A seat strength test is decided by four things before the first Newton of load is applied: what each axis is set to, whether every axis has reached its preload, how the load is controlled, and what filter class the recorded data carries.
This article describes how the seat strength test system in our published product range is operated. It is not a test method: the method comes from the standard the test is being run to.
What the test has to establish
A seat system strength test loads the individual parts of a seat — frame, back, cushion, head restraint and the belt anchorage points on the seat or the body — and records how the structure responds. The number that matters is a force at a defined point, measured with a defined measuring chain.
Step 1 — set the test conditions axis by axis
Each hydraulic cylinder is controlled individually, so the load and the test conditions can be set per axis. That matters because a seat test is rarely a single push: several axes are loaded, each with its own target.
Step 2 — reach the preload on every axis
An initial load can be set for each test axis. The test load is applied only once every axis has reached its initial load. Loading one axis to its test force while another is still loose would load the specimen in a way the test method does not describe.
Step 3 — apply the test load
- Control mode: force control or displacement control.
- Hydraulic cylinders reach the preset force within 2 s, and travel at no less than 320 mm/s when unloaded.
- Under load control, the specified load can be reached in as little as 1 s.
- The load can be held for 0.2 s to 120 s, adjusted without steps.
Step 4 — record the data
The system samples at 1000 Hz and filters the recorded data to the CFC60 filter class of ISO 6487. The filter class belongs in the test report: a peak load is only comparable with another peak load when the channel bandwidth is the same.