PSI - Issue 28

Haibao Liu et al. / Procedia Structural Integrity 28 (2020) 106–115 Liu H et al./ Structural Integrity Procedia 00 (2020) 000–000

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Keywords: Composite laminates, low velocity impact, C-scan, delamination, failure analysis

1. Introduction Due to their high strength-to-weight ratio, fibre-reinforced composite materials have been widely used in the manufacture of structural components (Roeseler et al. 2009)(Liu et al. 2018a)(Tehrani et al. 2013). However, for a long time, their wider application in the primary load-carrying structures has been hindered by their relatively poor impact performance (Elder et al. 2004)(Liu et al. 2018b)(Donadon et al. 2008). Since, impact loading can lead to damage and strength reduction in a composite structure (Liu et al. 2018c)(Rivallant et al. 2014)(Eyer et al. 2017)(De Freitas and Reis 1998). To increase confidence in using composite materials in the latest generation of transport vehicles, which are lighter but stronger, a better understanding of the impact behaviour of composite materials is required by industry. With this in mind, considerable efforts have been made by both academia (Borg et al. 2004; Israr et al. 2014; Raimondo et al. 2012) and industry (González et al. 2012; Petit et al. 2007; Rivallant, Bouvet, and Hongkarnjanakul 2013) to study the impact performance of composites. For example, Hosseinzadeh et al. (Hosseinzadeh et al. 2006) have conducted a detailed experimental study to compare the impact behaviour of different composite laminates. In their research, four types of commercial laminates were designed and manufactured. In detail, they were a thin woven reinforced glass-fibre, a relatively thick woven reinforced glass-fibre, a non-woven reinforced carbon-fibre and a woven reinforced hybrid glass-/carbon-fibre composite laminate. Standard impact experiments were performed on these four types of composite laminates at three different energy levels. Subsequently, the damage zones in the composite were studied using ultrasonic inspection. The experimental results indicated that the carbon-fibre reinforced composite laminates gave the best structural behaviour when subjected to low-velocity impacts. Robinson and Davies (Robinson and Davies 1992) have conducted an experimental study on the effects of impactor mass and specimen geometry in the low-velocity impact of composite laminates. The damage extent in the composite specimens was assessed by visual inspection and by ultrasonic C scanning. The experimental results demonstrated that, for a given specimen size, damage in the composites was only related to the magnitude of the impact energy, not the impactor mass nor the impact velocity. In the present research, a detailed experimental study of the impact behaviour of composite laminates is conducted using T700/Epoxy CFRP composite panels, with a lay-up of [+45 3 /0 3 /-45 3 /0 3 ] s and which were manufactured using an autoclave. The composite specimens are subjected to drop-weight impact experiments. The specimen dimensions and experimental set-up described in ASTM 7136 standard (ASTM 2014) are adopted. During the experiments, a round nosed steel (RNS) impactor is employed to strike the composite specimens at two velocities (i.e. at 2.40 m.s -1 and at 4.16 m.s -1 ) to investigate the effects of the impact velocity. A flat-faced steel (FFS) impactor is also used to impact the composite specimens at a velocity of 2.40 mꞏs -1 to study the effects of impactor head-shape. Subsequently, all the tested specimens are examined using a C-scan device to evaluate the extent of impact damage.

2. Impactors and specimens 2.1. Impactors

In the present research, two types of impactors, the round-nosed steel (RNS) impactor and the flat-faced steel (FFS) impactor, were employed. Both of these impactors have a diameter of 16 mm. The round-nosed steel impactor and the flat-faced steel impactor were manufactured using stainless steel. Schematics of the two impactors are shown in Fig. 1.