Experimental Characterization of Internal Structure and Physical Properties of Unidirectional Ply‐Level Hybrid Carbon Composite Material

Abstract

The complexities associated with the response of carbon fiber composites to different loading cases and methods of improving it without increasing their cost are still being researched. Herein, by an experimental approach, the ply‐level hybridization technique for tailoring the composite response is explored, and two different types of unidirectional prepregs with the same fiber type but different quality and prices are mixed. The purpose of this study is to analyze the influence of this type of hybridization on the structure and mechanical response of carbon fiber composites and to assess the compromise between manufacturing cost reduction and mechanical response. Hybridization is obtained in both layer thickness and material quality and reference materials are also manufactured. The properties of the unidirectional hybrid and nonhybrid composites are evaluated by density and fiber volume fraction measurements. The in‐plane mechanical properties are determined using quasistatic tensile tests, in 0° and 90° directions. No thickness effects are noticed on the stress–strain response under both longitudinal and transverse directions and hybrid composites exhibit an improved 0° failure stress.

Damage assessment through cyclic load-unload tensile tests for ply-level hybrid carbon fiber composites

“…The HSC laminates were constructed with 3 and 4 plies and will be referred to as HSC3 and HSC4, respectively. The stacking sequence of the laminates is described in Table 1, and fiber volume fractions determined in previous work are provided as well [29]. Cross-section views of the described laminates are shown in Figure 1 [12].…”

“…Cross-section views of the described laminates are shown in Figure 1 [12]. The same laminates were used in previous studies [12,29], in which characterization of internal structure, physical properties, and on and offaxis quasi-static mechanical properties are provided.…”

“…All mechanical tests were carried out at ambient temperature (20 °C) using an electromechanical testing machine INSTRON ® 5960 (Instron, Norwood, Massachusetts, USA) with a load cell of 50 kN and controlled in displacement at 1 mm/min, giving an approximate strain rate of 10 -4 1/s. As in previous works [12,29], Digital image correlation (DIC) was used for strain measurements because it is a powerful optical technique that enables non-contact, full-field measurements [30][31][32]. GOM Aramis ® 5M package (GOM Metrology, Braunschweig, Germany) was used for DIC measurements, post-processing, and extraction of the strain values.…”

“…Different models used to predict the nonlinear behavior of unidirectional fiber reinforced composites loaded off-axis attribute the nonlinearity of the response either to plastic deformation of the matrix [17][18][19][20], to internal damage and stiffness reduction [21,22], or both [23][24][25][26][27][28]. Building upon the groundwork of prior studies [12,29], this research explores the origins of nonlinear behavior in off-axis tests for the studied unidirectional ply-level hybrid composite materials. In this regard, cyclic load-unload (LU) tests are performed, with the amplitude of the stress level increasing for each cycle.…”