Effect Of Impact Damage Research Articles

スキーポール用CFRPシャフトの強度に及ぼす衝撃損傷の影響

スキーポール用CFRPシャフトの強度に及ぼす衝撃損傷の影響

Effects of low-energy impact on the fatigue behavior of carbon/epoxy composites

The fatigue behavior of a [0/45/90/−45]2S carbon/epoxy laminate subjected to low-energy impact has been investigated. The strength, residual strength and penetration impact responses of the laminate are measured; the fatigue behavior of the impacted and unimpacted laminates is compared in this study. The fatigue tests were performed at various stress levels under tension–tension (T–T) loadings with a fatigue frequency of 3Hz. The median rank method and Weibull distribution are applied to predict the failure probabilities of the specimen under monotonic and fatigue testing. The S/N curves are obtained and the S/N curves of these two laminates (with and without impact loading) are compared. The tensile strength is reduced slightly when a relatively low-energy impact is applied; however, a significant decrease with wider data distribution in tensile strength is observed when a higher-energy impact is used. It is also found that both the spread and the cycles of fatigue life are reduced after low-energy impact. C-scanning is used to inspect the damage zone of the specimens subjected to low-energy impact, and it is found that the damage zone increases with an increase in impact energy. The delamination propagation is monitored, and the effect of impact damage on delamination propagation during fatigue testing is revealed in this work.

A constant-life model of fatigue behaviour for carbon-fibre composites: the effect of impact damage

Following earlier work on the development of a life-prediction method for four types of carbon-fibre composites subjected to constant-stress fatigue, we now attempt to assess the validity of the method for composites which have sustained damage from low-velocity impacts. This part of the work was carried out on a fifth carbon-fibre composite, HTA/982A, having the same structure, a [(±45,02)2]S lay-up, as those previously investigated. Replicate stress/life data were obtained at four stress ratios (R) of +0·1, −0·3, −1·5 and +10 on virgin samples and on samples damaged by a falling weight delivering 1J of energy. The constant-life model is shown to be valid for the undamaged laminate and is also able to account for the effects of the impact damage in reducing the compression strength and consequent compressive fatigue response of the material.

Effect of impact damage on residual compressive strength of glass-fibre reinforced polyester (GFRP) laminates

The effect of impact damage on residual compressive strength of thick glass-fibre reinforced woven fabric laminates has been investigated. A number of damage mechanisms induced in two sets of circular coupon specimens have shown to be of both local and global effects. It is demonstrated that damage force and incident kinetic energy (IKE) maps can be used to identify damage initiation. However, the use of IKE and damage area for assessing damage tolerance has limitations, in particular for thick laminates, so that the use of impact force can be an additional damage measure. It is found that delamination or multiple delamination degrading local flexural stiffness causes impacted panels to fail in compression with kink-band shear at a load level that is significantly lower than that of unimpacted panels. But when the impacted panels are completely delaminated, they can still retain 30% strengths for the glass-polyester and 20% strengths for the glass-phenolic laminates if they are under subsequent compressive loading.

Fracture Mechanisms of Plain Woven CFRP Composite by Acoustic Emission Monitoring. Effects of Impact Damage.

Effects of impact damage on fracture mechanisms of plain woven CFRP composite are studied by means of acoustic emission monitoring. The maximum load and the AE characteristics of 0 specimen differ from those of 45 specimen, where 0 and 45 are the angles between the directions of yarn and loading. When a load Pb is determined by AE energy gradient method, the ratio of Pb/Pb(N) is used to estimate the residual strength, when Pb is the load at which the damage mechanisms are changed and Pb(N) is the maximum load of a non-impact specimen. It is found that the reliability of CFRP with the impact damage can be evaluated by the load ratio.

Fatigue behaviour of mechanically fastened joints in composite materials

This paper describes the results of a research activity, carried out at the Department of Aerospace Engineering at the University of Pisa in conjunction with AGUSTA, aimed at the characterisation of the fatigue behaviour of composite joints. The activity was performed as a support to the certification of the tail of the new helicopter EH 101. Two types of specimens were defined taking the move from the design of the structure; they mainly differed in the thickness of the laminates, 2 and 4 mm, and were representative of critical areas. The specimens were impact damaged with an energy level capable of inducing a barely visible indentation, as required by the Certification Authority. Fatigue tests, under sinusoidal loading, R = 0.2, were carried out both in dry and wet conditions; the stiffness of the specimens was monitored during the fatigue tests. The comparison between the results obtained shows the considerable effect of impact damage and of humidity absorption on the fatigue resistance of composite joints.

Experimental techniques for the investigation of the effects of impact damage on carbon-fibre composites

Low-velocity impact damage to composite laminates causes a complicated pattern of matrix cracks, fibre cracks and delamination. A significant effect of this damage is to reduce the strength of the laminate, particularly in compression; however, owing to the complexity of the damage the precise mechanisms controlling the strength reduction are unclear. In this paper a technique is described for replicating impact damage artificially by including PTFE film delaminants and cut plies during lay-up. Comparisons between real and artificially reproduced damage are made to demonstrate the validity of the technique. Experimental methods of X-radiography and resin injection are developed to allow the mechanisms controlling strength reduction to be assessed, both under tensile and compressive loading. Under tensile load the reduction in strength caused by impact damage is found to be entirely due to fibre cracks and may be estimated by using a net-section calculation. Meanwhile under compression, strength reduction is largely caused by the redistribution of stress resulting from buckling of delaminated plies and may be predicted by calculating stresses in the undelaminated part of the laminate.

52157 Quantitative assessment of impact damage in composites

The effect of impact damage resulting from drop-weight impact testing of AS4/3501-6 laminates with a quasi-isotropic lay-up on residual compressive strength was quantitatively assessed. The damage based on the volume of the material affected by the impact was determined nondestructively using an ultrasonic time-of-flight C-scanning technique. Compression-after-impact tests were performed which provided data for correlating damage volume to residual compressive strength. During compression testing, damage progression was continuously monitored using a photoelastic method and D-sight. The isochromatic patterns observed, which are proportional to the maximum shear strains, were found to be consistent with the directions of damage growth under load. The continuous change in the surface curvature of the impact damaged specimens showing localized buckling under the increasing compression load was observed under D-sight. Various approaches for the development of residual strength prediction models for impact damaged laminates are discussed.

Impact-Damaged Graphite-Thermoplastic Trapezoidal-Corrugation Sandwich and Semi-Sandwich Panels

The results of a study of the effects of impact damage on compression- loaded trapezoidal-corrugation sandwich and semi-sandwich graphite-thermoplastic panels are presented. Sandwich panels with two identical face sheets and a trapezoidal corrugated core between them, and semi-sandwich panels with a corrugation attached to a single skin are considered in this study. Panels were designed, fabricated and tested. The panels were made using the manufacturing process of thermoforming, a less-commonly used technique for fabricating composite parts. Experimental results for unimpacted con trol panels and panels subjected to impact damage prior to loading are presented. Little work can be found in the literature about these configurations of thermoformed panels.

Characterization of mechanical behaviors of advanced thermoplastic composite after impact

The objective of this study is to characterize the effect of impact damage on static and fatigue mechanical behaviors of advanced thermoplastic composites Gr/PEEK (AS-4/APC-2 and IM-7/APC-2), and the conventional thermoset composite, Gr/Epoxy (T-300/976) for comparison purpose. The specimens of 16-ply quasi-isotropic stacking sequence were drop-weight impacted, and compression and tension after impact were tested to measure the reduction of the static compressive strength and tensile strength. The results show that the compressive and tensile retention strength after impact for the three materials are both in the order: IM-7/APC-2 > AS-4/APC-2 > T-300/976. To characterize the fatigue mechanical behavior, tension-tension cyclic loading were applied on impact damaged laminates. The results show that the impact damages have no effect on the fatigue characteristics of laminates, but will reduce the fatigue life. The fatigue life of impact damaged laminate can be predicted by the parameters of the S-N curve of un-impacted laminates and the static retention strength of impact damaged laminates.

Impact on Laminated Composite Materials

Laminated composite materials are used extensively in aerospace and other applications. With their high specific modulus, high specific strength, and the capability of being tailored for a specific application, these materials offer definite advantages compared to more traditional materials. However, their behavior under impact is a concern, since impacts do occur during manufacture, normal operations, or maintenance. The situation is critical for impacts which induce significant internal damage, undetectable by visual inspection, that cause large drops in the strength and stability of the structure. Impact dynamics, including the motion of both the impactor and the target and the force developed at the interface, can be predicted accurately using a number of models. The state of stress in the vicinity of the impact is very complex and requires detailed analyses. Accurate criteria for predicting initial failure are generally not available, and analyses after initial failure are questionable. For these reasons, it can be said that a general method for estimating the type and size of impact damage is not available at this time. However, a large amount of experimental data has been published, and several important features of impact damage have been identified. In particular, interply delaminations are known to occur at the interface between plies with different fiber orientation. Their shape is generally elongated in the direction of the fibers in the lower ply at that interface. The delaminated area is known to increase linearly with the kinetic energy of the impactor after a certain threshold value has been reached. The effect of impact damage on the properties of the laminate has obvious implications for design and inspection of actual structures. Experimental results concerning the residual strength of impact damaged specimens subjected to tension, compression, shear, bending, and both static and fatigue loading are available. Analyses concentrate primarily on predicting residual tensile and compressive strength. In order to fully understand the effect of foreign object impact damage, one should understand impact dynamics and be able to predict the location, type, and size of the damage induced and the residual properties of the laminate. This article is organized along these lines and presents a comprehensive review of the literature on impact of laminated composites, considering both experimental and analytical approaches.

An experimental investigation into the effect of impact damage on the compressive strength of step lap joints

This paper examines the effect of impact damage at composite to metal joints. Attention is focused on the residual compressive strength of the joint. Various impact energies are considered. The experimental results indicate that as the extent of the damage is increased a stage is reached after which a further significant increase in damage size does not result in a further significant decrease in residual strength.

Assessment of the effect of impact damage in composites: Some problems and answers

In order to provide through-life support for structural components, fabricated from advanced composite materials, it is desirable to establish a damage tolerance methodology. The availability of this methodology would greatly aid the design of safe, efficient composite structures as well as their management in service. There are, however, many difficulties in meeting this objective, including the multiplicity of failure modes in the composites, the numerous types of potentially significant defects which may arise during manufacture or in service and the sensitivity to moisture and temperature. This paper discusses the analysis and testing of impact damage composite laminates. Selected experimental studies in the literature are briefly discussed. It is shown that uniaxial S−N curves for damaged laminates have a generic shape with a pronounced threshold level. Indeed, it is clear that further research is needed to understand the physical reasons for such a threshold value.

Assessment of the effect of impact damage in composites: Some problems and answers

In order to provide through-life support for structural components, fabricated from advanced composite materials, it is desirable to establish a damage tolerance methodology. The availability of this methodology would greatly aid the design of safe, efficient composite structures as well as their management in service. There are, however, many difficulties in meeting this objective, including the multiplicity of failure modes in the composites, the numerous types of potentially significant defects which may arise during manufacture or in service, and the sensitivity to moisture and temperature. This paper discusses the analysis and testing of impact damage composite laminates. Selected experimental studies in the literature are briefly discussed. It is shown that uniaxial S-N curves for damaged laminates have a generic shape with a pronounced threshold level. Indeed, it is clear that further research is needed to understand the physical reasons for such a threshold value.

The influence of genotype on the effects of impact damage on the accumulation of glycoalkaloids in potato tubers

The effects of impact damage on the accumulation of glycoalkaloids in tubers were studied in a wide range of potato genotypes. Damage, caused by drop tests, resulted in increased glycoalkaloid levels, which sometimes exceeded the toxic limit of 20 mg/100 g fresh weight; there were large differences in levels between genotypes. When the total damage index was high, the severe damage types—shatter cracks and splits—were responsible for the initiation of glycoalkaloid synthesis in stressed tuber tissue, whereas the less severe damage types—bruises and black spot—were not. Genotypes which had the highest shatter crack indices often had the greatest increases in glycoalkaloids. The high correlation between the initial glycoalkaloid level and the increased level after damage showed that selection for low glycoalkaloid potato clones is important.

Effect of Impact Damage on Sucrose Loss in Sugarbeets During Storage

Received for publication September 5, 1978 INTRODUCTION Injury of sugarbeet roots during h a rvesting, handling, and piling has a significant effect upon their storage lit e. Respiration rates increase with the severity of the damage and continue throu gh the entire storage period (1, 5, 10, 11). Wound respiration is responsible for the higher losses during the early storage period (1, 7). The damaged surfaces are infected b y fungi such as Botrytis and Penicillium (9) which increase sucrose losses through higher respiration rates and higher invert sugar accumu­ lation during the remainder of the storage period (1, 9, 11) .

Impact damage effects on boron-aluminium composites: Carlisle, J.C. et al. Conference on Composite Reliability, ASTM STP 580 (American Society for Testing and Materials, 1975) pp 458–470

Impact damage effects on boron-aluminium composites: Carlisle, J.C. et al. Conference on Composite Reliability, ASTM STP 580 (American Society for Testing and Materials, 1975) pp 458–470

Compression after Impact: Damage Characterization of Multi-Directional 10-Ply Carbon- Epoxy Prepreg Laminates Subject to Quasi-Static Impact Force

During the course of service, aerospace structures inevitably will suffer some form of damage, including the possibility of impact. Two general types of impact damage, either resulting from a quasi-static force or a dynamic impulse force, characterize the nature of impact threats for analysis and experimentation in a lab setting. Using ASTM D7137 Standard Test method for Compressive Residual Strength Properties of Damaged Polymer Matrix Composite, this study subjects multidirectional carbon-fiber/epoxy laminates to Compression After Impact (CAI) tests to determine whether the results may be used to characterize and quantify the effects of impact damage on laminate compressive strength. Characterization of impact damage in regions of a structure subject to high-strain compression could assist decision-making in implementing repairs. In addition, this paper examines the effects of different impacting patterns on the behavior in compression.Â