Steel and Composite Structures, Vol. 18, No. 6 (2015) 1465-1478 DOI: http://dx.doi.org/10.12989/scs.2015.18.6.1465 1465 Copyright © 2015 Techno-Press, Ltd. http://www.techno-press.org/?journal=scs&subpage=8 ISSN: 1229-9367 (Print), 1598-6233 (Online) Dynamic load concentration caused by a break in a Lamina with viscoelastic matrix Arash Reza 1 , Hamid M. Sedighi 2 and Mahdi Soleimani 3 1 Department of Mechanical Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran 2 Mechanical Engineering Department, Faculty of Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran 3 Department of Mechanical Engineering, Shoushtar Branch, Islamic Azad University, Shoushtar, Iran (Received July 21, 2014, Revised November 25, 2014, Accepted December 02, 2014) Abstract. The effect of cutting off fibers on transient load in a polymeric matrix composite lamina was studied in this paper. The behavior of fibers was considered to be linear elastic and the matrix behavior was considered to be linear viscoelastic. To model the viscoelastic behavior of matrix, a three parameter solid model was employed. To conduct this research, finite difference method was used. The governing equations were obtained using Shear-lag theory and were solved using boundary and initial conditions before and after the development of break. Using finite difference method, the governing integro-differential equations were developed and normal stress in the fibers is obtained. Particular attention is paid the dynamic overshoot resulting when the fibers are suddenly broken. Results show that considering viscoelastic properties of matrix causes a decrease in dynamic load concentration factor and an increase in static load concentration factor. Also with increases the number of broken fibers, trend of increasing load concentration factor decreases gradually. Furthermore, the overshoot of load in fibers adjacent to the break in a polymeric matrix with high transient time is lower than a matrix with lower transient time, but the load concentration factor in the matrix with high transient time is lower. Keywords: viscoelasticity; load concentration factor; transient stress; unidirectional lamina; finite difference method; break 1. Introduction Today, due to the widespread use of composite materials in different industries, having enough and accurate knowledge of how stress distributes in these materials is vital. When in a composite material one or more of the fibers get ruptured or a crack develops, the amount of load that these fibers carried before rupture, is transferred to adjacent fibers and results in normal stress concentration which is quite temporary. On the other hand, polymeric materials have a widespread application in industries as a composite materials matrix. Polymeric materials possess a significant viscoelastic property which results in many changes in their mechanical properties under the passage of time or rate of loading (Shaw and MacKnight 2005). Corresponding author, Assistant Professor, E-mail: arashreza@gmail.com