Fracture Energy Of Matrix Research Articles

Damage behavior and toughening mechanism of SiCf/SiC-Ti3SiC2 composites: A combination of digital image correlation and acoustic emission

Matrix modification is an effective method to improve the mechanical properties of ceramic matrix composites, while the elucidation of corresponding damage mechanism is essential for the design and engineering application of composites. In this work, Ti3SiC2 particles were introduced into SiC matrix to fabricate Ti3SiC2 modified SiCf/SiC (SiCf/SiC-Ti3SiC2) composites by a hybrid technique of slurry suspension impregnation combined with polymer infiltration and pyrolysis. Compared with SiCf/SiC composites, the flexural strength and modulus of SiCf/SiC-Ti3SiC2 composites were increased by 17.8 % and 61.0 %, respectively. The three-point flexural damage behavior and failure mechanism of composites were systematically investigated and compared by the combination of digital image correlation and acoustic emission techniques. Based on the collaborative analysis of in-situ damage process, matrix micro-zone toughness and fracture morphology, the modification effect and toughening mechanism of Ti3SiC2 were revealed. The improved mechanical properties of SiCf/SiC-Ti3SiC2 composite could be ascribed to the more sufficient matrix cracking before composite failure and the increased matrix fracture energy by microcrack deflection. After matrix modification, the failure mechanism was dominated by the gradual propagation and growth of microcracks until the critical crack size, instead of the fast and unstable propagation of main crack.

An overview of tensile and shear failure mechanisms of silicon carbide-based ceramic matrix composites

The successful applications of silicon carbide-ceramic matrix composites (SiC-CMCs) in aeronautical and aerospace industries require deeper understanding of their mechanical behaviors and failure mechanisms. The overview on tension and shear is then presented from meso-mechanics perspective, including matrix cracking, interface de-bonding and sliding, matrix crack propagation as well as fiber bridging. The results reveal that the matrix cracking stress is proportional to the interface sliding stress and the matrix fracture energy. The ratio of tensile to shear stress of the matrix cracking remains constant both in tension and in shear. In addition, the deflection of matrix cracks in the interface depends on the elastic modulus matching parameter, the angle between matrix cracks and interface, as well as the residual thermal stress. The matrix cracks propagate in a random or periodic pattern, which are proportional to the sliding length at the matrix cracking stress. The fiber bridging mechanism, related to the Weibull distribution of the fiber strength, determines the tensile and shear behaviors after the saturation of matrix cracks.

Preparation of low-cost green engineered cementitious composites (ECC) using gold tailings and unoiled PVA fiber

The current study aims to establish low-cost green engineered cementitious composites (ECC) using gold tailings, unoiled PVA fiber and large-volume fly ash. Through compression test, four-point bending test, direct tensile test, matrix fracture toughness test and single-crack tensile test, the mechanical properties of ECC were explored. It is found that incorporation of gold tailings leads to the enhanced compressive strength and reduced ductility. When quartz sand was fully replaced by gold tailings, the compressive strength increased by 19.5%, the strain capacity decreased by 22.3%, the deflection decreased by 15.8% but no obvious change occurred in first crack stress as well as tensile strength. A rougher surface of unoiled PVA leads to reduced slip hardening response. At micro-scale, replacement of the quartz sand using gold tailings leads to higher complementary energy (Jb’) available for strain hardening during the crack development and reduced matrix fracture energy (Jtip) for crack initiation. This contributes to the increased pseudo strain-hardening PSHE (=Jb’/Jtip) index and ductility. When fiber content is 2.0%, the values of PSHS (=σ0/σfc) index reached 1.2, which ensures the saturated multi-joint cracking behavior.

Mitigating cryogenic microcracking in carbon-fibre reinforced polymer composites using negative thermal-expansion nanoparticles functionalized by a polydopamine coating

Herein, we report a new method of mitigating cryogenic microcracking in carbon-fibre reinforced-plastics (CFRPs) using a negative thermal-expansion nanomaterial, zirconium tungstate (ZrW2O8), to simultaneously reduce the thermal residual stresses and enhance the fracture energy of the epoxy matrix of CFRPs. The results show that 1 wt% of added ZrW2O8 nanoparticles functionalized by polydopamine can increase the fracture energy of the matrix material by 140%, reduce the coefficient of thermal expansion by 20% and, more importantly, enhance the interlaminar fracture energy of the resulting CFRP by about 100% at −196 °C. The ZrW2O8-modified matrix has been demonstrated to successfully prevent microcracking at −196 °C in a blocked cross-ply CFRP laminate with a [04/908/04] fibre architecture.

Temperature dependent fracture toughness model for whisker‐reinforced ceramic matrix composites

AbstractA temperature dependent fracture toughness model for whisker‐reinforced ceramic matrix composites was developed in this study, which considers the effects of matrix fracture toughness, residual thermal stress, crack bridging, crack deflection, and their temperature dependence. Its predicted results were compared with the fracture toughness of six types of whisker‐reinforced ceramic matrix composites at different temperatures, and good agreement between predicted results and experimental results is obtained. Furthermore, based on this model, we systematically analyzed the effects of the volume fraction and aspect ratio of whisker, Young's modulus of matrix and whisker, thermal expansion coefficient difference, stress‐free temperature, the ratio between the fracture energy of matrix and that of interface, on their temperature dependent fracture toughness for the first time. Finally, insights and suggestions which could help to optimize and improve the composite fracture toughness at different temperatures are provided.

Temperature-dependent proportional limit stress of SiC/SiC fiber-reinforced ceramic-matrix composites

AbstractIn this paper, the temperature-dependent proportional limit stress (PLS) of SiC/SiC fiber-reinforced ceramic-matrix composites (CMCs) is investigated using the micromechanical approach. The PLS of SiC/SiC is predicted using an energy balance approach considering the effect of environment temperature. The relation between the environment temperature, PLS, and composite damage state is established. The effects of the fiber volume, interface properties, and matrix properties on the temperature-dependent PLS and composite damage state of SiC/SiC composite are analyzed. The experimental PLS and interface debonding length of 2D SiC/SiC composites with the PyC and BN interphase at elevated temperatures are predicted. The temperature-dependent PLS of SiC/SiC composite increases with the fiber volume, interface shear stress and interface debonding energy, and the matrix fracture energy and decreases with the interface frictional coefficient at the same temperature.

Time-dependent matrix fracture of carbon fiber-reinforced silicon carbide ceramic-matrix composites considering interface oxidation

ABSTRACTIn this paper, the time-dependent matrix fracture of carbon fiber-reinforced silicon carbide ceramic-matrix composites (C/SiC CMCs) is investigated considering the interface oxidation. The time-dependent fiber/matrix interface oxidation length and temperature-dependent fiber/matrix interface shear stress in the oxidation and deboned region, interface debonded energy, fiber and matrix modulus and matrix fracture energy are considered in the analysis for the micro stress field, interface debonding criterion and critical matrix strain energy (CMSE) model. The relationships between the time, temperature, applied stress, fiber/matrix interface debonding, and matrix fracture are established. The effects of fiber/matrix interface shear stress, fiber/matrix interface frictional coefficient, fiber/matrix interface debonded energy, and matrix fracture energy on the matrix cracking density and interface oxidation ratio are discussed for different temperatures and oxidation time. The experimental matrix cracking density and interface oxidation ratio for unidirectional C/SiC composite at different testing temperatures and oxidation time are predicted.

Synergistic effects of temperature and time on proportional limit stress of silicon carbide fiber-reinforced ceramic-matrix composites

ABSTRACTIn this paper, the synergistic effects of temperature and time on the proportional limit stress (PLS) of SiC/SiC composites are investigated. The temperature-dependent constituent properties and time-dependent interface oxidation are considered to determine the PLS. The effects of fiber volume fraction, interface shear stress, interface debonded energy and matrix fracture energy on the temperature/time-dependent PLS and interface debonded length of SiC/SiC composite are discussed. The experimental PLS of SiC/SiC composite corresponding to different temperature and time are predicted.

Modeling matrix multi-fracture in SiC/SiC ceramic-matrix composites at elevated temperatures

In this paper, the matrix multi-fracture of SiC/SiC ceramic-matrix composites (CMCs) is investigated using the critical matrix strain energy (CMSE) criterion. The BHE shear-lag model is used to analyze the micro-stress field of the damaged composite, and the fracture mechanics method and the CMSE criterion are adopted to determine the fiber/matrix interface debonded length and matrix multi-fracture density. The temperature-dependent fiber/matrix interface shear stress, Young’s modulus of the matrix, the matrix fracture energy, and the fiber/matrix interface debonded energy are considered in the micro-stress field analysis, fiber/matrix interface debonding criterion, and matrix multi-fracture model. The effects of fiber volume fraction, fiber/matrix interface shear stress, fiber/matrix interface frictional coefficient, fiber/matrix interface debonded energy, matrix fracture energy, and temperature on the matrix multi-fracture of SiC/SiC composite are discussed. When the fiber volume fraction and matrix fracture energy increase, the first matrix cracking stress and matrix saturation cracking stress increase; when the fiber/matrix interface shear stress and interface frictional coefficient increase, the first matrix cracking stress, saturation matrix cracking stress, and saturation matrix cracking density increase with the decrease of the fiber/matrix interface debonded length; when the fiber/matrix interface debonded energy increases, the saturation matrix cracking stress decreases and the saturation matrix cracking density increases due to the decrease of fiber/matrix interface debonding ratio. The experimental matrix multi-fracture and fiber/matrix interface debonding curves of unidirectional SiC/SiC composite at elevated temperatures are predicted. The predicted results agree with experimental data, which proves the efficiency of the developed matrix multi-fracture model.

Design of strain hardening cement-based composites with alkali treated natural curauá fiber

The work in hand presents the design process of Strain Hardening Cement-based Composite reinforced with natural curauá fiber. The matrix fracture energy and matrix-fiber bond were studied and implemented into the theoretical model for critical fiber volume prediction, which was verified by mechanical tests for tensile, bending and compression strength. The influence of matrix-fiber bond on critical fiber volume is presented. The fiber properties are improved by two-stage treatment. Firstly, hot water (80 °C) washing in water changed every 3 h. Secondly, immersion in 1% solution of calcium hydroxide Ca(OH)2 with water for 60 min for calcium deposition on fiber surface to increase bond properties. The critical fiber volume predicted by the model was 4% for 20 mm treated curauá fiber and was verified on the composites, which presented strain-hardening behavior under tensile test and deflection-hardening under bending.

Graphene/epoxy interleaves for delamination toughening and monitoring of crack damage in carbon fibre/epoxy composite laminates

Functionalized graphene sheets were fabricated by a simple thermal reduction method in air at 700 °C and used to prepare graphene/epoxy (G/E) composites. The incorporation of 1.0 wt% of graphene into epoxy was found to significantly improve the matrix fracture energy by ∼150% and reduce the thermal expansion coefficient by ∼30%. When these partially cured G/E composites were used as interleaves in carbon fiber/epoxy (CF/E) composites and co-cured, a remarkable 140% increase in mode I interlaminar fracture energy was achieved. Detailed toughening mechanisms of the graphene sheets in both G/E and CF/E composites were studied. Moreover, the damage sensing capacity of the graphene interleaved CF/E composites with a simple electrical response method was demonstrated, where the electrical resistance change increased almost linearly with crack increment.

Oxidation effects on in-plane and interlaminar shear strengths of two-dimensional carbon fiber reinforced silicon carbide composites

Effects of oxidation on in-plane shear strength and interlaminar shear strength of two-dimensional carbon fiber reinforced silicon carbide composites (2D C/SiC) were studied based on the corresponding shear damage mechanisms. The results showed that oxidation had resulted in severe degradations of the two strengths, however, it had little influence on the shear failure mechanisms. Under in-plane shear loading, large-scale fiber bridging mechanism controlled the shear behaviors. A modified rigid body sliding model was proposed to characterize the in-plane shear strength. In Comparison, interface sliding mechanism controlled the interlaminar shear strength. Based on above failure mechanisms, the two shear strengths were quantitatively characterized by the constituent properties, such as diameter of carbon fibers, interface sliding stress, matrix fracture energy and matrix cracking spacing. Therefore, oxidation effects on them were attributed to the decreased constituent properties which mainly results from oxidation consumption of the carbon phases. Finally, for the conditions of this study, a relationship was proposed that the interlaminar shear strength equals the in-plane shear strength minus the fiber bridging stress.

Multiple Cracking Model of Fiber Reinforced High Performance Cementitious Composites under Uniaxial Tension

A theoretical model of multiple cracking failure mechanism is proposed herein for fiber reinforced high performance Cementitious composites. By introducing partial debonding energy dissipation on non-first cracking plane and fiber reinforcing parameter, the failure mechanism model of multiple cracking is established based on the equilibrium assumption of total energy dissipation on the first crack plane and non-first cracking plane. Based on the assumption of the first crack to be the final failure crack, energy dissipation terms including complete debonding energy, partial debonding energy, strain energy of steel fiber, frictional energy, and matrix fracture energy have been modified and simplified. By comparing multiple cracking number and energy dissipations with experiment results of the reference's data, it indicates that this model can describe the multiple cracking behavior of fiber reinforced high performance cementitious composites and the influence of the partial debonding term on energy dissipation is significant. The model proposed may lay a foundation for the predictions of the first cracking capacity and post cracking capacity of fiber reinforced high performance cementitious composites and also can be a reference for optimal mixture for construction cost.

Maximum pore volume fraction and size for high fracture energy in porous bodies

ABSTRACTThe fracture energy of a body containing pores might be expected to decrease linearly in proportion to the area fraction of material in the crack plane. However, there is experimental evidence that the fracture energy of porous materials only decreases when the pore volume fraction exceeds some critical value. To understand this, experiments have been conducted to directly observe the interaction between a growing crack with model distributions of pores. It is seen that cracks do not simply pass through the pores but spread around them causing the crack front to become curved and increase in length. For just two pores (or a line of pores) this is observed to continue until the crack has completely spread around the pores. It is observed that this increase in length increases the energy required for cracking, suggesting that the maximum fracture energy should rise with the volume fraction of pores. However, when this exceeds a certain value, the spreading crack front impinges on the pores ahead of the crack front before the maximum length of crack front due to bowing is reached. Beyond this critical volume of porosity, the resistance to fracture drops rapidly with porosity. Predictions of the relative fracture resistance of bodies containing spherical as well as cylindrical pores give good agreement with experimental observations, and are consistent with observations that the matrix fracture energy and pore size have little effect, provided the pores are much smaller than the sample.

Temperature Dependence ofin situConstituent Properties of Polymer-infiltration-pyrolysis-processed Nicalon™ SiC Fiber-reinforced SiC Matrix Composite

Temperature dependence ofin situfiber strength, effective interface shear stress, Young's modulus of matrix, and matrix fracture energy in a polymer-infiltrationpyrolysis (PIP)-processed two-dimensional plain-woven fabric carbon-coated Nicalon™ SiC fiber-reinforced SiC matrix composite was studied through a tensile test in air at 298 (room temperature), 800, and 1200 K.In situfiber strength and effective interface shear stress were determined by fracture mirror size and fiber pullout length measurements, respectively. The fiber strength was insensitive to test temperature up to 800 K but dropped significantly at 1200 K. Conversely, the interface shear stress showed a strong temperature dependence, decreasing at 800 K and drastically increasing at 1200 K. The temperature dependence of both values was reasonably explained. Temperature dependence of Young's modulus of matrix was derived from Young's modulus of the composite and fiber and ranged from ≈40 to ≈38 GPa. Matrix fracture energy was also determined from the transverse matrix cracking stress and ranged from ≈16 to ≈5.5 J/m2. Both Young's modulus of matrix and the matrix fracture energy showed only slight temperature dependence up to 800 K; however, both values decreased significantly at 1200 K.

Tough low profile additives in sheet molding compound

AbstractThermosetting polyester in a sheet molding compound (SMC) shrinks by 7 to 10% and causes fiber show‐through and poor surface quality. Adding certain thermoplastics results in zero shrinkage and smooth surfaces; these are called low‐profile additives (LPA). Poly(vinyl acetate) (PVAc), a highly effective LPA, decreases the fracture energy from 66.3 to 35.1 J/m2 when present as 14 wt% of the matrix, even though the PVAc is tough. It produces a nodular three dimensional network; the crosslinked polyester nodules are interconnected by weak polyester bridges and the PVAc forms a thin coating on each nodule. The macroscopic crosslinking shrinkage is offset by void formation in the PVAc phase. Crack follows the void structure and cleaves the bridges between the nodules. Low matrix fracture toughness leads to high microcracking and early gross failure of the SMC. This paper presents alternative low profile additives that give excellent low profile effect with improved matrix fracture energy and SMC strength. Commercially available styrene‐butadiene block copolymers were studied. These are less polar and form discrete cavitated domains of a few 100 μm in the solid polyester matrix. With this morphology, good low profile and toughening usually are contradictory, since the former requires small LPA particles for smooth surfaces and the latter requires large particles for crack bridging by the rubber. However, a good compromise was found in Epoxidized Kraton D1300X (a 50% diblock and 50% triblock copolymer of styrene and butadiene) with the compatibilizer Ricon 131MA17 (a maleic anhydride‐polybutadiene adduct). This produces a low profile effect equivalent to PVAc, but with a higher matrix fracture energy of 70.7 J/m2 and higher matrix modulus. With the epoxidized rubber, the flexural strength of the SMC increases by 13% over that with PVAc, with no sacrifice of the modulus or strain‐to‐failure.

Mechanism for tensile strain hardening in high performance cement-based fiber reinforced composites

The mechanism responsible for the improvement in tensile strain capacity of FRC (fiber reinforced concrete) as a result of the addition of high volume fraction of discontinuous fibers was investigated, using energy changes associated with cracking. The energy terms considered include: matrix fracture energy, matrix strain energy. debonding energy, fiber strain energy and fiber frictional energy. Assuming that the first observed crack is also the failure crack, it was found that multiple cracking occurs in high performance FRC. In such composites the energy needed to open the critical cracks exceeds the energy needed to form a new crack. The analysis predicts that the major energy term determining this behavior is the fiber debonding energy. Multiple cracking was observed in fiber reinforced small densified DSP (particles) containing a high volume fraction (higher than 3%) of fine and short steel fibers. Because crack localization did not occur during multiple cracking, very large increases in total strain capacity were achieved with increasing fiber volume fraction. At 12% fiber volume fraction, a total strain capacity of about 0·2% was measured from flexures tests; an increase of about 15 to 20 times over that of the plain matrix.

TEMPERATURE DEPENDENCE OF THE IMPACT FRACTURE ENERGY OF THE SHORT GLASS FIBER-EPOXY COMPOSITE AND THE SHORT GLASS FIBER-UNSATURATED POLYESTER COMPOSITE

The temperature dependence of the impact fracture energy of composites reinforced with random-planar orientation of short fibers was studied theoretically and experimentally.The theoretical impact fracture energy of composites could be given by the sum of the fracture energy of matrix and fibers, and the energy to pull out fibers on crack surface, taking the temperature dependence of the critical fiber length and the breaking probability of fiber into consideration. The impact fracture energy was studied experimentally for epoxy resin and unsaturated polyester resin reinforced with random-planar orientation of short glass fibers. The theoretical values of impact fracture energy were in good agreement with the experimental ones. It was found for both composites that at room temperature, the impact fracture energy of fibers in a composite, while at higher temperature, the energy to pull out fibers, mainly contributes to the fracture energy of the composite.