Fracture Mechanical Properties Research Articles

Gradient changes in fiber bundle content and mechanical properties lead to asymmetric bending of bamboo

Natural biomaterial bamboo has excellent strength and toughness. The content of fiber bundles and the gradually increasing tensile strength of fiber bundles from the inside to the outside in the radial direction of the bamboo wall are the two main factors leading to significant differences in the fracture behavior and mechanical properties of bamboo under loading from different sides of bamboo strip. In this study, the flexural strength, toughness, and bending fracture energy of the bamboo loaded from the inside of the sample (Mode B) were found as 28%, 191%, and 174%, respectively, higher than those of the bamboo loaded from the outside of the sample (Mode A). The mechanical properties of samples loaded radially (Mode C) were higher than Mode A and lower than Mode B. The fracture process of the sample and the corresponding fracture morphology showed parenchyma fracture (matrix failure), fiber fracture, and interfacial debonding (fiber–fiber, fiber-parenchyma, parenchyma-parenchyma) occurring in all samples. Tearing of the cell wall, fiber debonding, fiber bridging, fiber pull-out, and crack deflection are the major fracture-toughening mechanisms of bamboo. This study reveals the relationship between the gradient changes in the mechanical properties and content of bamboo fiber bundles and the bending and fracturing behavior of bamboo, which provides theoretical basis and ideas for the development of new bamboo engineering materials, the bionic design of bamboo structures, and the structural optimization of fiber-reinforced composite materials.

Post-fatigue fracture load, stress concentration and mechanical properties of feldspathic, leucite- and lithium disilicate-reinforced glass ceramics

ObjectiveTo evaluate the mechanical properties of different CAD/CAM ceramic systems and the post-fatigue fracture and stress distribution when used as cemented crowns. Materials and methodsSixty (60) CAD/CAM monolithic crowns were milled using three different ceramic materials (FD – Feldspathic [Vita Mark II]), LE - Leucite-based ceramic [IPS Empress CAD] and LD - Lithium Disilicate [IPS e.max CAD]) and adhesively cemented on resin composite dyes. Specimens were stored in distillated water (37 °C) for 7 days. After, half of the crowns were submitted to immediate fracture load test while the other half was submitted to fatigue cycling. The average cement layer of approximately 80 μm was assessed using scanning electron microscopy (SEM). The average thickness was used in the three-dimensional (3D) Finite Element Analysis (FEA). For each ceramic material, the density, Poisson ratio, shear modulus, Young modulus, fracture toughness, and true hardness were assessed (n = 3). The data was used to assess the Maximum Principal Stress throughout 3D-FEA according to each material during load to fail and post-fatigue. Data were submitted to two-way ANOVA and Tukey test (α = 0.05). ResultsLD showed the highest compression load, density, shear modulus, Young modulus, fracture toughness and true hardness values. While LE presented the lowest mechanical properties values. There is no difference in the Poisson ratio between the evaluated ceramics. ConclusionLD was susceptible to aging process but presented stronger physicomechanical properties, showing the highest post-fatigue fracture load and highest stress magnitude.

On fabrication of acrylonitrile butadiene styrene-zirconium oxide composite feedstock for 3D printing-based rapid tooling applications

The 3D-printed rapid tools are being used in finishing operations such as drilling, milling, broaching, roller burnishing, and other finishing operations that need anti-wear plastic composite materials. Zirconium oxide (ZrO2) is one of the ceramic materials which is highly appreciated due to its anti-wear properties. This study aims to develop the ZrO2 ceramic particles reinforced acrylonitrile butadiene styrene (ABS) thermoplastic composite feedstock filaments for 3D printing of rapid tools. In the first stage, the multiple numbers (as per Taguchi L9 orthogonal array (OA)) of ABS-ZrO2 feedstock filaments were developed by varying the loading of ZrO2 in ABS matrix (2 wt.%, 4 wt.%, and 6 wt.%), processing temperature (200, 205 and 210°C), and rotation speed of screw (4, 6 and 8 RPM). The optimum setting obtained for manufacturing ABS-ZrO2 composite feedstock filaments is the combination of 2% ZrO2 loading, 205°C processing temperature, and 6 RPM screw speed. In the next stage, fused filament fabrication (FFF) based 3D printing has been used to prepare the rapid tools. The wear test performed for 3D printed ABS-ZrO2 composites rapid tools shows only .62% weight loss which is lower as compared to virgin ABS (.91% weight loss). The results of the study are supported by fracture analysis, morphology, and mechanical properties.

Evaluation of fracture behavior of lightweight magnesia‐based refractories via wedge splitting test along with acoustic emission detection

AbstractThe effect of spinel powder on the fracture behavior and mechanical properties of lightweight magnesia‐based refractories containing microporous magnesia aggregates with high apparent porosity (37.4%) were investigated by the wedge splitting test (WST) with the digital image correlation and acoustic emission. With the addition of spinel powder, lightweight magnesia spinel refractories showed a higher cold compressive strength compared with lightweight pure magnesia refractories. From the WST, the addition of spinel powder increased the specific fracture energy and characteristic length of lightweight magnesia spinel refractories, which improved the crack propagation resistance. The increased tortuosity of main crack and a higher ratio of crack propagation along the aggregates/matrix interface were main reasons for reducing the brittleness of lightweight magnesia spinel refractories. Besides, acoustic emission (AE) signal activity indicated that the propagation of pregenerated micro‐cracks by the thermal mismatch and the development of fracture progress zone were primary ways to consume energy in lightweight magnesia spinel refractories. The reduced proportion of crack propagation within aggregates was also detected by the peak frequency of AE signals in lightweight magnesia spinel refractories. For microporous magnesia aggregates with high apparent porosity (37.4%), lightweight magnesia spinel refractories also showed reduced brittleness fracture behavior than lightweight pure magnesia refractories.

An Experimental Investigation of the Mechanical Performance of EPS Foam Core Sandwich Composites Used in Surfboard Design.

Surfboard manufacturing has begun to utilise Expanded Polystyrene as a core material; however, surf literature relatively ignores this material. This manuscript investigates the mechanical behaviour of Expanded Polystyrene (EPS) sandwich composites. An epoxy resin matrix was used to manufacture ten sandwich-structured composite panels with varying fabric reinforcements (carbon fibre, glass fibre, PET) and two foam densities. The flexural, shear, fracture, and tensile properties were subsequently compared. Under common flexural loading, all composites failed via compression of the core, which is known in surfing terms as creasing. However, crack propagation tests indicated a sudden brittle failure in the E-glass and carbon fibre facings and progressive plastic deformation for the recycled polyethylene terephthalate facings. Testing showed that higher foam density increased the flex and fracture mechanical properties of composites. Overall, the plain weave carbon fibre presented the highest strength composite facing, while the single layer of E-glass was the lowest strength composite. Interestingly, the double-bias weave carbon fibre with a lower-density foam core presented similar stiffness behaviour to standard E-glass surfboard materials. The double-biased carbon also improved the flexural strength (+17%), material toughness (+107%), and fracture toughness (+156%) of the composite compared to E-glass. These findings indicate surfboard manufacturers can utilise this carbon weave pattern to produce surfboards with equal flex behaviour, lower weight and improved resistance to damage in regular loading.

Failure characteristics and the law of the energy evolution of granite with different pre-crack inclination angles under uniaxial compression loading

Cracks affect the strength of rock masses and eventually threaten their stability in engineering. In order to study the fracture characteristics and mechanical properties of cracked rocks, uniaxial compression tests of pre-cracked granite samples with a central circular through hole were carried out by using MTS816 rock mechanics testing system. The inclination angles of different pre-cracks are 0°, 15°, 30°, 45°, 60°, 75°, and 90° respectively, and the influence of the crack stop hole near the crack tip on the failure behavior of pre-cracked samples is also considered. The results indicate that, compared with the intact sample, the peak strength of pre-cracked samples decreases significantly and is related to the pre-crack inclination angle. The failure mode of the sample varies with the pre-crack inclination angle, and the crack stop hole near the crack tip also has a certain influence on the crack growth to a certain extent. However, in terms of failure mode and its transformation law, the influence of central circular through hole and crack stop hole can be ignored. Generally speaking, the larger the inclination angle of the pre-crack, the more the total energy required for failure of the sample, and the more the stored elastic strain energy. Before the peak strength, the elastic strain energy of the sample is greater than the dissipated energy, after the peak strength, the dissipated energy gradually exceeds the elastic strain energy due to energy conversion. It is found that the pre-crack reduces the energy storage capacity of the sample, and the total energy is ultimately dominated by sample integrity. The dissipated energy rate increases first, then decreases, and finally increases again, the inflection points are the end of micro-crack closure and the peak strength, respectively. The crack stop hole changes the law of energy evolution to a certain extent, which can improve the ability of rocks to accumulate energy when designed at an appropriate position, so as to improve its load-bearing capacity in a certain range. The results display the mechanical properties of pre-cracked granite samples under uniaxial compression and are conducive to its application in engineering.

Biomechanical analysis of internal fixation system stability for tibial plateau fractures.

Background: Complex bone plateau fractures have been treated with bilateral plate fixation, but previous research has overemphasized evaluating the effects of internal fixation design, plate position, and screw orientation on fracture fixation stability, neglecting the internal fixation system's biomechanical properties in postoperative rehabilitation exercises. This study aimed to investigate the mechanical properties of tibial plateau fractures after internal fixation, explore the biomechanical mechanism of the interaction between internal fixation and bone, and make suggestions for early postoperative rehabilitation and postoperative weight-bearing rehabilitation. Methods: By establishing the postoperative tibia model, the standing, walking and running conditions were simulated under three axial loads of 500N, 1000N, and 1500N. Accordingly, finite element analysis (FEA) was performed to analyze the model stiffness, displacement of fractured bone fragments, titanium alloy plate, screw stress distribution, and fatigue properties of the tibia and the internal fixation system under various conditions. Results: The stiffness of the model increased significantly after internal fixation. The anteromedial plate was the most stressed, followed by the posteromedial plate. The screws at the distal end of the lateral plate, the screws at the anteromedial plate platform and the screws at the distal end of the posteromedial plate are under greater stress, but at a safe stress level. The relative displacement of the two medial condylar fracture fragments varied from 0.002-0.072mm. Fatigue damage does not occur in the internal fixation system. Fatigue injuries develop in the tibia when subjected to cyclic loading, especially when running. Conclusion: The results of this study indicate that the internal fixation system tolerates some of the body's typical actions and may sustain all or part of the weight early in the postoperative period. In other words, early rehabilitative exercise is recommended, but avoid strenuous exercise such as running.

A comprehensive study of damage characteristics and acoustic emission response mechanism of sandstone with different water contents

The mechanical characteristics and fracture mechanisms of rocks are usually affected by water–rock interaction. This study conducted uniaxial compression tests on sandstone to analyse the variation law of its mechanical properties and macroscopic failure morphology for various water contents. Furthermore, the relationships between the roughness of the crystal fracture surface and mechanical properties were discussed based on the scanning electron microscope (SEM) fracture morphology. The development of an internal fracture in sandstone was described using acoustic emission (AE) and low-field nuclear magnetic resonance (NMR) techniques, and the response mechanism and controlled factors of an AE dominant frequency–amplitude signal were revealed. Results reveal that the uniaxial compressive strength and elastic modulus of sandstone exhibit a nonlinear decreasing trend with an increase in water content. The deterioration to the sandstone structure by water is divided into three periods: intense, stable growth, and calm. The macroscopic fracture shape of sandstone gradually changes from single-shear failure to axial-split failure, whereas the roughness of the crystal fracture surface positively correlated with the water content, with the mechanical strength negatively correlating. Four response mechanisms of the AE spectrum exist in sandstone fracture process: sliding friction between the mineral particles or crystal fracture (transgranular or intergranular crack) corresponds to the LF–LA signal, friction of microcracks corresponds to the IF–LA signal, fracture of microcracks corresponds to the HF–LA signal, and large-scale macroscopic cracks correspond to the LF–HA signal. Moreover, the characteristics of the AE dominant frequency–amplitude signal are affected by the mineral composition and pore structure of sandstone. This study can enrich the existing research literature on sandstone damage characteristics in water-bearing state and provide new perspectives and approaches for quantitatively describing the fracture mechanism of rock.

Numerical Simulation of the Mechanical Properties and Fracture of SiCp/6061Al Composite Materials Based on Microstructure

SiCp/6061Al composites with volume fractions of 5%, 10%, and 15% were prepared by the vacuum hot pressing sintering. Their microstructure and fracture morphology were observed and analyzed with an optical microscope and a scanning electron microscope. The elastic–plastic behavior of the 6061Al matrix in the composites was studied by using the load–displacement curve obtained by the nanoindentation test, and the plastic constitutive equation was established. The representative volume element (RVE) model was established based on the geometric characteristics of the SiC particles identified by using image processing technology from the metallographic structure. The deformation and fracture process of the SiCp/6061Al composites under the uniaxial tensile load was simulated microscopically, and the microscopic deformation and fracture characteristics and mechanical properties of SiCp/6061Al composites under different interface strengths and different SiCp volume fractions were revealed.

Anisotropy of fracture mechanical properties of carbon-containing refractories and its impact on cracking in a steel ladle lining

Cracks are occasionally observed in bricks installed in steel ladle sidewalls. Three magnesia-carbon refractories used in steel ladles were investigated in terms of the anisotropy of the mechanical properties and their possible contribution to crack formation. The main differences between these bricks were the direction of the moulding force and the type of press used (spindle or hydraulic press). This study aimed to clarify the reasons for the inferior performance of one refractory material compared to other materials from a thermomechanical point of view. The results showed clear anisotropy in the elastic and fracture mechanical data. Brittleness was the lowest and crack propagation resistance was the highest when the crack extended parallel to the moulding force. Therefore, the lowest cracking vulnerability was observed in the case of a moulding force perpendicular to the longest brick edge and this was verified via field observations.

Fracture properties of steel fibre reinforced high-volume fly ash self-compacting concrete

This paper presents an experimental investigation on the fracture mechanical properties of steel fibre-reinforced high-volume fly ash self-compacting concrete (HFSCC). Specifically, self-compacting concrete (SCC) of various toughness was designed at desired steel fibre volume fractions of 0, 0.25 v%, 0.50 v%, 0.75 v% and 1.00 v% by volume and fly ash contents of 40 wt%, 50 wt%, 60 wt% and 70 wt% by mass. The fracture mechanical properties of HFSCC (cured for one year) were studied by a three-point bending beam test. The influence of fly ash and steel fibre content on fracture parameters was systematically discussed. The research indicated that the fracture mechanical properties of HFSCC with different fly ash percentage were improved by adding steel fibres. The fullness of the force (F)-crack mouth opening displacement (CMOD) curves gradually increased with the steel fibre volume fraction (Vf). The peak load (Fp), peak CMOD (CMODP), fracture toughness (KIC) and fracture energy (GF) of the fracture parameters linearly increased with Vf. Furthermore, the correlation between them was analysed numerically. The slope of the fitting line increased with increasing fly ash content, indicating that high-volume fly ash was more conducive to improving the fracture mechanics of SCC after long-term ageing. After the hydration reaction, residual calcium hydroxide was observed only in the cross-sectional image of HFSCC-70, it helped to improve the fracture mechanical properties of HFSCC.

Interlaminar and intralaminar fracture resistance of recycled carbon fibre/PPS composites with tailored fibre/matrix adhesion

The production of advanced composites from recycled carbon fibres (rCFs) is critical for the sustainable development of carbon fibre industry. Herein, non-woven mats consisting of commingled rCFs and Polyphenylene-sulfide (PPS) fibres were compression moulded to manufacture rCF/PPS composites, with the fibre/matrix adhesion being tailored by UV-irradiating the non-woven mats. The intralaminar and interlaminar fracture resistance and mechanical performance of the rCF/PPS composites were characterised. The experimental results had demonstrated that improving the PPS/rCF adhesion of the composites significantly increased the intralaminar fracture energies and mechanical properties under tensile and shear loading conditions. However, it also negatively affected the interlaminar fracture resistance. The main fracture mechanism was observed to be fibre evulsion for the intralaminar fracture mode, while crack bridging by the rCFs was the primary fracture mechanism for the interlaminar fracture condition. That led to the contrary influences of the improved fibre/matrix adhesion on the intralaminar and interlaminar fracture resistance of the rCF/PPS composites. In summary, this study had shedded lights on tailoring the crack resistance and mechanical performance of rCFRPs by adjusting the fibre/matrix adhesion using the UV-treatment technique.

Influence of the interfacial transition zone between a steel inclusion and cement-based composite on the fracture response of a bent specimen

The influence of the interfacial transition zone (ITZ) between a steel inclusion and fine-grained cement-based composite on fracture behaviour of the specimen with the inclusion is investigated. Three-point bending fracture tests were conducted and the mechanical fracture properties of the composite were evaluated based on the results of the tests. The numerical analysis of the fracture test was performed and related to the experimental data obtained during crack propagation, and the microstructure of fracture surfaces. The crack propagation conditions were assessed based on the criterion of the average value of tangential stress calculated over certain distance in dependence on the polar angle (GMTS criterion). We concluded that the fracture toughness of the interface KIc, ITZ is equal to 33 % of the fracture toughness of matrix KIc, MTX. The poor fracture properties of ITZ are responsible for the reduction of load-bearing capacity of whole specimen with inclusion in comparison to the sample without the inclusion.

Experimental Study on the Influence of Humidity on Double-K Fracture Toughness and Fracture Energy of Concrete under Water Environment

Saturated concrete is significantly different from dry concrete in fracture mechanical properties. Using the wedge-splitting tensile method to research the rule of change in moisture content, double-K fracture toughness and fracture energy of three strength grades (C20, C30, and C40) of concrete immersed in a free water environment for 0 h, 2 h, 5 h, 24 h, and 120 h were studied in order to provide support for the safety evaluation of concrete structures in a water environment. The initial cracking fracture toughness of C20, C30, and C40 concrete in saturated state were, respectively, 29.6%, 23.2%, and 33.4% lower than that in dry state. The unstable fracture toughness of C20, C30, and C40 concrete in saturated state were, respectively, 22.7%, 23.9% and 33.8% lower than that in dry state. The fracture energy of C20, C30, and C40 concrete in saturated state are only 71.99%, 70.29%, and 66.11% of that in dry state, respectively. The initial cracking fracture toughness and unstable fracture toughness of concrete all show a linear, decreasing trend with an increase in moisture content. Before the crack initiation, the measured P–CMOD curve had an obvious linear elastic stage, stable expansion stage, and unstable expansion stage. The critical crack opening displacement gradually decreases with an increase in moisture content; the deformation capacity and toughness of concrete are shown to decrease. The humidity state should be fully considered when evaluating the fracture mechanical properties of concrete.

Composition-dependent fracture energy in metallic glasses

The interplay between metallic glasses (MGs) mechanical properties, fracture energy $(G)$, and glass-forming ability (GFA) and their dependence on alloy composition remain poorly understood. Here, we perform molecular dynamics simulations to investigate the intrinsic composition dependence of $G$ in ${\mathrm{Cu}}_{x}{\mathrm{Zr}}_{100\ensuremath{-}x}\mathrm{MGs}$ $(x=20,30,40,50,64)$. The results indicate that the value of $G$ increases with Cu content. In addition, it is revealed that MGs with higher $G$ values display higher Poisson's ratio (\ensuremath{\nu}) and GFA, suggesting a close correlation between fracture toughness, mechanical properties, and GFA. This correlation between G, \ensuremath{\nu}, and GFA can be understood based on the fragility ($m$) of supercooled liquids, which is directly related to the structural heterogeneity in MGs. Larger $m$ values are related to dynamic slowdown and supercooled liquid stabilization, which enhance GFA and the formation of pronounced structural heterogeneity, comprised of loosely packed regions that favor \ensuremath{\beta} relaxation and the activation of shear transformation zones. Those concurrently promote the expansion of the plastic zone at the crack tip, enhancing the observed value of $G$. These simulation results shed light on the intrinsic relationship between fracture toughness, mechanical properties, and alloy composition in MGs.

Fracture Analysis of Butt Welding Area of 5″ Drill Pipe Internal Thread End in an Oilfield

This paper tested fracture morphology analysis, mechanical properties and chemical, metallographic analysis and micro analysis to find out the factors of fracture in the butt welding area of the internal thread of the 5″ drill pipe, which is made of S135 in the casing pulling process of an oilfield. The results show that the chemical element, tensile strength and yield strength, impact performance, metallographic structure, inclusions in microstructure and grain size of the Fracture drill pipe meet the relevant data of the oilfield and industry standards, but the hardness of the fracture does not meet the requirements of the national standard. The important reason of the fracture of the drill pipe is that the oxide skin was not cleaned before the drill pipe joint was welded with the body. During welding, the oxide skin entered the molten weld metal, and large slag inclusions formed in the weld resulted. The secondary cause is improper subsequent heat treatment of drill pipe weld, which leads to increased weld brittleness and accelerated crack growth. This paper puts forward corresponding countermeasures to improve the quality of the drill pipe’s weld and prevent the failure accidents of drill pipe.

Parameters Calibration of the GISSMO Failure Model for SUS301L-MT

With the development of the rail transit industry, more attention has been paid to the passive safety of rail vehicles. Structural damage is one of the main failure behaviors in a rail vehicle collision, but it has been paid little attention to in past research. In this paper, the quasi-static fracture experiments of SUS301L-MT under different stress states were carried out. The mechanical fracture properties of this material were studied, and the corresponding finite element simulation accuracy was improved to guide the design of vehicle crashworthiness. Through the tests, the fracture behavior of materials with wide stress triaxiality was obtained, and each specimen's fracture locations and fracture strains were determined. Parameters of a generalized incremental stress state dependent damage model (GISSMO) of the material were calibrated, and the model's accuracy was verified with test results from a 45° shear specimen. The GISSMO failure model accurately reflected the fracture characteristics of the material. The mesh dependency of this model was modified and discussed. The results show that the simulation agrees well with experimental data for the force-displacement curve after correction, but the strain distribution needs to be further studied and improved.

Fracture properties of a concrete-epoxy mortar interface with precoating treatment applied through image correlation technology

Random defects on concrete surfaces are a key factor affecting the bonding property of concrete–epoxy mortar interfaces. In this study, an epoxy–acetone solution was employed to pretreat such defects on concrete surfaces, and resin concentrations of 20, 40, 60, and 80 wt% diluted by acetone were used. The fracture mechanical properties and propagations of the fracture process zone (FPZ) of 14 concrete–epoxy mortar composite specimens were analysed using digital image correlation technology and the four-point bending test. The results revealed that there was a great influence of resin concentration on the fracture properties of the concrete-epoxy mortar interface. Precoating solution with an appropriate resin concentration (20 ∼ 40 wt%) could effectively delay crack formation at the interface and markedly improve the bearing capacity, stiffness, ductility, FPZ length, and energy release rate of the specimens. The precoating solution with a resin concentration of 40 wt% exhibited the optimal repair effect on the concrete surfaces. However, the improvement from the pretreatment with high resin concentrations (60 ∼ 80 wt%) on the fracture properties was less than satisfactory. The toughening mechanism of this precoating solution was analysed through scanning electron microscopy, which revealed that the concrete surface could be effectively repaired and improved by the precoating treatment with an appropriate resin concentration, which in turn enhanced the interfacial connection performance between epoxy mortar and concrete.

The effects of microstructures on the mechanical performances and fracture mechanisms of boron-alloyed ferritic and martensitic stainless steels fabricated by powder metallurgy

Porosity is generally the major cause of the inferior mechanical properties of powder metallurgy (PM) steels. Boron (B) is an effective element for improving the sintering densification of PM steel via liquid phase sintering (LPS). To date, the microstructure and mechanical properties of B-alloyed PM stainless steels remain to be determined. The objective of this research was to study the influences of B on the LPS, microstructures, mechanical performances, and fracture mechanisms of PM 410L ferritic and 410 martensitic stainless steels. The roles of the Fe-based matrix, eutectic areas, and pores in the fracture behavior and mechanical properties were examined.The results showed that after 1250 °C sintering, the 0.6 wt% B additive in 410L and 410 obviously induced LPS and decreased the porosity from 8.9 vol% to less than 4 vol%. In both 410L+0.6B and 410+0.6B, the B-containing compounds were identified by electron backscatter diffraction as M2B boride with a tetragonal structure. The 0.13 wt% C additive in 410L+0.6B increased the ultimate tensile strength from 420 MPa to 843 MPa but decreased the elongation from 10.4% to 2.7% and the impact energy from 21 J to 6 J due to the transformation of the Fe-based matrix from ferrite to martensite. In the combination of fracture analyses and strain distribution as a function of tensile stress, the results indicated that in 410L+0.6B and 410+0.6B, the predominant sites for strain localization and fracture were respectively the ferritic grains and intergranular eutectic areas. Furthermore, the pores played different roles in the deformation and fracture of the two B-alloyed PM stainless steels.

Tensile Fracture Property of Concrete Affected by Interfacial Transition Zone

As a weak link between aggregate and mortar in concrete, interfacial transition zone (ITZ) usually plays a key role in concrete fracture. To investigate the tensile fracture property of concrete affected by the mechanical properties of ITZ numerically, the geometrical models of heterogeneous concrete were established with the parameterization modeling. They include three phases, namely, mortar, ITZ, and randomly distributed aggregates with distinct sizes and orientations. The cracking behaviors of mortar and ITZ were characterized by the bilinear cohesive zone constitutive model. Based on the experiments, the mechanical properties of ITZ were mediated by changing the water–cement ratio of mortar, the aggregate surface roughness and the content of silica fume in interfacial agent. A series of numerical simulations were conducted on the concrete models in tension after the numerical modeling method was validated. The macroscopic tensile fracture properties of concrete were quantitatively connected with some microscopic variables, including the water–cement ratio of mortar, the aggregate surface roughness and the silica fume content in interfacial agent. It was found that the tensile fracture properties of concrete have negative linear correlations with the water–cement ratio of mortar, while the effects of the aggregate surface roughness and the silica fume content in interfacial agent are very complex. The tensile fracture mechanical properties of concrete have a bilinear relationship with the aggregate surface roughness and an approximate quadratic parabola relationship with the content of silica fume in the interfacial agent. This study is beneficial to improve the fracture resistance of concrete by some interface handling measures.