Deciding whether to do tensile or flexural fatigue testing for car parts depends on how the parts are used and what kind of problems they might have.

Think about how the parts are used: If they're mainly pulled or stretched, like in parts of the suspension, you'd want to do tensile testing. But if they're mostly bent or flexed, like in the frame of the car, flexural testing is better.

Also, consider how the parts might break: Tensile testing shows if the part might crack or break when pulled apart. Flexural testing shows if it might crack or break when bent.

And think about the shape and job of the part: If it's a weird shape or gets pulled and bent, you might need to do both tests to really understand how it holds up.

The results from each test show how the material reacts to different kinds of stress. Tensile testing shows how it handles being stretched, like when you pull on it. Flexural testing shows how it handles being bent, like when you bend a piece of metal.

So, whether you choose tensile or flexural testing depends on how the parts are used, what might go wrong with them, and what shape they are. Both tests help figure out if the materials are strong enough for making good car parts.

The attached article entitled "Carbon Fiber Reinforced Thermoplastics" has a section on long term mechanical properties that discusses fatigue that may be helpful.

Hi, there are three basic modes of mechanical deformation - tension, compression, and shear. A flexture is a complex mode consisting from a tension on one side, shear in the middle, and compression on the opposite side. Generally speaking, some micromechanical effects can only apply in specific modes, influencing the properties. For instance, a rope may be tough in tension, but it would be very plyable and collapse under compression. The testing of your part should reflect the loading conditions as close as possible. Also, its not uncommon to do more tests on the same material to see how it behaves in different situations.

Это зависит от того, каким видам деформациям будут подвержены данные детали, и самое важное какая их цикличность. В зависимости от этого и будут рассчитываться напряжения.