PSI - Issue 19

Thorsten Voigt et al. / Procedia Structural Integrity 19 (2019) 4–11 Dr.-Ing. Thorsten Voigt / Structural Integrity Procedia 00 (2019) 000 – 000

8

5

0 100 200 300 400 500 600

Woehler curve AlSi7Mg (R=-1, RFS=60MPa, k=6) variable amplitudes test #5

= −0,36 = 0,45 #5 = 0,31

[MPa]

1,0E+03 Stress (double amplitude)

1,0E+04

1,0E+05

1,0E+06

1,0E+07

cycles (log)

= 8.91 MPa was determined. To evaluate the test results, the material Woehler curve for AlSi7Mg with the stress ratio = −1 was used. It has a slope of = 6 and a breaking point at a stress amplitude a = 60 MPa and = 5 ∙ 10 6 load cycles. For a com parison with the load program used (# 5), this must be transformed to the same stress ratio = −1 via the mean stress sensitivity = 0.45 of the material. A damage calculation with the thus determined collective yields the damage sum = 0.31 . This is a typical result for a damage sum in the range of = 0,1. . .1 for non-welded components in 80% of the cases (Eulitz and Kotte (1999)). The determined damage sum thus shows good agreement between the local fatigue strength and the parameters of the Woehler curve. The constant and variable amplitude tests show a uniform failure pattern under lateral loading, starting from the outside of the vehicle outer bearing eye of the control arm. The influence of a salt spray environment on the lifespan of the component can be specified by the factor 1.45 (load without salt / load with salt). The control arm is sufficiently dimensioned with regard to the lateral load requirements expected in customer use over 10 5 km . This applies both for use under normal atmospheric conditions and under environmental conditions. From the numerical stress analysis and the linear damage accumulation, it can be concluded that the material quality in the fracture region seems to be in a normal range for the considered aluminium alloy. Figure 8: control arm, FEM analysis Figure 9: comtrol arm, test validation with hot spot stress-analysis 3.5. Conclusion of the experiments Besides of partial component testing the interaction between control arm, spring-damper-system, wheel suspension and wheel should be investigated at the subsystem of a half rear axle (Figure 10). The tests should be examined under variable amplitude loading conditions similar to the service loads. As load signal again the synthetic load program STAMAS was applied, focusing on two load directions: lateral and vertical load, which are the ones with the biggest influence on damage for this subsystem. Those two channels were extracted from the four-channel STAMAS load program. Again 100 repetitions of the load sequences, corre sponding to 10 5 km were defined as target for the testing of the half axle. Three specimens were to be tested. For the endurance test at the half axle of the city car a two-channel test rig was designed (Figure 11). The test specimen is mounted to a quasi-stiff test-setup. The brake drum is attached to a wheel-replacement. The wheel-replacement itself carries a wheel force transducer to directly measure the loads which occur at the wheel hub. At the wheel replacement two attachment points are foreseen to attach the load introduction for each direction respectively. The forces are applied by servohydraulic cylinders in lateral and vertical direction via a traverse and two rods respectively. The elastomeric bearings of the control arm were replaced by plastic sleeves. This was done to ensure a free rotation of the control arms suspension and to reduce wear during the test run. 4. Testing of a half axle module 4.1. Objectives, load program and test setup

Figure 10: half axle tests, specimen

Figure 11: half axle tests, test setup

Figure 12: half axle tests, test rig