Delamination Fracture Toughness Research Articles

Fabrication and comparison of interlaminar fracture toughness behaviour of glass epoxy composites with recycled milled Kevlar-carbon hybrid fillers

Current research uses a novel recycled milled carbon (rmCF), recycled milled Kevlar (rmKF), and innovative Hybrid fillers (rmHF) of both to increase glass/epoxy composite laminate delamination resistance. This study examines how crack propagation and fibre orientation affect laminated composite delamination fracture toughness. Recycled milled Fillers in the interlayer increase stiffness, delamination resistance, and fracture toughness by increasing the energy needed to crack the interlaminar domain. Here, Mode I, Mode II, and Mixed Mode (I/II) with GIGII = 25 %, 50 % and 75 % were studied for four different Interface fibre orientations. It appears [06/902/06] increased delamination toughness. Adding the novel recycled milled fillers improved delamination resistance. Among the three fillers, rmCF increased fracture toughness by 271 % and rmHF and rmKF composites had 220 % and 182 % higher fracture toughness. The synergy compensated for Kevlar's lower fracture toughness in the hybrid (rmHF). SEM analysis of fractured surfaces revealed crack deflection, individual debonding, and filler/matrix interlocking, all of which increase fracture toughness on different levels.

Modified mode I fracture toughness calculation method for composite laminate with large scale fiber bridging

Experimental investigation and theoretical analysis have been carried out in this study to assess the application limitation of the current ASTM D5528 method for Mode I fracture toughness calculation of composite laminate with fiber bridging. It is revealed that additional toughening effect introduced by the fiber bridging is not fully considered in the current method and consequently there are uncertainties associated with the fracture toughness calculated by the current ASTM method. Based on the same principle used in the development of the original ASTM method, a modified method is proposed to extend the applicability of the current method. The modified method is verified with mechanisms based cohesive zone modelling and numerical simulations of the Mode I delamination double cantilever beam tests. The significant improvement of the prediction results compared with experimental results by the modified method over the current method demonstrated its applicability for Mode I delamination fracture toughness calculation of composite laminates with large scale fiber bridging.

The low velocity impact properties of three- dimensional (3D) warp interlock woven composites according to the fabric architecture

Three-dimensional (3D) warp interlock woven composites (3DWIWC) are in demand in various industries due to their excellent delamination resistance, damage tolerance and fracture toughness properties. The 3D warp interlock woven fabric architecture can be defined by numerous fabric parameters such as: the binding and stuffer warp yarns, the woven pattern, the presence of yarn groups, etc. …. The effect of the fabric architecture on the impact behaviour of 3DWIWC made with carbon yarns has not been fully investigated. The binding warp yarns with the weave pattern play the main role in the arrangement of yarns within the final composite. In order to highlight their main influence, the 3D woven composites had been differentiated according to the main fabric architectural parameters, which are the angle and depth of binding warp yarn, presence of stuffer warp yarn and weave pattern of binding warp yarn. Afterward, their low velocity impact properties and damage mechanisms were examined. Thanks to the precise combination of these internal parameters of the fabric architecture, the contact force and absorbed energy values of 3DWIWC could be increased almost %50 and %15, respectively. Moreover, their damage mechanisms could be significantly improved.

Dual-scale numerical analysis of delamination in composite materials with varied fiber orientations at the interface

What is the relationship between the fiber orientation at delamination interface and the interlaminar fracture toughness of the composite? The answer is inconclusive based on experimental results. The conflicting observations stem from inconsistencies and inaccuracies in characterization techniques. As an alternative approach to circumvent the experimental challenges, the present study proposes a numerical dual-scale model for delamination, incorporating both micro- and meso-scale features. The model investigates two different fiber orientations at the mid-thickness interface: 0°/0° and 90°/90°. Comparative analyses demonstrate the importance of including a refined region with micromechanics to accurately predict the crack path during delamination. The results exhibit agreement with the literature models and enable estimation of early-initiation fracture toughness, considering delamination interacting with the microstructure while simulating a double cantilever beam specimen with reduced width. The approach provides a deeper understanding of delamination behavior and fracture toughness estimation, contributing to improving composite characterization techniques and design strategies.

Investigation of the mode-I delamination behavior of Double-Double laminate carbon fiber reinforced composite

Double-Double (DD) laminate, consisting of a repeat of a 4-ply sub-laminate [±Φ/±Ψ], has attracted widespread attention. The delamination damage of composites is always a significant failure problem in the application and a challenge for DD laminate. However, the mode-I delamination propagation behavior and fracture toughness of DD laminate with different interface angles were seldom reported. In this study, the interface angles of DD laminate were variable and could be classified into two types: Ψ/Φ and –Ψ/Φ interfaces. The effect of interface angle on the delamination propagation of DD laminate was explored using the double cantilever beam test. The delamination damage mechanisms of the above interfaces were revealed using macroscopic and microscopic characterization methods. The results showed that the initial fracture toughness values of laminates at the 0°/0°, 90°/0°, Ψ/Φ, and –Ψ/Φ interfaces were similar, and the steady-state fracture toughness values of laminates at the Ψ/Φ interfaces were at least 20% higher than that of the –Ψ/Φ interfaces. Moreover, the maximum bridging stresses at Ψ/Φ and –Ψ/Φ interfaces were approximately equal, while the final failure displacements at Ψ/Φ interfaces were about 1.4–1.5 times than that at –Ψ/Φ interfaces.

Mode II and mode III delamination of carbon fiber/epoxy composite laminates subjected to a four-point bending mechanism

Accurate determination of mode III interlaminar fracture toughness is paramount in composite materials due to its critical role in edge delamination, which nonetheless remains a significant challenge encountered. As such, this study focused on the investigation of mode II and III interlaminar fracture behavior of carbon fiber (CF)/epoxy composite laminates using four-end notched flexure (4ENF) tests and four-point bending plate (4PBP) tests, respectively. In particular, a cohesive zone model was employed for the simulation of the delamination process via finite element analysis (FEA). The mode II fracture toughness of CF/epoxy composites was determined to be 1.41 N/mm in experimental work. Additionally, experimental data in relation to force-displacement curves were in good agreement with numerical simulation results, which validated this simulation approach to successfully capture the mechanical response of composite laminates. In a similar manner, mode III delamination fracture toughness for CF/epoxy composites was numerically estimated to be 2.1 N/mm. Microscopic analysis indicated shear cusps were observed in both mode II and III specimens, as opposed to existing flakes discovered in mode III specimens only. Overall, this research enlightens a simple and effective way to estimate pure mode III fracture toughness and corresponding delamination behavior with respect to crack initiation and propagation.

Investigation of crack propagation in filament wound composite samples of Mode-I by using acoustic emission technique

A common industrial method of fabricating composite structural is filament winding, which is widely used to manufacture axisymmetric components. One of the most prevalent damage mechanisms in these composite structures is delamination, which occurs in various types of loading. In this research, the mechanical behavior and propagation of the initial crack of Mode-I in carbon/epoxy filament wound (FW) composite curve beams have been investigated via the acoustic emission (AE) method. For this purpose, at first, a composite tube was made with considering the artificial interlayer separation, and the beam specimens were cut from the longitudinal direction. At first, the initiation of the failures was determined using the AE method. Then, the growth and spread of interlayer delamination were investigated by the energy of AE signals and the sentry function. By determining the speed of the AE waves and providing a method to filter unwanted signals, the momentary position of the interlayer delamination tip during growth is predicted. The results showed that the fiber bridging phenomenon was due to the penetration of the two regions adjacent of the separation interface, and the fiber bridging length considerably affected the Mode-I delamination fracture toughness. In addition, the fracture toughness increased as the fiber bridging zone enlarged. Finally, good agreement was observed between the fracture toughness values obtained from the AE method and those found in the standard ASTM D5528.

Insights into the effect of fiber–matrix interphase physiochemical- mechanical properties on delamination resistance and fracture toughness of hybrid composites

Insights into the effect of fiber–matrix interphase physiochemical- mechanical properties on delamination resistance and fracture toughness of hybrid composites

On the applicability of rate-dependent cohesive zone models in low-velocity impact simulation

This paper studied the applicability of logarithmic, exponential and power cohesive zone models by carrying out experiments and simulations of low-velocity impact on composite laminates. The results show that the dynamic mechanical response and delamination damage under low-velocity impact simulated by the logarithmic rate-dependent CZM have the best agreement with experimental ones than other two models. The delamination damage simulated by exponential model are significantly higher than experimental results, which indicates that the delamination initiation strength and fracture toughness are less estimated under impacting load. The simulation by power model also generally has a good agreement with experimental result but the predicted dynamic mechanical response is a little bit worse than logarithmic model. This study suggests that logarithmic rate-dependent CZM is optimal during low-velocity impact simulation, followed by power model and exponential model.

Effect of PEEK Particles on Physiomechanical Behavior of Carbon/Epoxy Composite

The inherently brittle nature and the susceptibility to impact damage hinder the use of carbon/epoxy composite in some areas. In this study, poly ether ether ketone (PEEK) microparticles were incorporated to increase the resistance to delamination and interlaminar fracture toughness. A hand lay-up technique followed by compression molding was used to fabricate composite. The influence of PEEK particles was evaluated by tensile, flexural, short beam shear (SBS), compression, and Charpy impact test. The Barcol hardness, density, fiber volume fraction, and void content were also determined. According to the result, a maximum improvement in the tensile and flexural strength was observed for 2% incorporation of PEEK particles. However, there is downturn found in the flexural modulus. Moreover, a notable increment in the matrix-dominated properties (short beam shear, compression, and Charpy impact strength) was found with the addition of the PEEK particles.

Study of the winding methods influence on the aramid fibers impregnation degree for high-pressure pipes manufacturing

The purpose of this work is to compare the impregnation degree of samples made from an aramid-polyurethane composite material produced by three methods of winding. The para-aramid impregnation degree assessment was made on the basis of a microscopic examination of a sample’s section, as well as the results of determining the delamination fracture toughness of ring samples. Based on the studies, it was concluded that the best impregnation degree for para-aramid fibers is achieved in case of using binder sputtering assisted dry winding technology. This technology can be used for high-pressure flexible pipes manufacturing to increase their strength, which can lead to the product’s working pressure increasing.

Enhancement of Fracture Properties of Composite Laminate with Si C Additive

ASTM standards for short beam test, double cantilever beam and end notched specimen test are followed to compare control specimen with different percentage of Si C test data. Present study shows interlaminar shear strength (ILSS) and delamination fracture toughness values of multilayered composite laminate can be enhanced considerably with the use of Si C admixture in epoxy resin system as nonpolar elements compatible with to polar glass fiber. With respect to control specimen one percentage by weight of Si C w.r.t resin can bring up the ILSS value by as much 70% while the DCB test data on the critical energy release rate of mode I increases by 85% and mode II toughness value becomes double for 1% by weight of Si C. The bidirectional cloth provides more resistance for mode-I delamination fracture toughness when compared to UDL reported in literature and hence for higher fracture properties. The study is useful for design of rocket nozzles and input required for the cohesive zone model to assess the residual strength of composite structures with of delamination.

Finite Element Analysis of Delamination Behaviors of Composite Laminates under Hygrothermal Environment Using Virtual Crack Closure Technique

This research aims to study the delamination behaviors of T700/8911 composite laminates under hygrothermal environment. For two mixed-mode I/II delamination specimens: single-leg bending delamination and over-leg bending delamination, finite element analysis using virtual crack closure technique as a ABAQUS module is comparatively performed to study the delamination growth and load responses, in which different delamination growth criteria are used. Mechanical tests and analytical solutions for two kinds of specimens are used to get the delamination fracture toughness. Results show that hygrothermal environment decreases the load-bearing ability and delamination resistance to some extent. This work provides a new thread for studying the delamination mechanisms of composite laminates under hygrothermal environment.

The Double Drum Peel (DDP) test: A new concept to evaluate the delamination fracture toughness of cylindrical laminates

Standard delamination tests of monolithic composites prescribe configurations where the crack is a symmetry plane for both overall geometry and stacking sequence, ensuring a controlled mode ratio. These normalized configurations do not enable testing of curved specimens, like those manufactured by filament winding. Here, we propose a new concept for the delamination testing of cylindrical laminates, the Double Drum Peel, related to the peel tests used for adhesives or thin-films debonding. A global energy analysis, including all sources of energy release and dissipation, provides the expression of the critical strain energy release rate. As in the classical peel test, the energy dissipated by mechanisms other than delamination should be accounted for to determine intrinsic interface properties. The local mode mixity is evaluated based on analytical results on the classical peel test. Tests using carbon-peek rings manufactured by laser assisted tape placement are presented to illustrate the potential of the DDP.

Composite Laminate Delamination Simulation and Experiment: A Review of Recent Development

Composite laminate has extensive usage in the aerospace and automotive industries. Thus delamination, one of its most prevalent and challenging failure modes, has attracted substantial research efforts, and lead to the rapid development of both simulation and experiment method. Although reviews exist about simulation and experiment methods, there are not many that cover the development in the last five years. This paper is targeted to fill that gap. We covered a broad range of topic in delamination, from the basic delamination onset and propagation theories to complex loading scenarios, like impact and fatigue loading. From a simulation point of view, virtual crack closure technique (VCCT) and cohesive zone model (CZM), the two most famous methods of delamination modeling, are compared and elaborated. Their implementation techniques are described, and their merits and drawbacks are discussed. We also covered the failure mode of combined delamination and matrix cracking, which is prevalent in impact loading scenarios. Simulation techniques, along with the failure mechanisms, are presented. From experiment point of view, the discussed topics range from delamination fracture toughness (DFT) tests under static, dynamic, or cyclic loading conditions, to impact tests that aim to obtain the impact resistance and residual strength after impact. Moreover, a collection of recent experiment data is provided.

Numerical models of delamination behavior in 2G HTS tapes under transverse tension and peel

In extreme operating environments, delamination in 2G HTS tapes occurs within and/or near the superconductor layer from high transverse tensile stresses caused by fabrication, Lorentz forces and thermal mismatch, etc. Generally, transverse opening and peeling off are the main delamination modes, and are always studied in anvil and peel tests, respectively. Numerical models of these modes for 2G HTS tape are presented wherein the mixed-mode traction-separation law at the interface of the silver and superconductor layers is considered. Plastic deformations of copper, silver, and Hastelloy® in the HTS tape are taken into account. The results obtained from the transverse opening model show that the maximum average tensile stress is smaller than the delamination tensile strength because delamination is asynchronous in the tape. When a crack appears in the tape, only a small stress ( ≤ 1 MPa) is required to expand the crack to other stress free areas through peeling. Using the peeling model, the dependency of the peel strength on peeling angle is investigated under constant fracture toughness. Peel strength decreases with the peeling angle until the minimum value is reached at 150°, and thereafter increases slightly. Other results indicate that peel strength depends strongly on delamination strength, fracture toughness, and thickness of copper layer. The fracture toughness of the delamination interface, which is difficult to obtain by experiment, can be extracted using the present model.

Virtual Crack Closure Technique on Delamination Fracture Toughness of Composite Materials Based on Epoxy Resin Filled with Micro-Scale Hard Coal

Virtual Crack Closure Technique on Delamination Fracture Toughness of Composite Materials Based on Epoxy Resin Filled with Micro-Scale Hard Coal

Delamination fracture toughness of continuous glass-fiber/epoxy composites for structural applications

This paper presents experimental results of delamination fracture toughness tests on glass-fiber/epoxy composites which are manufactured in a novel Compression Resin transfer molding (CRTM) process in comparison to the performance of a well-studied RTM reference process. The examined laminates are built out of six plies, with a plain weave fiber orientation. 90% of the fibers are in longitudinal direction and 10% are perpendicular woven in. The influence of the process regarding interlaminar fracture toughness is tested under pure mode I (DCB), pure mode II (ENF) and mixed mode loading (MMB). The aim of this study is to establish a semi-empirical criterion to derive the interlaminar fracture toughness of all mixed-mode ratios using the pure mode I or II loading fracture toughnesses. It has been found, that the materials performance for both processes are comparable, however the fracture behavior is strongly influenced by the fabric structure. The examination of the laminates polymer system showed a strong R-curve behavior for mode I and mode II loading. It was possible to establish a semi empirical criterion that shows good agreement with the experimental results.

Prediction of mode I delamination resistance of z-pinned laminates using the embedded finite element technique

A new finite modelling approach is presented to analyse the mode I delamination fracture toughness of z-pinned laminates using the computationally efficient embedded element technique. In the FE model, each z-pin is represented by a single one-dimensional truss element that is embedded within the laminate. Each truss is given the material, geometric and spatial properties associated with the global crack bridging traction response of a z-pin in the laminate; this simplification provides a computationally efficient and flexible model where pin elements are independent of the underlying structural mesh for the laminate. The accuracy of the FE modelling approach is assessed using mode I interlaminar fracture toughness data for a carbon-epoxy laminate reinforced with z-pins made of copper, titanium or stainless steel. The model is able to predict with good accuracy the crack growth resistance curves and fracture toughness properties for the different types of z-pinned laminate.

Delamination fracture toughness of UHMWPE fibers/polyurethane laminates interleaved with carbon nanotube‐reinforced polyurethane films

The main cause for failure of composite laminates is delamination under shear or transverse loading. A common approach to prevent such failure is to introduce a discrete interleaf at the midplane of the laminate in order to increase its fracture toughness and, consequently, its resistance to delamination. Accordingly, a study of Mode I fracture toughness of ultra‐high molecular weight polyethylene fibers/polyurethane matrix composite laminates interleaved with thin polyurethane films reinforced with either untreated or functionalized carbon nanotubes is presented here. The results show that—depending on the surface treatment of the carbon nanotubes—the introduction of an interleaf at the midplane of the laminate generates a significant improvement of the Mode I initiation and propagation fracture toughness compared to the non‐interleaved laminates and to laminates interleaved with un‐reinforced polyurethane films. The Mode I fracture toughness results correlate with the “trouser‐leg” fracture surface energy of the films. Copyright © 2016 John Wiley & Sons, Ltd.