Analytical modification of the V-notched rail shear test apparatus for dynamic testing

Abstract

Dynamic testing is required in structural engineering applications to characterize material properties over a wide range of strain rates and temperatures. One of the major concerns to obtain accurate data during dynamic testing is the oscillations in the test apparatus. If the frequencies of the system were increased to a point where the acceptable bandwidth of measured signal is within the first natural frequency, accuracy of the measured data could be improved by minimizing the effects of fixture vibrations. Since frequency is directly proportional to stiffness and inversely proportional to mass, this work presents several cases where structural modifications were applied to the test fixture based on the stiffness and mass to increase the bandwidth. V-notched Rail Shear test apparatus is widely used for characterizing laminated composite materials because of its advantages over other shear test methods. Present work uses numerical modeling of test apparatus as it gives a flexibility to modify any component and to isolate the source of vibrations. With a series of structural modifications to the test fixture which are primarily based on either changing its stiffness or mass, the apparatus is analyzed for a range of loading rates. The results are later analyzed in the frequency domain and an increase in the bandwidth is observed. As discussed, significant increment was observed in one of the methods presented in this work which deals with a reduction in mass of the apparatus by half. An analysis to check the effect of fixture bending on the specimen loading was carried out and it was observed that the specimen was undergoing a combined loading effect at very high loading rates. This suggests the physical limitation of the test apparatus. Also, a simple demonstration of variations encountered in the test data, as a result of filtering data using low-pass and band-stop filters is also presented in this work.