Abstract
This paper studies the feasibility of improving structural performance of composites in the presence of stress concentrators. Matrix grading through local deposition of additive-enhanced matrices and fibre steering by varying fibrous architecture are examined independently and in combination on a glass-fibre triaxial braided composite subjected to open hole tensile test. Stiffened and toughened matrices were incorporated through precise point-wise injections of liquid reactive resin into dry preforms (Liquid Resin Printing). Fibre steering was implemented by varying the braiding angle along the length of the braided sleeve. It has been shown that these novel forms of architecture modification enable a significant improvement in composite strength through a variety of deformation mechanisms. This includes local stiffening of composite in the direct vicinity of the stress concentrator and damage accumulation away from the stress concentrators. The experimental observations are explained by using simple finite-element models.
Highlights
Grading material properties is known to enhance mechanical performance of components with stress concentration features
The study showed several ways to improve the strength of composites with stress concentration that can be applied in isolation and in combination
Increased strength was realised through matrix grading: local integration of stiff or tough matrices and by fibre steering: varying braid angle and preform density along the length of the sample
Summary
Grading material properties is known to enhance mechanical performance of components with stress concentration features. It is expected that the non-uniformly distributed micro- or nano-scale additives will affect stiffness and stress concentration in the matrix at the micro-scale This technique of combining matrices offers new opportunities for manipulating damage accumulation mechanisms. Wisnom and Hallett [14], provided important insights on these phenomena for conventional unidirectional prepreg-based laminates subjected to open hole tests They demonstrated that more extensive damage in the vicinity of a feature, such as delaminations, can sometimes have a strong positive effect on composite strength due to reducing stress concentration in the vicinity of the hole. This paper builds on a previous preliminary study [15], but extends the range of systems compared and develops the analysis of these architectures It presents manufacturing trials, explores the peculiarity of the matrix-graded and fibre-steered architectures, and provides insight into the deformation mechanisms occurring in the graded composites. We assess the feasibility of creating a more resilient material by altering properties in structurally critical locations
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