Residual Strength Of Composite Laminates Research Articles

A study of tensile residual strength of composite laminates under different patch-repaired series

The tensile behavior of composite laminate structures repaired by bonding external patches was studied in the paper. Two different types of patches including wedge patches and inverted wedge patches were used and failure mechanisms, failure load and strength predictions were studied. A convenient and fast method of building 2-D finite element modeling (FEM) of laminate structure repaired was proposed and the strength of repaired laminate structures was calculated by FEM. The results showed that more than 80% tensile strength of the undamaged laminate could be recovered by bonding patch repairs. Moreover, the results indicated that the strength of inverted wedge patches repair were higher than that of wedge patches repair. FEM simulation results indicated that high stress concentration was found along the edges of invert patches and the most weakness part located in the adhesive bondline. FEM analysis results showed that the strength predicted matched well with the test strength.

Analysis and Experiment of Compressive Residual Strength of Composite Laminates with Holes

Experiment and Finite element analysis were used to study the strengths of composite laminates with and without holes. Finite element progressive damage analysis with Tsai-Wu criteria was applied to calculate the compressive residual strength of composite laminate. Abaqus and its user subroutine USDFLD were used for the finite element analysis. Tsai-Wu criteria as the failure criteria was realized in USDFLD as a Fortran program segment, and the stiffness degradation for the damaged elements was also realized by USDFLD. Analytic results gotten by progressive damage method were very close to the experimental results.

Analysis on Low Velocity Impact Damage and Compressive Residual Strength of Composite Laminates

This paper studies the impact damage under low velocity impact for composite laminates based on a nonlinear progressive damage model. Damage evolution is described by the framework of the continuum damage mechanics. The real impact damage status of composite laminates has been used to analyze the residual compressive strength instead of assumptions on damage area after impact. The validity of the methodologies has been demonstrated by comparing the numerical results with the experimental data available in literature. The delamination area has an error of 11.3%. The errors of residual strength and compressive displacement are 8.9% and 15%, which indicate that the numerical results matched well with the experimental data.

Buckling analysis of laminated composite plates submitted to compression after impact

The aim of this work is the experimental evaluation of the residual strength of composite laminates under compression after low velocity impact. Different kinds of delaminations, partial, embedded and through-the-width, were studied. Carbon-fibre reinforced epoxy composite was used and the experimental tests were performed on [0]16, [0, 90, 0, 90]2S and [0i, 90i]s with i=2, 3, 4, 5, using a drop-weight-testing machine. The impacted plates were inspected by the ultrasonic C-Scan to evaluate the size and the shape of the delamination. Results show that the presence of delamination decreases the compressive strength. The stacking sequence and laminate thickness were verified to have a remarkable influence on the value of the residual compressive strength, and play an important role on the observed buckling failure modes.

놋취가 있는 복합적층판의 잔류강도 해석

This study reviews several fracture models for predicting the residual strength of notched composite laminates. Representative experimental results on the residual strength of composite laminates containing a notch subjected to static uniaxial tensile loading have been collected from open literature. And notched strength data for T300/5208 are analyzed. The various parameters associated with the fracture models have been determined for laminates. Notched strength data sets are compared with fracture models and the applicability of the different fracture models in predicting the notched strength of composite laminates is discussed. And static tests have been performed on 2.0mm depth notched specimen. And the test results are compared with analysis models.

Residual strength of composite laminates containing scarfed and straight-sided holes

This investigation is motivated by the needs to quantify the load-carrying capacity of composite laminates with scarfed holes, a damage cut-out shape employed to achieve flush repairs of composites. Both experimental testing and analytical modelling were carried out to investigate the damage progression behaviour of composite laminates containing either straight-sided or scarfed holes. Hoop strains were recorded by strain gauges located along the scarf surface and the results indicate a much greater extent of damage progression than specimens containing straight-sided holes. Three different strength-prediction models were employed to quantify the residual strength, including an analytical cohesive zone model developed in this work, an analytical inherent-flaw fracture mechanics method and a finite element-based continuum damage model. Comparisons of the experimental results with the model predictions reveal that the continuum damage model, calibrated using data from coupons with straight-sided holes, provides promising correlation with experimental results.

Failure Factor Research of Composite Laminates Containing Holes Based on MSC.Nastran

With the extensive use of composite materials in aviation industry, the research of holes which affect composite residual strength has become very important. Based on MSC.Nastran, the stress of each laminate unit was calculated. Failure factor of composite laminates containing holes were calculated with the Tsai-Wu failure criterion. In this paper, the influence of hole shape and size on the composite laminate failure factor under compressive loading was studied. The relationship of hole shape, size and residual strength of composite laminates was briefly discussed. The results show that, under compressive loading, the stress concentration appears near the hole, there is a proportional relationship between the failure factor and hole size, the hole size and residual strength is the inverse relation.

Residual strength of composite laminates with a centre crack under tension

An empirical relationship between the failure stress and stress intensity factor at failure is examined for the estimation of residual strength of various types of laminates with different layup sequence and having centre cracks. The estimated fracture strengths for these laminates under tension are compared with existing experimental results. They are found to be in reasonably good agreement with each other.

RESIDUAL STRENGTH OF NOTCHED COMPOSITE LAMINATES

Several fracture models used for prediction of notched residual strength of composite laminates are reviewed. Emphasis has been placed on analytical fracture models which are simple to utilise. Published experimental results on the notched strength of composite laminates containing a circular hole or centre crack and subjected to quasi-static axial tensile loading are also reviewed. Characteristic parameters associated with fracture models have been determined and theoretical predictions of residual strength are compared with all notched strength data sets. Applicability of the different fracture models in predicting the residual strength of composite laminates is also discussed.

Fatigue behaviour of CF/PEEK composite laminates made from commingled prepreg. Part I: experimental studies

Abstract The static and fatigue properties of continuous AS4 carbon fibre reinforced polyetheretherketone (PEEK) composite laminates made from commingled unifabric prepreg were investigated under static tension and tension–tension fatigue loading. Three different lay-ups were studied, namely [0]16, [90]16 and [02/902]2S. The results for static stiffness and strength as well as fatigue life and residual strength under different fatigue stress amplitudes were evaluated and compared with those of composite laminates made from other preforms. The damage and failure mechanisms of the composite laminates were discussed. The wear-out model was applied to fit the S–N curves and estimate residual strength of composite laminates, and good correlation was obtained. Compared to composite laminates made from pre-impregnated tape prepreg (e.g. APC-2), the commingled CF/PEEK composite laminates are much more sensitive to fatigue loading because of imperfect fibre bundle alignment.

A Progressive Damage Model and Analysis Methodology for Predicting the Residual Strength of Composite Laminates

The durability and damage tolerance of laminated composites are critical design considerations for airframe composite structures. Therefore, the ability to model damage initiation and growth and predict the life of laminated composites is necessary to achieve efficient and economical structural designs. The purpose of the research presented in this paper is to experimentally verify the application of the damage model developed by the authors to predict progressive damage development in a toughened material system. Damage growth, stiffness degradation, and residual strength were experimentally determined for cross-ply and quasi-isotropic IM7/5260 graphite/bismaleimide laminates due to monotonic and tension-tension fatigue. The damage model, which has been implemented into a finite element code, was used to predict the stiffness loss and residual strength of unnotched and notched laminates. The model predictions were in good agreement to experimental results for several different fatigue loading histories and several different laminate stacking sequences.

Effective Crack Growth and Residual Strength of Composite Laminates with a Sharp Notch

The main objective of this study was to evaluate the residual strength of composite laminates with a sharp notch using an effective crack growth model (ECGM). Damage is assumed to initiate when the local normal stress ahead of the notch tip reaches the tensile strength of the unnotched laminate. The damage was modelled by a fictitious crack with cohesive stress acting on the cracks surfaces and the damage growth was simulated by extension of the fictitious crack and reduction of the cohesive stress with crack opening. The apparent fracture energy (G?) was used to define the relationship between the unnotched strength and the critical crack opening. Based on the global equilibrium condition, an iterative technique was developed to evaluate the applied load required to produce the damage growth. The residual strength of notched composite laminates was defined by the applied load instability with damage growth. The effect of damage increment on the convergence of the residual strength was investigated and the stress redistribution with damage growth in the composite laminates was discussed. The residual strength simulated from the new model correlated well with experimental data in the published literature for the different laminate configurations.

An Effective Crack Growth Model for Residual Strength Evaluation of Composite Laminates with Circular Holes

A new effective crack growth model (ECGM) is developed to evaluate residual strength of composite laminates with circular holes. When the local normal stress reaches the tensile strength of the unnotched laminate, damage is assumed to initiate and it propagates with increase of the applied load. The damage is modelled by a fictitious crack with cohesive stress acting on the crack surfaces and the damage growth is simulated by extension of the fictitious crack and reduction of the cohesive stress with crack opening. The apparent fracture energy (G:) is used to define the relationship between the unnotched strength and the critical crack opening. Based on the equilibrium condition, an iterative technique is developed to evaluate the applied load required to produce the damage growth. The residual strength of notched composite laminates is defined by the unstable point of the applied load with damage growth. AS4-carbon/948A1 epoxy [0/90]4s, and [0/±45/90]2s, composite laminates were manufactured and residual strength tests were conducted for composite laminates with various hole diameters and specimen widths. Effect of the damage increment on the convergence of the residual strength was investigated and the stress redistribution with damage growth in the composite laminates was discussed. The residual strength predicted from the new model correlates well with experimental data for the different laminate configurations.

Damage Containment and Residual Strength of Composite Laminates

Damage in composite laminates caused by low‐velocity impact may produce significant reductions in compressive strength. Lockheed conducted an experimental program to investigate the damage‐containment capability of simple composite laminates of two graphite‐epoxy systems: T300/5208 and AS/3501‐6. Four different lay‐ups, including two hybrid laminates, were investigated for each material system. Results are presented for comparison. Laminates with Kevlar layers, especially where the layer is on the surface of the laminate, demonstrate better impact resistance.

Residual Strength of Composite Laminates Subjected to Tensile-Compressive Fatigue Loading

Results are presented on the measurements of the residual strengths of T300/934 graphite epoxy laminates, in tension and in compression, after the samples were exposed to tension-compression fatigue loading (R = -1). Four laminate ocnfigurations were tested: unidirectional, cross-ply, angle-ply, and quasi-isotropic. It was found that the fatigue behavior of laminates was dependent on the quasi-static strengths and the specific structure of the laminate. No direct correlation was found between remaining residual strengths and the percentage of average fatigue life. However, a correlation scheme was developed for the individual specimen under test, based on a cumulative damage model and a stiffness change of the material.

Fatigue and residual strength of composite laminates

The mechanics of fatigue failure of laminated composite materials are completely different from that of conventional materials. The mechanics of fatigue failure of conventional materials involve the initiation and propagation of a single crack, which causes the material to fail. Laminated composite material can arrest the propagating crack to within a single lamina, thus avoiding immediate failure. Only after accumulation of cracks the laminate fails. The fatigue life of the laminate is best described by S-N curves. A theory for residual strength is developed which is based on a cumulative damage theory. The theory predicts that the static strength of the laminate is maintained almost to the final failure by fatigue. Experimental results verify this phenomenon.