and process representative of production. 2. By agreement from Customer, for prototype: (a) multiple specimens may be taken from the designated control location in the same

part, (b) data available from similar parts already in production may be used to establish prototype capability. 3. Initial PPAP only. In tooling undergoing PPAP, the 30 samples should be distributed among each available cavity. 3.4.2.4 Deviations from these requirements must be approved by Customer. 3.4.3 Fatigue Strength (Classes 1 and 2)

3.4.3.1 Fatigue strength should be specified at 1E7 cycles and under load ratio R=-1 (fully-reversed loading). Alternative conditions may be specified at discretion of Customer.

3.4.3.2 Conduct fatigue tests under uniaxial, sinu-soidal loading. Procedures for staircase (Fa-tigue/SC) and overstress probe (Fatigue/OP) test-ing are listed in Appendices C and D.

3.4.3.3 For Class 1, prototype-level fatigue strength is to be determined by the staircase method (Fatigue/SC).

3.4.4 Other Mechanical Properties. This specifi-cation may be used to establish requirements for mechanical properties other than tensile and fa-tigue per the following requirements:

- The property name must be noted in the material specification callout along with a reference to a national or international test standard. Any op-tions allowed by the test standard, including

specimen geometry, must be noted under Ex-ceptions.

- For properties other than tensile and fatigue, only Class 3 or 4 may be specified.

- A separate callout may be used to designate a Class that is different from other mechanical property requirements.

- Testing and reporting requirements are to follow those for tensile testing in the specified Class, see Tables 2C and 2D.

3.5 Statistical Basis. Three (3) statistical meth-ods that may be used to quantify requirements are listed in Table 4.

3.5.1 Minimum (Min) requires that all tensile test results be greater than the specified property level, except those subject to retest and replacement testing per 3.8. Min is used as follows:

- For Class 1, specifying a lot control minimum for each tensile property listed.

- For all Classes, specifying minimum tensile elongation.



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Table 3: Properties for Specification, Codes and Test Methods

Property Code Method Applicable Standards

Ultimate Tensile Strength

UTS

Yield Strength (Note 1)

YS

% Elongation (Note 2) % EL

Tensile Test

ASTM E8M ASTM B557M ISO 6892

Fatigue/ SC

Staircase test

GMN7152, Ap-pendix C

ASTM E466 Fatigue Strength (Note 3)

Fatigue/ OP

Overstress probe test (Note 4)

GMN7152, Ap-pendix D

ASTM E466

Elevated Temperature Tests(Note 5)

NA General procedure ASTM E21

Notes: 1. Use 0.2% offset method. 2. See text for requirements for determining elongation. 3. Must specify desired fatigue strength and cycle count. 4. The overstress probe test results in a stress-time percent

parameter, see Appendix D. 5. Follow procedures in ASTM E21 for elevated temperature

testing where applicable.

Table 4: Choices for Statistical Basis

Statistical Basis Code Class Requirements

Minimum Min 1 - 4

Test results shall be equal or exceed listed value, except those subject to retest or replace-ment

Mean – 3 Sigma – 3 Sigma 2 - 4

Weibull B1 B1 1

Must be calculated with at least 30 samples. Cus-tomer must be notified if the calcu-lated value does not meet the part spec.

3.5.2 Mean minus 3 sigma (−3 Sigma) is the result of a calculation from a body of data. This statisti-cal basis is used as follows:

- For Class 2, specifying required fatigue strength.

- For Classes 2-4, specifying required UTS and YS.

3.5.3 Weibull B1 is the result of a calculation from a body of data. It is used as follows:

- To specify required statistical minimums for UTS and YS in Class 1.

- To specify the statistical minimum for the re-quired 100% STP result from the Overstress Probe Test in Class 1. A complete explanation of this test is given in Appendix D.

3.6 Frequency of Testing and Data Analysis

3.6.1 Samples may be accumulated and tested in intervals not exceeding a calendar month, except as follows:

- Timing shall be respected for GP-11, PPAP, and GP-12 data reporting periods.

- For Class 1, tensile properties shall be deter-mined on a lot-by-lot basis, prior to shipment.

3.6.2 Statistical property data (− 3 Sigma and B1) shall be recalculated and compared to the specifi-cation at least monthly using a minimum of 30 test results for each required property.

3.6.2.1 If more than 30 results are available, use all data accumulated during the reporting period.

3.6.2.2 If less than 30 tests have been executed in a reporting period, augment the sample count to 30 with the latest results from the previous period with the following exception:

- Data from prototype and any PPAP submission shall be calculated separately.

3.6.2.3 Fatigue data obtained during production will often span more than one reporting period. When this occurs add the results of the monthly fatigue tests to the body of data. If more than 30 test results have accumulated, omit the oldest data.

3.7 Acceptability of Properties, Lot Control 3.7.1 Class 1. Tensile properties are to be used for lot control. Statistical properties (B1) for tensile and fatigue are to be used to monitor process ca-pability.

3.7.1.1 Tensile testing is required prior to shipment of each lot. If specified lot control minimums are not met, subject to retest or replacement testing, the lot shall be rejected or reworked.

3.7.1.2 Statistical properties for tensile and fatigue are to be monitored. If statistical property require-ments are not met, Customer is to be notified; parts are not to be segregated or recalled except by discretion of Customer.



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3.7.1.3 Classes 2, 3, and 4. Properties (including both minimum and statistical) are to be monitored. If property requirements are not met, Customer is to be notified; parts are not to be segregated or recalled except by discretion of Customer.

3.8 Retests and Replacement Tests1

3.8.1 When a test result fails to meet a specified minimum, retesting may be permitted per 3.8.3. If a discrepancy occurs with a test, a replacement test may be permitted per 3.8.4.

3.8.1.1 A complete explanation of retests and re-placement tests shall be summarized in each peri-odic report.

3.8.2 Excluded Data. Statistical calculations may exclude results subject to retest or replacement.

3.8.3 Retests. If one or more specimens fail to conform to specified minimum (Min) property lev-els, retests will be permitted under the following conditions:

- Retesting for each specimen that failed, at least two additional specimens from the same desig-nated control location in either the original part (if sufficient material remains), or from other parts from the same lot.

- For Class 1, if any retest fails, the lot is subject to rejection or rework.

- For Class 2-4, if any retest fails, Customer is to be notified per procedures herein.

3.8.3.3 Limitation. Retesting of otherwise valid tests, for the purpose of inflating results of statisti-cal calculations, is prohibited.

3.8.4 Replacement Tests. A test specimen may be discarded and a replacement specimen se-lected from the same lot of material in any of the following situations:

- The specimen was poorly machined.

- The test procedure was incorrect or the test equipment malfunctioned.

- Either the fracture or necking occurred outside the gage length, and the elongation was below the specified value.

- If the specimen failed at a discontinuity that is not present in parts that pass quality control pro-cedures in the process control plan.

1Requirements for retests and replacement tests herein are based on those from ASTM B557M.

3.8.4.1 For separately cast test specimens, pre-existing cracks exhibited in the fracture are grounds for selecting replacement test specimens.

3.8.4.2 For test specimens excised from parts, however, discontinuities revealed in the fracture that are indicative of inferior material, such as cracks, ruptures, flakes, and porosity, are not rea-sons for a replacement test.2

3.9 Designated Control Location 3.9.1 Data submitted under this specification shall be derived from specimens excised from a desig-nated control location noted on the part print.

3.9.1.1 Class 1. A general area may be desig-nated where specified properties are to be met. Supplier is responsible for specified properties throughout the designated area.

3.9.1.2 Classes 2, 3, and 4. A region in the part for extraction of mechanical test specimens should be precisely specified, allowing for sample size and machining stock.

3.9.2 More than one control location may be des-ignated for a part, each having different property requirements.

3.9.3 The control location is not limited to the part itself. Co-cast or separately cast specimens may be designated under the following condition:

- Separately cast specimens must be processed concurrently with associated lots.

3.9.4 The control location is to be processed by the same foundry and post-casting practices (e.g., shakeout time, heat treatment) that affect me-chanical properties throughout the part or the re-gion of the part it represents. Exceptions agree-able to Customer shall be noted on the part print under Exceptions.

3.9.5 Mechanical properties are to be determined per Tables 2A-2D for each control location speci-fied.

3.10 Specimen Requirements 3.10.1 Specimen geometry is specified in the stan-dards listed in Table 3. The minimum diameter or thickness of test specimens is to be 6 mm. 2Note that this specification is intended to audit material properties in parts (not material per se), as affected by part design and casting parameters.



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3.10.1.1 Tensile Specimens - Round bars are recommended. Flat bars may

be used in thin sections with approval from Cus-tomer.

- Gage length to diameter ratio may be either 4:1 or 5:1.

3.10.1.2 Fatigue Specimens. Round bars having straight (cylindrical) gage length nominally 2 x diameter are recommended.

3.10.2 Specimen geometry, including gage length, shall not be changed after PPAP without agree-ment by Customer.

3.10.3 Parts scrapped for reasons that do not af-fect mechanical properties may be used to furnish test specimens, provided this is documented on the test report.

3.10.4 For aluminum parts in the F or T4 tempers, or after any other thermal processing known to produce an unstable structure, samples should be tested within two weeks after production. How-ever, storage time under refrigeration (<0°C) does not count toward elapsed time. Any variation from this requirement shall be noted on the test report.

3.11 Data Report Requirements. Mechanical property data determined per 3.6 shall be summa-rized and reported to Customer semi-annually. Required elements for complete report are as fol-lows:

- Summary of mechanical test results in a format after the form in Appendix E, including notice of any scrap parts used and why they were scrapped, and summarized explanations for re-tests and replacement tests.

- Tabular or graphical listing of results of individual tests in chronological order.

- A record of machining and testing sources, with specimen sizes noted (plus drawing if non-standard).

- A statement summarizing any deviations and exceptions agreed to by Customer.

- Process control plan containing procedures to satisfy requirements in this specification and PFMEA showing response to insufficient proper-ties.

- If applicable, current reporting period results of correlation study made between gage mark ver-sus extensometer measurement of % EL.

3.12 Notification Procedure 3.12.1 Customer is to be notified immediately if results of mechanical tests or statistical data fail to meet the specification for parts that have been shipped or where shipment is pending. However:

- Notification is not required if retests or replace-ment tests per 3.8 are successful.

- Notification is not necessary for parts that are scrapped or otherwise rejected.

3.12.2 After initial notification a report should be assembled including:

- Test data or statistical data that fail to meet the specification, along with historical data from pe-riods when the specification was successfully met.

- Documentation of the number of parts affected, the time period they were produced and identify-ing markings to that effect.

- Reaction plan including increased sampling and root-cause investigation.

3.13 Lab Certification. All testing to generate data against this specification shall be performed in laboratories accredited to either ISO/IEC Stan-dard 17025 (successor to ISO/IEC Guide 25:1990), QS 9000, or one of their successors.

3.14 Deviations and Exceptions 3.14.1 Deviations and exceptions to requirements stated herein are permissible if explicitly agreed to in writing by Customer.

3.14.2 Deviations and exceptions may be noted, at the discretion of Customer, on the part specifica-tion per Figure 1 and Section 7.

4 Manufacturing Process Not applicable

5 Rules and Regulations 5.1 Rules and Regulations for Material Specifi-cations. All materials supplied to this specification must comply with the requirements of GMW3001, Rules and Regulations for Material Specifica-tions. 5.2 Restricted and Reportable Substances for Parts. All materials supplied to this specification must comply with the requirements of GMW3059, Restricted and Reportable Substances for Parts.



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6 Approved Sources Not applicable

7 Coding System 7.1 This material specification shall be referenced in drawings, CTS, VTS, statements of require-

ments, BOM/BOP/BOD, or other documents in the format given in Figure 1.

8 Release and Revisions 8.1 Release. This material specification was origi-nated in March 2001 and was approved by the GMNA Casting Specialist Team in August 2001. It was first published in December 2001.

Figure 1. Coding system to be used on drawings or other documents (choose one)

Mechanical properties per GMN7152 – Class 1: Mechanical properties per GMN7152 – Class 2: UTS: ___ MPa B1, ___ MPa Min UTS: ___ MPa –3Sigma YS: ___ MPa B1, ___ MPa Min YS: ___ MPa –3Sigma %EL: ___ % Min %EL: ___ % Min Fatigue/OP: ___ MPa, 100% STP B1 Fatigue/SC: ___ MPa –3Sigma Test conditions: ___°C, 1E7 cycles, R = –1 Test conditions: ___°C, 1E7 cycles, R = –1 Control location: _______________________ Control location: _______________________ Exceptions: _______________________ Exceptions: _______________________ Mechanical properties per GMN7152 – Class 3: Mechanical properties per GMN7152 – Class 4: UTS: ___ MPa –3Sigma UTS: ___ MPa –3Sigma YS: ___ MPa –3Sigma YS: ___ MPa –3Sigma %EL: ___ % Min %EL: ___ % Min Test conditions: ___°C Test conditions: ___°C Control location: _______________________ Control location: _______________________ Exceptions: _______________________ Exceptions: _______________________ Notes: 1. Replace blanks by specific part requirements (property value, test temperature, control location, exceptions). 2. Class 1: Include a specified minimum for lot control of tensile properties. The statistical basis for Fatigue/OP refers to results of STP calculations, per Appendix D. 3. CUSTOMER may designate alternative fatigue cycles-to-failure and load ratio (R). 4. It is not mandatory to use all properties listed. Omit any not specified. 5. Properties other than tensile and fatigue may be specified. Use Class 3 or 4, write out the property name plus required prop-

erty level, and detail test method under “Exceptions”.



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Appendix A: Definitions 3 Sigma: A statistic calculated as mean minus three times the standard deviation. Coded as –3 Sigma.

Co-cast: Pertaining to material appended to a casting that will be removed for the purpose of providing a test specimen.

Customer: The organization responsible for specifying and receiving production or service parts from Supplier.

Deviation and Exception: Any alteration to re-quirements herein.

Elongation: Mechanical property describing ten-sile ductility at break. This specification follows ASTM E557M which defines elongation as plastic elongation at fracture, excluding the elastic portion of the total elongation at break. Note that elastic elongation at fracture is equal to 100% x [stress at fracture]/[elastic modulus].

Extensometer Method: This refers to the calcula-tion of percent tensile elongation from the stress vs. strain results of a tensile test.

Gage Mark Method: This refers to calculation of percent tensile elongation from the increase in the distance between gage marks applied to a speci-men prior to test.

Lot: A group of parts processed together repre-senting a short series of casting heats and a single heat treatment batch or, in the case of continuous furnaces, a group of racks or baskets quenched together.

Minimum Specification: Requires individual test results to be greater than or equal to a specified value. Coded as Min.

Overstress Probe Fatigue Test: A fatigue testing strategy that results in a stress time percent (STP) parameter representing cumulative cycles suc-cessfully tested in a series of increasing stress amplitudes. See Appendix D. Coded as Fa-tigue/OP.

Particular Property Level: A specification listing predetermined values to be applied to a particular part or family of parts.

PFMEA: Process Failure Mode Effects Analysis, whereby likely scenarios of failures in the process are investigated.

Recall: Logistical process whereby selected parts are segregated from parts already delivered to a customer and physically removed. (Here customer may be downstream from the entity referred to herein as Customer.)

Root-Cause Investigation: Actions taken to di-agnose an out-of-specification condition.

Segregate: Physical separation of one series of parts from others.

Staircase Fatigue Test: A fatigue testing strategy that results in estimates for mean and standard deviation of the fatigue strength. See Appendix C. Coded as Fatigue/SC.

Statistical Specification: A specification requir-ing calculated statistics based on a plurality of individual test results.

Supplier: Providers of production or service parts to Customer.

Temper: In ferrous alloys, an intermediate-temperature heat treatment applied after harden-ing. In cast non-ferrous alloys, a series of heat treatments (a special case is the F temper for as-cast or as-fabricated).

Thermal History: Time exposure of the part to temperatures, both intentional and unintentional, during processing and use.

Unstable Structure: A condition whereby the microstructure of a part is subject to change due to exposure to thermal conditions in its intended envi-ronment.

Weibull B1: A statistical specification based on the Weibull distribution representing a property value that 99% of test results would exceed. Coded as B1.



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Appendix B: Correlation Study for Per-centage Elongation Between Exten-someter and Gage Mark Method B1 Scope. This section describes (1) a procedure for correlating results of extensometer and gage mark methods for measuring tensile elongation, and (2) whether the difference between the two methods is acceptably small.

B2 Description. Percentage elongation is most accurately measured by an extensometer. The gage mark method tends to yield a larger result, 0.5 - 2% (absolute) greater than that of the exten-someter method. The extensometer should con-form to ASTM E83, Class B2 or better.

B3 Test Procedure. The following correlation study shall be conducted whenever any supplier adopts the gage mark method of elongation meas-urement.

B3.1 Pretest. Prior to testing the original gage length must be marked and measured.

B3.1.1 Use a fine mark or scriber line to identify each end of the original gage length. Do not use notches or center punches, which can result in premature fracture. In order to render the fine scribe line more easily visible, a dye bluing film may be applied to the test piece before marking.

B3.1.2 For the correlation study, the extensometer gage length must be equal to the original scribed gage length. The original gage length should be measured to an accuracy of ± 0.05 mm by each operator to be qualified.

B3.2 Extensometer Method B3.2.1 Place the extensometer on the specimen, with its knife-edges at the gage marks. Leave the extensometer on the specimen during the tensile test until the specimen fractures. Follow similar procedures for non-contact extensometers.

B3.2.2 The total elongation at fracture consists of elastic elongation plus plastic elongation. It is necessary to subtract the elastic elongation from the total elongation to obtain the percent elonga-tion (which is the value measured by the gage mark method). Use the following formula:

−=moduluselastic

stress breaking100%n%elongatio totalEL%

B3.2.3 In addition, examine the load vs. extension curve. If the gage slips during testing, the data must be discarded and a replacement test per-formed.

B3.2.4 Report elongation by the extensometer method to the nearest 0.1%.

B3.3 Gage Mark Method B3.3.1 The same specimen from the extensometer method is to be used for the correlation study. To reduce bias, the operator should not have prior knowledge of the elongation value reported by the extensometer method.

B3.3.2 Each operator should have individually measured the gage length of each specimen be-fore testing. Each operator should repeat this for the final gage length.

B3.3.3 When measuring the final gage length spe-cial precautions must be taken to ensure proper contact between the broken halves of the test specimen.

- First, remove any partially torn fragments that might influence the final measurement from the broken ends of the specimen.

- Place the halves in a fixture that holds them together with an axial force applied by means of a spring-loaded screw. The force should be suf-ficient to hold the pieces together firmly without crushing the fracture surface.

B3.3.4 Measure the final gage length to the near-est ± 0.05 mm. To improve accuracy in measure-ment, a measuring microscope or other suitable instrument should be used. Report the gage mark elongation to the nearest 0.1%.

B3.4 Correlation Study - Use ten specimens

- For manual elongation measurement, all opera-tors seeking qualification are to individually measure each specimen before and after test.

- Calculate gage mark elongation for each combi-nation of specimen and operator.

- For each sample record the differences between the extensometer result and elongation results from each of the operators, heretofore known as the Differences.

- Calculate mean and standard deviation of Differ-ences for each operator and for the combination of all operators.

B4 Report B4.1 Summarize data from the correlation study.

B4.2 Acceptability standard - Mean of Differences less than 1.0% for each

operator.



October 2001 of 16

- Standard deviation of Differences must be less than 0.40% for each operator and for all opera-tors.

B4.2.1 If the above two tests are not met, then the gage mark method may not be used to measure elongation except by express agreement from Customer.

B5 Limitations. This procedure must be repeated using recently tested specimens for each data reporting period, whenever new mechanical testing operators are added, and whenever the mechani-cal testing system is recalibrated.



of 16 October 2001

Appendix C: Procedure for Staircase Testing for Fatigue Strength (Fatigue/SC) C1 Scope. This section describes how to conduct a load-controlled staircase fatigue test and how to analyze the results.

C2 Description. The load-controlled staircase fatigue (SC) test is a convenient algorithm for es-timating mean and standard deviation of fatigue strength at a given number of cycles-to-failure. While convenient and easily understandable, the test suffers the following disadvantages: (1) it is insensitive to bimodal distributions of stress ampli-tude vs. life1 and (2) it can be time consuming.

C3 Recommended Sample Size. Thirty-five (35) samples (30 for test, 5 for setup)

C4 Recommended Test Equipment (1) Servo-hydraulic, uniaxial test machine,

equipped to control and measure loads to within 1.0% in the range needed for the mate-rial tested and the test frequency used, and also to stop the test when the specimen breaks2.

(2) Gripping mechanism to hold specimen, aligned per ASTM E1012. Collet grips are recom-mended as they align more reliably and re-quire smaller specimen ends.

(3) Heating device capable of heating entire gage section of specimen to targeted temperature ±3°C with a maximum temperature gradient of 5°C across the specimen. Measures must be taken to overcome the tendency for grips to act as heat sinks.

C5 Test Conditions. Use a fully reversed (R = -1), sinusoidal waveform in load control unless other-wise specified.

C6 Test Procedure C6.1 Unless otherwise noted, procedures shall follow ASTM E466.

1 A bimodal distribution of stress amplitude versus life may occur in the presence of two equally likely crack initiation mechanisms exhibiting different probability functions for stress amplitude vs. cycles to failure.

2 It is particularly advantageous if the ends of the speci-men are not crushed together after the specimen breaks. An unmarred fracture surface can reveal important in-formation about fracture mechanisms.

C6.2 A series of tests are run during which the stress amplitude for each test depends on the stress amplitude of the preceding test, and whether the preceding test resulted in a failure (complete separation) or a runout. The cycles-to-failure should already be noted on the part specifi-cation. A common number is 107 cycles, which permits testing at the rate of about one sample/day at 120 Hz.

C6.3 Choose step size: The step size should be approximately the fatigue strength standard devia-tion. Since this is rarely known in advance, make the choice based on previous experience. Take into account that a step size too small results in poor estimation of the mean, and one too large, poor estimation of standard deviation. A step size of 5 – 10% of anticipated fatigue strength is com-monly chosen.

C6.4 Choose the initial stress amplitude. This should be three standard deviations (-20 MPa for aluminum) above the part print minimum.

C6.5 Begin preliminary testing using an inflated step size. This economizes on specimens while searching for the first turnaround (individual test that breaks a succession of failures or runouts). An initial step size of 1.5 – 2 times the final step size is common for preliminary tests.

C6.6 At the first turnaround, record the stress am-plitude as the first data point, adjust the step size, and test 29 additional samples. Samples from runouts are not to be reused.

C6.7 After each individual test, mark the position of the specimen while it is still in the test machine, remove the specimen, and then record both the clock position of the crack initiation point and where the sample broke along its length. Crack initiation at a preferential clock position or failure outside the gage length may indicate load column misalignment.

C6.8 Whenever any sample has broken in the shoulder, disregard the result and retest. (This indicates a misalignment of the load column or excessive grip pressure.)

C7 Calculations C7.1 Refer to the example in Figure C1 and Table C1. Compute the mean and standard deviation of fatigue strength using the lesser (in number) of the runout or failure results.



October 2001 of 16

C7.2 Use the following formulas1:

+∑+= b

niN doS mean strength Fatigue i

Fatigue strength standard deviation = 1.62·d(C + 0.029)

( )22

ii2

n

iNNin C ∑ ∑−⋅

=

(C ≥ 0.30 for valid standard deviation)

Where: So = lowest stress level

d = step size

Ni = number of runouts or failures (which- ever is lower) at each stress level i

i = 0 for lowest stress level, 1 for next highest, etc.

n = total number of runouts or failures

b = +½ for runouts and –½ for failures

C = convergence factor

C7.3 The example test began using a setup step size of 7 MPa. After the first turnaround, the step size was decreased to 3.5 MPa and a total of 30 specimens were tested. Relevant data are enu-merated in Table C1. C7.3.1 Results Fatigue strength mean =

55.0 + 3.5(22/14 – ½) = 58.75 MPa

Convergence factor (C) =

[14(46) – (22)2]/(14)2 = 0.82 (OK)

Standard deviation =

1.62(3.5)(1.05 + 0.029) = 4.79 MPa

C7.4 If C < 0.3, a valid standard deviation cannot be calculated. This occurs when the step size is large enough that the test oscillates between fail-ures at one stress amplitude and runouts at an-other. C7.4.1 If this occurs an acceptable estimate for standard deviation is as follows:

Where: C < 0.30:

Fatigue strength standard deviation = 0.75 (step size)

1 Reference W. J. Dixon, A.M. Mood, J. Am. Statist. Assoc., vol. 43, p. 109 (1948).

Figure C1: Test Record for a Staircase Test

UTS01211(06/01)

48.0

51.5

55.0

58.5

62.0

65.5

69.0

72.5

76.0

79.5

83.0

-5 0 5 10 15 20 25 30

Initial stress increment: 7MPa (3 set-up tests)Stress increment: 3.5 MPaMean Fatigue Strength: 58.75 MPaStandard Deviation: 4.79 MPaConvergence Factor: 0.82

Failures

Runouts

Stre

ss A

mpl

itude

, MPa

Test Number

Table C1: Calculations for Staircase Data Stress i Ni iNi i2Ni

65.5 3 2 6 18

62.0 2 6 12 24

58.5 1 4 4 4

55.0 0 2 0 0

Failures N= 14 ΣiNI = 22 Σi2NI = 46

C8 Production Procedure. To determine the fatigue strength during production for Class 2, use the following procedure:

C8.1 Initially, four samples per month will be avail-able (GP-12 sampling rate).

C8.2 Start at an initial stress amplitude equal to the previously determined average fatigue strength.

C8.3 Do not calculate results for the first month. Notify Customer if all four test results are failures.

C8.4 Make the first calculation of average, stan-dard deviation and –3 Sigma the second month after eight total tests have been run.

C8.5 Continue to recalculate average, standard deviation, and –3 Sigma each month, adding addi-tional test results per the required sampling plan.

C8.6 After 30 test results are available, replace the earliest results with the newest results and con-tinue thereafter to perform calculations based on the latest 30 samples.

C8.7 Track individual test results, plus calculations of average, standard deviation, and –3 Sigma val-ues on a run chart.



of 16 October 2001

Appendix D: Procedure for Overstress Probe Testing for Fatigue Strength (Fatigue/OP) D1 Scope. This section describes how to conduct load-controlled overstress probe testing and how to analyze the results.

D2 Description. The overstress probe test results in a calculated parameter consisting of cumulative cycles at a succession of stress amplitudes, nor-malized at the specified fatigue strength and cycle count. While this test uses individual samples efficiently, it suffers from the following disadvan-tages:

(1) It does not determine the actual average fa-tigue strength.

(2) It may be inappropriate for certain steels that cyclically strain harden.1

D3 Recommended Sample Size. 30 samples.

D4 Recommended Test Equipment (1) Servo-hydraulic, uniaxial test machine

equipped to control and measure loads to within 1.0% in the range needed for the mate-rial tested and the test frequency used, and also to stop the test when the specimen breaks.2

(2) Gripping mechanism to hold specimen, aligned per ASTM E1012. Collect grips are recom-mended as they align more reliably and re-quire smaller specimen ends.

(3) Heating device capable of heating entire gage section of specimen to targeted temperature ± 3°C with a maximum temperature gradient of 5°C across the specimen. Measures must be taken to overcome the tendency for grips to act as heat sinks.

D5 Load Conditions. Use a fully reversed (R = -1), sinusoidal waveform in load control unless otherwise specified.

D6 Test Procedure D6.1 Unless otherwise noted, procedures shall follow ASTM E466.

1 Progressive increases in stress amplitude can cause a material that cyclically strain hardens to exhibit transient increases in fatigue resistance. 2 It is particularly advantageous if the ends of the speci-men are not crushed together after the specimen breads. An unmarred fracture surface can reveal important in-formation about fracture mechanisms.

D6.2 A series of samples are tested, each starting at a stress amplitude equaling the specified fatigue strength then retested in successive tests at higher stress amplitudes increased in equal 10% incre-ments. The test for each sample ends when it fractures.

D6.3 The cycles-to-failure should already be noted on the part specification. A common specification is 107 cycles, which are accumulated in 23 h at 120 Hz.

D6.4 Test the first sample at a stress amplitude equal to the specified fatigue strength and for the specified number of cycles. If the sample does not fail, increase the load by 10% and run the same sample for an additional number of cycles equaling 10% of the original cycle count. Continue this until failure, which is defined as complete separation2.

D6.5 Test the remaining samples following the same procedure.

D6.6 Calculate for each sample:

STP = 100% [Cycle life]/[Specified cycle count]

Where: STP = stress time percent

Cycle life = cumulative cycles

Specified cycle count

= number of cycles specified

D6.7 In the following example, the specification calls out a fatigue strength of 70 MPa at 107 cy-cles.

D6.7.1 The record of one sample is enumerated in Table D1 showing that it ran out (i.e., it did not fail) after 107 cycles. It was then successively tested for 106 cycles (10% of the specified cycle count) in increasing stress amplitude increments of 7 MPa (10% of the specified fatigue strength). The sam-ple failed when it was tested at a stress amplitude of 133 MPa. It accumulated 1.8 x 107 cycles.

D6.7.2 Hence, for this sample:

STP = 100% [1.8 x 107]/[1.0 x 107] = 180%

D6.8 Individual STP results for each sample are then fitted to the Weibull distribution. Procedures to do this may be found in any statistics textbook. The statistical minimum (B1) of STP must be greater than 100%.



October 2001 of 16

Table D.1 – Test Record for an Overstress Probe Test

Stress Ampli-tude Cycles Cumulative

Cycles 70 MPa 1 x 107 1.0 x 107

77 MPa 1 x 106 1.1 x 107

84 MPa 1 x 106 1.2 x 107

91 MPa 1 x 106 1.3 x 107

98 MPa 1 x 106 1.4 x 107

105 MPa 1 x 106 1.5 x 107

112 MPa 1 x 106 1.6 x 107

119 MPa 1 x 106 1.7 x 107

126 MPa 1 x 106 1.8 x 107

133 MPa failure

D7 Production Procedure. To determine the STP during production of Class 1, use the follow-ing procedure:

D7.1 Initially, four samples per month will be avail-able (GP-12 sampling rate).

D7.2 Test the first four samples per procedures herein. D7.3 Do not calculate Weibull results the first month. Notify Customer if any test result is below 100% STP.

D7.4 Make the first calculation of Weibull B1 the second month after eight total tests have been run.

D7.5 Continue to recalculate the Weibull statistics each month, adding additional test results per the required sampling plan.

D7.6 After 30 test results are available, replace the earliest results with the newest results and con-tinue thereafter to perform calculations based on the latest 30 samples.

D7.7 Track individual STP and calculated B1 val-ues on a run chart.

D8 Remark. This procedure is derived from Del-phi specification DCT-4627 on mechanical prop-erty testing of cast aluminum steering knuckles.



of 16 October 2001

Appendix E: Mechanical Test Data Report

UTS01212(06/01)

Part

nam

e:

Part

num

ber:

Con

trol l

ocat

ion:

Des

ign

leve

l:Su

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Prop

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Indi

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dim

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ons:

Ten

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:

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Fat

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:

x

Nam

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willi

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form

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mak

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ous

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or r

epre

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ns h

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Prop

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Out

of s

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GMN7152_2002

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