**5. Instrumentation**

**4. Accelerated tests**

2 0 1 0

**Table 2.** Range pair counting.

262 Contact and Fracture Mechanics

kilometers of the total life.

Component life testing is commonly designed to validate fatigue strength of a component based on a target customer usage and is based on loads acting on components. The measurement period is usually not long enough to be used directly in a test. The main target for extrapolated signals is based on time measurement restrictions and problems such as synchronicity, spikes, drifts observed on measurement devices. For this reason, the most representative road or proving ground is determined and that is extrapolated to reach the

**Figure 11.** Schematic spectrums versus components S-N curves: (a) constant amplitude, (b) variable amplitude.

**Range (Units) Cycle counts Events** 1.0 G-H,H-I 7 0.5 C-D 1.5 F-G, I-J,K-L 1.0 D-E,L-M 1.0 B-C,J-K 1.0 A-B,E-F

The advantages of finite element simulation are mainly in the early stages of design where the prototypes are not yet available, and also to improve its design without physical components. But also in this case, the loads for variable or spectrum as well as constant amplitude are developed to correlate with the accelerated tests. All the factors are evaluated in physical

The load measures are extrapolated to the requirement. These spectrums are evaluated to include all the behaviors, as is shown in **Figure 12**. Spectrum test is developed using different

tests, and the results are analyzed through statistical results.

**Figure 2** shows that the first point to acquire information is to install measurement devices on the component or in its vicinity, to obtain the responses of the components that induce stress. To obtain the most important information we install the measurement devices at the main stress points. To do this, it is necessary to perform a finite element simulation in order to get the point and the direction of the stresses. **Figure 14** shows the typical process used to perform this kind of simulation.

The components evaluated can be from different materials and built with different manufacturing process. In the next figure are shown instrumented components with a point selection from finite element evaluation [7]. Then to find the point and direction of the main stresses, components are instrumented with strain gauges. Its nominal resistance is 120 or 350 ohms. Higher resistance can be used for base material with low heat conductivity and higher voltage excitation than 10 Volts can be mainly used in environments with high electrical noise [18]. **Figure 15** shows chassis components instrumented, **Figure 15a** the rear subframe for a rigid axle, **Figure 15b** a front axle steering knuckle and **Figure 15c** a frontal axle track control arm.

**6. Case study**

control arm.

time length is 249.9 s.

The accelerated tests are developed to reduce the time and complexity of the test in order to have faster results. **Figure 16** shows a test stand to evaluate a frontal axle track control arm. The information collected from the strain gauges can be used to evaluate the component, perform a correlation with virtual or analytical tools and build a spectrum. In not all the cases, can we directly measure the microstrain to validate the virtual simulation. The acceleration can be used to validate the finite element model with experimental acceleration results. With this validation, the stresses are found in a virtual way and can be used to perform the real-life prediction [4]. In the next part, the process to develop an accelerated test is shown. The time history in **Figure 17** shows the raw data time history to evaluate a track control arm, its main characteristics is a range of 42,354 N, maximum value of 21,473.6 N and minimum value of −20,880.8 N and the

**Figure 15.** Instrumented components with strain gauges, (a) rear rigid axle subframe, (b) steering knuckle, and (c) track

Accelerated Fatigue Test in Mechanical Components http://dx.doi.org/10.5772/intechopen.72640 265

**Figure 14.** General procedure for simulation.

**Figure 15.** Instrumented components with strain gauges, (a) rear rigid axle subframe, (b) steering knuckle, and (c) track control arm.
