# random vibration Using ANSYS and fatigue calculation

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New Concept

Status Update 13th Sept 2012

*Objective & ApproachModal analysis

To Perform a Modal analysis to identify the significant modes and natural frequencies in X , Y and Z -directions affecting the vibrations

2. Random Analysis

To Perform a Random analysis to identify stress and amplitude levels in the geometry when subjected PSD based random input vibration in X , Y and Z - directions respectively. PSD random vibration input (Based on Danfoss Corporate Guideline 500B0432 curve A) will be provided at this stage.

3. Damage estimation analysis

To study the accumulated fatigue damage during a 2 hour testing in random vibration at the critical failure location. This is done using Miners three-band technique for cumulative damage.

ObjectiveApproach

To study stresses under the random vibration profile based on Danfoss Corporate Guideline 500B0432 curve A with base line design.13th Sept 2012

*Geometry , FE Model & AssumptionsModel is simplified as shown above.Only structurally important components which contribute to the stiffness of bottom flange is considered.Motor and all other components are modeled as a point mass.A damping value of 3% is considered in Random analysis.Two iterations need to perform with different material.In new concept design, mold residual stresses are not expected.13th Sept 2012

*Boundary conditions Fixed in all directions at the following locations(3 screw mountings)

Please confirm the boundary condition.13th Sept 2012

*Weight details and material propertiesIteration 1 (old Material - LEXAN 500R)13th Sept 2012

S.NO.COMPONENTUNITWEIGHT1Aluminum housingKg0.3682Aluminum ring cast into the Bottom flangeKg0.0263Motor cup Kg0.0164Aluminum frameKg0.0335Bottom flangeKg0.0846Point mass to represent other componentsKg1.373ICAD TOTAL WEIGHTKg1.896

S.NO.COMPONENTMATERIALDENSITYKg/mYOUNGS MODULUSPaPOISSONS RATIO1Aluminum componentsALUMINUM ALLOY27707.1E+100.332Bottom flangeLEXAN-500R (10% GR PC)12463.45E+090.37

Tensile Strength, yld, Type I, 5mm/min66MpaASTM D 638Tensile Strength, brk, Type I, 5mm/min55MpaASTM D 638

*Weight details and material propertiesIteration 2 (New Material - VALOX 420)13th Sept 2012

S.NO.COMPONENTUNITWEIGHT1Aluminum housingKg0.3682Aluminum ring cast into the Bottom flangeKg0.0263Motor cup Kg0.0164Aluminum frameKg0.0335Bottom flangeKg0.0986Point mass to represent other componentsKg1.373ICAD TOTAL WEIGHTKg1.915

S.NO.COMPONENTMATERIALDENSITYKg/mYOUNGS MODULUSPaPOISSONS RATIO1Aluminum componentsALUMINUM ALLOY27707.1E+100.332Bottom flangeVALOX 420 (30% GR PBT)15308.50E+090.37(assumed)

Tensile Strength, yld, Type I, 5mm/min145MpaASTM D 638Tensile Strength, brk, Type I, 5mm/min145MpaASTM D 638

*Fatigue data Of lexan-500Source : Sabic innovative plastics : PC resin product brochureFatigue properties were not available for 20%GF variant of lexan-500.Therefore, properties of Lexan resin 500 is used for these calculations.

13th Sept 2012

Cycles to failureAlternating stress (Mpa)6.4E+01671.6E+02626.4E+02561.1E+04424.3E+04359.2E+04323.4E+05258.4E+05211.2E+06192.5E+06165.1E+06129.3E+0610

Referance point(1)Referance point(2)Number of cycles to fail 6409.3E+06Alternating Stress 5610 Slope of fatigue line in log(X)- linear(Y) plot-11.05

*Vibration spec used for Random vibrationThe flange must pass the following vibration test: IEC 60068-2-64 and Danfoss Corporate Guideline 500B0432 curve A. Random vibration (PSD) specification Frequency range : 18 Hz 1000 Hz. Vibration level : 7,54g RMS. Duration time : 3 axes ( X,Y&Z) x 2 hours in each direction, The following points have been extracted from the graph using digitizer: 13th Sept 2012

Frequency (Hz)Power spectral density (g^2/Hz)180.2451500.0610000.04

*PSD Random vibration in X AxisResultsNotes:-The RMS (Root Mean Square) stress levels observed from the random vibration analysis is only a statistical measure of the random stress levels experienced by the assembly.RMS stress levels are equivalent to 1sigma deviation of stresses following a Gaussian distribution. It means that during 68.27% of the time, the stress levels seen in the assembly will fall in the range +1sigma to -1sigma.As a thumb rule, the structure has to be designed to withstand the 3-sigma cyclic stress which is the stress range observed during 99.73% of test duration.

13th Sept 2012

*Significant mode in X axis vibrationThe most prominent vibration mode in X direction is ~198 Hz90% mass participation was found @197.896 Hz.This will be the most excited mode in X-axis vibration.During 2 hours of testing, it will undergo ~ 1,424,851 cycles13th Sept 2012

*Stress PSD response during X-axis vibration measured near failure locationRandom response X direction loadingFrequencyThe most damaging vibration during X-axis excitation is occurring at approximately 198 HzStress PSD 13th Sept 2012

*3-sigma RMS Stress (Mpa) @ X-axis vibration Notes:-3-Sigma RMS stress of 36.1 MPa is observed at the failure location. This means that actual stress values observed will not cross this value during 99.7% of the random vibration duration.Since this value is less than tensile strength of its material (~55MPa), the component is considered safe against yield failure.Considering the low stress level, fatigue damage is also less likely to occur.13th Sept 2012

*PSD Random vibration in Y Axis13th Sept 2012

*The most prominent vibration mode in Y direction is ~201 Hz89% mass participation was found @201.576 Hz.This will be the most excited mode in y-axis vibration.During 2 hours of testing, it will undergo ~1,451,347 cyclesSignificant mode in Y axis vibration13th Sept 2012

*The most damaging vibration during Y-axis excitation is occurring at approximately 201 HzFrequency response Y direction loadingFrequencyStress PSD response during Y-axis vibration measured near failure locationStress PSD 13th Sept 2012

*3-sigma RMS Stress (Mpa) @ Y-axis vibration Notes:-3-Sigma RMS stress of 37.85 MPa is observed at the failure location. This means that actual stress values observed will not cross this value during 99.7% of the random vibration duration.Since this value is less than tensile strength of its material (~55MPa), the component is considered safe against yield failure.Considering the low stress level, fatigue damage is also less likely to occur.13th Sept 2012

*PSD Random vibration in Z Axis13th Sept 2012

*The most prominent vibration mode in Z direction is ~765 Hz94% mass participation was found @765.433 Hz.This will be the most excited mode in Z-axis vibration.During 2 hours of testing, it will undergo ~5,511,117cyclesSignificant mode in Z axis vibration13th Sept 2012

*Frequency response Z direction loadingFrequencyThe most damaging vibration during Z-axis excitation is occurring at approximately 764 HzStress PSD response during Z-axis vibration measured near failure locationStress PSD 13th Sept 2012

*3-sigma RMS Stress (Mpa) @ Z-axis vibration Notes:-3-Sigma RMS stress of 17.532 MPa is observed at the failure location. This means that actual stress values observed will not cross this value during 99.7% of the random vibration duration.Since this value is less than tensile strength of its material (~55MPa), the component is considered safe against yield failure.Considering the low stress level, fatigue damage is also less likely to occur.13th Sept 2012

*Action PlanMaximum stress are seen on single node that calls for mash refinement study.So next action plan is to perform mesh refinement near pick stresses location.13th Sept 2012

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