Numerical and experimental investigation of an angle-ply laminate with a centre hole under tension load

Abstract

ABSTRACT The stress-strain fields for composite laminate [r 25] S4 containing a circular hole under uniform axial extension are investigated using numerical and experimental methods in this paper. The distributions of normal strain along the length direction around the hole on the specimen surface are measured using digital speckle correlation method (DSCM). Meanwhile, only the middle part of the laminate is taken into account to perform finite element (FE) analysis. For the side face of specimen, a tiny area (1.8mm u 2.4mm) over the hole is chosen to measure the normal strain and shear strain. The experimental results are in a good agreement with FE simulation. Additionally, the interlaminar stress analysis on the hole edge has been performed by FE method. Keywords: Angle-ply laminate, Hole, Stress-strain, Digital speckle correlation, Finite element analysis 1. INTRODUCTION Composite materials have been widely used in various engineering structures, mainly due to their attractive features, such as, high strength-to-weight and stiffness-to-weight ratios, low density, etc. PEEK (poly-ether-ether-ketone) is one of the best thermoplastic matrices for applications in composite structures. AS4/PEEK, a thermoplastic composite reinforced by graphite fibers, has an advantage over traditional thermosetting composite materials due to its excellent high temperature properties and damage tolerance and high impact toughness. Although its applications attract researches more attention to its mechan ical behaviors, there exist many problems which are not yet well understood. In practical applications, composite plates with cutouts and holes are required for various purposes, such as joining of riveted and bolted joints. However, notches existing in compos ite laminated plates generate stress concentrations, and the stress-strain relation is very complicated, resulting in progressive damage propagation [1]. It is, therefore, important to understand the structural response properties for notched composite plates. Jones R.M. had expounded this subject in his work [2]. But the previous studies were focused mostly on thermosetting composite materials [3]. Recently, more attention was paid to notched thermoplastic composites [4-6]. The researchers focused on th e mechanical performance of laminates under tensile and compressive loads respectively via the finite element analysis and experimental study, such as the strength, damage and fatigue failure of the laminate plates. Various optical experimental me thods have been used to measure the displacem ent, strain or stress around the notch in the composite laminates. Iarve E.V. et al . used moire interferometry to determine the strain and displacement fields in the surface layers of an open hole composite laminates [7]. Touchard-Lagattua F. and Lafarie-Frenot M.C. measured the strains around the hole in notched laminates based on the laser speckle pattern method [5]. Toubal L. et al. investigated the tensile strain field of a composites plate in the presence of a circular hole using electronic speckle pattern interferometer (ESPI) [8]. Ambu R. et al. adopted the strain maps around the hole obtained by digital image correlation method (DICM) to evaluate the damage progression near the stress riser [9]. The objective of this paper is to analyze the structural response properties for composite laminates with a centre hole under tension load. The strain fields for different regions on the surfaces of the laminate are measured using digital speckle correlation method. Additionally, a middle part of the laminate is used as finite element model to predict specimen response. The experimental data are compared with those computational results. This work will lay the foundation for the study of damage of thermoplastic composite in the presence of a hole.