PSI - Issue 57

Andrew Halfpenny et al. / Procedia Structural Integrity 57 (2024) 718–730 Andrew Halfpenny / Structural Integrity Procedia 00 (2023) 000–000

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1.2.4. Simulation Computer simulation involves CAE (Computer Aided Engineering) analysis of systems, subsystems, or relevant components under test. It is often applied twice during the design process:

1. Simulation of the component as mounted in the qualification test fixture. 2. Simulation of the component as mounted in the final vehicle.

The first analysis supports the verification process and ensures the simulation is properly representative of the real component. Once verified, the simulation model may be integrated into the overall structural model to simulate the overall performance of the component in the real-world. In the automotive industry, this is know as the ‘body-in-white’ model.

2. Complementary simulation and qualification testing

In an e ffi cient design process, simulation and qualification testing are mutually complementary. This is not always true for historical qualification tests because many of these predate the introduction of simulation. However, it is relatively simple and cost-e ff ective to enhance a qualification test to incorporate the benefits of simulation. Only two enhancements are necessary:

1. Test instrumentation is added in order to verify the simulation results. 2. Tests must be continued to failure to verify the fatigue simulation.

The benefits of simulation and qualification testing are discussed next. 2.1. Benefits of simulation prior to physical testing

Firstly, simulation is used to determine the probability of passing the qualification test. It can estimate the expected safety margin and therefore facilitates optimisation to reduce cost and weight at the early stages of design. It can also help to justify confidence in the design prior to expensive prototype testing. Secondly, simulation is used to predict failure modes and locations. This is useful in identifying if the failure mode is obvious or subtle. Additional instrumentation may be required to detect subtle failures, whilst safety precautions may be required to protect people and equipment from the most catastrophic failure modes. It also allows early confirmation that the failure modes correlate with expectation based on previous experience, or that gained through a Failure Modes and E ff ects Analysis (FMEA). Finally, simulation also models the extent of any beneficial or detrimental e ff ects resulting from test simplifications. For example, a component that is vibrated simultaneously in three directions is often tested on a uniaxial shaker table where each direction is applied sequentially. This often leads to an underestimation of the damage on test. Simulation can therefore help to improve the test by suggesting it be extended slightly in each axis thereby more closely representing the target usage and failure mode without adding significant test complexity. 2.2. Benefits of simulation during physical testing Historically, many qualification tests were sparsely instrumented. With the advent of simulation it became bene ficial to enhance the value of the test by adding further instrumentation. Simulation is used to determine the optimal positioning of measurement transducers such as accelerometers, strain gauges, displacement transducers, and thermo couples, in order to better characterise performance. Additional instrumentation permits a detailed verification of the simulation to be made. The use of virtual trans ducers allows the simulated response to be compared directly with test data. Furthermore, additional simulation parameters may be obtained using measurements from the physical test. For example, modal analysis of test data are used to calculate accurate damping properties. The use of additional instru mentation, therefore, significantly enhances the value of a qualification test which leads to an overall reduction in costs as well as improving model verification.