No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
A Progressive Failure Study of E-glass/Epoxy Composite in Case of Low Velocity Impact
Abstract
To predict the behavior of composites in case of low velocity impact, there are various material models available in literature. Either the complex implementation or determination of large number of required material parameters is proving a common major limitation among all these. In the present study, low velocity Impact experiments are performed on E-glass/epoxy composite and numerically simulated using a continuum damage mechanics based material model. The damage observed as back face signature on the laminate, contact forces and displacement plots with respect to time are studied and compared with FE results to demonstrate the effectiveness of the model. The digital image correlation (DIC) technique is used for experimentation to obtain displacement on the surface of the plate
ResearchGate has not been able to resolve any citations for this publication.
An investigation of the low velocity impact load level at which a composite laminate will delaminate is presented. The delamination threshold load is described as the load level, obtained from the load–time history or load–displacement plot, at which a sudden load drop occurs due to specimen stiffness loss as a result of laminate level damage. Approximately 500 low velocity impact load–time histories from the Air Force Research Laboratory (AFRL) Low Velocity Impact Database are used to investigate the delamination threshold load. The database contains laminate impact test data for graphite/epoxy (AS4/3501-6), graphite/PEEK (AS4/APC-2), and graphite/BMI (IM7/5260) material systems. The delamination threshold load observations are compared to C-scan damage measurements of impacted specimens to determine if the sudden load drop corresponds to delamination development.
Composites are used extensively in engineering applications. A constant concern is the effect of foreign object impacts on composite structures because significant damage can occur and yet be undetectable by visual inspection. Such impacts can range from the most ordinary at low velocity - a tool dropped on a product - to the hypervelocity impact of space debris on a spacecraft. This book explains how damage develops during impact, the effect of impact-induced damage on the mechanical behavior of structures, and methods of damage prediction and detection. Numerous examples are included to illustrate these topics. Written for graduate students, as well as researchers and practising engineers working with composite materials, this book presents state-of-the-art knowledge on impact dynamics while requiring only basic understanding of the mechanics of composite materials.
An original, ply-level, computationally efficient, three-dimensional (3D) composite damage model is presented in this paper, which is applicable to predicting the low velocity impact response of unidirectional (UD) PMC laminates. The proposed model is implemented into the Finite Element (FE) code ABAQUS/Explicit for one-integration point solid elements and validated against low velocity impact experimental results.Mesh-regularisation of the impact results is one of the greatest challenges in impact damage modelling of composite targets. Currently published mesh-regularisation strategies can produce mesh-size-independent impact results for a very limited range of mesh-sizes. The originality of the model presented in this paper is based on a novel mesh-regularisation strategy, which is applicable to predicting mesh-size-independent impact results for any target discretisation. Accurate modelling of composites’ impact damage using a relatively coarse mesh, and thus at a much reduced computational cost when compared to existing techniques, can be achieved with the proposed method.
The results of an experimental and analytical study of damage initiation in laminated composite plates subjected to low-speed impact are presented. Here, 8-, 16-, 24-, 32-, and 48-ply-thick quasi-isotropic and orthotropic graphite-epoxy and graphite-bismaleimide laminated plates have been impacted with dropped weights and the corresponding plate responses have been predicted analytically. Impact damage-initiation thresholds and damage-initiation mechanisms corresponding to a range of impact-energy levels are identified. Impact-damage initiation for the thicker plates occurs at both the impact site and the plate surface opposite to the impact site. Impact-damage initiation for the thinner plates is predominately due to tensile fracture on the plate surface opposite to the impact site. Three-dimensional stress states that correspond to the impact conditions that initiate damage are determined analytically to help identify damage-initiation mechanisms and to predict failure-initiation modes.
A realistic failure analysis of structural members made of FRP composites requires consideration of the non-linear stress/strain relationships. In laminate design and for determination of safety factors of FRP structural members, there is a strong need for fracture criteria and degradation models which are simple enough for application in common engineering problems while still being in good agreement with physical reality. It is essential to distinguish between fibre failure and inter-fibre failure by separate failure criteria. A recent success was the introduction of inter-fibre failure criteria which model the brittle failure behaviour of composites very realistically. These not only provide realistic stresses to failure, but also indicate the crack direction, which is an extremely important piece of information when evaluating the likely effect of fracture. After crack initiation, the stiffnesses of the affected plies degrade gradually with increasing load, until fibre fracture in one ply provokes ultimate failure of the laminate. Also, an inclined wedge-shaped inter-fibre crack can lead to ultimate failure. From now on, the risk of fracture caused by these phenomena can be evaluated. The determination of the fracture angle which is the key for this evaluation is derived in the present paper.
This paper deals with tridirectional composite material mechanical behaviour. The different constituents of the composite material are fibre-yarns, matrix and their respective interfaces. The mechanical behaviours of these constituents are built up for each of them. They are characterised by some parameters from the elastic domain, up to the rupture. These parameters are identified by using classical and original tests on a tridirectional carbon-carbon composite.Micro-macro mechanical relationships are then given. They derive from simple physical ideas and are founded on damage notion and homogenisation theory.This approach completes another mechanical model of the homogeneous behaviour for this material.Comparisons between the theoretical and experimental results are given.
Low velocity impact tests were carried out on carbon-fabric/epoxy laminates of different thicknesses, by means of a hemispherical impactor. The force and absorbed energy at the point of delamination initiation, the maximum force and related energy, and penetration energy were evaluated. From the experimental results, all these quantities, except the energy for delamination initiation, followed the same trend, increasing to the power of approximately 1.5 with increasing plate thickness. For what concerns the force at delamination initiation, it is shown that its trend agrees with the assumption of a Hertzian contact law, coupled with the hypothesis that only the shear stress is responsible for delamination. It is also demonstrated that the force/displacement curves recorded for the different thicknesses sensibly superpose with each other when the forces are scaled to the power 1.5 and the displacements are held unchanged. This explains the observed dependence of the maximum force, energy at maximum force, and penetration energy on the thickness. Finally, the energy at delamination initiation is calculated by an analytical model, assuming that the total energy is shared in two parts, one of which is stored in flexure, and the other in the material volume close to the contact zone.
This work deals with the characterization of composite material suitable for constructing structural parts devoted to dissipate kinetic energy during impacts. In particular glass-fiber-epoxy matrix laminates are considered, both with unidirectional layers and with woven layers stacking, with three different layers orientations.Experimental tests are performed according to ASTM standards using a free-fall drop dart testing machine. The specimens are plates completely constrained on a circular edge by the clamping fixture. Two energy absorption parameters (namely saturation impact energy and damage degree), two relevant characteristic values of the impact force history (namely the first damage force and the maximum force) and the sensitivity of the material mechanical characteristic to the strain rate effect are considered in order to describe the impact behavior of the material. Diagrams are presented to show the history of relevant kinematical, dynamic and energetic quantities, both to synthesize the dependency of the energy parameters and force threshold values on the impact velocity. The considered materials, under the considered loading conditions, show no sensitivity to the strain rate effect.
This paper presents a 3-D failure model for predicting the dynamic material response of composite laminates under impact loading. The formulation is based on the Continuum Damage Mechanics (CDM) approach and enables the control of the energy dissipation associated with each failure mode regardless of mesh refinement and fracture plane orientation. Internal thermodynamically irreversible damage variables were defined in order to quantify damage concentration associated with each possible failure mode and predict the gradual stiffness reduction during the impact damage process. The material model has been implemented into LS-DYNA explicit finite element code within solid elements and it has proven to be capable of reproducing experimental results with good accuracy in terms of static/dynamic responses, absorbed energy and extent of damage.
The behavior of different E-glass/epoxy laminated composite plates has been experimentally studied under impact of aluminum projectile at low velocities (0.53–3.1 m/s). The results were obtained using a drop weight impact machine and presented for three different cross-ply laminates [02/906/02], [03/904/03] and [04/902/04]. The time history of the impact process such as the acceleration impactor, the projectile displacement and the target circular plate deflection due to an impact force acting at the center has been measured. The effects of the projectile velocities and lamination sequences on composite plates behavior have been discussed. Applications of the theoretical model based on Hertzian contact law were used as an efficient guide for the experimental results validation.
A constitutive model for anisotropic damage is developed to describe the elastic-brittle behavior of fiber-reinforced composites. The main objective of the paper focuses on the relationship between damage of the material and the effective elastic properties for the purpose of stress analysis of structures. A homogenized continuum is adopted for the constitutive theory of anisotropic damage and elasticity. Internal variables are introduced to describe the evolution of the damage state under loading and as a subsequence the degradation of the material stiffness. The corresponding rate-equations are subjected to the laws of thermomechanics. Emphasis is placed on a suitable coupling among the equations for the rates of the damage variables with respect to different damage modes. Evolution equations for the progression of the passive damage variables complete the kinetic equations. Most material parameters are obtained from uniaxial and simple shear tests as demonstrated by the example.
The post-impact damage properties of composite laminates impacted by various impactor shapes are investigated herein. This investigation is a continuation of the research conducted in [Mitrevski T, Marshall IH, Thomson R, Jones R, Whittingham B. The effect of impactor shape on the impact response of composite laminates. Compos Struct 2005;67(2):139–48]. After impacting thin woven carbon/epoxy laminates using hemispherical, ogival and conical steel impactors all 12 mm in diameter using a drop weight test rig (Mitrevski et al., 2005), various post-impact analysis techniques have been employed, such as non-destructive inspection (NDI) and microscopy to assess the effect of impactor shape on the resulting damage. The blunter hemispherical impactor produced the largest damage area dominated by delamination. The rather sharp conical impactor produced the most fibre breakage which resulted in a localised damage area and the largest indentation/penetration depth. A significant reduction in tensile strength was found for all specimens. The specimens impacted by the hemispherical impactor at 4 J experienced a slightly higher residual tensile strength due to the barely visible impact damage (BVID) induced which was dominated by delamination.
This paper is concerned with evaluation of the in-plane dimensional effect of fiber-reinforced laminated composites under low-velocity impact. (0/90/0/90)s oriented cross-ply E-glass/epoxy laminates studied were manufactured and all of the material parameters of laminated composite materials were measured experimentally. The impact testing was conducted with a specially developed vertical drop-weight testing machine. Impact tests were performed at impactor masses of 135 and 2600 g and an impact velocity of 3 m/s. The studies were carried out on plate dimensions of , and with two opposite sides clamped and the other two free and impact load applied at the center of each plate. A numerical simulation was performed using 3DIMPACT transient dynamic finite element analysis code for calculating stresses and contact forces of the composite plates during impact along with a failure analysis for predicting the threshold of impact damage and initiation of delaminations.
The present paper outlines an unconventional energy based composite damage model capable of modelling woven and unidirectional composite materials. The damage model has been implemented into the LLNL-DYNA3D and LS-DYNA3D finite element codes for shell elements (plane stress), relevant to tensile, compressive and shear damage failure modes. The damage model uses five damage variables assigned to tensile, compressive and shear damage at a laminae level. The evolution of damage in each mode is controlled via a series of damage-strain equations, thus allowing the total energy dissipated for each damage mode to be controlled during a dynamic or impact event.The materials under investigation were a uni-directional (UD) carbon-epoxy and a woven carbon epoxy composite. Recent experimental test results from the CEC HICAS project have also been used to verify the behaviour of the model at elevated strain rates. Experimental data for the 0° and 90° tensile response indicates effectively rate independent, while matrix dominated modes, such as the shear response is highly rate dependent.The 0° and 90° tensile response and the tensile shear response have been modelled at a coupon level, including relevant strain rate effects, with the proposed damage model. Results show very good agreement with the available coupon experimental data. Suggestions are also presented for additional non-standard experimental tests to derive the material model parameters.A follow on paper describes the results of a series of simulations using the proposed material model on a number of experimental plate impact tests performed on the CEC HICAS project.