Nearly Mode I Fracture Toughness and Fatigue Delamination Propagation in a Multidirectional Laminate Fabricated by a Wet-Layup (original) (raw)
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Multi-directional composite laminates: fatigue delamination propagation in mode I—a comparison
International Journal of Fracture, 2019
Double cantilever beam (DCB) specimens composed of carbon fiber reinforced polymer laminate composites were tested. Two material systems were investigated. One consisted of plies from a woven prepreg alternating with tows in the 0 • /90 •-directions and the +45 • / − 45 •-directions. The second was fabricated by means of a wet-layup process with the same multi-directions as the prepreg. In addition, for the second material system, a unidirectional (UD) fabric ply was added. The delamination for this laminate was between the UD fabric and the woven ply with tows in the +45 • /−45 •-directions. Both fracture resistance Rcurve and fatigue delamination propagation tests were carried out. It is found that the initiation value of the interface energy release rate is substantially lower for the wet-layup; whereas, their steady state values are quite similar. The fatigue delamination propagation tests were performed at various cyclic R-ratios. The delamination propagation rate da/dN was calculated from the experimental data and plotted using a modified Paris equation with different functions of the mode I energy release rate. As expected, the da/dN curves L. Banks-Sills (B) • I.
On the Delamination of Multidirectional Laminates Under Mode I Loading
2012
The experimental characterization of the mode I interlaminar fracture toughness of multidirectional composite laminates is complicated because the crack tends to migrate from the propagation plane (crack jumping) invalidating the tests. However, the selection of the appropriate bending stiffness of the beam arms can avoid this tendency allowing this characterization. In the present work, six stacking sequences numerically analyzed have been experimentally tested to validate the methodology. The obtained results show that crack jumping can be effectively avoided by increasing the stiffness of the crack arms. Micrographies of the tested specimens show that the delamination is not a perfect interlaminar fracture as fiber tearing is also involved. The obtained toughness values show a dependency upon both the amount of fiber bridging and the interface angles.
Diagnostyka
Mechanically, composite laminates perform exceptionally well in-plane but poorly out-of-plane. Interlaminar damage, known as "delamination," is a major issue for composite laminates. Results from Mode-I and Mode-II experimental testing on twill-woven carbon fiber reinforced (CFRP) laminates are analyzed in this paper. Composite Mode-I fracture toughness was determined using three different methods in accordance with ASTM D5528: modified beam theory, compliance calibration, and a codified compliance calibration. Two methods, the Compliance Calibration Method and the Compliance-Based Beam Method, were used to determine the Mode-II fracture toughness in accordance with ASTM D7905. Stick-slip behavior is quite evident in the composite's Mode-I fracture toughness test findings. The MBT technique's Ic values for initiation and propagation are 0.533 and 0.679 KJ/m 2 , respectively. When comparing the MBT approach to the industry-standard ASTM procedure for determining fracture toughness Mode-I, the MBT method was shown to be highly compatible. Furthermore, the IIc values for the CBBM technique are 1.65 KJ/m 2 for non-pre cracked and 1.4 KJ/m 2 for pre-cracked materials. The CBBM method shows a good method to evaluate fracture toughness Mode-II, due to not needing to monitor the length of the crack during delamination growth to get the value of the fracture toughness.
diagnostyka, 2023
Mechanically, composite laminates perform exceptionally well in-plane but poorly out-of-plane. Interlaminar damage, known as "delamination," is a major issue for composite laminates. Results from Mode-I and Mode-II experimental testing on twill-woven carbon fiber reinforced (CFRP) laminates are analyzed in this paper. Composite Mode-I fracture toughness was determined using three different methods in accordance with ASTM D5528: modified beam theory, compliance calibration, and a codified compliance calibration. Two methods, the Compliance Calibration Method and the Compliance-Based Beam Method, were used to determine the Mode-II fracture toughness in accordance with ASTM D7905. Stick-slip behavior is quite evident in the composite's Mode-I fracture toughness test findings. The MBT technique's Ic values for initiation and propagation are 0.533 and 0.679 KJ/m 2 , respectively. When comparing the MBT approach to the industry-standard ASTM procedure for determining fracture toughness Mode-I, the MBT method was shown to be highly compatible. Furthermore, the IIc values for the CBBM technique are 1.65 KJ/m 2 for non-pre cracked and 1.4 KJ/m 2 for pre-cracked materials. The CBBM method shows a good method to evaluate fracture toughness Mode-II, due to not needing to monitor the length of the crack during delamination growth to get the value of the fracture toughness.
International Journal of Impact Engineering, 2017
A thorough experimental procedure is presented in which the mode II delamination resistance of a laminated fibre reinforced plastic (FRP) composite with and without Zpins is characterised when subjected to increasing strain rates. Standard three-point End Notched Flexure (3ENF) specimens were subjected to increasing displacement loading rates from quasi-static (~0m/s) to high velocity impact (5m/s) using a range of test equipment including drop weight impact tower and a Modified Hopkinson Bar apparatus for dynamic three-point bending tests. The procedure outlined uses compliance based approach to calculate the fracture toughness which was shown to produce acceptable values of GIIC for all loading rates. Using detailed high resolution imaging relationships between delamination velocities, apparent fracture toughness, longitudinal and shear strain rates were measured and compared. Confirming behaviours observed in literature, the thermosetting brittle epoxy composite showed minor increase in GIIC with increase in strain rate. However, the Z-pinned specimens showed a significant increase in the apparent GIIC with loading rate. This highlights the need to consider the strain rate dependency of the Zpinned laminates when designing Z-pinned structures undergoing impact.
The use of advanced carbon fibre-reinforced composites in aircraft primary structures has been steadily increasing over past two decades due to their high specific strength and stiffness, and their tailoring as per the need. The composite panels used in primary structures of aircraft are liable to be buckling during its service periods. It is observed that structures can withstand substantial amount of loads after they have buckled. Therefore, an approach to efficiently design the postbuckled composite structures is required to be developed. The designers of the next generation of aircraft are looking into the aspect of postbuckling composite structures to achieve substantial improvements in aircraft structural efficiency. In this work, the postbuckling response and growth of circular delamination in flat and curved composite plates are investigated for different delamination sizes and their locations through the laminate thickness. The prediction of delamination initiation and growth is carried out using the strain energy release rates obtained from the finite element analysis and comparing them to B-K's mixed-mode fracture criterion. The failure load is thus predicted. Predicted results for onset of delamination growth compared well with experimental results. Its variation with different delamination sizes and their locations across panel thickness was also investigated. It is observed that the failure loads are influenced by the delamination sizes depending on their locations across the laminate thickness. The different delamination sizes at H/3 laminate thickness did not have significant effects on the variations of compressive strengths of the delaminated composite panel. But, the compressive strengths of the panels having different delamination sizes at H/2 laminate thickness are more than that at H/3 and increase linearly with increase in delamination sizes.
Mechanical Behavior of Mode I Delamination of a Laminated Composite Material
2019
The objective of our work is to analyze numerically in three dimensions by the finite element method of the effect of a mechanical load on the delamination of unidirectional and multidirectional stratified composites in order to determine the energy release rate G in Mode I and the Von Mises equivalent stress distribution along the damaged area under the influence of several parameters such as applied load and delamination size. The results obtained in this study show that unidirectional composite laminates have better mechanical strength on the loading line than multi-directional composite laminates.
Delamination Modeling of Double Cantilever Beam of Unidirectional Composite Laminates
Journal of Failure Analysis and Prevention, 2017
Delamination crack growth in a double cantilever beam laminated composites is modeled by using simple stress analysis beam theory combined with simple linear elastic fracture mechanics and consideration of the theory of elastic failure in mechanics of material. Furthermore, advanced finite element (FE) model is built up. The FE approach employs surface cohesive zone model that is used to simulate the debonding and crack propagation. The analytical modeling, moreover, cracks growth and strain measurements, which are obtained from FE models, are compared with the available published experimental work. The predicted results give good agreement with interlaminar fracture toughness and maximum load which correspond to crack initiation point. The FE models results agree well with the available experimental data for both crack initiation and propagation.
Mode I fatigue delamination growth with fibre bridging in multidirectional composite laminates
Engineering Fracture Mechanics, 2018
Fatigue delamination in multidirectional composite laminates was experimentally investigated in present study. Both the Paris relation and a modified Paris relation (with a new similitude parameter) were employed to interpret fatigue delamination with significant fibre bridging. The results clearly demonstrated that fatigue delamination was independent of fibre bridging, if a reasonable similitude parameter was used in data reduction. As a result, a master resistance curve can be fitted to determine fatigue crack growth with different amounts of fibre bridging. The energy