Analysis of laminates with ply drops

• Published in: Composites science and technology Vol. 61; no. 5; pp. 749 - 758
• Main Authors: Vidyashankar, B.R., Krishna Murty, A.V.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-04-2001; Elsevier
• Subjects: A. Polymer-matrix composites (PMCs); Applied sciences; B. Strength; C. Finite element analysis (FEA); C. Laminates; C. Stress transfer; Exact sciences and technology; Forms of application and semi-finished materials; Laminates; Polymer industry, paints, wood; Technology of polymers; A. Polymer-matrix composites (PMCs); B. Strength; C. Stress transfer; C. Finite element analysis (FEA); C. Laminates; Laminate; Mechanical model; Fiber reinforced material; Mechanical properties; Theoretical study; Polymer; Tensile property; Modeling; Composite material; Finite element method; Variable section; Three dimensional model; Stress distribution; Size effect; Fiber orientation
• ISSN: 0266-3538; 1879-1050
• DOI: 10.1016/S0266-3538(01)00010-0

Thickness tapered laminates obtained by terminating a certain number of plies contain resin-rich areas called ‘resin pockets’ near ply drops, where high stress concentrations exist. Study of the effects of ply drops and resin pockets on the tensile behaviour of tapered laminates considering certain important parameters like taper angle, the number of plies dropped, and the fiber orientation is reported here. Estimation of the tensile strength of tapered laminates necessitates accurate determination of the state of stress near the ply-drop region, which is, in general, three-dimensional (3-D) in nature. Recognising the fact that full 3-D finite-element analysis becomes computationally exorbitant, special layered 3-D finite-element analysis is carried out. Laminates with ply drops along only one direction are analysed to elicit the nature of the local bending effects occurring near the ply drops. Complete 3-D Tsai–Wu criterion considering all the six stress components is used to obtain a quick and comparative assessment of the tensile strength of these laminates. High stress concentration zones are identified and the effects of number of plies dropped at a station and resin pocket geometry are illustrated. The mechanism of load transfer near ply drops and the local bending that occurs are described. Susceptibility of ply drop zones to the onset and subsequent growth of delaminations is also brought out.