The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
J. Costa - One of the best experts on this subject based on the ideXlab platform.
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mitigating the weak impact response of thin ply based thin laminates through an unsymmetrical laminate design incorporating intermediate grade plies
Composite Structures, 2019Co-Authors: A Sasikumar, J. Costa, D Trias, V SingeryAbstract:With aeronautic industries focussing on thinner structures and reducing manufacturing costs, recent research has been dedicated to the impact and post impact response of thin laminates (<2 mm) made of textile fabric composites. A recent study revealed that thin laminates based on thin plies exhibit extensive fibre failure and a reduced compression after impact strength. To mitigate this weakness, we propose a novel laminate concept based on combining plies of different thicknesses in an unsymmetrical configuration (intermediate grade plies are located only at the bottom of the laminate, i.e., the non-impacted face). C-scan inspection on impacted and quasi-statically indented specimens, allowed the damage sequence of the proposed unsymmetrical hybrid laminate to be compared with that of the thin-ply baseline. The hybrid laminate with intermediate plies at the bottom, delayed and reduced the fibre damage, decreased the projected Delamination Area and led to a 30% increase in the compression after impact strength in contrast to the thin-ply baseline laminate.
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improving damage resistance and load capacity of thin ply laminates using ply clustering and small mismatch angles
Composites Part A-applied Science and Manufacturing, 2019Co-Authors: P Maimi, G. Guillamet, A. Wagih, N. Blanco, S M Garciarodriguez, R P Issac, A Turon, J. CostaAbstract:Abstract Thin-ply composite laminates are currently receiving researchers’ attention due to their specific advantages in delaying or even suppressing some damage mechanisms such as matrix cracks. Lower load capacity during impact event is one of the main factors against thin-ply laminates use. This paper presents novel thin-ply laminate design with improved damage resistance and load capacity. First, the effect of mismatch angle on damage resistance and damage mechanisms occurring during an impact event on thin-ply composite laminates is studied by means of a series of quasi-static indentation tests and X-ray computed tomography and ultrasonic C-scan techniques. The results show that the projected Delamination Area in thin-ply laminates is independent of the mismatch angle. However, the different damage mechanisms and load capacity are dependent on the mismatch angle; the smaller the mismatch angle is, the higher the matrix cracking density, the lower number of delaminated interfaces, the higher fiber breakage density and higher load capacity are. Based on these results and other available in the literature, a thin-ply laminate with small mismatch angles between plies (to improve the maximum load) and clustered plies in the upper part of the laminate (to force damage growth in this part) is designed to present improved damage resistance and load capacity of thin-ply laminates. This laminate shows 38.8% lower Delamination Area when compared to the laminate with small mismatch angles.
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damage resistance and damage tolerance of dispersed cfrp laminates effect of ply clustering
Composite Structures, 2013Co-Authors: T A Sebaey, N. Blanco, E V Gonzalez, C S Lopes, J. CostaAbstract:Abstract In this paper, the effect of introducing ply clustering in a composite stacking sequence on the damage resistance and damage tolerance of CFRP composite plates is investigated. Three stacking sequences are considered. First, a baseline laminate with conventional 0°, ±45° and 90° orientations and without ply clustering. The other two laminates are dispersed laminates with orientations not limited to the conventional ones. In one of them, four layers of 0° fiber orientation are clustered together at the specimen mid-plane, whereas in the last configuration, two clusters of two layers of 0° fiber orientation are introduced at the specimen top and bottom surfaces. The in-plane and the out-of-plane stiffness of the dispersed laminates match within 2% those of the baseline laminate. Ant Colony Optimization algorithm is used to select the stacking sequences with the desirable clustering and stiffness constraints. The results obtained demonstrate that introducing clustering had a negative effect on the maximum peak load recorded at different impact energies and also on the projected Delamination Area. Regarding damage tolerance, the residual compressive strength can be improved up to 30% with ply clustering.
Stephen R. Hallett - One of the best experts on this subject based on the ideXlab platform.
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numerical analysis of high velocity oblique impacts and residual tensile strength of carbon epoxy laminates
Composite Structures, 2021Co-Authors: Ashwin R. Kristnama, Michael R Wisnom, Stephen R. HallettAbstract:Abstract This paper presents prediction of the high velocity, oblique impact response and quasi-static residual tensile strength of thin [45/90/−45/0]2s carbon/epoxy laminates using finite element (FE) models. A High-Fidelity Finite Element Method (Hi-FEM) with an automated unit cell meshing technique was employed. The predicted impact damage, characterised by the extent of fibre failure and Delamination Area, was validated against results from gas-gun tests for a range of impact velocities. The numerical results captured the trend of increasing impact damage with impact energy as observed from the tests. Changes in projectile orientation before impact were shown to increase the extent of fibre failure at high impact energies, up by 38% in edge impact cases. The residual tensile strength of the impacted laminates was then investigated, where the numerical results for edge-impacted laminates agreed with the test data within 8%. On the other hand, the residual strength modelling results of centre-impacted laminates were found to be unconservative, mainly due to the extent of fibre failure predicted during impact. Machined notches were also studied for their residual tensile strength in comparison to impact induced damage. The predicted strength of edge-notched laminates was found to be in close agreement with the experimental results for edge-impacted laminates, differing by an average of 9%.
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experimental investigation of high velocity oblique impact and residual tensile strength of carbon epoxy laminates
Composites Science and Technology, 2019Co-Authors: Ashwin R. Kristnama, Michael R Wisnom, Xiaodong Xu, D Nowell, Stephen R. HallettAbstract:Abstract Composite components are required to be resilient against Foreign Object Damage (FOD) induced by localised high velocity impact events. Here an experimental investigation into high velocity oblique impacts and residual tensile strength of thin quasi-isotropic carbon/epoxy laminates is reported. Oblique (45°) impacts between 100 m/s and 350 m/s were carried out using 3 mm steel cubes on the edge and the centre of the laminates, mounted as a cantilever beam. Impact induced damage was characterised using X-ray Computed Tomography (CT) and the residual strength of impacted laminates was determined through quasi-static tensile tests. The residual strength shows a strong dependence on the impact damage size, characterised in terms of fibre fracture width and Delamination Area. Machined notches were then investigated and compared to impacted laminates in terms of residual strength.
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Experimental investigation of high velocity oblique impact and residual tensile strength of carbon/epoxy laminates
Composites Science and Technology, 2019Co-Authors: Ashwin R. Kristnama, Michael R Wisnom, Xiaodong Xu, D Nowell, Stephen R. HallettAbstract:Abstract Composite components are required to be resilient against Foreign Object Damage (FOD) induced by localised high velocity impact events. Here an experimental investigation into high velocity oblique impacts and residual tensile strength of thin quasi-isotropic carbon/epoxy laminates is reported. Oblique (45°) impacts between 100 m/s and 350 m/s were carried out using 3 mm steel cubes on the edge and the centre of the laminates, mounted as a cantilever beam. Impact induced damage was characterised using X-ray Computed Tomography (CT) and the residual strength of impacted laminates was determined through quasi-static tensile tests. The residual strength shows a strong dependence on the impact damage size, characterised in terms of fibre fracture width and Delamination Area. Machined notches were then investigated and compared to impacted laminates in terms of residual strength.
Maria Kashtalyan - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Delamination in laminates with angle-ply matrix cracks: Onset of damage and residual stiffness properties
Structural Integrity and Durability of Advanced Composites, 2015Co-Authors: Maria Kashtalyan, Constantinos SoutisAbstract:Abstract The failure process of composite laminate under quasi-static or fatigue loading involves sequential accumulation of intra- and interlaminar cracking. Matrix cracking parallel to the fibres in the off-axis plies is the first damage mode observed. It triggers development of other harmful resin-dominated modes such as Delaminations. In this chapter, analytical modelling of crack-induced Delaminations in composite laminates subjected to general in-plane loading is presented and discussed. A two-dimensional shear lag analysis is used to determine ply stresses in a representative segment and the equivalent laminate concept is applied to derive expressions for mode I and mode II and the total strain energy release rate associated with uniform local Delaminations. These expressions could be used with appropriate fracture criteria to estimate the onset of local Delamination in an already cracked off-axis laminate. Dependence of strain energy release rate on crack density, Delamination Area and ply orientation angle in unbalanced symmetric laminates is examined and discussed, and the effect of crack-induced Delamination on the laminate stiffness is predicted.
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Analysis of local Delaminations in composite laminates with angle-ply matrix cracks
International Journal of Solids and Structures, 2002Co-Authors: Maria KashtalyanAbstract:Abstract In this paper, local Delaminations growing uniformly from the tips of angle-ply matrix cracks in composite laminates loaded in tension are modelled theoretically. A 2-D shear lag method is used to determine stresses in a laminate representative segment containing one crack and two crack tip Delaminations. For the calculation of the strain-energy release rate (SERR) associated with Delaminations, the damaged layer is replaced with an equivalent homogeneous one with effective elastic properties. Closed-form expressions for the total SERR and its mode I and mode II components as a linear function of the first partial derivatives of the effective elastic properties of the damaged layer with respect to Delamination Area are derived. Dependence of SERRs and the laminate stiffness properties on Delamination Area, crack density and ply orientation angle is examined for balanced [0 2 /θ 2 /− θ 2 ] s and unbalanced [0 2 /θ 2 ] s carbon/epoxy laminates. The total SERR obtained in this study is compared to a simple closed-form expression for a uniform local Delamination derived in earlier work by O'Brien (Local Delamination in laminates with angle-ply matrix cracks: Part II Delamination Fracture Analysis and Fatigue Characterization. NASA Technical Memorandum 104076/AVSCOM Technical Report 91-B-011). It appears that matrix crack density and Delamination size influence the SERR value significantly.
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The effect of Delaminations induced by transverse cracks and splits on stiffness properties of composite laminates
Composites Part A: Applied Science and Manufacturing, 2000Co-Authors: Maria Kashtalyan, Constantinos SoutisAbstract:Abstract In an effort to evaluate stiffness degradation due to Delaminations growing at the 0°/90° interface from the tips of transverse cracks in the 90° plies and splits in the 0° plies of cross-ply [0m/90n]s laminates, a new theoretical approach was developed. It employs the Equivalent Constraint Model of the damaged lamina [Fan J, Zhang J. In-situ damage evolution and micro/macro transition for laminated composites. Composites Science and Technology 1993;47:107–118], which allows one to avoid cumbersome consideration of the repeated laminate element defined by the intersecting pairs of transverse cracks and splits. It also uses an improved 2D shear-lag analysis [Zhang J, Soutis C, Fan J. Strain energy release rate associated with local Delamination in cracked composite laminates. Composites 1994;25(9):851–862] to determine the stress fields in the explicitly damaged lamina and the In situ Damage Effective Functions to describe its reduced stiffness properties. Reduced stiffness properties of the damaged lamina are found to depend explicitly upon the crack density and relative Delamination Area associated with that lamina and implicitly upon two damage parameters associated with the neighbouring lamina. Theoretical predictions reveal that transverse crack tip Delaminations cause significant reduction in the shear modulus and Poisson's ratio of cross-ply and symmetric balanced [±θm/90n]s laminates. Dependence of the laminate reduced elastic properties on the orientation angle of the constraining ply is examined. Contribution of each damage mode (transverse cracking, transverse crack tip Delaminations, splitting and split tip Delaminations) into stiffness loss is established.
Ashwin R. Kristnama - One of the best experts on this subject based on the ideXlab platform.
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numerical analysis of high velocity oblique impacts and residual tensile strength of carbon epoxy laminates
Composite Structures, 2021Co-Authors: Ashwin R. Kristnama, Michael R Wisnom, Stephen R. HallettAbstract:Abstract This paper presents prediction of the high velocity, oblique impact response and quasi-static residual tensile strength of thin [45/90/−45/0]2s carbon/epoxy laminates using finite element (FE) models. A High-Fidelity Finite Element Method (Hi-FEM) with an automated unit cell meshing technique was employed. The predicted impact damage, characterised by the extent of fibre failure and Delamination Area, was validated against results from gas-gun tests for a range of impact velocities. The numerical results captured the trend of increasing impact damage with impact energy as observed from the tests. Changes in projectile orientation before impact were shown to increase the extent of fibre failure at high impact energies, up by 38% in edge impact cases. The residual tensile strength of the impacted laminates was then investigated, where the numerical results for edge-impacted laminates agreed with the test data within 8%. On the other hand, the residual strength modelling results of centre-impacted laminates were found to be unconservative, mainly due to the extent of fibre failure predicted during impact. Machined notches were also studied for their residual tensile strength in comparison to impact induced damage. The predicted strength of edge-notched laminates was found to be in close agreement with the experimental results for edge-impacted laminates, differing by an average of 9%.
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experimental investigation of high velocity oblique impact and residual tensile strength of carbon epoxy laminates
Composites Science and Technology, 2019Co-Authors: Ashwin R. Kristnama, Michael R Wisnom, Xiaodong Xu, D Nowell, Stephen R. HallettAbstract:Abstract Composite components are required to be resilient against Foreign Object Damage (FOD) induced by localised high velocity impact events. Here an experimental investigation into high velocity oblique impacts and residual tensile strength of thin quasi-isotropic carbon/epoxy laminates is reported. Oblique (45°) impacts between 100 m/s and 350 m/s were carried out using 3 mm steel cubes on the edge and the centre of the laminates, mounted as a cantilever beam. Impact induced damage was characterised using X-ray Computed Tomography (CT) and the residual strength of impacted laminates was determined through quasi-static tensile tests. The residual strength shows a strong dependence on the impact damage size, characterised in terms of fibre fracture width and Delamination Area. Machined notches were then investigated and compared to impacted laminates in terms of residual strength.
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Experimental investigation of high velocity oblique impact and residual tensile strength of carbon/epoxy laminates
Composites Science and Technology, 2019Co-Authors: Ashwin R. Kristnama, Michael R Wisnom, Xiaodong Xu, D Nowell, Stephen R. HallettAbstract:Abstract Composite components are required to be resilient against Foreign Object Damage (FOD) induced by localised high velocity impact events. Here an experimental investigation into high velocity oblique impacts and residual tensile strength of thin quasi-isotropic carbon/epoxy laminates is reported. Oblique (45°) impacts between 100 m/s and 350 m/s were carried out using 3 mm steel cubes on the edge and the centre of the laminates, mounted as a cantilever beam. Impact induced damage was characterised using X-ray Computed Tomography (CT) and the residual strength of impacted laminates was determined through quasi-static tensile tests. The residual strength shows a strong dependence on the impact damage size, characterised in terms of fibre fracture width and Delamination Area. Machined notches were then investigated and compared to impacted laminates in terms of residual strength.
G P Rodriguez - One of the best experts on this subject based on the ideXlab platform.
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damage resistance of carbon fibre reinforced epoxy laminates subjected to low velocity impact effects of laminate thickness and ply stacking sequence
Polymer Testing, 2017Co-Authors: M A Caminero, I Garciamoreno, G P RodriguezAbstract:Abstract A major concern affecting the efficient use of composite laminates is the effect of low velocity impact damage on the structural integrity [1–3]. The aim of this study is to characterize and assess the effect of laminate thickness, ply-stacking sequence and scaling technique on the damage resistance of CFRP laminates subjected to low velocity impact. Drop-weight impact tests are carried out to determine impact response. Ultrasonic C-scanning and cross-sectional micrographs are examined to assess failure mechanisms of the different configurations. It is observed that damage resistance decreases as impact energy increases. In addition, thicker laminates show lower absorbed energy but, conversely, a more extensive Delamination due to higher bending stiffness. Thinner laminates show higher failure depth. Furthermore, quasi-isotropic laminates show better performance in terms of damage resistance. Finally, the results obtained demonstrate that introducing ply clustering had a negative effect on the damage resistance and on the Delamination Area.