Determination of Some Elastic Constants of Materials Using Impact Analysis

Materials with increased stiffness and lesser weight are widely used in aerospace, automotive and other manufacturing industries. Nondestructive testing (NDT) is used to identify elastic characteristics of materials such as Young's modulus and stiffness. NDT is popular due to its several advantages over destructive testing methods. This paper presents an algorithm for determination of elastic constants using Thomson multi-tapered periodogram. A Thomson multi-tapered periodogram is used to estimate the fundamental frequency of the material under consideration. The experimental set up comprises of mechanical assembly for free ball impact testing along with data acquisition hardware. The impact induced vibration signal obtained is preprocessed and power spectral density is obtained using Thomson multi-tapered periodogram to estimate the fundamental frequency of the material. Elastic constants as Young's modulus and stiffness are determined using the estimated fundamental frequency of the test specimen. The experimental results are validated using finite element method technique (ANSYS). The experimentation is carried out for two different materials stainless steel SA 240 Gr 304 and copper with varying test conditions such as change in weight of the ball, change in release height of the ball and change area of plate. The Average percentage error in estimating the fundamental frequency for SS is observed to be 1.72% and 3.86% or copper. Average percentage error for computing Young's modulus of SS is observed to be 2.62% and 7.75% for copper. The experimental analysis shows that the proposed technique is robust to noise. The proposed method has been successfully used to obtain some elastic constants.