Epoxy Composite Plates Research Articles

Effect of strain rate on the compression behavior of a woven glass fiber/SC-15 composite

Strain rate dependent compression behavior of a plain-weave S-2 glass fabric SC-15 epoxy (rubber toughened resin) composite plate, currently studied as the backing plate for composite armor applications, was determined in the through-thickness direction (normal to the fiber plane) in the strain rate regime of 1×10 −4 to 1.1×10 3 s −1. In the studied strain rate regime, the modulus and failure strength of the composite were found to be rate sensitive and increased with increasing strain rate. Microscopic observations showed that the composite failed by ductile failure, involving matrix cracks and, later, cracking through and between the fiber layers. Crack deflections at rubber particle/matrix interface and particle pull-out were observed in the failed samples, contributing to the toughness of the composite.

An experimental and numerical investigation of strength characteristics of carbon-epoxy pinned-joint plates

An experimental and numerical study has been carried out to investigate the strength of a pinned-joint carbon epoxy composite plate with [0°/45°/−45°/90°] S and [90°/45°/−45°/0°] S stacking configurations. The experiments were carried out according to the ASTM D953 standard [Standard Test method for Bearing Strength of Plastics, ASTM Designation, 342–346], and the numerical analyses were performed by the finite element method. The ratio of the edge distance to the pin diameter ( E/ D), and the ratio of the specimen width to the pin diameter ( W/ D) were systematically varied during analyses. The results from both analyses show firstly that the prepared specimen configurations give bearing mode, secondly that the [90°/45°/−45°/0°] S configuration is stronger when compared to [0°/45°/−45°/90°] S, and finally that both configurations reach their upper limit bearing strengths when E/ D and W/ D ratios are equal or greater than 4.

Stresses in a thin, circular aeolotropic plate subjected to uniform lateral load

Closed form, approximate stress solutions for simply supported cubic and orthotropic plates subjected to a lateral pressure are presented and compared with a series solution. The accuracy of the approximate solutions depends on the degree of anisotropy. For cubic plates exhibiting significant anisotropy, the approximate solution is within ∼10% of the series solution. For a graphite–epoxy composite plate of orthotropic symmetry, the approximate solution is within 10% of the series solution for the maximum stress at the plate centre and within 23% for the minimum stress at the plate centre. Single crystal plates tend to exhibit a large tangential stress where the stiff directions intersect the plate edges, implying that the edges of brittle single crystal test specimens must either be prepared better than those of isotropic specimens or have more of the plate overhanging the support.

Dynamic Characteristics of Laminated Woven E-Glass–Epoxy Composite Plates Subjected to Lowvelocity Heavy Mass Impact

The main goal of this study is to examine the size effects including both in-plane dimensional and thickness effects for laminated woven E-glass–epoxy composite subjected to low velocity heavy mass impact. The studies have been carried out with plate dimensions of 150 × 150 mm, 150 × 100 mm and 150 × 50 mm for in-plane dimensional effect. Two nominal thicknesses with averages of 1.4 and2.8 mm are used for studying the thickness effect. The impact testings are conducted with a vertical drop-weight testing machine developed in the department laboratory. Affixed to the drop-weight device, a piezoelectric force transducer, localized in the hemispherical impactor nose, yields the complete force versus time history of impact event. Impact tests are performed at increasing impact velocities 1, 2 and 3m/s and impactor mass of 2.6 kg on clamped plates. A numerical evaluation of these specimens is also carried out by using 3DIMPACT transient dynamic finite element analysis code. The contact forces between the impactor and the composite plate as functions of time, transient stresses during impact and the predicted delamination sizes of composites are found numerically.

Progressive failure analysis of pin-loaded carbon–epoxy woven composite plates

The present investigation deals with the failure strength and failure mode of a pinned-joint carbon–epoxy composite plate of arbitrary orientations. The main objective is to investigate the possibility of predicting the properties of the joint from the properties of the material measured with standard tests. The failure load and the failure mode are analysed numerically and experimentally. A computer program developed for such an analysis is used to calculate the failure load, the failure mode, and the propagation of failure of plate with different fiber orientation, different material properties and different geometries. Hoffman and Hashin failure criteria are used in failure analysis. Experimental results concerning damage progression and ultimate strength of the joint are obtained and compared with predictions. A good agreement between experimental results and numerical predictions is obtained.

Lamb and SH waves generated and detected by air-coupled ultrasonic transducers in composite material plates

Electrostatic, air-coupled, ultrasonic transducers are used to generate and detect guided waves in anisotropic solid plates. Waves considered in this study are Lamb-type and SH-type, guided modes. If the plane of propagation coincides with a plane of symmetry of the material, then Lamb modes only are launched and detected by the transducers. If the plane of propagation does not coincide with a plane of symmetry of the material, then Lamb modes are still generated and detected, but guided, SH-like modes are, too. The variation of phase velocity with frequency is measured for several modes propagating in different directions along a glass–epoxy composite plate. A numerical model that takes into account the anisotropy of composite materials is developed to predict the dispersion curves (phase velocity, group velocity or wave-number versus frequency) and the displacement fields of plate waves, the plane of propagation being either a plane of symmetry or not. The experimental phase velocities are in good agreement with the predicted dispersion curves, thus showing that the forward problem concerning the propagation of plate waves in anisotropic, homogeneous, composite material plates is properly solved. The dispersion curves associated with the predicted displacement fields show that guided modes in composite plates have different behaviors depending on their direction of propagation.

Experimental observations of intersonic crack growth in asymmetrically loaded unidirectional composite plates

Abstract Some recent experimental observations of highly dynamic crack growth events in thick unidirectional composites are presented. The specimens used in this study were 48-ply thick unidirectional graphite–epoxy composite plates which were either symmetrically (mode I) or asymmetrically (mode II) loaded by impact in a one-point bend configuration with an edge pre-notch machined in the fibre direction. Moderate impact speeds of up to 57 ms−1 were used. The lateral shearing interferometric technique of coherent gradient sensing in conjunction with high-speed photography was used to visualize the failure process in real time. Mode-I cracks propagated subsonically with crack speeds increasing to the neighbourhood of the Rayleigh wave speed. For asymmetric mode-II types of loading the results revealed highly unstable and intersonic shear-dominated crack growth along the fibres. These cracks propagated with unprecedented speeds reaching 7400 ms−1, a speed which is more than three times the shear wave speed ...

Analytical and finite element comparisons of stress intensity factors of composite materials

In this paper, a comparative study regarding the determination of stress intensity factors (SIF) for non-standard thin composite plates is presented. Carbon–epoxy composite plates are considered for the study. Unnotched specimens and specimens containing either 4, 6 or 8 mm diameter holes are prepared and then tested. Based on the experimental data thus obtained, two analytical approaches and a finite element fracture analysis tool called FRANC2DL have been used to compare the critical SIF values for this composite material.

Damping improvement of machine tool columns with polymer matrix fiber composite material

In order to improve the damping capacity of the column of a percision mirror surface grinding machine tool, a hybrid column was manufactured by adhesively bonding glass fiber reinforced epoxy composite plates to a cast iron column. To optimize the damping capacity of the hybrid column, the damping capacity of the hybrid column was calculated with respect to the fiber orientation and thickness of the composite laminate plate and compared to the measured damping capacity. From experiments, it was found that the damping capacity of the hybrid column was 35% higher than that of the cast iron column.

An Experimental Study of Low Velocity Impact Damage in Woven Fiber Composites

A study is made on the low velocity impact response and post-impact mechanical capacity of woven fiber [0/90,-45/45,0/90]s carbon epoxy composite plates. This complements the work done by numerous other researchers who have also examined low velocity impact of composites, but have focused on unidirectional, cross-ply or quasi-isotropic laminates. In the present study, post-impact static uniaxial tension, compression, as well as tension-compression fatigue tests are performed. The damage mechanisms for woven laminates are found to be predominantly delamination and fiber breakage, with the area of impact-induced delamination increasing linearly with impact energy for the range of energies examined. Damage extent and type are also dependent on the curvature of the impactor tip and deformation generated by a sharp impactor is more localized. The existence of a threshold energy level below which no delamination discernible by C-scan occurs is noted. In contrast with previous findings, it is observed that the peak in the impactor deceleration-time response is not associated with the onset of fiber failure, which can occur earlier. The amount of energy absorbed when this peak occurs therefore does not indicate the energy required to initiate fiber breakage. It is observed that residual tensile strength is a function of delamination area and impactor tip radius. For static compression and tension-compression fatigue, the residual load-bearing capacity is only dependent on delamination area. Under compression, delamination promotes the micro-buckling of fibers, whereas in tension, failure is predominantly via fiber breakage. For a common impact energy and impactor, a damaged specimen is weaker in compression than in tension.

Exact solutions for dynamic analysis of composite plates with distributed piezoelectric layers

Exact solutions are presented for analyzing dynamics of composite plates with piezoelectric layers bonded at the top and the bottom surfaces. The expressions for mechanical displacements, stresses, electric displacements and potential are derived from constitutive relations and field equations for the piezoelectric medium under applied surface traction and electric potential. The procedure is illustrated with a simply supported symmetric cross-ply (0°/90°/0°) graphite–epoxy composite plate covered with piezoelectric material polyvinylidene fluoride (PVDF). Results are in good agreement with those obtained from finite element model.

Stress analysis of laminated E-glass epoxy composite plates subject to impact dynamic loading

The transient response of an E-glass epoxy laminated composite plate impacted by a steel circular cylinder is analyzed. The analysis is performed by using a three-dimensional hybrid stress finite element program. The contact force between the projectile and the laminated plate is modeled by the Hertzian impact law. The predicted transverse deflection at the center of the laminated plate agrees with the deflection determined experimentally. The effects of projectile velocity and thickness of the laminated plate on the impacted stress distributions and the central transverse deflection are also investigated.

Scaling of Energy Absorbing Composite Plates

The energy absorption response and crushing characteristics of geometrically scaled graphite-Kevlar epoxy composite plates were investigated. Two different trigger mechanisms including notch, and steeple geometries were incorporated into the plate specimens to initiate crushing. Sustained crushing was achieved with a new test fixture which provided lateral support to prevent global buckling. Values of specific sustained crushing stress (SSCS) were obtained which were lower than values reported for tube specimens from previously published data. Two sizes of hybrid plates were fabricated; a baseline or model plate, and a full-scale plate with inplane dimensions scaled by a factor of two. The thickness dimension of the full-scale plates was increased using two different techniques: the ply-level method in which each ply orientation in the baseline laminate stacking sequence is doubled, and the sublaminate technique in which the baseline laminate stacking sequence is repeated as a group. Results indicated that the SSCS has a small dependence on trigger mechanism geometry. However, a reduction in the SSCS of 10-25% was observed for the full-scale plates as compared with the baseline specimens, indicating a scaling effect in the crushing response.

Impact de plaques composites : caractérisation et modèles

We are concerned with the behavior of thin stratified carbon- or glass- epoxy composite plates. The present work is presented as a part of a more wide study carried out which purpose is the numerical simulation of damage evolution within such plates when subjected to a localized transverse low-velocity impact. To establish a correlation between the measured intemal damage and the corresponding absorbed energy, from works presented in the literature, is the aim of this one. We first focuse our attention on the typical loading conditions of a direct transverse low-velocity impact. Indeed, we point out the respective role of the impactor/plate contact, indentation and flexion process of the plate on the localization, initiation and propagation of intralaminar cracking and interlaminar delamination. A phenomenological model of interactive evolution of these damages which takes into account the loading and energy absorption process is then proposed, and we identify the interaction between the experimental parameters and the up mentioned damages. We further expose a discussion about some contact law models, and our approach of the loading/structure interaction simulation in terms of the damage phenomenology model presented.

Modification of Lamb wave spectrum in fluid coupled plate

It has been accepted previously that for most practical eases when a plate is immersed in a liquid the Lamb wave spectrum is only slightly perturbed due to energy loss related to leakage of the wave from the plate to the liquid. In contrast it was recently discovered by D. E. Chimenti and A. H. Nayfeh [Appl. Phys. Lett. 49 (9) (1986)] that for leaky Lamb waves in a graphite epoxy composite plate in water a strong anomaly appears in the topology of the S0 mode as a function of frequency. Although it was caused by the fluid, the reason for this anomaly was still not clear. The nature of the anomalous behavior of leaky Lamb waves is discussed in this paper. It is shown that for an understanding of the spectrum topology, the full complex spectrum of propagating and nonpropagating modes should be considered. It is demonstrated that the topological changes in the S0 mode are related to its nearness to the first complex branch of the spectrum. Increasing liquid density leads to interaction between these modes and mutual interchange between their branches in the complex plane. It is shown that, in general, as the density of the immersion liquid increases from zero to infinity the complex spectrum of plate modes gradually transforms from a spectrum of Lamb waves in a free plate to a spectrum of waves in a plate clamped on its surfaces with slip (boundary conditions σxy = 0, Uy = 0).

Stress waves induced in graphite‐epoxy composite structures by current pulses

A technique to generate ultrasonic waves in graphite‐epoxy composite structures using electrical current pulses flowing in the structure is described. The difference between the thermal expansion coefficients of graphite and epoxy create large stress waves in response to localized heating by current pulses flowing in the individual graphite fibers. Experimental results are presented demonstrating the applicability of the method to nondestructive testing problems. The anisotropic elastic and electrical properties of a T‐300 graphite/DER‐332 epoxy composite plate were determined. In the experiments, a piezoelectric receiver transducer was used to detect the thermoelastic waves in the composite plate. Distinct ultrasonic waves were detected with 20 μsec current pulses below 50 mA.