For the development of sophisticated digital (e.g., Finite-Element-models like CASIMIR) or physical (e.g.,ASPECT-Dummy) models of the mechanisms of human-seat-interaction it is very important to know the shape of the contact surface between the human buttocks and back and the seat cushion and backrest, respectively. Currently, these surfaces are usually determined by purely experimental procedures, that require complicated and expensive measuring equipment.
This paper presents an alternative hybrid approach of standard experimental investigations of the pressure distributions between human body and seat (cushion and backrest) and proceeding numerical simulations with the Finite-Element-Method (FEM).
Pressure distributions are measured with standard measuring equipment for individual persons or defined percentile groups. Due to the simplicity of these measurements, they can be performed for a larger number of individuals at low cost.
The results of these measurements - the pressure distributions on seat cushion and backrest - are then appropriately applied to a nonlinear FEM-model of the seat the measurements have been performed on. The material properties of the highly nonlinear foam materials are described by a hyperelastic material constitutive law, parameters of which have to be identified from material test data. This identification is performed by a special nonlinear gradient optimization procedure.
The result of the numerical simulation is the desired contact surface that results from the human gravity loading acting on the undeflected seat surface.
This method has been applied for the determination of deflected contact surfaces for different percentile groups, ranging from the 5th female to the 95th male percentile group.