Translaminar Fracture Toughness Research Articles

Translaminar fracture toughness characterisation for a glass fibre/polyamide 6 laminated composite by a novel approach based on fictitious material concept

This paper proposes a novel approach for the characterisation of the material fracture toughness associated with translaminar tensile failure, consisting in the application of the Fictitious Material Concept (FMC) by using the testing configuration of the Modified Two Parameter Model (MTPM). The main advantage of such an approach is to avoid the use of nonlinear fracture mechanics for material fracture toughness characterisation. The novel approach is applied to compute the translaminar fracture toughness of a unidirectional glass fibre (GF)/polyamide 6 (PA6) laminated composite. Moreover, the experimental campaign carried out is numerically simulated by means of a micromechanical finite element model, and the fracture toughness is computed by employing two different approaches, that is, the novel one and the MTPM. The present study proves, for the first time, that the Fictitious Material Concept can be applied by considering both experimental and numerical structural responses since it provides, in both cases, quite satisfactory accuracy in term of laminated composite fracture toughness. Therefore, the great advantage is that, when a validated numerical model is available, experimental campaigns may be avoided, saving time and money. Moreover, it is proved that the FMC can be used to investigate specimen size effect on fracture toughness.

Effects of translaminar edge crack and fiber angle on fracture toughness and crack propagation behaviors of laminated carbon fiber composites

Abstract In this study, the translaminar fracture toughness of carbon fiber laminated composites with different layer sequences was investigated experimentally and numerically for different crack directions. In the numerical study, first of all, the critical stress intensity factor was determined by using the M-integral method. Three-dimensional model and M-integral analysis were achieved in the ANSYS finite element package program. The non-local stress fracture criterion was used to in order to find failure curves of the materials. Then, in order to find the crack propagation directions numerically, the solid model was transferred to the LS-DYNA program and progressive failure analysis was performed. Fracture toughness decreased by 9.92 % with the change of crack angle from 15° to 90°. As the fiber angle changed from 0° to 45°, it decreased by 9.17 %. The biggest error between the experimental and numerical study results was found at α = 45°, with a rate of 12.3 %.

Machine learning-based determination of Mode II translaminar fracture toughness of composite laminates from simple V-notched shear tests

This paper presents a novel method for measuring the translaminar crack resistance curve of composite laminates under Mode II shear loading. A machine learning (ML)-based approach is utilized to extract the inapparent information of the crack resistance curve from the translaminar shear strength measurements obtained from simple V-notched shear tests. The entire campaign is built on the framework of the Finite Fracture Mechanics (FFM) combined with Finite Element Method (FEM). Special emphasis is made on the nonlinear mechanical behavior of composites under shear stress since the original FFM models are designed for quasi-brittle materials. With the well-trained recurrent neural network model, the Mode II R-curve of composite laminate can be obtained with un-notched and V-notched shear strength values as inputs. Experiments were conducted on carbon fiber-reinforced composites to validate the accuracy of the R-curve obtained by the proposed approach and that by the traditional compact shear test. The successful implementation of the method suggests a more convenient and low-cost way of obtaining this important damage-related parameter for composites.

Enhanced damage tolerance and fracture toughness of lightweight carbon-Kevlar fiber hybrid laminate

Low damage tolerance and residual strength are the main drawbacks of carbon fiber composite laminates that limit their application in many lightweight structures. This study demonstrates the exceptional damage tolerance and high fracture toughness of carbon-Kevlar hybrid laminate, where Kevlar plies are placed between two carbon fiber face sheets. Flexural strength after damage and mode I translaminar fracture toughness of carbon and Kevlar and the hybrid laminates were evaluated using three-point bending and single-edge notched bending tests, respectively. The damage mechanisms in the three configurations were investigated using micro-computed tomography and correlated with their mechanical responses. The results showed that the hybrid laminate could sustain 70% of the laminate strength after fiber damage occurs and can sustain the same strength for large strains, unlike carbon and Kevlar fiber laminates, where they both lose their mechanical integrity after fiber breakage. Moreover, this laminate showed 200% and 170% larger specific absorbed energy than carbon and Kevlar laminates, respectively. The improvement can be justified by the propagation of fiber breakage at three different positions in the Kevlar core and the delamination at the carbon-Kevlar interface that allowed larger energy dissipation during fracture. Additionally, it showed 21% and 42.7% larger absolute and specific fracture toughness, respectively, than the carbon fiber laminate.

Mechanical and electromagnetic interference shielding properties of natural fiber reinforced polymer composite with carbon nanotubes addition

AbstractMechanical and electromagnetic interference (EMI) shielding properties are investigated for developed synthesized green composite. The varying content of kenaf fiber‐reinforced high‐density polyethylene (HDPE) composite has been fabricated using microwave‐assisted compression molding techniques with and without the addition of multi‐walled carbon nanotubes (MWCNTs). X band range has been used for EMI shielding characterization. Optimization for mechanical strength has been done using tensile test, impact test, and translaminar fracture toughness test. Fractography by scanning electron and optical microscopy concluded that interfacial adhesion between kenaf fiber and HDPE matrix and the degree of ductility of the matrix are primary governing factors for change in mechanical properties. The differential scanning calorimetry confirmed no change in the degree of crystallization of the matrix with the addition of MWCNTs. Composite with EMI shielding effect above 30 dB along with superior mechanical properties is obtained at 16% (v/v) kenaf fiber content with the addition of 5% (wt.) conductive MWCNTs for possible application in electronic equipment casing, overhead bin, or unmanned aerial vehicles.

Interlaminar and translaminar fracture toughness of 3D‐printed continuous fiber reinforced composites: A review and prospect

AbstractFracture toughness is a critical parameter in the evaluation of a component's structural integrity and damage tolerance. For 3D‐printed continuous fiber reinforced composites (CFRCs) based on the fused deposition modeling (FDM) technique, the fracture behavior differed from that of composites manufactured by traditional processes due to the presence of voids and interfaces at different scales, receiving significant attention. Recently published research attempted to apply various testing standards (for other materials) to investigate the fracture behavior of 3D‐printed CFRCs. In these results, the fracture toughness of CFRCs was influenced by the manufacturing parameters dependent on structural porosity and interfacial bonding quality. This paper reviewed fracture toughness measurement standards compatible with CFRCs, factors influencing fracture behavior, and methods improving the fracture toughness of CFRCs. Lastly, this review explored limitations in current studies focused on fracture toughness measurement of 3D‐printed CFRCs and future perspectives for the fabrication of 3D‐printed CFRCs with improved fracture toughness.Highlights This review focuses on fracture toughness measurement standards compatible with 3D‐printed continuous fiber reinforced composites (CFRCs). The manufacturing parameters influencing fracture behavior and methods improving fracture toughness were summarized. This review explores limitations in current studies focused on fracture toughness measurement of 3D‐printed CFRCs.

Hygrothermal effects on translaminar fracture toughness of quasi-isotropic laminates with different stacking sequences

Hygrothermal effects on the translaminar fracture toughness of the carbon/epoxy composite with two different stacking sequences at 120 °C were studied and the failure mechanisms are explained. The eccentrically loaded single-edge-notch tension (ESET) experiments showed that two different quasi-isotropic stacking sequences ([90/45/0/-45]4s and [45/90/-45/0]4s) have negligible difference in translaminar fracture toughness. It was found that the fracture toughness of conditioned specimens at hot temperature wet (HTW) condition increased by 75 % compared to that at room temperature dry (RTD). The average saturated damage height at HTW increased by 48 % compared with that at RTD according to ex situ X-ray computed tomography (CT) observation. The larger saturated damage height observed in the 0° plies of the HTW specimens results in the higher translaminar fracture toughness.

Experimental characterization of tensile and compressive translaminar fracture toughness coupling multi-physics measurements

The study of the failure modes of carbon fiber reinforced polymers is essential due to their extensive use in industry. Translaminar failure (at the scale of the laminate) has been studied extensively the main goal being to compute the critical strain energy release rate in mode I of the ply GIC_ply but large variations can be observed between papers. This study investigates this failure mode of a carbon/epoxy laminate, using Compact Tension (CT) and Compact Compression (CC) specimens. The stacking sequence used is [45/-45/(0/90)4]s where 45° plies on the outside efficiently prevented the buckling of the specimen to be observed, as well as plasticity of the matrix. Moreover, this layup is rather similar to real-life industrial stacking sequences. Strains fields and axes displacement were obtained using digital image correlation. Infrared images were used to follow the crack propagation during the loading of the specimen and compared to DIC and X-ray tomography crack length measurements. IR measurements studied from a qualitative point of view were thus shown to be an efficient and reliable method. GIC of the laminate GIC_lam was computed with both the ASTM-E399 and compliance methods, and finally GIC_ply was computed using a rule of mixtures. Secondary damage was detected and its effects on the energy dissipated were quantified using strain fields, X-ray and infrared images. This enabled a more accurate rule of mixtures to be redefined. The failure scenarios of all specimens were eventually exhibited. GIC_ply values in tension were found to be higher than in the literature whereas in compression it was found to be lower than in the literature, due to crack propagation being detected earlier by means of IR measurements.

Fracture assessment of U-notched diagonally loaded square plates additively manufactured from ABS with different raster orientations

This paper investigates the fracture behavior of 3D-printed notched specimens under various combinations of mode I and mode II loadings, including pure mode I and pure mode II loadings. The study employs fused deposition modeling (FDM) to fabricate U-notched diagonally loaded square plate (UNDLSP) specimens using Acrylonitrile Butadiene Styrene (ABS) filaments. To experimentally measure the fracture load and fracture initiation angles, 120 UNDLSP specimens are 3D printed with different notch tip radii, notch orientation angles, and [0, 90], [45, −45] raster orientations. Tensile characteristics and translaminar fracture toughness of ABS plates with [0, 90] and [45, −45] raster orientations are obtained using dog-bone and cracked DLSP samples, respectively. Considering the layered nature and anisotropy of the material, the virtual isotropic material concept (VIMC) is utilized along with two well-known stress-based brittle fracture models: the maximum tangential stress (MTS) and the mean stress (MS) criteria. The test results are predicted using the fracture limit curves and fracture initiation angle curves developed for these fracture models in terms of the notch stress intensity factors (NSIFs). Furthermore, a general equation is established to estimate the fracture initiation angle of U-notched ABS specimens under mixed mode I/II loading, irrespective of geometry, raster orientation, and notch tip radius, based on the curves obtained from the MTS and MS criteria. The fracture surfaces of the UNDLSP specimens are examined using scanning electron microscopy (SEM) to study the micro-mechanisms involved in the fracture process. The findings indicate that both the VIMC-UMTS and VIMC-UMS criteria accurately predict the experimentally achieved fracture loads. Additionally, it is observed that the fracture initiation angle curves for both criteria are nearly identical and accurate. The significance of this research is not only providing numerous new experimental results on mixed mode I/II fracture of notched 3D-printed ABS plates, but also providing simple, fast, accurate, and robust criteria for predicting the critical loads of such plates, without the need for conducting layer-by-layer failure analysis using progressive damage models.

On the mixed mode I/II translaminar fracture of plain-weave carbon, E-glass and Kevlar reinforced laminated composites

The main aim of this study is to investigate the influence of long fiber types on the translaminar fracture behvior of epoxy-based composites subjected to pure mode I, mixed mode I/II and pure mode II using a combined experimental study and finite element (FE) analysis. Compact tension shear (CTS) test configuration was used to determine the critical strain energy release rate (CSERR) of the laminated composites reinforced with three types of high-performance fibers: Carbon, E-glass and Kevlar fiber. We believe that this is the first published report on the full combination of mode I, mixed mode I/II and mode II translaminar fracture toughness of laminated composites reinforced by three types of fiber. The translaminar fracture envelopes of the tested materials were illustrated. The results revealed that the translaminar CSERR of the composite systems is strongly dependent on the reinforcement type and the loading condition. The mode I translaminar CSERR of E-glass, Carbon and Kevlar fiber reinforced composites are equal to 16.87, 13.52, and 18.29 kJ/m2, respectively. Besides, under mode II loading condition, the translaminar CSERR of the laminated composites reinforced by E-glass, Carbon and Kevlar is obtained as 15.21, 7.82, and 8.45 kJ/m2, respectively. Fractographic analysis manifested that fiber pull-out clustering, fiber splitting, fiber breakage and matrix cracking are the main energy dissipating mechanisms happened on the fracture surface of the laminated composites.

Experimental investigation on translaminar fracture behavior of cross-laminated bamboo

Cross-laminated bamboo (CLB) is a bamboo-based construction product with bamboo's advantages, which are green, environmentally protective, and sustainable. However, bamboo is easy to crack. Structural elements in bamboo constructions are assembled onsite, making splitting cracks easily form at joints and bolt connections. Therefore, it is essential to assess cracked structure safety with fracture mechanics. However, rare studies are addressed on fracture properties of bidirectional laminated bamboo, especially the translaminar fracture resistance, which represents the ability to arrest a catastrophic crack in structures. This paper studies the translaminar fracture properties of CLB composite using three-point bending beam tests. Load-displacement and load-CMOD curve characteristics, fracture process, and the failure modes of bidirectional laminated bamboo are analyzed. The R-curve expressed by the energy release rate is calculated by three methods. Results demonstrate that the R-curves obtained by the three different methods show similar results. The methods to determine R-curves employed in this study are simple and can describe the translaminar fracture toughness of laminated bamboo. The methods are validated by comparing the traction-separation relations calculated from the R-curves to those measured by double-edge notched tests (DENT). A comparison of the bidirectional laminated bamboo's energy release rate to the matrix-dominated energy release rate of unidirectional laminated bamboo reveals that bidirectional fiber arrangement has a remarkable improvement on the toughening of laminated bamboo at and after crack initiation. Moreover, the lay-up effects of CLB are analyzed by relating the energy release rate results to the failure pattern of fractured specimens. It is found that fiber pullout/bridging caused by 90°direction crack propagation around fiber bundles is the dominant toughening mechanism of CLB. The lay-up sequence of 0° and 90° plies also has an effect on 90°direction crack propagation; therefore, it will influence the toughness of CLB.

Numerical modelling of quasi-static and dynamic compact tension tests for obtaining the translaminar fracture toughness of CFRP

In the recent past, several studies have been undertaken to characterise the loading rate dependency of the translaminar fracture toughness GIcf+, however, no consensus has yet been reached. In an attempt to make a first step towards resolving this inconsistency, this work employed a modelling campaign based on the experimental data generated in Hoffmann et al. [Compos Sci Technol 164 (2018) 110–119] in order to identify the driving mechanism behind the negative loading rate trend observed in said study. The numerical analysis employed detailed FE models of the quasi-static and high-rate experiments, as well as a high-fidelity strain-rate- and pressure-dependent user material model to represent the intralaminar behaviour of the composite material. This study found the energy release rate along the macroscopic crack to be practically rate-insensitive. Loading rate, however, was shown to have a pronounced effect on the extent of “secondary” energy dissipation mechanisms away from the macroscopic crack in the form of matrix damage and plasticity. This damage zone was significantly larger under quasi-static than under high-rate loading, thus providing an explanation for the observed drop of GIcf+ under elevated loading rates in Hoffmann et al. (2018).

Investigating the translaminar fracture toughness of 3D printed semi-woven and non-woven continuous carbon fibre composites

Investigating the translaminar fracture toughness of 3D printed semi-woven and non-woven continuous carbon fibre composites

Influence of flax fiber orientation on mechanical, thermo-mechanical and interfacial adhesion properties of epoxidized methyl ricinoleate modified epoxy composite: A sustainable green composite for cleaner production

Renewable natural fibers have been better eco-friendly reinforcing agents for plant oil toughened epoxy composites in order to achieve the desired properties for structural applications. In the current work, epoxy methyl ricinoleate (EMR) synthesized from castor oil was used to modify epoxy to tailor the stiffness-toughness balance. For the first time, an epoxy/EMR blend has been used to fabricate the composite. The fiber pull-out test showed a 17% increment in interfacial shear strength on adding 20% EMR to epoxy and hence this modified epoxy was reinforced with UD (Unidirectional) mat at three different orientations i.e. [0/0], [0/90] and [90/90]. The [0/0] orientation laminates displayed the highest tensile, flexural, and impact strength with an increment of 120%, 151% and 858% respectively as compared to epoxy/EMR copolymer, whereas [0/90] orientation laminates showed superior translaminar fracture toughness and critical strain energy release rate with an increment of 216.5% and 494% respectively. Different theoretical models and a combination of classical lamination theory and modified rules of mixture were adopted to fit with the obtained experimental tensile strength and modulus values of appropriate laminates. Thermogravimetric and dynamic mechanical analysis confirmed the desired thermal stability and damping ability of the composites. Scanning electron microscope (SEM) morphology of the fractured surface and Water Contact Angle (WCA) of the surface of composites were studied to explain the fiber-matrix interface mechanism and wettability of the samples respectively. The results demonstrated that the EMR Modified Epoxy Composite can be an alternative to synthetic epoxy composites in automobile and structural applications. • Less viscous and reactive epoxy methyl ricinoleate (EMR)bio-resin is synthesized • High performance bio-composite using 20%EMR/epoxy as matrix was fabricated. • Effect of fiber inter-ply orientation on various mechanical properties was studied. • Failure mechanisms were validated with by Scanning Electron Microscope (SEM).

Characterizing and predicting the relationship between translaminar fracture toughness and pull-out length distributions under distinct temperatures.

The translaminar fracture toughness reflects the damage tolerance of a fibre-reinforced composite under longitudinal tension, which often governs the final failure of structures. One of the main energy-dissipation mechanisms that contributes to the translaminar toughness of composites is the fibre pull-out process. The present study aims to quantify and model the statistical distribution of fibre pull-out lengths formed on the translaminar fracture surface of composites, for the first time in the literature; this is done under different temperatures, so that the relationship between pull-out length distributions, micromechanical properties and the translaminar fracture toughness can be established. The fracture surfaces of cross-ply compact tension specimens tested under three different temperatures have been scanned through X-ray computed tomography to quantify the extent of fibre pull-out on the fracture surfaces; the distribution of pull-out lengths showed alarger average and larger variability with an increase in temperature, which also lead to an increase in translaminar fracture toughness. A similar trend has been captured by the proposed analytical model, which predicts the pull-out length distribution based on the analysis of quasi-fractal idealizations of the fracture surface, yielding an overall accuracy of more than 85%. This article is part of the theme issue 'Ageing and durability of composite materials'.

An experimental and numerical study on the translaminar fracture of cross-ply non-crimp fabric composites

In this paper, the damage propagation of a cross-ply Non-Crimp Fabric composite under Compact Tension is numerically modelled. The work includes an experimental study through which the internal structure of the composite is characterised, the translaminar fracture toughness values are obtained and the sequence of failure mechanisms are identified. Based on the experimental findings, a new exponential law is introduced during element failure under fibre tension to describe the unloading phase incorporating the fracture toughness as the governing parameter for material degradation. Furthermore, a power law based on the maximum strain criteria for transverse tension and in-plane shear loading is proposed to formulate the interactive damage propagation of the 90o layers. A set of physically-based failure criteria at layer level which account for the induced in- and out-of-plane fibre misalignment is associated with an energy-based damage mechanics method and implemented in Abaqus/Explicit as a VUMAT subroutine. The load–displacement response at all stages as well as the evolution of the translaminar fracture toughness during damage propagation are compared successfully against the experimental results.

Experimental characterization and numerical modelling of the translaminar fracture of woven-ply hybrid fibers reinforced thermoplastic laminates

The understanding of fracture mechanisms and the assessment of fracture toughness are key factors to the design of high-performance composite structures to be used in aeronautics. Thus, this work addresses the influence of initial notch orientation on the translaminar fracture of woven-ply hybrid fibers reinforced thermoplastic polyether ether ketone (PEEK) laminates. The translaminar fracture of Single-edge-notch bending (SENB) specimens is experimentally characterized depending on two initial notches (0° and 45°). Such geometry results in a complex stress state within the laminates plies as well as simultaneous tension/compression failures. A full-field measurement technique has been implemented to monitor the crack initiation and growth on the specimen surface during mechanical loading. To better understand the role played by the initial notch orientation as well as the plies orientation contribution to fracture behavior, a specific Finite Element mesoscale model was built to account for the deformation mechanisms (namely local plasticity) and the different damage behaviours (fiber breakage in tension and compression, kinking/crushing in compression, delamination) occurring within the plies of quasi-isotropic laminates. Linear elastic fracture mechanics concepts have been applied to quantify the critical translaminar fracture toughness (about 40 kJ/m2 in both cases). Finally, this study provides useful information on the fracture toughness values for engineers willing to design thermoplastic-based composite parts with stress concentrators.

On the use of Brazilian disk specimen for measuring mixed-mode I/II translaminar fracture toughness of notched glass/epoxy composite laminates: A comprehensive study

In this work, a comprehensive experimental and theoretical study is performed on laminated composites containing V- and U-notch to evaluate the last-ply-failure (LPF) load in mixed-mode I/II loading conditions. Numerous tests are conducted on the composite laminates using the Brazilian disk specimen for the first time. The samples are fabricated of E-glass/epoxy in three different lay-up configurations, namely unidirectional, cross-ply, and quasi-isotropic. Three notch opening angles of 2α = 30°, 60°, and 90° are considered for the V-notched samples, while for both V- and U-notches three notch tip radii of ρ= 1, 2, and 4 mm are taken into account. Four mixed-mode I/II loading angles of β = {0°, 10°, 20°, mode II} and three repetitions for each notch opening angle and composite lay-up configuration lead to an overall of 432 fracture tests in the experimental section of the paper, which can provide a good amount of experimental data set for other researchers. Subsequently, in the analytical section, two stress-based fracture criteria accompanied by the virtual isotropic material concept (VIMC) are employed to estimate the fracture loads theoretically. It is demonstrated that using the VIMC approach can yield accurate predictions, while it has much less computational costs compared to the traditional approaches in the literature.

Study of the fracture behaviour in hybrid fibers reinforced thermoplastic laminates: Influence of temperature and initial notch orientation

The present work was aimed at investigating the failure of quasi-isotropic fibers reinforced thermoplastic laminates solicited at different testing temperatures. Single-edge-notch bending (SENB) tests were conducted at room temperature (RT) and at a temperature higher than the glass transition temperature (Tg) to investigate the influence of failure mode (depending on initial notch orientation) as well as matrix ductility and toughness (depending on testing temperature) on: (1) damage mechanisms – (2) critical translaminar fracture toughness Gc and (3) G-R curves evolution. The mixed mode fracture toughness GI+II,c is dramatically lower than the mode I fracture toughness GIc, with −52% and −67% decreases, at RT and 150 °C respectively. In 45° notched specimens, most of the fracture energy (about 80%) stems from the mode I failure. Though they are not prominent on fracture, the failure mechanisms associated with mode II are instrumental in limiting the contribution of mode I on fracture behavior. Finally, though a temperature increase has very little influence on GIc, it significantly reduces the value of GI+II,c (−32%). This change primarily results from the formation of plastic-kink bands in compression that are promoted by both the ductility of the polyether ether ketone (PEEK) matrix at T > Tg and the mixed-mode failure.

Translaminar mode-I fracture toughness experiment of pultruded GFRP laminates using extended compact tension specimen

This paper conducted experiments and theoretic analysis of the fracture performance of pultruded GFRP (Glass Fiber Reinforced Polymers) laminates. The mode-I fracture toughness of pultruded GFRP laminates was evaluated by the eccentrically loaded, Extended Compact Tension (ECT) specimen. The geometry of specimen and experimental procedure refer to ASTM E1922. A total of 16 specimens were tested, which included 0° and 90° roving orientation. Finite element analysis with the Virtual Crack Closure Technique (VCCT) was implemented to calibrate the experimental results. A correction function for normalized notch length was proposed for pultruded GFRP translaminar fracture toughness. Carpet plot was designed to discuss the relationship between fiber volume ratio and fracture toughness, which demonstrated that the fracture toughness strongly correlated with the fiber volume ratio. Also, the effect of fraction of 0° layers on fracture toughness and material orthotropy was studied. The relationship of material orthotropy parameter and fracture toughness was discussed.