Response of 3D woven composites under low velocity impact with different impactor geometries

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Abstract

This paper deals with experimental and numerical investigations into the impactor shape effects on the low velocity impact behavior of 3D woven composites. The samples were made of E-glass fibers and unsaturated polyester resin. Conical, hemispherical and flat-ended impactors were used. The damage modes and areas of the specimens are inspected using microscopic and optical images. The finite element package ABAQUS is used to simulate the impact event. The contact force, displacement and dissipated energy of different impactors are compared. A good agreement between experimental and numerical results is observed. The results show that the blunter impactors produce greater damage areas and threshold loads. However, the damage initiation time is not dependent to the impactor shape. Besides, the damage intensity of the composites is greatly influenced by the impactor shape and z-fibers volume fraction.

Introduction

Composite laminates have been widely used in structural applications in recent years. These applications include those that require light weight, high stiffness and strength such as aerospace manufacturing, civil engineering and automobile industries [1], [2], [3], [4]. Composite structures are usually subjected to impact loads in working conditions, such as collision of birds and hail stones to a plane wing or in manufacturing process like dropping tools on them [5], [6], [7], [8]. Thus, they are highly susceptible to impact damages, particularly delamination [9], [10], [11], [12]. 3D orthogonal woven composites (3DOWC) have specifically been used to resolve this weakness, as they enjoy fibers in thickness direction, called binder yarns, distinguishing them from 2D ones (see Fig. 1) [1], [13], [14], [15]. In fact, 3D woven composites consist of in-plane orthogonal weft and warp yarns that are perpendicular to out-of-plane z-fibers, making them strong against delamination [16], [17].

Impact response and damage modes of composite structures are affected by impactor shape. Since the majority of impact studies have concentrated on 2D composite structures, it is important to investigate the influence of the impactor shape on 3D woven composites under low velocity impact. In the following paragraph, a brief review concerned with the effects of impactor shape on impact response of 2D composites is provided to give the readers a feel for the necessity of such research on 3D composites.

Yao et al. [18], [19] methodically examined the impactor shape influence on the low-velocity impact behavior of fiber metal laminates (FMLs). They observed a great dependency of FLMs impact behavior on impactor shape and energy as well as metal layer distribution. Liu et al. [20] investigated the influence of the impactor shape and energy on the impact response of conventional composites. They found that damage modes of the specimens depended on the impactor parameters. Mitrevski et al. [21] studied the influence of impactor nose on the impact behavior of thin glass fiber reinforced polymer (GFRP) composites. They found that the maximum contact force increased as the impactor nose became blunter. Mahesh et al. [22] showed that the composite thickness and impactor shape have considerable influence on impact resistance of jute-epoxy laminates. Wen [23] presented analytical relations to calculate penetration and perforation of different impactors in fiber-reinforced plastic (FRP) laminates under high velocity impact. Ulven et al. [24] investigated the influence of impactor shape on the ballistic perforation of VARTM carbon/epoxy composite panels. They observed that the conical impactor had the highest ballistic limit, followed by the flat, hemispherical-ended ones. Kursun et al. [25] examined the effect of indenter shapes on the damage behavior of composite sandwich panels under low velocity impact. They observed that the flat impactor initiated the damage of the specimens sooner. There are also several studies on the effect of other impactor parameters like radius and contact surface. For example, Christoforou [26] presented a methodology for evaluating damage resistance of the composite structures under low-velocity impact. He concluded that when the amount of impact energy is constant, the nature of the impact response varies according to the characteristics of the impactor and the composite structure. Icten et al. [27] provided an exhaustive investigation about the effect of impactor diameter on the impact behavior of 2D woven glass-epoxy laminates. Fan et al. [28] scrutinized the effect of the impactor radius on the glass fiber reinforced metal laminates under low-velocity impact. They observed that when the impactor diameter increased, the energy required to puncture the plate became more. Ben-Dor et al. [29], [30] minimized the ballistic limit velocities by obtaining an optimum impactor shape, which was very similar to blunt conical impactor. The response of composites impacted by a specific impactor may vary based on fiber materials [31], [32], [33]. Myler and Farooq [34], [35], [36], [37] concluded that carbon fiber reinforced polymer (CFRP) composites have greater peak force, less contact duration and better indentation performance than GFRP ones. Besides, CFRP composites tend to fail at higher stresses but lower strains and undergo larger delamination [38], [39], [40], [41]. Using composites as the facesheets of a honeycomb core sandwich panel, He et al. [42] evaluated the effects of impact damage on their residual flexural strength considering various structural configurations and presented useful practical results. Elaldi et al. [43] studied the influence of impactor geometry on 2D woven composites and observed that the impactors with higher contact surfaces were less penetrative.

Overall, a lot of research that concerns with impact event has been performed on 2D woven composite structures. However, to the best of the authors' knowledge, there are only few studies in which the performance of the 3D composites under different impactor shapes is evaluated. There are strong grounds for considering this important. For one thing, the damage modes of 3D woven composites are remarkably affected by the impactor shape. Herein, we have focused on the effects of impactor shape and z-fiber volume fraction on the low velocity impact behavior of 3D woven composites by experimental and numerical methods.

Section snippets

Impact tests in composite structures

In this part, the manufacturing method of composite specimens and their specifications are described. In addition, the used drop-weight impact device is explained well.

Finite element method

ABAQUS software has been used to investigate the impact behavior of 3D woven composites numerically. The damage initiation is investigated on the basis of 3D Hashin orthotropic failure model as follows [49], [50], [51]:

for matrix tensile failure:(σy+σz)2YT2+(τyz2σyσz)Syz2+(τxy2τxz2)Sxy2=1 for matrix compressive failure:((YC2Syz)21)2(σy+σz)YC+(σy+σz)24Syz2+(τyz2σyσz)Syz2+(τxy2τxz2)Sxy2=1 for fiber tensile failure:(σxXT)2+(τxy2+τxz2)Sxy2=1 for fiber compressive failure:(σxXc)2=1 for

Results and discussion

Numerical and experimental studies have been performed to investigate the effect of impactor shape on the 3D woven composites with different volume fraction of z-fibers. The results are presented in three categories. The first part is related to the experimental and numerical results extracted from contact force-time, contact force-displacement and energy-time curves. The damage area is discussed in the second part using optical images taken from the specimens. Finally, the third part has to do

Conclusions

In the present study, the effects of the impactor shape on the low velocity impact behavior of 3D woven composites and their damage resistance have been investigated experimentally and numerically. The damage modes in the front and back surfaces of the impacted specimens have been analyzed using the observations from the stereomicroscope. The most important results of this study can be summarized as follows:

  • The sharper impactors produced lower damage threshold load. Nevertheless, the damage

Declaration of Competing Interest

The authors declare that they have no conflict of interest.

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