Determination of viscoelastic material properties and impact force from measurements on impacted bodies

Sammanfattning: Methods are presented for identification of linear and nonlinear viscoelastic materials and for prediction of impact force on the basis of measurements made on impacted bodies. The complex modulus is identified from measured end-point accelerations of an impacted rod specimen, and in-situ from measured strains at three sections of a rod-like member of an impacted structure. The two methods for identification of complex modulus have been tested experimentally on two polymers, viz., polypropylene and polyamide 6, and results have been obtained in frequency ranges of up to two decades. Furthermore, the complex modulus of polyoximethylene has been determined during creep recovery by using the method based on acceleration measurements. Moreover, a method is proposed for identification of nonlinear viscoelastic materials on the basis of displacements measured at two sections of an impacted rod specimen. The displacements were measured by means of electro-optical displacement transducers. The first step of the method is model identification, i.e., choice of constitutive model. The second is parameter identification, i.e., determination of the parameters of the model chosen. The method has been applied to five polymers of interest in engineering, viz., polypropylene, polyamide 6, polyoximethylene, high density polyethylene, and 60 percent carbon-black filled natural rubber. Finally, a method is established which permits prediction of impact force history from the velocity response of each impacting body to an impulsive force applied to its impact face, and the impact velocity. It is assumed that the impacting bodies behave linearly. The method has been applied to several cases of impact between linearly elastic and linearly viscoelastic bodies. The predicted impact forces are compared to impact forces measured in impact tests. Generally, there is a good agreement.