Tensile Failure Mechanisms Research Articles

Review on the design and application of concrete canvas reinforced with spacer fabric

Concrete canvas reinforced with spacer fabric has increasingly gained popularity due to its lightweight, great flexibility, high strength and low contamination compared to ordinary concrete. In order to fully explore the structure and performance of this novel composite, this review illustrates how to design high-performance concrete canvas and presents a summary of recent application status of it. Firstly, the structure and properties of knitted and woven spacer fabric and concrete material that comprise concrete canvas is introduced. Secondly, internal and external mechanisms affecting the properties of concrete canvas have been described. To illustrate how to evaluate and test the mechanical behavior of concrete canvas, typical mechanical experiments such as tensile and flexural experiment and failure mechanisms are explained. In terms of the characteristics of concrete canvas, the present article reviews current applications of it in disaster relief tent, slope protection, ditch lining and furniture design areas. Nevertheless, its practical applications are still in the preliminary stage, it is of great necessity to expand its application from the point of view of replacing traditional materials, changing structural design, external reinforcement and perfecting performance evaluation system.

Influence of the heating force in rotational friction welding on mechanical properties and tensile fracture mechanism of dissimilar welded joints of 30KhGSA and 40KhMFA steels

This article presents the results of evaluating the effect of heating force, as one of the parameters of rotational friction welding, on the mechanical properties and mechanism of tensile failure of dissimilar welded joints of medium-carbon steels 30KhGSA and 40KhMFA. The results of studies of the microstructure and microhardness of welded joints are presented. The fracture mechanism of welded specimens during tensile testing was evaluated on the basis of strain distribution maps obtained by the digital image correlation method and the results of fractographic analysis. The features of the development of deformation and failure of welded joints obtained at different heating forces are shown. From the point of view of the equal strength of the structure with a welded joint the optimal values of this parameter of rotary friction welding for joining steels 30KhGSA and 40KhMFA are recommended.The reported study was funded by RFBR according to the research project № 20-38-90032.When conducting mechanical tensile tests and studying the distribution of deformation fields, equipment was used that is part of the Plastometriya collective centre of the IES named after E. S. Gorkunova of the Ural branch of the RAS

Tensile behavior and failure mechanism of 3D woven fabric reinforced aluminum composites

This paper aims to study the mechanical behavior and the complicated failure mechanism of a novel Al matrix composites reinforced with 3D orthogonal woven carbon fiber. The quasi-static tensile behavior, local stress response and progressive failure process are investigated via numerical and experimental approach. According to the microstructure at fiber and yarn scale, microscopic and mesoscopic finite element models were established to carry out multiscale simulation. The calculated tensile stress-strain curve is basically in accordance with the experimental curves, where the elastic moduli, tensile strength, and elongation are 118.6 GPa, 777.3 MPa and 0.84%, respectively. Local stress distribution of the matrix pocket and yarns exhibits apparent periodicity and heterogeneity, which is related to the specific fabric architecture. Interface debonding induces the local damage of matrix alloy and transverse cracking of binder and weft yarns successively, resulting in nonlinear response of the tensile curves. The catastrophic rupture of the composites is caused by the axial fracture of warp yarns that resulted from the combination of matrix failure and transverse yarns cracking. The fracture morphology of binder and weft yarns is flat and that of warp yarns exhibits limited fiber pull-out, which can be interpreted by the predicted failure mode. Based on the validated model, the influence of fabric structure parameters on the macroscopic properties was further evaluated. The results indicate that the increase of warp or weft density could improve the tensile strength and elastic modulus, but the tensile elongation decreases with the increase of weft density.

Effects of microstructure heterogeneity on tensile properties and failure mechanism of GTAW joint of as-cast Ti2531

In this study, as-cast dual-phase titanium alloy Ti2531 was welded by Gas Tungsten Arc Welding, and the effects of microstructure heterogeneity on tensile properties and failure mechanism was analyzed. Tensile test results showed that the specimens fractured in the base metal region, and the tensile strength R m of the welded plate was 855 MPa ~ 859 MPa, which was almost the same as that of the base metal. It was found that, compared with the base metal region, the fine and basketweave phase in the weld zone and heat-affected zone resulted in higher hardness and yield strength. Therefore, plastic strain concentration occurred in the base metal region and a large number of kink bands were found, which accounts for the relatively good plasticity with the fracture strain of 0.073–0.09. In addition, by means of intergranular orientation analysis, it was demonstrated that [0001] α and [101] β were the rotation axes of kink bands in the α and β phases, respectively. Furthermore, by observing the high-resolution electron microscopy, it was found that these kink bands were formed by the arrangement of edge dislocations. As a consequence, when the lattice distortion was severe, the unstable expansion of kink bands occurred and cracks were formed in widmanstätten colonies, inducing the failure of the specimen in the base metal region and great tensile strength equivalent to that of base material. • The weld joint of Ti2531 had good tensile strength close to that of base material. • Plastic deformation was concentrated in base metal region rather than other regions. • Kink bands were formed to coordinate severe plastic deformation in base metal region. • The instable expansion of kink bands resulted in the fracture of the welded specimen.

Effect of acetylated citrate plasticizer on mechanical properties of poly(vinyl chloride)

In this work, the effects of acetylation modification on the plasticization properties of citrates (triethyl citrate (TEC), acetyl triethyl citrate (ATEC), tributyl citrate (TBC) and acetyl tributyl citrate (ATBC)) were investigated by using a combination of characterization techniques and molecular dynamics (MD) simulation. The tensile test show that the acetylated ATEC and ATBC have better plasticizing efficiency compared to their non-acetylated counterparts, and consequently the tensile strength and elongation at break of ATEC/PVC (ATBC/PVC) are 13.9% (18.7%) and 8.3% (2.2%) higher than those of TEC/PVC (TBC/PVC), respectively. The MD simulation results corroborate these observations and further reveal the reason for these changes. The research mainly includes three aspects: 1. Effect mechanism of acetylation modification on the interaction between citrate and PVC; 2. The changes of microstructure, energy and motion state of PVC composites during tensile process; 3. Tensile failure mechanism of PVC composites under large tensile force. In addition, the effect of acetylation treatment on toxicity of citrate was also studied. Thus, our study contributes to better understanding of the plasticizing mechanisms of citrate and proposes an optimized citrate structure with higher performance.

Experimental and Numerical Investigation of the Tensile Performance and Failure Process of a Modified Portland Cement

A better understanding of the tensile performance and tensile failure mechanism of cement paste is significant in preventing rock reinforcement failure. Therefore, this paper aims to reveal the tensile performance and failure mechanism of a modified Portland cement: Stratabinder HS cement. To achieve this objective, the split tensile test was conducted on specimens followed by simulating the failure mechanism numerically. The results indicated that the water–cement rate significantly influenced the tensile performance of the cement paste. When the water–cement rate increased from 0.35 to 0.42, the tensile strength declined from 1.9 MPa to 1.5 MPa. It was also observed that vertical tensile failure constantly occurred regardless of the water–cement rate. During the testing process, tensile cracks and shear cracks occurred. The increasing rate in the number of specimen cracks was dependent on the tensile stress state. Before the tensile stress reached the peak, the crack quantity increased slightly. After the peak, the crack quantity increased dramatically. During the vertical loading process, horizontal tensile stress occurred in the specimen. This horizontal tensile stress zone showed a diamond shape. The higher the tensile stress is, the larger the area of the horizontal tensile stress zone. When the tensile strength was reached, horizontal tensile stress mainly concentrated at the vertical centre of the specimen. This finally led to tensile failure of the specimen. This paper indicated that the water–cement rate was the key factor in evaluating the tensile strength of the Stratabinder HS cement.

Effect of geogrid reinforcement on tensile failure of high-strength self-compacted concrete

In this study, the tensile strength, failure mechanism and ductile behaviour of geogrid-reinforced high-strength self-compacting concrete discs subjected to both the Brazilian tensile strength test and a biaxial compressive test are studied. To determine the combined effects of geogrid layer numbers and inclination angle on the ultimate tensile strength of concrete samples, 21 experiments were conducted with up to three layers of geogrids inclined at angles of 0° to 90°, at increments of 15°. In addition, discrete-element numerical simulations were conducted using two-dimensional particle flow code to examine the failure behaviour of geogrid-reinforced high-strength self-compacting concrete discs. The numerical models were first calibrated by the experimental results and then the failure behaviour of models containing geogrids was investigated. Both experimental and numerical results demonstrate that augmenting the concrete discs with geogrids increases the ductility of specimens, especially after failure. As the number of geogrid layers increased, the tensile strength of specimens also increased, whereas the tensile strength and absorbed energy were the same for specimens with different numbers of geogrid layers and inclination angles of 75° and 90°. The specimen with three horizontal geogrid layers had the highest tensile strength, biaxial compression strength and ductility of all specimens tested.

Testing and Evaluation of Flexural Tensile Strength of Prestressed CFRP Cables.

To expand the application scope of prestressed carbon fiber-reinforced polymer (CFRP) cables in civil engineering, the ultimate tensile strength of these cables was tested and evaluated under bending conditions. First, the study analyzed the tensile failure mechanism of CFRP cables under bending conditions based on elastic bending analysis theory. Thereafter, the ultimate stress state of individual tendons and cables was derived and a calculation model for the tensile strength of bent CFRP cables was established. Second, 14 sets of test conditions were created for CFRP cables under bending angles of 20–40° and bending radii of 1.5–3 m. Then, bending tensile tests were conducted to evaluate the effects of the above factors on the ultimate tensile strength, and the correctness of the computational model was verified using experiments. Finally, the ultimate performance of CFRP cables was theoretically predicted using the established model. The results showed that the cable bending tensile strength was associated with the radius r, tensile strength f, and elastic modulus E of the reinforced material and the bending radius R, but was not correlated with the interface buffer material or the bending angle of the steering system. Moreover, the flexural tensile residual strength was only affected by R/r and E/f. When E/f involved conventional material parameters, the residual strength increased nonlinearly with increased R/r. When R/r ≥ 600, the residual strength reached more than 80%. Therefore, R/r at 600 could be used as the design basis for a safe critical radius.

Size-dependent tensile failure of epitaxial TiN/Cu/TiN sandwich pillar structures: A combined experimentation – Atomistic simulation study

A combined experimentation - molecular dynamics simulation study was conducted to understand tensile failure of TiN/Cu/TiN interfacial regions. Tensile loading was conducted on micro-pillar specimens fabricated from TiN/Cu/TiN thin film sandwich structures. The Cu layer and the TiN layer underneath were grown epitaxially on MgO(001) substrates, with Cu[110]//TiN[001] in the growth direction and Cu<111>//TiN<100> and Cu<112>//TiN<100> within the growth plane. The Cu layer contains numerous nanotwins with the {111} twin plane parallel to the growth direction, with 2–10 nm wide twin bands rotated in-plane by 90° in different yet symmetry-equivalent epitaxial domains. Tensile loading in-situ a scanning electron microscope measured tensile fracture stress ∼1.5 GPa and revealed a surprising failure mode transition. At a larger Cu layer thickness, ductile tensile fracture occurred within the Cu layer. At smaller Cu layer thicknesses, apparently brittle fracture occurred close to or at the Cu/TiN interface. The accompanying molecular dynamics simulations illustrate a significant dependence of the failure mode on the aspect ratio of Cu pillars under tensile loading. With pillars of small height-to-diameter ratios, tensile loading leads to a significant hydrostatic tension within, as well as significant plasticity throughout the Cu pillar, in particular near the top and bottom Cu/TiN interfaces. The high degree of dislocation activities close to or at the interface, combined with dislocation pile-up, serves to create nanovoids. The high hydrostatic tension furnishes a driving force for growth of such nanovoids, leading to rapid tensile fracture. The simulation results offer an analogy to experimental observations and mechanistic understanding of tensile failure mechanisms for ceramic/metal/ceramic interfacial regions.

A novel micromechanical model to study the influence of cure process on the in-plane tensile properties of z-pinned laminates

This paper proposes a novel micromechanical model to study the curing effects on the in-plane tensile properties and failure mechanisms of carbon/epoxy laminates reinforced with z-pins. The microstructures including fiber distortion and resin-rich pockets caused by z-pins are characterized. The results indicate that cure-induced residual stresses greatly exist with increasing z-pin density. Thermal expansion and volume shrinkage mismatch between z-pins and resin-rich regions attribute to the high stress concentration. The existence of interfacial stress concentration and resin-rich channels produce a loss of tensile strength and lead to an initial pathway for crack growth under tension. The failure mode changing from the interfacial cracking to softening and damages of both interface and resin-rich regions is also revealed with increasing z-pin density.

Effect of elevated test temperature on the tensile strength and failure mechanism of hot-pressed dissimilar joints of laser ablation-treated AA5754-H111 and thermoplastic composite

Abstract Evaluation of directly bonded single-lap joint (SLJ) obtained using Al5754 alloy and 20 wt% long glass fiber-reinforced polypropylene (PP) is performed via the lap-shear testing at various temperatures. A fiber laser is used to form a multi-groove microstructure on the aluminum (Al) surface. The bonding regions are investigated microscopically before and after the mechanical testing. Dissimilar joint is manufactured under a 100 kN force at 200 °C for 60 min through hot-pressing technique without using any adhesives. Afterward, lap-shear strength of the joints is determined under elevated working temperatures (25, 75 and 125 °C). Damaged surfaces are also scrutinized for studying the failure mechanism of the joints. According to the experimental results, mechanical anchoring between the Al alloy substrate and thermoplastic composite (TPC) is formed at the interface through the applied laser treatment. Strength exhibits a significant decrease with the test temperature increasing from 25 to 125 °C. Fiber/matrix debonding is the dominant failure mode in the composite adherend. The SEM observations also highlight the pulled-out fibers in the PP composite at the elevated temperatures.

Anisotropic tensile mechanics of vertically aligned carbon nanotube reinforced silicon carbide ceramic nanocomposites

Vertically aligned carbon nanotubes (VACNTs)/silicon carbide (SiC) nanocomposites (VSNs) present remarkably anisotropic mechanical properties originated from their intrinsic heterogeneous microstructures. However, the studies related to tensile mechanical behaviors and failure mechanisms of VSNs are still suspended so far. In this work, the tensile mechanical properties of VSNs were investigated by an in-situ transmission electron microscopy (TEM) tensile test combined with classic molecular dynamics (MD) simulation. The testing results show that the fracture strength and Young's modulus of VSNs along CNT-axis (∥ direction) are higher than those perpendicular to CNT-axis (⊥ direction). In addition, the fracture surface along ∥ direction is uneven whereas it is flat along ⊥ direction. The MD simulation reveals that the stronger behavior along ∥ direction is mainly benefited by the excellent tensile mechanical properties of CNTs, however, the relatively weak van der Waals interaction between CNTs and SiC matrix dominates the tensile performances of VSNs along ⊥ direction. Finally, the remarkable mechanical anisotropy of VSNs is explained by pulling-out and peeling-off failures of CNTs based on MD simulation. This work provides experimental and theoretical insights into the dominant mechanisms of mechanical anisotropy in typical VACNT/ceramic nanocomposites.

Combined tensile and bending fatigue behavior and failure mechanism of a blade-like specimen at elevated temperature

Combined tensile and bending fatigue (CTBF) behavior and failure mechanism of a blade-like specimen, made of a Ni-based alloy DZ125, are experimentally investigated. In order to reveal the geometrical feature and the stress state of the fillet between turbine blade bottom and platform, a blade-like specimen was designed. A novel high temperature experimental methodology was developed to apply the cyclic tensions and high frequency transverse vibration, to the blade-like specimen. CTBF, dwell fatigue (DF) and high stress ratio bending fatigue (BF) tests were performed at 850 °C. Experiment results show that the introduction of high frequency vibration significantly reduced the cyclic life in comparison with DF, while the cyclic tension related dynamic strain aging (DSA) has a positive effect on high cycle fatigue (HCF) life. LCF-related and HCF-related multi-cracks are initiated at the surface due to the effect of bending stress gradient. During CTBF at elevated temperature, LCF, HCF, creep, oxidation, and their interactions contribute to the crack initiation, and linked creep voids, oxidation, and carbide precipitates accelerate the crack growth.

Tensile behavior of the titanium-steel explosive welded interface under quasi-static and high-strain rate loading

Explosive welding is well known for its capability to join a wide variety of both similar and dissimilar metals. The strengths of the welded composite plates are largely influenced by the bonding strengths of the welding interfaces, which generally exhibit a periodic wavy shape. The measurement of the tensile properties of the bonding interface is challenging due to the difficulties in preparing conventional direct tensile specimens arising from the millimeter-sized thickness of the flyer plate. In this paper, a novel small-sized (15 mm × 14 mm × 8 mm) double-T-shaped specimen was designed to study the tensile properties and failure mechanisms of the titanium/steel bonding interface, in which a clamping apparatus was used to apply compressional load on the specimen to generate tensile stress. The quasi-static (∼0.001/s) tension was conducted using the Instron MTS and the high strain rate (2000–5000/s) tension was performed using the split Hopkinson pressure Bar apparatus. Further, the microstructure of interfacial zone was characterized by optical microscopy, scanning electron microscopy and energy dispersive spectrometer. The experimental results indicated that the interface strength increased with increasing strain rate, showing an obvious positive strain rate effect. The fluctuation in tensile strengths and failure strain of the titanium/steel bonding interface were due to the presence of non-uniform defects, (e g. cavities, cracks and brittle intermetallic etc.) formed on the bonding interface. Those defects as discontinuities and stress concentration points would result in degraded mechanical properties. The fracture morphology mainly reveals brittle fracture under quasi-static, while ductile fracture existed in some zone at high strain rate. Failure mainly occurred in the bonding interface near the steel side from the interface, which showed microcracks, cleavage plane, tearing ridges, dimples, fragmentation of brittle intermetallic compounds. Meanwhile, the double-T-shaped specimen has proven to be effective to measure the tensile mechanical properties of the interface of materials with small thickness.

Effects of concrete/gypsum bedding layers and their inclination angles on the tensile failure mechanism: Experimental and numerical studies

This paper investigates the influence of concrete/gypsum bedding layers and their orientation angles on the tensile failure mechanism in the three-point bending test based on experiments and numerical simulations. Rectangular samples containing different combinations of concrete and gypsum layers were prepared, i.e. one layer of gypsum and one layer of concrete, one layer of gypsum and two layers of concrete, and two layers of gypsum and two layers of concrete. In each configuration, bedding layer angles varied between 0° and 90° with increment of 30°. A total of 36 specimens including 12 configurations were prepared and tested. In addition, numerical simulations were conducted on the concrete/gypsum bedding layers at different angles of 0°, 15°, 30°, 45°, 60°, 75°, and 90°. Results show that the bedding layer orientation and bedding layer thickness affect the observed tensile failure process including the failure pattern and tensile strength. A pure tensile failure occurred when the bedding layer angle was 0°, while a sliding failure evolved by increasing the joint angle. When the bedding layer angle was 90°, the failure in boundary of layer was observed. Specimens with one layer of concrete and one layer of gypsum at 0° inclination angle had the highest tensile strength. However, increasing the number of layers and inclination angles decreased the tensile strength of specimens as the number of weak layers in the direction of loading increased.

Influence of thermoplastic interleaves and its healing effect on the failure mechanisms of open-hole notched composite laminates

This paper has explored the effect of thermoplastic interleaves on the mechanical performance of open-hole notched Carbon Fibre Reinforced Polymer (CFRP) composites. A fully verified FE model was produced to replicate the experimental results, as well as to study the sensitivity of the interlaminar properties on the open hole tensile failure mechanism sequence. Both experimental and numerical analysis results show that, the failure mechanisms and sequences are closely linked to the interfacial toughness, strength, and stiffness. With the addition of thermoplastic interleaves, the higher interfacial fracture toughness allows for a stable and gradual delamination growth. This effect lowered the interfacial strength, thereby releasing stress concentrations at the open-hole site. These features result in the higher overall load carrying capacity. A healing treatment on the thermoplastic interleaves post drill operation was conducted and assessed their effectiveness to fix the drill-induced damage through detailed microscopy inspections, to understand the condition of specimens’ interfaces before and after the healing treatment. In comparison to non-healing treated interleaved sample, the healing treatment increased the tensile strength of the sample with the failure sequence changed.

Strength of asymmetric tapered composite foam core sandwich structures subjected to thermomechanical loading

An experimental test program and companion analytical study were designed and conducted to gain understanding of the tensile failure mechanisms in asymmetrical tapered sandwich core structures at cold temperatures. Representative test coupons were subjected to a tensile load in an environmental chamber to induce foam tensile failure in the core. Finite-element modeling with a proposed maximum principal stress criterion was used to predict the failure loads of the tapered test coupon design at the test temperatures. The predicted failure loads were in good agreement with test results. An important finding is that the cure stresses in the foam are significant and should not be ignored. Additionally, the analysis correctly predicted the failure initiation location, which was verified using high speed photography during the tensile test. The study identified the critical failure regions of asymmetrical tapered sandwich core designs and the failure load dependence on the temperature gradient in the structure.

Mechanical properties of composite T-joints subjected to laser ablation

The tensile properties of composite T-joints after being subjected to laser ablation were investigated in this work. The ablation test results show that the area of ablation pits and heat affected zones decrease, while the ablation depth and mass loss rate increase as the spot diameter declines. There are massive coarse and fine cracks around the ablation zone, which have a significant impact on the tensile strength and failure mode of T-joints. The tensile test results indicate that the failure load decreases dramatically after laser ablation with decreasing spot diameter. The failure mode of the T-joints after laser ablation under tensile loading shows delamination at the interface of the triangular zone/skin. Finally, the progressive damage model (PDM) was established based on the cohesive zone model to reveal the tensile failure mechanism of T-joints with and without laser ablation. It was shown that laser damage primarily affects the interlaminar tensile and shear strength of the heat affected zone, leading to interlaminar failure in this region and thereby causing a decrease in the stiffness of the skin. The predicted results obtained by the PDM correspond well with those of the experiments.

Fractographic Analysis of Tensile Failures of Zirconia Epoxy Nanocomposites

This work characterizes the fractographic features of the neat epoxy and ZrO2 epoxy nanocomposites. All samples were subjected to a tensile test to determine the tensile strength and tensile modulus. SEM images were used to study the morphology of the fractured surface. The fractographic of the fracture surfaces were studied by microstructure analysis program (j-images) to specify the effect of ZrO2 nanoparticles on tensile performance and failure mechanism for ZrO2 epoxy nanocomposites. The tensile test results show that the addition of ZrO2 nanoparticles (2, 4, 6, 8, and 10 vol.%) to the epoxy matrix leads to increase the tensile strength about 40% for optimal content of ZrO2 nanoparticles at 4 vol.%, tensile modules of ZrO2 epoxy nanocomposites increased about 200% for optimal content of ZrO2 nanoparticles at 4 vol.%. SEM images show that the patterns of fractured surfaces of ZrO2 epoxy nanocomposites are different from the pattern of the neat epoxy. The fracture roughness of ZrO2 epoxy nanocomposites increased with the increases of the percentages of ZrO2 nanoparticles, where the increment of fracture roughness about 30% for optimal content of ZrO2 nanoparticles at 4 vol.% can be indicator for the improvement of mechanical properties (tensile strength and modules).

An experimental study on the dynamic flexural tensile behavior of glass

Understanding of the dynamic tensile behavior of glasses is of great importance in designing impact-resistant transparent structures. The current study revealed the effects of loading rate, specimen size and stress wave on the dynamic tensile behavior of brittle glass. The quasi-static, unidirectional (UD) and uniaxial bidirectional (BD) dynamic tests were systematically performed. The electromagnetic split Hopkinson pressure bar (ESHPB), which is able to launch simultaneously two stress pulses from two opposite directions, was introduced for dynamic flexural test. A high-speed photography system was used to capture the failure process of the specimen. The test results demonstrated that the loading rate and specimen size affected the measured flexural strength significantly. The captured images revealed that the dynamic tensile stress within the specimen reached its maximum at the same time as the crack starts. The flexural strength measured from dynamic UD and BD tests were essentially equivalent, which is different from the dynamic compressive strength of brittle materials. Fractographic analysis was also carried out using a scanning electron microscope (SEM) and the flexural tensile failure mechanism was discussed.