Mixed-mode Fracture Properties Research Articles

Improving Mixed-Mode Fracture Properties of Concrete Reinforced with Macrosynthetic Plastic Fibers: An Experimental and Numerical Investigation

Improving Mixed-Mode Fracture Properties of Concrete Reinforced with Macrosynthetic Plastic Fibers: An Experimental and Numerical Investigation

Experimental and theoretical investigation of the influence of post-curing on mixed mode fracture properties of 3d-printed polymer samples

This study explores the mechanical properties and fracture characteristics of additively manufactured acrylonitrile butadiene styrene specimens, focusing on the impact of raster angle and post-process heat treatment. To this end, a large number of tensile and semi-circular bending samples with three distinct raster angles of 0/90°, 22/ − 68°, and 45/ − 45° were prepared and exposed to four types of heat treatments with different temperature and pressure conditions. Simultaneously, theoretical models of maximum tangential stress (MTS) and generalized MTS (GMTS) were developed to estimate the onset of specimen fracture under mixed-mode in-plane loading conditions. Recognizing the non-linear behavior within the stress–strain curve of tensile test samples, particularly in the annealed samples, an effort was undertaken to transform the original ductile material into a virtual brittle material through the application of the equivalent material concept (EMC). This approach serves the dual purpose of bypassing intricate and tedious elastoplastic analysis, while concurrently enhancing the precision of the GMTS criterion. The experimental findings have revealed that while the annealing process has a minimal effect on the yield strength, it considerably enhances energy absorption capacity, increases fracture toughness, and reduces the anisotropy. Additionally, the combined EMC-GMTS criterion has demonstrated its capability to predict the failure of the additively manufactured parts with an acceptable level of accuracy.

Mixed mode fracture properties of interface for composite MPC and cement concrete specimen with asymmetric semicircular bending beam

This paper investigates the interface fracture behavior of composite magnesium phosphate cement (MPC) and concrete asymmetric semicircular bending beam (ASCB) specimens under various loading conditions including pure mode I, mixed mode I&II, and pure mode II. Initially, finite element simulations are employed to compute and analyze the basic geometric characteristics of the ASCB specimens.. Subsequently, experimental tests are performed to determine the flexural strengths for different pre-crack lengths, and the critical stress intensity factors of ASCB specimens are obtained through testing. Then, parameters for the interface cohesive model are derived. Finally, the interface cohesive model for the composite MPC and concrete ASCB specimen is validated through numerical simulation. The present work show that a pure mode I opening crack represents the weakest form of the structure, and the flexural strength decreases with an increase in precrack length. The crack resistance at the repair interface is approximately 60% lower than the bearing capacity of pure mode II fractures. Intensity factor envelope analysis reveals that mixed mode I&II fractures should be avoided in composite structures experiencing complex stress states. The cohesive model effectively captures the interfacial bonding performance. When combined with the extended finite element method (XFEM), the cohesive model facilitates accurate simulation of the specimen’s interface fracture, demonstrating consistency with experimental results.

Mixed-mode fracture of compacted tailing soils. II: Crack properties from full-field displacement fields

This paper deals with the acquisition of the crack evolution and propagation behaviors of the compacted tailing soils from full-field displacement fields by incorporating two-dimensional optical technique-digital image correlation (2D DIC). Meanwhile, the fracture properties, such as mode I+II fracture toughness were also measured and compared to the results obtained in Part I. Cracking properties, such as strain energy rate, cracking initiation angle, and size of critical distance were investigated from the perspective of full-field displacement field and compared to the classic fracture mechanics. It is more intuitive to recognize the mixed mode fracture properties of the compacted tailing soils under asymmetric loading conditions by using optical techniques in full-field displacement fields. This work largely enriched the database of the fracturing properties of compacted tailings soils.

Effect of heat-treatment on the pure- and mixed-mode fracture properties of a homogeneous sandstone

Fracture-mechanical properties of the sedimentary rocks at elevated temperature strongly control hydraulic fracturing in rocks, geothermal energy extraction, deep tunnelling, and spent fuel disposal in geological medium. This paper investigates the relationship between the strength properties (e.g. tensile strength, brittleness index and Young’s modulus) and the pure-mode and mixed-mode fracture toughness of Dholpur sandstone at temperatures ranging from room temperature to 500 °C. A suitable brittleness index definition was identified to quantify the deformational changes. Additionally, evolution of the stress–strain behaviour, change in the degradation degree (DD), peak strain, and evolution in porosity values were closely studied to comment on the potential brittle–ductile transition of the rock. The fracture toughness remained unchanged between 25–150 °C, sharply increased 3%–28% between 150–200 °C, and followed by a 75%–80% decrease from 200–500 °C. All the pure- and mixed-mode fracture toughness were found to maintain an exponential relationship with the Young’s modulus, tensile strength, and brittleness index of the heat-treated rocks across all the temperatures. A potential brittle to quasi-brittle/semi-ductile transition temperature of 225 °C was identified for Dholpur sandstone. Additionally, mixed mode fracture behaviour of the heat-treated rock was investigated using generalized maximum tangential stress (GMTS) criterion. It was noticed that GMTS is far better at predicting the KII/KI ratio of mode-II fractures than the conventional maximum tangential stress (MTS) criterion. Statistical analysis of the test data indicate that a 3-parameter Weibull function can be successfully employed to predict the mode-II fracture toughness of heat-treated sandstone in terms of the mode-I data.

Investigation of mixed-mode fracture of aligned steel fibre reinforced cementitious composites

Mixed-mode fracture experiments were conducted on aligned steel fibre reinforced cementitious composite (ASFRC) and ordinary steel fibre reinforced cementitious composite (SFRC) three-point bending beams. Mixed-mode fracture performances of the ASFRC and SFRC specimens were studied by changing the crack offset distance. The fracture processes of the ASFRC and SFRC specimens were simulated using the extended finite element method. A good agreement was found when the simulation results were compared with the experimental ones. The alignment of steel fibres significantly improved mixed-mode fracture properties. The peak load $$P_{\mathrm {max}}$$ and crack initiation angle of the ASFRC specimen were obviously greater than those of the SFRC specimen because more steel fibres bridged the crack. Compared to the SFRC, the $$P_{\mathrm {max}}$$ of the ASFRC increased by 58%, 49% and 38% with the crack offset distances of 0, 50 and 100 mm, respectively. The crack initiation angle of the ASFRC increased by 11% and 17% with the crack offset distances of 50 and 100 mm, respectively. In addition, the influences of the initial crack length to depth ratios a/D and the steel fibre volume fraction $$V_{\mathrm {f}}$$ on the ASFRC specimens were simulated. The $$P_{\mathrm {max}}$$ significantly increased with $$V_{\mathrm {f}}$$ and decreased with a/D

On the elastic and mixed-mode fracture properties of PVC foam

Sandwich structures are widely used for the design and fabrication of lightweight structural systems, due to their capability to exhibit excellent structural and thermal performances at low material usage. Understanding the phenomena of propagation of macro-cracks in the core and delamination at the face-to-core interface are aspects of great computational interest. Linking sophisticated models with the actual characterisation of their mechanical properties is essential in view of real engineering applications. The elastic and fracture characterisation of the materials composing the core is particularly relevant because its cracking affects the capacity of the sandwich structures to carry out transverse loads. In this work, PVC foams typically used as the inner core in structural applications are investigated over a range of foam densities. Firstly, the elastic properties of foams under compressive uniaxial loading are measured using a full-field methodology. Subsequently, Semi-Circular specimens are tested in bending varying the position of supports to generate all range of mixed fracture modes. Suitable fracture criteria are also considered in order to assess their capability to evaluate fracture parameters in PVC foams. Finally, the parameters experimentally determined have been used to validate the response provided by a numerical model developed by the authors.

Mixed-mode fracture toughness of a structural adhesive by the single-leg bending test

To increase the confidence in the design of adhesive structures, it is important to be able to accurately predict their strength and fracture properties (e.g., critical strain energy release rate in tension, JIC, and shear, JIIC). Since in most cases the applied loads induce mixed-mode crack growth, it is highly relevant the perception of fracture under these conditions. This work presents an experimental study using the Single-Leg Bending (SLB) test on specimens bonded with Araldite® 2015, to study and compare the mixed-mode fracture properties. For this purpose, the J-integral method was applied to estimate the tensile (JI) and shear fracture energy (JII). Framing the obtained values in the fracture envelope enabled to select which power-law failure criterion is more appropriate for the Araldite® 2015. Moreover, the tensile and shear cohesive zone model (CZM) laws were obtained for the adhesive by the direct method. Overall, a very good agreement on the fracture properties was obtained between specimens. The CZM laws also showed a good correspondence between specimens, resulting in a novel methodology for integrated mixed-mode material characterization of structural adhesives for possible use to design adhesive joints.

J-integral analysis of the mixed-mode fracture behaviour of composite bonded joints

ABSTRACTTo increase the confidence in the design of adhesive structures, it is important to be able to accurately predict their strength and fracture properties (e.g. critical strain energy release rate in tension, JIC, and shear, JIIC). Since in most cases the applied loads induce mixed-mode crack growth, it is highly relevant to address fracture under these conditions. This work presents an experimental study using the Single-Leg Bending (SLB) test on specimens bonded with three adhesives, to study and compare their mixed-mode fracture properties. For this purpose, the J-integral method was applied to estimate the tensile (JI) and shear fracture energy (JII). Framing the obtained values in several fracture envelopes enabled to select which power-law failure criterion is more appropriate for each adhesive. Moreover, the tensile and shear cohesive zone model (CZM) laws were obtained for each adhesive by the direct method. Overall, a very good agreement on the fracture properties was obtained between specimens of the same adhesive. The CZM laws for each adhesive also showed a good correspondence between specimens, resulting in a novel methodology for integrated mixed-mode material characterization of structural adhesives for possible use to design adhesive joints.

Experimental and numerical analysis of the fracture envelope of composite adhesive joints

To increase the confidence in the design of adhesive structures, it is necessary to accurately predict their strength and fracture properties (critical strain energy release rate in tension, GIC, and shear, GIIC). It is of great importance the perception of fracture under mixed-mode, namely in which relates to the strain energy release rate in tension, GI, and shear, GII. This allows choosing the best failure criterion to use in cohesive zone models (CZM), to predict the joints’ behaviour. This work presents an experimental and numerical study using the Single-Leg Bending (SLB) test on bonded specimens to obtain the mixed-mode fracture properties. The analysis of GI and GII obtained during the experimental phase were addressed. Framing the obtained values in several fracture envelopes enable to select which failure criterion is more appropriate for each adhesive. In the numerical simulations it was possible to reproduce the observed behaviour of the experimental tests, with a positive validation of the chosen propagation criteria.

Characterization of mixed mode fracture properties of nanographene reinforced epoxy and Mode I delamination of its carbon fiber composite

Abstract Motivated by previous research performed by the authors investigating Mode I toughness enhancement using nanographene in EPON 862 epoxy, this article aims to investigate (a) the changes in mixed mode fracture properties of a thermoset polymer (EPON 862) reinforced with hydrogen passivated nanographene platelets (HP-NGPs) and, (b) Mode I fracture properties of EPON 862/IM7 unidirectional laminate with and without dispersed HP-NGPs. For (a), mixed mode fracture experimentation was performed using an asymmetric four-point bending specimen on baseline (0 wt%), 0.1 wt% and 0.5 wt% HP-NGP reinforced EPON 862 polymer. Three different mode mix (KII/KI) ratios (0.78, 1.53, 117) were used to obtain an experimental fracture envelop encompassing pure Mode I to Mode II. Remarkable increase in the fracture envelop both in Mode I (∼3 times) and Mode II (∼2.5 times) was observed with only 0.5 wt% of HP-NGP. For case (b), Double Cantilever Beam (DCB) experiments were used to obtain the fracture toughness of the unidirectional laminates with the HP-NGP reinforced matrices as in (a), in accordance with ASTM D5528. Significant increase (∼100%) in resistance to crack propagation was observed for 0.5 wt% NGP reinforced system in comparison to baseline samples.

Effect of particle size on mixed-mode fracture of nanographene reinforced epoxy and mode I delamination of its carbon fiber composite

Motivated by the lack of available mixed-mode test data in the literature on graphene nanocomposites, this article aims to investigate two cases: (a) the changes in mixed-mode fracture properties of a thermoset polymer (EPON 862) reinforced with hydrogen passivated nanographene platelets (HP-NGPs) and, (b) Mode I fracture properties of EPON 862/IM7 unidirectional laminate with dispersed HP-NGPs. For case (a), mixed mode fracture experimentation was performed using an asymmetric four-point bending specimen on baseline (0wt%), 0.1wt% and 0.5wt% HP-NGP reinforced EPON 862. Three different mode mix (KII/KI) ratios (0.78, 1.53, 117) were used to obtain a fracture envelop encompassing pure Mode I to Mode II. Remarkable increases in the fracture envelop both in Mode I (3 times) and Mode II (2.5 times) was observed with only 0.5wt% of HP-NGP. For case (b), Double Cantilever Beam (DCB) experiments were used to obtain the fracture toughness of the unidirectional IM7/EPON 862 laminates with the HP-NGP reinforced matrices. Significant increase (100%) in resistance to crack propagation in DCB specimens was observed. A brittle to ductile transition at the crack tip due to a novel nanoscale size effect is postulated and verified using TEM as the reason for the toughness increase.

Mixed-mode fracture analysis of composite bonded joints considering adhesives of different ductility

The use of adhesive joints in industrial applications has been increasing. To increase the confidence in the design of adhesive structures, it is important to be able to accurately predict their strength and fracture properties (critical strain energy release rate in tension, \(G_{\mathrm{IC}}\), and shear, \(G_{\mathrm{IIC}})\). As in most cases loads induce mixed-mode (tension plus shear), it is of great importance the perception of fracture under these conditions, in which relates to the strain energy release rate in tension, \(G_{\mathrm{I}}\), and shear, \(G_{\mathrm{II}}\). This analysis allows choosing the best failure criterion to use in cohesive zone models, to predict the behaviour of bonded joints. This work presents an experimental and numerical study using the Single-Leg Bending (SLB) test on specimens bonded with three adhesives, to study and compare their mixed-mode fracture properties. For this purpose, data reduction methods were applied to estimate \(G_{\mathrm{I}}\) and \(G_{\mathrm{II}}\) that require the measurement of crack length (a) and methods using an equivalent crack length (\(a_{\mathrm{eq}})\). The analysis and comparison of \(G_{\mathrm{I}}\) and \(G_{\mathrm{II}}\) obtained during the experimental phase were addressed. Framing the obtained values in several fracture envelopes enable to select which failure criterion is more appropriate for each adhesive. Overall, a very good agreement was obtained between methods for the determination of \(G_{\mathrm{I}}\) and \(G_{\mathrm{II}}\). Actually, apart from one of the methods that produced higher errors, the highest deviation to the \(a_{\mathrm{eq}}\)-based method (considered as the most robust) was 9.3%, obtained for \(G_{\mathrm{I}}\). In the numerical simulations it was possible to reproduce the observed behaviour of the experimental tests, with a positive validation of the chosen propagation criteria obtained from the experimental results.

Mixed mode fracture properties of GFRP-adhesive interfaces based on video gauge and acoustic emission measurements from specimens with adherend fibres normal to the interfaces

Mixed-mode bending tests were performed on fifty-three GFRP-adhesive-GFRP specimens. In each specimen the pre-crack was located near the GFRP adherend with fibres normal to the GFRP-adhesive interface, so as to encourage crack propagation along this interface rather than through the GFRP. The other GFRP adherend contained fibres parallel to the interface, leading to asymmetry of GFRP material (but not of specimen geometry) with respect to the adhesive layer in each specimen. This switching, across the adhesive layer, between normal and parallel fibres in the adherends, reflects a T-joint detail considered for a wave energy device. All tests used a video gauge system to measure crack propagation. Some tests also employed an acoustic emission (AE) system. Comparisons between the AE results and the video gauge-based crack propagation data strongly suggest that the AE energy vs time curve is a much clearer indication of crack initiation than is the widely used AE hit count vs time curve. Increase in Mode II ratio during the tests led to fewer but larger post-peak load drops. Williams's approach, based on beam theory for asymmetric sections with correction factors for large displacements and shear deformation included, led to fracture toughness (G(c)) values in the range 0.3-2.8 kJ/m(2), with a trend of increasing Gc values as pure Mode II is approached. The ASTM approach, developed only for symmetric specimens, gave much lower Gc values. (C) 2017 Elsevier Ltd. All rights reserved.

Numerical Investigation of Adhesively Bonded Joints

The study focuses on using fracture mechanics to evaluate mixed-mode fracture properties of adhesively bonded aerospace material systems. As a part of experimental efforts, mixed-mode fracture tests were performed using modified Arcan specimens consisting of several combinations of adhesive, composite and metallic adherends using a special loading device. Experimental and numerical studies of mixed-mode fracture behaviour of adhesively bonded aluminum and steel were also performed using an adhesive in the aerospace industry. Finite element analyses were carried out on specimens with different adherends. Based on those analyses, many fundamental numerical results were obtained.

Mixed mode fracture properties characterization for wood by Digital Images Correlation and Finite Element Method coupling

This paper seeks to characterize the mixed-mode energy release rate for orthotropic media subjected to a mixed-mode complex loading under service conditions. Experimental full-field information on Digital Image Correlation along with numerical modeling by the Finite Element Method have been considered as complementary approaches to determining fracture behavior in wood. An optimization technique allows calculating the kinematic state from Crack Relative Displacement Factor. A finite element analysis is performed in the local stress field characterization based on Stress Intensity Factor. This hybrid method has proven that the mixed-mode energy release rate uncoupling for fracture mode separation is achieved without taking into account local elastic mechanical properties; these properties can then be deduced by computing reduced elastic compliances from the additional information provided by Digital Image Correlation and Finite Element Method coupling. Such a hybrid method has been employed for cracked Douglas fir specimens undergoing complex loading in tension for various mixed-mode ratio values.

Experimental and Numerical Investigation of Mixed-Mode Fracture Properties of Woven Laminated Composite

Delamination is a major problem associated with composite materials that reduce the stiffness of structure used in aerospace, marine and automotive technology. Interlaminar fracture toughness, non dimensional stress intensity factors and delamination crack growth behavior were investigated for carbon fiber (CF)-polyester laminates. All tests were performed with modified version of Arcan specimen. By changing the loading angles in range of 0-90°, mode-I, mode-II and all mixed mode fracture toughness data were obtained. Correction factors were obtained with finite element analysis using Abaqus software. By employing experimentally measured critical loads and the aid of the finite element method, mixed-mode fracture toughness for the composite under consideration determined. The fracture surfaces of the CF-P under different mixed-mode loading conditions were examined by optical and scanning electron microscopy (SEM) to gain insight into the failure responses.

Rock fracture characterization using the modified Arcan test specimen

This study presents an application of fracture mechanics to determine mixed-mode fracture properties of rock using the numerical and experimental methods. The modified version of Arcan specimen test was, in association with a special loading device, an appropriate apparatus for experimental mixed-mode fracture analysis. Using the finite-element results, correction factors were applied to the specimens and a polynomial fit was proposed to evaluate the stress-intensity factors of a modified version of Arcan specimen with a crack subjected to mixed mode loading. The finite element analyses of specimens were also studied for various materials, different thickness and crack length. The mixed-mod fracture-toughness tests were carried out by using the modified Arcan test specimens over a wide range of loading angles. Using the finite element results, non-dimensional stress-intensity factors applied to the fracture specimen. By employing experimentally measured critical loads and the aid of the finite element method, mixed-mode fracture toughness for rock under consideration determined. The fracture surfaces under different mixed-mode loading conditions were examined by optical and scanning electron microscopy (SEM) to gain insight into the failure surfaces.

Interfacial mixed-mode fracture characterization of adhesively bonded joints

This paper presents an application of fracture mechanics to determine interfacial mixed-mode fracture properties of adhesively bonded aerospace material systems using the numerical and experimental methods. By means of the finite-element results, correction factors were applied to the specimens with different adherends and a polynomial fit was proposed to evaluate the stress intensity factors of a modified version of Arcan specimen with an interface crack subjected to mixed-mode loading. The finite-element analyses of bonded joints were studied using various materials and different crack length along the interface. The interaction J-integral method was used to separate the mixed-mode stress intensity factors at the interface crack-tip under different loading conditions. The mixed-mode fracture toughness tests were carried out using specimens consisting of several combinations of adhesive, composite and metallic adherends over a wide range of loading angles. Stress intensity factors and associated energy release rates were obtained for various cases of interest. The result of fracture toughness tests revealed that the interfacial fracture of bonded joints is strong under the shearing-mode loading but weak to the opening-mode loading. Several criteria for interface fracture under mixed-mode conditions were examined and compared to test results obtained with different adherends specimens.

Specimen Design for Mixed Mode Interfacial Fracture Properties Measurement in Electronic Packages

A four-layer center cracked beam (CCB) under four point bending loading is developed for the interfacial fracture properties measurement of electronics packaging materials. Determination of the mixed mode interfacial fracture properties along the second and third layers of the CCB specimen is carried out analytically. For a given test specimen, a stable test window (material combination and thickness ratio) has been identified using the analytical expression. Data yield from interfacial mixed mode fracture properties experimental measurement can be enhanced by testing within the testing window. [S1043-7398(00)00101-8]