Abstract
The effect of reinforcement phases on indentation resistance and damage behavior of glass/epoxy laminates was investigated in this research work. Woven glass fiber mat and nonwoven chopped glass fiber mat were used as fiber reinforcement phases for fabricating the laminates. Low‐velocity impact and quasi‐static indentation tests were performed on both laminates to investigate the contact behavior and energy‐absorbing capability. Moreover, the acoustic emission (AE) technique was employed to monitor the indentation damage resistance. AE parameters including normalized cumulative counts (NCC), normalized cumulative energy (NCE), rise angle (RA), and felicity ratio (FR) were analyzed. The bidirectional laminates showed premature load drops and drastic changes in the normalized cumulative counts/energy profile in the beginning of loading cycles, indicating the development of macrodamage such as debonding/delamination. AE sentry function results of bidirectional laminates show longer PII function at the earlier stages, associated with minor PIII function and greater PIV function, indicating the continuous degradation and progression of damage. In contrast, the chopped laminates exhibited superior postimpact performance than the bidirectional laminates. The presence of randomly oriented fibres prevents the delamination crack propagation during compression loading, which was attributed with the increased residual compressive strength.
Highlights
Due to their unique properties, such as high specific strength and modulus, better temperature resistance, corrosion resistance, tailorability, and stability, fiberreinforced polymer composite materials have been widely used in engineering applications such as aerospace, automobile, marine, and wind turbine industries
The damage caused by low-velocity impact (LVI) is identical to that caused by quasi-static indentation (QSI) loading, which was experimentally proved by Kumar et al [5] and Xiao et al [6]. ey concluded that loading speed had little effect on penetration energy
Load-Displacement Response. e typical force-displacement response of bidirectional and chopped glass/ epoxy laminates subjected to out-of-plane loading is shown in Figures 3(a) and 3(b)
Summary
Due to their unique properties, such as high specific strength and modulus, better temperature resistance, corrosion resistance, tailorability, and stability, fiberreinforced polymer composite materials have been widely used in engineering applications such as aerospace, automobile, marine, and wind turbine industries. Impact/indentation-induced damage in laminated composite structures can result in a significant reduction of structural strength [1]. Under LVI and QSI tests, several parameters such as peak force, incident energy, elastic energy, absorbed energy, and dent depth were used to evaluate impact- and indentation-induced damage. When a material deforms or fractures, transient elastic strain waves are produced inside the material, causing AE [11, 12] As a result, this approach may identify damage initiation and progression in composite laminates under loading in real time [13,14,15,16]. A few studies have used QSI loading with AE monitoring to simulate LVI behavior and evaluate damage initiation and progression [18]. The relationship between mechanical strain energy and AE energy was employed to better understand the damage progression and residual compressive strength
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