Fracture Behavior Of Composites Research Articles

Exploring the influence of specimen types on the intralaminar fracture behavior of fiber-reinforced polymer matrix composites

The accurate determination of fracture toughness of fiber-reinforced composites is critical for the assessment of structural integrity. Although there have been many studies on the intralaminar fracture behavior of composites, satisfactory results have not yet been obtained regarding the influence of specimen types. In this paper, commonly used fracture specimens (DCT, CT, ESET, pin-loaded SENT and clamped SENT specimen) are applied to study their applicability in the fracture behaviors of composites with different orientations. And the impact of data processing methods for the area method, GC-compliance and GC-stress intensity factors on fracture performance was analyzed. The results showed that the above three data processing methods have obtained relatively consistent fracture properties. Different specimens obtained significantly various results, showing a gradually decreasing trend from clamped SENT, ESET, pin-loaded SENT, CT to DCT. Furthermore, considering that the clamped SENT specimen is closest to the Mode-I fracture toughness obtained from the DCB specimen, and there is no compression damage in the experiments under different orientations, this specimen type is the most recommended specimen. Finally, the failure mechanisms of carbon fiber-reinforced composite under different specimen types and orientations were revealed. As the orientation angle increases (β from 0° to 90°), the failure mode gradually transitions from matrix cracking and interface debonding to matrix shear and fiber fracture. The above achievements will contribute to a deeper understanding of the intralaminar fracture process and failure mechanism of fiber-reinforced composites.

Fracture behaviors of nacre-like composites via phase-field fracture modeling

Nacre-inspired composites, composed of hard and soft phases, exhibit exceptional combinations of stiffness, strength, and fracture toughness. However, the fracture behaviors of these composites are significantly influenced by the geometric factors and material properties of their constituents. In this study, we systematically investigate the fracture behaviors of nacre-like composites by employing a phase-field fracture model considering the effects of oblique angle between loading and platelet directions, a critical factor often overlooked in previous studies, coupled with the effect of other geometric and material parameters, such as the aspect ratio, Young's modulus and fracture toughness ratio between hard and soft phase. Our findings highlight the significant influence of the oblique angle on the mechanical properties and fracture behaviors of these composites. Particularly, it is found the maximum Young’s modulus and strength are obtained when the direction of hard platelet is aligned with the tension direction, while the maximum toughness is achieved at a moderate oblique angle, especially in cases of large aspect ratios, small Young's modulus and fracture toughness ratios between the hard and soft phases. Besides, the maximum fracture toughness is more likely to be obtained at a small aspect ratio and large Young's modulus ratio between hard and soft phases. The insights gained from our study would offer valuable guidance for the design and practical application of nacre-mimetic composites.

Effects of void shape and location on the fracture and plastic deformation of Cu (crystalline) /Cu64Zr36 (amorphous) composites

Voids are probably the most widely studied type of manufacturing defects since they are often formed during material processing. In this paper, the fracture and plastic deformation of Cu/Cu64Zr36 crystalline/amorphous composites with different void locations and shapes are investigated by molecular dynamics simulations. The results show that changes of the void location and shape in the composites significantly change the dislocation motion, shear transformation zones (STZs) activation, shear band propagation, and fracture strength of the composites. The largest shear strain is always found around the void, where it is most likely to activate dislocation motion, STZs and shear band formation. A stepwise increase of the shear localization is mainly related to the nucleation and emission of dislocations, while the very rapid increase is caused by shear band formation. Moreover, the variation of dislocation density and activity of shear bands are mainly responsible for the stress fluctuations in the composites. This paper provides important information for understanding and improving the plastic and fracture behaviors of composites by changing the location and shape of void from an atomistic perspective.

Fatigue life and fracture behaviors of aligned steel fiber reinforced cementitious composites (ASFRC)

Aligned and random steel fiber reinforced cementitious composites (ASFRC, SFRC) are prepared to study how fiber orientation and volume fraction affect the fatigue life and fracture behaviors of composites. The experimental results indicate the fatigue life of ASFRC exceeds that of SFRC by more than 8 times. Compared with SFRC, the critical effective crack length of ASFRC is improved by more than 17%, which can withstand greater deformation and crack propagation. And the improvement increases with enlarging fiber volume fraction (Vf). Furthermore, based on the experimental results, a two-parameters fracture model considering Vf is developed to predict the fatigue life.

The effect of temperature on the tensile properties and failure mechanisms of two-dimensional braided composites

Abstract Two-dimensional (2D) braided composites have excellent structural integrity and damage tolerance. Currently, there are few researches focused on the effect of temperature on tensile failure behaviors of 2D braided composites. In this study, 2D biaxial braided composites with different fiber materials were prepared, and the tensile properties and failure mechanisms of these braided composites at different temperatures were studied by means of the tensile test and the high-definition charge coupled device optical microscope. The results show that temperature has significant effects on the tensile properties and fracture damage of 2D braided composites. As the temperature increases, the tensile properties of the two braided composites decrease obviously, and their external fracture failure becomes subtle, while their internal deformation damage becomes significant. Moreover, the differences between the two fibers in tensile fracture behaviors of composites can be more conspicuously observed at higher temperatures.

A nonlinear crack bridging model for the composites with curved reinforcement

Both artificial nanocomposites and biological materials typically contain nanofillers with curved forms, which allows them to develop excellent mechanical characteristics and functionalities. In order to measure the fracture toughness of the composites contributed by the bridged reinforcement with curved morphology, a theoretical model based on micromechanics and taking into account the reinforcement's curvature is developed in this study. It is found that the fracture toughness of the composites is more sensitive to the reinforcement waviness rather than its curvature. Larger waviness contributes to higher fracture toughness. By increasing platelet length, volume fraction, and modulus ratio, as well as increasing the interfacial frictional stress after debonding, the fracture toughness of composites is dramatically improved. This study expands our understanding of how reinforcement morphology affects fracture behaviors of composites and offers theoretical insights for elucidating the structure–property relationships of complex micro-structured advanced composites.

High-speed grinding fracture mechanism of Cf/SiC composite considering interfacial strength and anisotropy

Cf/SiC composite is connected through the bonding interface to achieve the toughening effect, which makes the fiber direction and interface strength in the material directly affect the composite properties and grinding quality. Aiming at the high-quality processing of Cf/SiC composite, a single abrasive particle model is built to reveal the variation law of grinding force in the process and the surface damage phenomena such as interface debonding, fiber fracture and matrix fracture. Based on the constitutive relationship among matrix, reinforcement and interface phase, the constitutive model of composite was established. However, Cf/SiC composite is a typical hard brittle material. Low grinding speed cannot yield to good machining quality. Thus, to improve the output quality, high speed grinding is applied in this paper. Meanwhile, by considering the heterogeneous structure characteristics of composite materials, the two-dimensional simulation of grinding of single abrasive particle grinding, based on FEM (Finite Element Model) method, is realized. Finally, composite fracture behavior is analyzed by observing microstructure in the grinding process. The effects of fiber orientation, surface strength, grinding speed, and grinding depth on the surface properties and the quality of Cf/SiC composite are studied by grinding force and surface analysis. The mechanism of high-speed grinding of ceramic matrix composites, as well as the practical approach and theoretical underpinnings of grinding process optimization, are examined.

The influence of SAP particle size and extra water on the dynamic mechanical behavior of SAP-modified cement-based composites

Superabsorbent polymers (SAP)-modified cement-based composites (abbreviated as composites) have excellent frost resistance, internal curing efficiency, self-sealing and self-healing capacity. However, the effects of SAP particle size and extra water on the dynamic mechanical behavior of composites are still unclear. In this study, the total porosity and macropore (>100 μm) porosity of composites were studied with a mercury intrusion porosimetry test and an image analysis. The influence of SAP particle size and extra water on the quasi-static and dynamic mechanical properties of composites was analyzed. The fracture behavior of composites was investigated based on the fractal dimension and crack morphology. The results reveal that adding extra water can respectively raise the total porosity and macropore porosity by 33 %–39 % and 36 %–50 %, thereby declining the compressive strength and elastic modulus of composites under quasi-static and dynamic compression. The rise of strain rate from 63 s−1 to 102 s−1 elevates the dynamic compressive strength, elastic modulus, and fracture degree of composites by 39 %–44 %, 4.9 %–6.0 %, and 5.2 %–7.4 %, respectively. Raising particle size of SAP and adding extra water can raise the dynamic increase factor of compressive strength and elastic modulus. Which originates from the change of crack path, the increase of fracture degree, and the delayed response of strain induced by the rise of total and macropore porosity.

Fracture behaviour of fibre-reinforced composite materials subjected to shear loading: An experimental and numerical study

Compared to fibre-dominated behaviour, a response dominated by the matrix under shear loading can considerably limit the load-bearing capability and restrict the utilisation of composite materials. It is therefore practically significative to understand the shear response of composite materials. This paper presents a detailed experimental and numerical investigation on the fracture behaviour of composite laminates subjected to shear-dominated loading. Composite specimen with a lay-up of [(0/90)4/0]S are tested using the V-Notched Rail (VRS) shear test method. Subsequently, the Scanning Electron Microscope (SEM) investigation is also conducted on the fracture surfaces of the tested specimens to get insights into the damage mechanisms due to shear loading. In addition, a high-fidelity computational damage model is developed to predict the shear fracture behaviour of fibre-reinforced composites. Simulation results, including loading response, strain distribution and shear fracture, well correlated with experimental results, which demonstrates the predictive capability of the developed elastic-plastic damage model.

A coupled mix-mode cohesive law based on a cylindrical potential function

A novel mixed-mode cohesive law derived from a potential function is presented. The potential function is formulated using physical parameters that can be extracted from any fracture mechanics test capable of providing R-curves in terms of the J-integral as a function of the normal and tangential end-openings. The proposed cohesive law is able to describe the fracture behaviour of composites with large fracture process zones, including fibre bridging. As such, it is capable of describing both the crack tip, as well as the bridging region. An important aspect of the formulation is that the shape of the mixed-mode cohesive laws are derived and not assumed. The mixed-mode cohesive law was tested using synthetic data emulating mixed-mode fracture mechanics tests. The cohesive tractions extracted from the method exhibited characteristics which were not seeded on the model such as negative normal tractions under pure mode shear loading and non-zero shear loading under pure normal mode loading.

Optimization of Speed and weight fraction parameters for Al2024-NITINOL composites through ANOVA

In this research, the reinforcement effect of Nickel-Titanium (Ni-Ti) alloys on aluminum 2024 and optimum weight fraction to achieve the enhanced mechanical properties have been studied. The experiments are designed in analysis of variance (ANOVA) and two factor interaction test is performed to obtain the best fit. The properties such as tensile, impact strength and percentage elongation have been studied at different weight fractions namely 2, 4, 6 and 8% of reinforcing materials. It is found that the 6% inclusions producing overall enhanced properties whereas different fractions showing individual improvements. The results obtained from the numerical analysis is tested experimentally and confirmed the optimality through tensile, hardness tests. The proper inclusion of reinforcing alloys into metal matrix, composite fracture behavior after tensile test is confirmed with SEM analysis. The observations inferred from the numerical and experimental investigations are presented in the article.

In situ observation of fracture in homogeneous and functionally graded 6061Al/SiCp composites

In the present work, 6061Al/SiCp homogeneous composites and 6061Al/SiCp functionally graded materials were prepared by vacuum hot pressing sintering. Fracture behaviors of composites were studied through three-point bending tests and fracture toughness tests with in situ observation. Results show that SiC content in the composite has a great influence on bending strength and fracture toughness. Bending strength and fracture toughness of functionally graded materials are the results of the strength, plasticity, and interlayer synergy. The fracture mechanism of composites is the initiation and growth of microcracks. A large number of microcracks initiate in matrix of the crack tip region and connect with each other to make the main crack propagate.

Loading rate dependence of mode II fracture toughness in laminated composites reinforced by carbon nanotube films

In this study, the loading rate sensitivity of the mode II fracture behaviour of composites toughened by carbon nanotubes (CNTs) was investigated. CNTs were inserted into laminates in the form of films. The specimens for the mode II fracture test were subjected to loading rates varying from the quasi-static 8 × 10−6 m/s) to dynamic (15 m/s) states using an Instron machine and electromagnetic Hopkinson bar, respectively. Under the quasi-static loading conditions, the fracture toughness of the composites increased monotonously with an increase in the number of CNT layers and approached a maximum value when 30 layers of the CNT film were added, which is twice the value of the virgin specimen (without CNTs). However, under the dynamic loading conditions, the fracture toughness of the composites improved only by 25% compared with that of the virgin specimen, and the change in the number of CNT layers had little effect on the fracture toughness of the composites. This indicated that under dynamic loading, the failure mode of the interlaminar region changed. Microscope observation results illustrate that a large amount of in-plane (x-y plane) shear failure occurs in the CNT-interleaved zone under the dynamic loading conditions.

An electromechanical cohesive zone model merging with contact and friction effects for fiber debonding and pushing-out in piezoelectric fiber composites

Owing to electromechanical coupling of piezoelectric fiber composites, they have been widely used in sensing and active control of aeronautic and aerospace structures. In order to describe the interface fracture of piezoelectric fiber composites, a micromechanically motivated interface model based on a cohesive zone model is developed, and it is closer to the actual debonding process including contact and friction effects. In this study, the proposed interface model is formed through incorporating contact effect and a Coulomb friction law into a bilinear traction-separation law, and the electromechanical relationships across separated and contacted crack surfaces are provided. And for purpose of analyzing single piezoelectric fiber debonding, an axisymmetric model and its double series solution are adopted. Comparing with existing experiment and simulation results, the proposed model takes the friction related to the normal pressure varying with the gap between crack surfaces into account, and it is able to qualitatively capture salient features of the experimental record, and guarantee a smooth transition from cohesive debonding to frictional sliding. Furthermore, the piezoelectric fiber push-out behavior is investigated including initial perfect bonded, partial debonding with interface softening and frictional sliding after complete debonding. The dependences of different parameters, such as fiber radius, fiber length, electric field and interface properties, on the load-displacement curve and the responses around piezoelectric fiber are also investigated. It can be revealed that piezoelectric fibers can be designed to monitor and tailor the fracture behavior of composites.

Micro-structure and mechanical properties of microcrystalline cellulose-sisal fiber reinforced cementitious composites developed using cetyltrimethylammonium bromide as the dispersing agent

This paper reports new hierarchical cementitious composites developed using microcrystalline cellulose (MCC), sisal fibers and cetyltrimethylammonium bromide (CTAB) as the dispersing agent. MCC was dispersed in water without and with CTAB at different concentrations using ultrasonication and the optimum CTAB concentration for achieving homogeneous and stable MCC suspensions was found to be 40%. Hierarchical composites were fabricated using MCC (0.1–1.5 wt% of cement), sisal fibers (20 mm, 0.25% and 0.50 wt% of cement), 40% CTAB and tri-butyl phosphate as the defoaming agent. Mechanical strengths of composites improved significantly at 0.1 wt% MCC, which along with 0.5% sisal fibers improved compressive and flexural strengths by ~ 24% and ~ 18%, respectively. The hybrid reinforcement exhibited a synergistic effect on the fracture behavior of composites improving the fracture energy up to 40%. Hierarchical composites also showed improved fiber-matrix bonding, lower porosity and water absorption, superior hydration, carbonation resistance and durability up to 90 ageing cycles.

Effect of silica particle size and filler content on the fracture properties of epoxy resin composite

Silica particles were used as a filler to produce silica-epoxy composite. Silica particles with two mean diameters of 1 μm and 37 μm and filler content of 20, 30, 40, and 60 wt. % were used to investigate the effect of particle size and filler content on the fracture behavior of epoxy resin composite, respectively. The fractural behavior of composites was characterized by linear elastic fracture mechanics according to standard of ASTM-D5045 in which three-point bending test procedure was used to investigate plane-strain fracture toughness (Kıc) and strain energy release rate (Gıc) of the composite specimens. Glass transient temperatures of the samples were evaluated by using differential scanning calorimetry (DSC). Fracture surfaces of the produced specimens were examined by SEM. The highest Young’s modulus value was 10.48 GPa for the sample produced with 37 μm particle size and 60 wt. % filler content and it was found that a considerable increase was obtained according to the 3.05 MPa values of the unfilled epoxy. Experimental results show that fracture toughness value of the silica filled epoxy composite was improved by 98% compared to unfilled epoxy.

Multi-phase field modeling for various fracture mechanisms in composites

Composite possesses wide spectrum of mechanical responses along with remarkable fracture strength and toughness. Such properties evolve due to combination of different failure mechanisms across multiple phases. Understanding the contribution of these mechanisms on overall behavior is necessary to fabricate the composite with desired fracture properties. Although numerous studies have been performed to correlate the fracture response with crack propagation characteristics, they fail to account several underlying micro-mechanical events. Therefore, in the present study, a multi-phase field fracture model is proposed. We consider that constituents are homogeneously distributed within the matrix, while macro-scale phase field descriptors are utilized to represent the failure of its constituents. Further, the reinforced elements are assumed to be anisotropic in nature with preferential fracture direction. Therefore, by employing the rule of mixture in free energies and applying thermodynamic principles, the governing equations together with evolution laws of phase field parameters are derived. Using multi-field approach and extracting the weak form for governing equations, we develop finite element based numerical framework. Coupled sets of linear equations are solved using staggered scheme in parallel computing architecture. Proposed scheme is verified with analytical solution of a composite where separate evolutions of damage within phases are correlated with emergent stress–strain response. Numerical simulations are performed to predict the mechanical response by interpreting the competitive involvement of fracture mechanisms within matrix and inclusion phases. The present findings and future scopes highlight the predictive capability of the proposed scheme for analyzing fracture behavior of composites.

Computational modeling of meso-scale fracture in polymer matrix composites employing peridynamics

We present a novel approach for investigating the fracture and mechanical behavior of polymer-matrix composites at the mesoscale. The proposed approach takes advantage of the peridynamics equation of motion and its nonlocality. We show that the approach can predict the fracture behavior and the ‘homogenized’ stress–strain response which agrees well with experiments. Various volume fractions (in the range between 0.2% to 50%) and particle–matrix stiffness ratios (between 2 to 1000) are considered and the effect of stiffness and the particles density on the mechanical response of the samples are quantified. The particle–matrix stiffness ratio has minimal effect on the fracture behavior of the composite. We find that volume fractions between 15% to 35% improve best the mechanical and fracture response of the composite.

Wear and Tensile Behavior of Titanium Carbide and Fly Ash–Reinforced Magnesium Matrix Composites

Abstract Metal matrix composites are considered as suitable materials for enhancing the properties of materials used for automobile and aerospace sectors. This research work is about magnesium matrix composites reinforced with 7 wt. % of titanium carbide and fly ash fabricated by stir casting technique. The particle distribution of the reinforcements in matrix material was examined by using optical microscope and scanning electron microscopy technique. The mechanical and microstructural properties of composites were investigated and compared with stir-cast pure magnesium. Titanium carbide and fly ash–reinforced composite showed around a 55.5 % and 33.3 % increase in hardness, respectively. Titanium carbide–reinforced composite displayed more wear resistance as related to fly ash composite and stir-cast pure magnesium. There was also an increase in tensile strength of composites as equated to stir-cast pure magnesium. The fracture behavior of composites showed the presence of surface cracks, voids, and particles of reinforced material in composites. As compared to titanium carbide–based composite, fly ash composite showed wider voids and agglomeration of fly ash particles in fracture surface. However, the fractured surface of pure magnesium showed deep voids as compared to composites along with elongated dimples.

The effect of carbon fibers distribution on fracture behavior of carbon fiber reinforced aluminum matrix composites prepared by ultrasonic vibration

Controlling the distribution of carbon fibers(CFs) in the matrix has important influence on obtaining the composites with excellent properties. In this paper, the distributions of CFs under different amplitudes and the fracture behavior of the composites during tensile process were investigated. The results show that the amplitude has an important effect on infiltration behavior of aluminum melt into carbon fiber bundle and the distribution of CFs in the matrix. With the increase of amplitude, the fibers bundle can be completely infiltrated, and the carbon fiber distributes evenly in the matrix. However, excessive amplitude will cause the flow velocity to exceed the turbulence threshold and the CFs cannot be evenly distributed in the matrix to generate fiber cluster defects. CFs can be uniformly distributed in the matrix at an amplitude between 37 μm and 39 μm. In this case, the fibers can bear the larger load, and the tensile strength can reach 172 MPa. As well as the effect of carbon fiber distributions in the matrix on the fracture behaviors of composites were elaborately analyzed. The CFs changed from uniform distribution to partial fiber clusters, the fracture behavior changed from single fibers pullout to fiber bundles pullout state. The inhomogeneous distribution of CFs and the existence of defects in the fiber clusters would reduce the properties of the composite by 10% compared to the uniform distribution of carbon fibers in the matrix.