Tension Shear Tests Research Articles

The effectiveness of rubber short fibers reinforcing on mechanical characterization of clay adobe elements under static loading

According to the evidence of numerous advantages of earthen buildings, there is an increasing interest to study adobe elements for sustainable development. This paper presents experimental investigation alongside numerical simulation of several adobe elements under compression, direct tension, three-point bending and indirect shear tests to have a better understanding of their basic mechanical properties. Two different mix-design of clay adobes including plain and short tire fibers reinforced adobes with unique soil type, water content and compacting level are provided. The tire fibers are the waste production of tire factories which are hazardous to the green environment. Numerical simulations are conducted in ABAQUS software for further analysis. In this direction, the material constitutive model and the damage indices are defined based on the experimental stress-strain relations which are achieved during this study and the model of concrete damage plasticity was considered in the software. Furthermore, the experimental observations for direct tensile and indirect shear tests were documented by means of a Digital Image Correlation (DIC) technique from a 2-D DIC system. The effectiveness of the added short fibers on the mechanical properties of the reinforced adobe were thoroughly discussed.

Comparative Investigation on the Compression–Shear and Tension–Shear Behaviour of Sandstone at Different Shearing Rates

Direct shear tests on rocks under compression–shear stress conditions have been widely conducted, whereas few have been performed under tension–shear stress conditions. However, rocks exhibit tension–shear failures in many scenarios, such as in the excavation disturbed zone in deep underground caverns and high slopes. A series of direct shear tests were performed with cuboid sandstone specimens under different normal tensile stresses (σn = − 3, − 2, and − 1 MPa) and compressive stresses (σn = 1, 3, and 5 MPa) at different shearing rates (v = 0.2, 1, 5, and 10 mm/min). The tension–shear tests were performed using an auxiliary device in combination with a compression–shear testing machine. The results showed that the fracture, shear stress–displacement curve, shear stiffness and shear strength were affected by both σn and v, and the differences in these mechanical behaviour between compression–shear and tension–shear cases were analysed in detail. The shear strength had a nonlinear relationship with both σn and v in the full region of tested normal stress (namely, the normal stress range from tension to low compression). The Hoek–Brown criterion $$(\tau = A(\sigma_{{\text{n}}} - \sigma_{{\text{t}}} )^{B} )$$ considering the shearing rate effect (the relationship between parameter A (B) and shearing rate v is represented by a natural logarithm function) was proposed as the optimal shearing rate-dependent strength criterion for sandstone in the tested normal stress range.

Effect of position and force tool control in friction stir welding of dissimilar aluminum-steel lap joints for automotive applications

Widespread use of aluminum alloys for the fabrication of car body parts is conditional to the use of appropriate welding methods, especially if dissimilar welding must be performed with automotive steel grades. Friction stir welding (FSW) is considered to be a reasonable solution to obtain sound aluminum-steel joints. In this context, this work studies the effects of tool position and force control in dissimilar friction stir welding of AA6061 aluminum alloy on DC05 low carbon steel in lap joint configuration, also assessing proper welding parameter settings. Naked eye and scanning electron microscopy (SEM) have been used to detect macroscopic and microscopic defects in joints, as well as to determine the type of intermixture between aluminum and steel. The joint strength of sound joints has been assessed by shear tension test. Results point out that tool force control allows for obtaining joints with better quality and strength in a wider range of process parameters. A process window has been determined for tool force conditions to have joints with adequate strength for automotive purposes.

A two-dimensional lattice model for simulating the failure and fracture behavior of wood

A two-dimensional lattice model consisting of truss elements was developed in this study to characterize the failure behavior under arbitrary loading and fracture behavior of wood. The characteristic of this model is to use the integral analytical procedure to determine the elastic stiffness and ultimate strengths of bonds based on energy and strength criteria, respectively, instead of using the trial-and-error method adopted by the current scholars in the field of timber. To prove the feasibility of the lattice model, the tension test, compression test, shear test, and off-axis test on Korean pine were carried out, and two types of fracture tests of Pinus pinaster were cited. The properties of the truss elements were determined from the basic mechanical parameters of wood. The simulated results from using the proposed lattice model were compared with the experimental data, and good agreements including deformation and stress–strain curves were observed. The lattice model in this paper can accurately simulate the failure and fracture behavior of heterogeneous wood, and this method can promote the use of lattice models in the wood mesoscopic and microscopic fields.

Experimental and numerical investigation of failure during bending of AA6061 aluminum alloy sheet using the modified Mohr-Coulomb fracture criterion

In this paper, the modified Mohr-Coulomb (MMC) ductile fracture criterion was adopted to analyze the fracture behavior of the AA6061-T6 aluminum alloy sheet during the U-bending process. Appropriate calibration procedures were employed using various tension tests. A finite element (FE) model was built using the commercial FE code Abaqus/Explicit incorporating the calibrated MMC fracture criterion. It was found that the MMC criterion calibrated by the uniaxial, plane strain, notched, and modified in-plane shear tension tests can predict the onset of fracture in the U-bending process with reasonable accuracy. The error of the predicted fracture displacement was about 2% as compared to experiments. Due to the dependency of the fracture prediction accuracy on the stress state, the effects of process parameters on stress triaxiality and normalized Lode angle parameter were investigated. The negligible effect of process parameters on the stress state confirmed that the calibrated fracture criterion (MMC) was able to predict fracture in different forming conditions with equal accuracy. Also, the proportional stress and strain state in the U-bending process indicate that, besides the high fracture prediction accuracy of the MMC’s damage accumulation function, the fracture forming limit diagram (under proportional loading assumption) can serve as a reliable tool for estimating the onset of fracture in the U-bending process. Therefore, a series of studies were also conducted on damage evolution, crack propagation, principal strains, and fracture displacement during the U-bending process under various forming conditions.

Stress Analysis of Friction Stir Spot Welded Magnesium Alloy Sheet under Tensile-Shear Load

The strength, failure location and modes of AZ31B Magnesium sheets with 1.5 mm thickness, joined using friction stir spot welding (FSSW), can be determined using tension-shear tests. However, the joined materials have different tension test and elastic-plastic characteristics. Elastic analysis methods for spot welding have been examined in detail in literature. However, if the material has narrow elastic and large plastic area characteristics, such as AZ31B, elastic-elastic analysis methods are deficient. The development and application of elastic-plastic analysis methods are required for such soft metal materials. In this study, the elastic-elastic and elastic-plastic analytical stress mechanisms were investigated. Strain and force equations were then derived using an analytical approach. These developed equations were based on the FSSW-Tension-Shear-Test and verified using Finite Element Method (FEM)-Analysis and tension-shear tests. In addition, the location of failure was also determined. It is possible to predict failures without performing tension-shear tests using the proposed analytical equations.

Shear behavior of cement stabilized rammed earth assemblages

Adoption of rammed earth technology in building construction has witnessed a surge during the recent times and hence it is essential to understand the mechanical behavior of rammed earth under various loading conditions. In this study, in-plane shear behavior of cement stabilized rammed earth (CSRE) is assessed by conducting two types of tests namely (i) Direct shear test of CSRE causing shearing along two adjacent rammed earth layers similar to triplet shear test of masonry bed joints which is henceforth called as triplet test and (ii) Diagonal tension (shear) test of CSRE panels. Three types of bonding techniques between the rammed layers of CSRE are explored in this study, namely, (i) making conical dents which act as shear connectors between rammed earth layers, (ii) applying a coat of fresh cement slurry along the interfaces of rammed layers and (iii) combination of dents and fresh cement slurry and their influence in enhancing the interface shear strength of CSRE is assessed. The bonding techniques are adopted for both, triplet specimens and diagonal panels. Further, the effect of compressive stress normal to the rammed earth layers on the interface shear behavior of triplet specimens is examined. The different levels of normal pre-compression considered are 0.05 MPa, 0.3 MPa and 0.9 MPa. The triplet and diagonal tension (shear) tests on CSRE assemblages are conducted under both, dry and wet conditions. Shear behavior is assessed in terms of shear strength, shear modulus, strain at peak stress, post-peak behavior and failure patterns. Among the different bonding techniques assessed in this study, CSRE specimens with a coat of fresh cement slurry exhibited higher shear strength in comparison to specimens with other types of bonding techniques or no bonding technique. Further, CSRE triplet specimens exhibited steady increase in interface shear strength with increase in normal pre-compression, both in dry and wet conditions. Also, shear strength of CSRE was found to be lower in wet condition, in comparison to shear strength in dry condition, for all the bonding techniques. A Mohr-Coulomb failure envelope was developed for CSRE under wet and dry conditions based on the results of triplet tests conducted in this study. Overall, the study aims to understand the efficacy of the proposed bonding techniques in enhancing the shear strength of CSRE and the influence of normal pre-compression and moisture content on shear behavior of CSRE.

Development of a constitutive law for numerical simulation of artificial leaflet-structures for transcatheter heart valve prostheses

Abstract While the current generation of devices for minimally invasive treatment of severe symptomatic aortic valve stenosis is based on xenogenic leaflet-material, artificial polymeric leaflet-structures represent a promising approach for future improvement of heart valve performance. For enhanced long-term success of polymeric leafletstructures, limitations regarding calcification and durability have to be addressed. The objective of the presented study was the development of a constitutive law representing the material properties of artificial polymeric leaflet-structures of transcatheter heart valve prostheses in numerical simulation to assess the in silico leaflet-performance. Mechanical characterization of cast films and nonwoven specimens of a polycarbonate based silicone elastomer were conducted by means of uniaxial tension and planar shear testing, respectively. For validation purposes, experimental data were compared with the results of finite-element analysis (FEA) using different hyperelastic models. Strain energy function for third-order ogden hyperelastic model achieved the best fit of the non-linear stress-strain behavior of the isotropic polymeric material with the experimental data. It was chosen for further FEA of valve leaflet-performance under physiological pressurization to analyze the suitability of various manufacturing processes for polymeric leafletstructures. Therefore a specific leaflet-design with a wall thickness of 400 μm was used. As a result of FEA, time dependent leaflet-deformation, leaflet coaptation surface area (CSA) and leaflet opening area (LOA) of cast and nonwoven leaflet-structures were calculated. While LOA was comparable for cast and nonwoven leaflet-structures, obtained leaflet-dynamics in a cardiac cycle under physiological pressurization demonstrated crucial influence of the manufacturing process. For nonwoven leafletstructures, an enhanced CSA could be demonstrated in comparison to cast structures. FEA using a validated hyperelastic constitutive law represents a useful tool for in silico performance evaluation of polymeric leaflet-structures under physiological loading and proves the suitability of the polymeric artificial leaflet-material for percutaneous heart valve prostheses.

Characterization of Static Performance and Failure of Resistance Spot Welds of High-Strength and Press-Hardened Steels

The static performances and failure characteristics of resistance spot welds (RSW) of steel sheets were studied in this work. Both similar and dissimilar joints of press-hardened steel grade 22MnB5 and as-rolled high-strength steel grade 1000 were examined. From metallographic analyses and micro-hardness measurements, it was shown that the microstructures of base metal (BM), heat affected zone (HAZ) and fusion zone of steel joints were noticeably different. In particular, the HAZ close to BM or subcritical HAZ (SCHAZ) of 22MnB5 steel exhibited greatly decreased hardness due to occurring tempered martensite, in which carbide precipitation was clearly observed. Furthermore, tensile shear test and cross-tension test of the welded steel sheets were carried out. The determined maximum loads, energy absorbability and corresponding failure mechanisms were analyzed and compared. The RSW samples of similar steel grade 1000 provided the highest load-carrying capacity and absorbed energy in both tests. Due to the large hardness difference and soft zone in weldment of dissimilar steel specimen, failure loads and static absorbed energies were deteriorated up to 17 and 68%, respectively. The observed fracture occurrences of all investigated joints were pullout failure mode, in which BM and HAZ were the crack initiation sites of grades 1000 steel and 22MnB5 steel, respectively. The SCHAZ of welded boron steel considerably caused the failure onset in tension shear test, but seemed to have negligible effect on cross-tension test.

Seismic Behavior of High-Performance Fiber-Reinforced Cement Composites Beam-Column Connection with High Damage Tolerance

The purpose of this study is to investigate and evaluate the feasibility of using high-performance fiber-reinforced cement composites (HPFRCC) to satisfy the requirement of transverse reinforcement in beam-column joint under seismic loads. The basic mechanical properties of the HPFRCCs are determined by compression, uniaxial tension, and direct shear tests. Four half-scale exterior beam-column connections are cast and tested under cyclic loads. The cracking patterns, hysteresis behavior, ductility, energy dissipation with damping characteristics and joint shear capacity of the HPFRCC beam-column connections are analyzed, investigated, and compared to the cyclic responses of normal concrete connections designed with/without seismic criteria of ACI. The test results revealed that HPFRCC connections considerably enhances shear and flexural capacity and also improved the deformation and damage tolerance behavior in post-cracking stage comparing to normal concrete connections in ultimate stages. Also, the failure mode of HPFRCC specimens changed from shear mode to flexural mode comparing to the connections without seismic details. Severe damages are observed in normal concrete connection designed without considering seismic criteria. Wide diagonal cracking and damage are observed on the designed NC connections under large cyclic displacement at drift 6%. However, in HPFRCC connections, joint remained intact without any cracks and damage until the test end. This implies that the shear stress requirement can be satisfied without any need to the transverse reinforcement in the HPFRCC joint.

Critical strain energy release rate for rubbers: single edge notch tension versus pure shear tests

In order to estimate mode I fracture strain energy release rate of a rubber upon monotonic loadings, the material is submitted to pure shear and single edge notch tension tests. Catastrophic failure happens suddenly for both tests, revealing mirror-like crack surfaces, assessing the fragile fracture. Nonetheless, Griffith failure analysis could be carried out on pure shear tests only. This analysis leads to an energy release rate value that allows challenging approximate expressions existing in the literature for pure shear and single edge notch tension tests. The pure shear approximate expression provides quantities that match the Griffith analysis. Meanwhile, the strain energy release rate values calculated directly from the single edge notch tension tests differ significantly from the values obtained in pure shear. This discrepancy is explored and possible explanations are discussed showing that pure shear tests should be favored.

Experimental and numerical study on the strength and hybrid fracture of sandstone under tension-shear stress

Hybrid tension-shear fracture of rock usually occurs in underground openings, rock slopes, transtension faults, and en echelon cracks. To investigate the tension-shear strength and the transition between tensile and shear fractures in rock, experimental and numerical tension-shear tests were carried out using an auxiliary device and particle flow code (PFC2D), respectively. The deformation and shear strength of a sandstone under tension-stress were analyzed. The initial crack (the first micro-crack) and the shear failure ratio (the proportion of shear cracks in the total number of cracks) were proposed and used to describe the mechanical properties of hybrid fracture. In addition, the force chains of parallel-bonds in the PFC model were investigated. The results show that the initial crack is a tensile crack if the normal tensile stress is large, whereas it is a shear crack when the normal tensile stress is smaller. The shear failure ratio decreases linearly with increasing normal tensile stress, and the micro-cracks are all tensile cracks in the uniaxial tensile simulation, which suggests that the transition from tensile to hybrid and shear fracture is continuous and linear. Most of the bonds between particles are subjected to tension-shear stress, while some bear compression-shear stress. In the tension-shear tests, shear micro-cracks may be formed under either tension-shear stress or compressive-shear stress. A new tension-shear failure criterion was proposed, which is more accurate than the existing failure criteria and is associated with the features of microscopic fractures. The proposed criterion can account for the microscopic physical significance of the parameter in the Hoek–Brown criterion.

The effect of tension compression asymmetry on modelling the bending response of sheet moulding compound composites

Phenomenological models are required to predict the behaviour of a glass fibre reinforced Sheet Moulding Compound (SMC) composite material for use in the automotive industry. Material testing is conducted in tension, compression, in-plane shear, and three-point bending. The SMC composite exhibits tension-compression asymmetry and in-plane anisotropy. A model, which incorporates an anisotropic and asymmetric yield function, is developed. The model is calibrated to the experimental tension, compression and in-plane shear tests and are validated using the three-point flexure test. The model captures the flexure response within 8.1% of the experimental observations. The importance of including tension compression asymmetry within the model is demonstrated.

Durability and degradation mechanisms of GFRP reinforcement subjected to severe environments and sustained stress

Despite the large amount of research that has been carried out to date on the use of glass fibre reinforced polymer (GFRP) bars in concrete, one factor still hindering their widespread use in civil engineering applications is the lack of comprehensive data on their long-term in-service performance. This paper presents the test results of an experimental study investigating the physical and mechanical properties of GFRP bars exposed to severe environments and subjected to different levels of sustained load. The test environments included moist concrete, alkaline solution and tap water, with temperatures varying from 20 °C to 60 °C. The mechanical properties of the bars were characterized through direct tension, flexural and inter-laminar shear tests, while the physical and chemical properties were determined through the implementation of a series of complementary techniques, including moisture absorption measurements, scanning electron microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Energy dispersive X-ray analyses (EDX). The test results showed that the elevated temperatures play a key role in triggering and accelerating the development of critical degradation mechanisms. The reduction in the tensile strength of all conditioned samples subjected to a sustained stress equivalent to 3000 με was always within the limits recommended in existing codes for high durability bars, while a lower average strength retention was observed for higher levels of sustained stress (equivalent to 5000 με). Finally, it can be concluded that the long-term mechanical properties of the tested GFRP bars appeared to be mainly affected by moisture diffusion through the resin rich layer and debonding at the fibre/matrix interfaces due to the dissolution of the silane coupling agents.

Experimental diagonal tension (shear) test of Un-Reinforced Masonry (URM) walls strengthened with textile reinforced mortar (TRM)

The presented study is part of ongoing experimental program on Un-Reinforced Masonry (URM) walls strengthened with Textile reinforced mortars (TRM). Ten walls were tested under diagonal tension (shear) test method in order to consider the effect of strengthening system on the behavior of brick walls. One plain wall was tested as reference. Two walls were overlaid with 15 and 25 mm thick of high strength mortar on one face without any textile sheet. Another seven walls were externally strengthened with 15 and 25 mm thick of AR-Glass Textile Reinforced Mortar (TRM) on one or both faces. Results confirmed the efficient possibility of shear strengthening of existing URM walls using TRM, especially for those strengthened on both faces. On the other hand, one face strengthened walls were sensitive to the applied load and can buckle or experience out-of-plane deformations. TRM extremely improved diagonal load carrying capacity and deformation capacity, which caused the strengthened walls fail in a ductile manner. The governing failure mode was out-of-plane deformation for one face strengthened walls, and failure of both faces strengthened walls was controlled by initiation of substrate toe crushing in compression continued by diagonal crashing. Results showed that for masonry walls strengthened on both faces, during pure in-plane diagonal load, there is no need to mechanical connection between TRM and masonry substrate. However, out-of-plane failure is an important issue for masonry walls, especially for those strengthened on one face. Therefore, connectors must be designed for out-of-plane lateral force to ensure that masonry wall and TRM reinforcement layer work together properly.

Anisotropic Continuum Stored Energy Functional Solved by Lie Group and Differential Geometry

An anisotropic continuum stored energy (CSE), which is essentially composed of invariant component groups (ICGs), is postulated to be balanced with its stress work done, constructing a partial differential equation (PDE). The anisotropic CSE PDE is generally solved by the Lie group and the ICGs through curvatures of elasticity tensor are particularly grouped by differential geometry, representing three general deformations: preferred translational deformations, preferred rotational deformations, and preferred powers of ellipsoidal deformations. The anisotropic CSE constitutive models have been curve-fitted for uniaxial tension tests of rabbit abdominal skins and porcine liver tissues, and biaxial tension and triaxial shear tests of human ventricular myocardial tissues. With the newly defined second invariant component, the anisotropic CSE constitutive models capture the transverse effects in uniaxial tension deformations and the shear coupling effects in triaxial shear deformations.

Quasi-Static and Dynamic Large Strain Shear-Tension Testing

A new shear specimen is designed, evaluated and tested quasi-statically and dynamically. The specimen consists of a long cylinder having a horizontal gauge section created by two diametrically opposed semi-circular slots machined parallel to the longitudinal axis. This geometry imposes a rather uniform stress state, close to pure shear in the gauge section. Quasi-static and dynamic tension-shear tests up to a strain rate of 104 1/s were carried out on 1020 cold-drawn steel specimens. The obtained stress–strain curves and ductility were validated numerically. The new specimen can be used to study the shear mechanical characteristics of a material using tensile testing.

Ultrasonic time-frequency method to evaluate the deterioration properties of rock suffered from freeze-thaw weathering

Cyclic freeze-thaw (F-T) is a serious natural weathering mechanism for rock engineering and stone constrictions in cold regions. Considering the universality and destructiveness of rock F-T weathering, evaluation of rock deterioration is of vital importance. In this work, ultrasonic detections and mechanical experiments including uniaxial compression, splitting tension and angle-changed shear tests were carried out on red-sandstone specimens without and after different F-T cycles. Attenuation occurred to almost all of the indexes of red-sandstone after F-T weathering, including mechanical properties such as uniaxial compressive strength (UCS), deformation modulus (Ed), splitting tensile strength (STS), cohesion (C) and friction angle (ϕ), and ultrasonic properties such as the P-wave velocity (Vp), head-wave amplitude (Ah), centroid frequency (fc) and kurtosis of frequency spectrum (KFS). After 25F-T cycles, the UCS, Ed, STS, C, ϕ, Vp, Ah, fc and KFS decreased by 42.5, 63.0, 87.3, 33.7, 22.6, 50.6, 24.6, 38.3 and 0.56%, respectively. With increasing number of F-T cycles, similar convergent decrease tendencies between the UCS, Ed, STS, C and the Vp, Ah, fc, KFS were found, confirming the effectiveness of the ultrasonic time-frequency method to estimate the deterioration of rock suffered from F-T weathering. Similar degradation behavior in ultrasonic time-frequency properties and in mechanical properties resulted from the microscopic damages of red-sandstone suffered from F-T weathering. An ultrasonic evaluation auxiliary graph is suggested as a convenient practical evaluation method in rock engineering.

Dynamic large strain characterization of tantalum using shear-compression and shear-tension testing

The dynamic large strain behavior of polycrystalline tantalum has been characterized using shear-compression and shear-tension experiments over a wide range of high strain rates (103–1041/s). Tests were carried out using the recentlymodified shear compression specimen (SCS) on a split Hopkinson pressure bar. For shear compression, very large plastic strains of more than 5.0 were reached, in comparison with the previously reported 0.4–0.6 for cylindrical and regular SCS specimens. The large strains, which combine effects of strain rate and temperature, allow separation of these effects using the Johnson-Cook material model without performing tests at different environmental temperatures.The dynamic shear-tension tests reached plastic strainsof 2.5 at fracture, but the material's ability to sustain load in shear–tension, at a triaxiality of 0.67, starts to degrade early from plastic strain levels of 0.15. For larger plastic strains, the slope of the stress-strain curve becomes negative due to damage evolution combined with strain rate and temperature effects.Our results indicate that the material dynamic failure behaviorat high strain rates in shear-tension is markedly different from that in shear-compression, for which the rate of damage accumulation is more moderate, and hence ductility is higher.

Influence of nanoparticles on the interfacial properties of fiber-reinforced-epoxy composites

The effects of nanoparticles on interfacial properties between fiber and epoxy resin were evaluated based on micro- and macro-mechanical experiments, including micro-droplet, transverse fiber bundle tension and short-beam shear tests. All results indicated that the sol-gel-formed silica nanoparticles did improve the interfacial properties effectively. According to scanning electron microscope morphologies of fracture surfaces, these improvements were likely ascribed to the toughening effects of nanoparticles, i.e., nanoparticles offered better energy dissipation and more efficient stress transfer during fracture in the fiber/epoxy composites.