how to do automobile frame testing

Automobile frames are need to be evaluated against overall torsional stiffness. The test is performed on a test bench made from a foundation block characterized by a stiffness well above the values to be measured. On this block additional structures are installed to fix the frame properly.

Before testing, the interiors (dashboard, seats and side panels), complete power train (engine, transmission, exhaust pipe, etc.) bumpers and wheels are removed from a unitized frame. Suspensions are maintained, but springs and shock absorbers are exchanged with rigid spacers to freeze the geometry under investigation.

In bending tests, both axles are fixed, but one of them is capable of having longitudinal motion. 

In torsion tests, the rear axle is linked to the block while the front axle is linked to a torque application structure. Both links are restrained for any kind of longitudinal and transverse motion.

In bending tests, a vertical load is applied by an auxiliary beam to thecentre of the structure, while in torsion tests, a pure torque is applied to the front axle through an articulated frame. In both the cases, displacements are measured by linear transducers the vertical axis. For measuring deformation due to bending, one transducer is placed at the middle of the car and others are used to check the local deformation. In case of torsion, a pair of transducers is placed at upper pivot of each suspension.

Many linear sensors are applied along the primary side beams and lateral side beams to measure vertical displacements. In case of torsion, these sensors used to calculate the local rotation angle of the structure. These displacements are drawn on a graph with respect to x, the coordinate of the frame. Local variations of the slope of this curve, which can be detected through the first derivative diagram, highlights local critical areas or structural discontinuities caused by inaccurate welding or design mistakes.

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