Date of Award

6-2026

Degree Name

MS in Mechanical Engineering

Department/Program

Mechanical Engineering

College

College of Engineering

Advisor

Eltahry Elghandour

Advisor Department

Mechanical Engineering

Advisor College

College of Engineering

Abstract

Maximizing the shear modulus and strength, as well as predicting failure mode and location, when designing a stacking sequence of quasi-isotropic carbon fiber laminated plates is essential to predict stability, resistance to deformation, and overall stiffness of the structure. This research investigates the effect of the stacking sequence of quasi-isotropic laminated composite plate materials in accordance with ASTM D5379: Standard Test Method for Shear Properties of Composite Materials by the V-Notched Beam Method.

In this research, experimental testing and Finite Element Analysis (FEA) were first used on aluminum to validate the simulation process before applying it to composite materials. The Iosipescu shear test was simulated in Abaqus to evaluate the modulus of rigidity and strength trends. Strong agreement between the experimentally obtained modulus of rigidity of aluminum and the numerical FEA results confirmed the accuracy of the elastic region of the model. Once the experimental validation was successfully completed, the validated FEA model was then applied to various quasi-isotropic laminated carbon fiber composites with different stacking sequences and layup orientations.

Four different layups of quasi-isotropic laminated plates made from unidirectional carbon fiber were selected to analyze the impact of the number of ply orientations, as well as ply location in the stacking sequence, on in-plane laminate shear properties. Impact of stacking sequence was observed by holding the number of each ply orientation constant but changing the location of ply orientations within the laminate. In this research, this was done by alternating the location of four (4) 90°, four (4) 0°, and sixteen (16) ±45° plies for 3 different laminate stacking sequences. Also, changing the layup schedule requires the number of each ply orientation to change. An additional layup schedule with eight (8) ±45°, eight (8) 0°, and eight (8) 90° plies was also studied to analyze the impact of layup schedule on shear stiffness and strength.

These four configurations were fabricated and cured in an oven with the recommended curing cycle per the AX-6200 material datasheet. Five test articles of each configuration were cut to the dimensions of the test article described in ASTM D5379 with a waterjet. The test articles were experimentally tested for modulus of rigidity and failure mode using a shear fixture attachment on a tensile testing machine. These laminates were analyzed with Classical Laminate Plate Theory (CLPT), FEA, and experimental shear testing, in order to evaluate their elastic behavior within the shear fixture and identify potential failure trends.

Despite variability in the experimental results, agreement in trends between the MATLAB, FEA elastic and failure simulations, and experimental results suggested varying stacking sequence does not impact in-plane shear modulus and ultimate shear strength. The findings also suggested that varying layup schedule does impact in-plane shear modulus and ultimate shear strength. Another argument that can be made as result of this research is that the Iosipescu fixture is a valid in-plane shear measurement technique. The three laminates with varied stacking sequences experienced different failure modes. Also, the laminate analyzed with less ±45° plies was found to have a lower in-plane shear modulus and ultimate shear strength. Understanding shear modulus and strength as well as failure mode and location will help guide engineers when designing laminated structures. The learnings from this thesis will be the backbone of a new composite shear testing lab at Cal Poly SLO.

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