Average Tensile Stress Research Articles

Model representation of an axisymmetric steel-aluminum sample for simulation of a separation test

The object of research is a bimetallic composite material with a thin intermediate layer of aluminum. The aim of the work is to determine the features of the stress-strain state at the interlayer boundaries of a steel-aluminum composite material with a thin layer using the computational exper-iment method and to calculate separation resistance using the energy criterion. The stress-strain state along the boundaries of the joint at delamination is determined from the results of modeling the de-formation of axisymmetric samples made of a steel-aluminum bimetallic composite material with a thin intermediate layer of aluminum. A series of computational experiments with varying the critical rate of elastic energy release under separation conditions, including under the combined influence of low temperatures and static loads, is implemented. The energy criterion is used to evaluate the stress level that leads to the separation of the bimetallic compound. The dependence of the separation re-sistance along the ring contour on the critical rate of elastic energy release, which is variable in the range of 0.1 to 0.5 N/mm, is calculated. It is established that, for the studied variants of the compu-tational experiment, a rigid stress state with a predominance of normal tensile stresses is realized at the place of delamination onset.

Temperature oscillations influence in asphalt concrete layers on stress-deformed condition of road pavement

The durability of asphalt pavement depends on the stress-strain state of the pavement structure, which is significantly affected by temperature fluctuations. The calculation and analysis of the stress-strain state of typical pavement structures with asphalt concrete pavement for roads at different temperatures of their operation are performed. It is established that a significant role in predicting the strength and durability of asphalt pavement is played by temperatures that vary in annual and daily conditions. Tensile stresses in the coating occur not only at low temperatures during the spring waterlogging of soils, but also at other temperatures. Thus, with increasing temperature, the modulus of elasticity of asphalt concrete naturally decreases, which leads to a decrease in the value of horizontal normal tensile stresses of asphalt concrete layers during their bending during transport, but at the same time more significantly reduces the tensile strength of asphalt concrete.

Influence of the Cross-Sectional Shape of a Reinforced Bimodular Beam on the Stress-Strain State in a Transverse Impact

The paper considers the stress-strain state of a reinforced concrete beam, as a bimodular material, under the action of an impact. The behavior of bimodular concretes with different moduli of elasticity in tension and compression has not been studied enough. At the same time, taking into account the bimodularity of concrete makes it possible to design a more economical structure, especially for dynamic load. In this article, the impact is considered as an absolutely plastic impact of an absolutely rigid body on an elastic system. The stress state is investigated for beams of rectangular, T-section and I-sections, and is compared with and without the bimodularity of reinforced concrete. The analysis of the dependence of the stress state on the shape, cross-sectional dimensions, and the location of reinforcing bars in the compressed and tensioned zones was carried out for lightweight concrete (Et < Ec) and for heavy concrete (Et > Ec) under the action of shock load with and without regard to the mass of the beam. The numerical study shows that taking into account the mass of the beam upon impact significantly decreases the magnitude of the normal stresses in both the tensioned and compressed zones. Beams of rectangular cross-section have the highest load-bearing capacity when the cross-section height is equal for both light and heavy concrete. An increase in the size of the flange of the I-beam in the stretched zone leads to a sharp decrease in normal tensile stresses and a slight increase in normal compressive stresses. The proposed engineering method makes it possible to numerically study the effect on the stress-strain state of a beam under the action of a concentrated impact of various geometric characteristics of the cross-section, bimodularity of the material, size, number and location of reinforcement.

Effect of semi-solid forming temperature and heat treatment on mechanical properties and microstructure of Mg-Al-Zn Alloy (AZ91D) for automotive light application

Magnesium alloy usage in manufacturing engineering components resulting in weight reduction and as a consequence, reduction in fuel and energy consumption. Magnesium has a relatively low density and roughly 30% lighter than aluminum. However, magnesium is considered to be difficult to deform because of the HCP structure. In this present work, the effect of semi-solid forming temperature and heat treatment on mechanical properties of Mg-Al-Zn were investigated. Mg-Al-Zn ingot was machined into a billet and formed with three different temperatures and underwent T4 heat-treatment process. To determine the mechanical properties and microstructure of the magnesium alloy, tensile and hardness test were performed and the result indicates that the highest average maximum tensile stress was achieved at 209 MPa at 530ºC after forming with T4 heat treatment and highest hardness value was at 21.44 HRB at 560ºC. On the other hand, effect of the forming temperature gives impact to the evolution of the microstructure from large grain size (as-cast) to the smaller grains size (0.00797mm2) forming at 560°C. This relate to the extensive dynamic recrystallization (DRX) occurs during forming and Mg-Al-Zn was sensitive with heat either direct or indirect heating method.

Modeling Shear Behavior of Woven Fabric Thermoplastic Composites for Crash Simulations

Woven fabric thermoplastic composites possess high specific strength and stiffness along with thermoformability. To utilize the full potential of these materials to achieve better crash-safe designs in automotive structural parts, the measurement of non-linear shear behavior and its material modeling for FEM simulations is required. The standard testing method was used to measure the pure shear behavior of woven fabric composites. These results were compared with the shear behavior of material in the presence of normal stresses along the fiber direction. Tensile and compression cyclic testing of ± 45° laminate were carried out to measure the stiffness degradation and hardening of the material in the presence of tensile normal and compression normal stress. A methodology is proposed for taking into account the differences in shear behavior under different loading directions in an FEM simulation. Based on the experimental evidence, improvements in the mathematical description of plasticity and damage in continuum damage mechanics models are proposed. The model was implemented as a user-defined material subroutine (VUMAT) for Abaqus. The experimental results from coupon tests were used to verify the results of a single element simulation. Finally, a three-point bending test was used to validate the predictions of the user material model.

Safety Factor on Rock Slopes with Tensile Cracks Using Numerical and Limit Equilibrium Models

Through the research it describes an analytic methodology, which allows to determine the minimum safety factor depending on the depth of tensile crack and the inclination of surface failure on the most critical condition, considering at the same time, surcharge, seismic effect and water pressure. Therefore, it studies the stability of rock slopes considering that the potential of failure surface it is constituted by two blocks with different inclinations. The superior block is limited by a tensile crack that is represented by a fracture without displacement. On the other hand, on the inferior block, geometry is formed by a potential slide plane of α inclination with the horizontal axis, in which are acting shear stresses. Fracture on superior block is characterized by a normal-tensile stresses field that act over the crack whose presence originates when the rock loses its original cohesion. Finally, comparisons are made through examples with the limit equilibrium method and finite elements method, where it determines the safety factor on dry state, water and seism, being all of them too similar. Besides, the methodology compares the track depth and the distance between the intersection point of tensile crack and the edge of the slope face, results shows that the analytic methodology is very conservative and throws the less values of this distances.

Pengaruh Variasi Bentuk Permukaan Forging Dan Suhu Preheat Terhadap Kekuatan Tarik Friction Welding

Most of the railway facilities use steel as the constituent material. The method of joining (joining methods) of steel materials, especially in the railroad industry, the most widely used is the welding technique (welding) so that knowledge of the welding process is very important for welding enginers and metallurgists as well as for designers, fabricators, users of welding results. The purpose of this study was to determine the tensile strength of the joint resulting from the friction welding method with variations in the shape of the forging surface and preheat temperature. The shape of the forging surface is 8 mm, 10 mm and 12 mm. Variations in preheat temperature of 200 C, 400 C and 600 C. The results showed the highest tensile strength of the friction weld joint with an average tensile stress value of 407, 48 MPa on the forging surface shape of 12 mm and a preheat temperature of 600 C. And the tensile strength of the joint The lowest friction welding with an average tensile stress value of 120 MPa on the forging surface shape of 8 mm and a preheat temperature of 200 C.
 Keyword: friction welding, forgings, preheat temperature

Modeling of Cold Plastic Deformation of the Holes Made in Specimens of Shape-Memory Alloy

The process of cold plastic deformation of a hole in a plate made of shape-memory alloy is simulated by the finite-element method by setting the mechanical characteristics and the temperatures of the onset and termination of direct and reverse phase transformations. By using the ANSYS Workbench software, we determine the distribution of residual stresses in the plate in the vicinity of a functional hole. The highest normal compressive and tensile stresses are formed in the middle part of the plate and at a distance of 2–4 mm from the edge of the hole, respectively.

Effects of heat treatment on microstructure and mechanical properties of TiC/TiB composite bioinert ceramic coatings in-situ synthesized by laser cladding on Ti6Al4V

To improve the wear resistance of titanium alloy, in this work, TiC/TiB composite bioinert ceramic coatings were synthesized in-situ via laser cladding using Ti and B4C mixed powders as precursor materials. And to decrease the impact of the excessive residual tensile stress generated by the uneven temperature distribution on the performance of coatings, the coatings were then subsequently heated for 3 h at different temperatures (400 °C, 600 °C, and 800 °C) and then air cooled. The effects of heat treatment on the microstructure, residual stress, micro-hardness, fracture toughness, and wear resistance of the coatings were investigated. The results showed that phase compositions and microstructure of the heat-treated coatings were virtually identical to that of the untreated coatings; however, the precipitation of acicular TiB enhanced mechanical properties of the heat-treated coatings. In addition, the average residual tensile stress values of the coatings decreased as the heat treatment temperature increased, which improved fracture toughness of the coatings from 3.95 to 4.68 MPa m1/2. Moreover, wear resistance of the coatings was greatly enhanced by heat treatment; as the wear volume of the heat-treated coatings decreased by 50% at 800 °C compared with that of the untreated coatings. Lastly, the coatings showed good biocompatibility after being evaluated in vitro, and therefore had broad application prospects in the field of orthopedic implants.

Research on Residual Stress of a BS700 Butt-Welded Box Section and Its Influence on the Stability of Axial Compression Members.

BS700 high-strength steel is widely used in engineering. Welding residual stress during the manufacturing process has a significant influence on the structural safety and service life of steel structures. In this study, the residual stress of a BS700 butt-welded box section axial compression member was studied by the blind-hole method, its distribution law was summarized, and a residual stress distribution model was established. By establishing a finite element model considering initial geometric imperfection and residual stress, the influence of residual stress on the stability of axial compression members was analyzed. The results illustrated that the residual tensile stress near the weld in the welded box section axial compression members was the largest: the average residual tensile stress reached 76.6% of the measured steel yield strength, the residual tensile stress at the roof and web were almost the same, and the residual tensile stress at the corner was approximately 11.6% of the measured yield strength. The residual stress had a different influence on the stability factor of the axial compression members with different width-thickness ratios, and the influence decreased with the increase in the width-thickness ratio. In addition, when the slenderness ratio of members ranged between 20 and 70, the residual stress had a significant influence on the stability of members, while outside that interval, the influence was relatively small.

Cracking evolution of atmospheric plasma-sprayed YSZ thermal barrier coatings subjected to isothermal heat treatment

It is known that residual stress is the main factor causing the final failure of thermal barrier coatings (TBCs). However, it is still unclear how the stress governs the cracking sequence. In this paper, atmospheric plasma-sprayed (APS) 8 wt% yttria-stabilized zirconia (YSZ) TBCs were subjected to isothermal heat treatment at 1050 °C for different time. The cracking evolution and the underlying mechanical mechanisms for cracking were investigated. Residual stress distribution through the YSZ thickness was evaluated using Raman spectroscopy. It is found that, after thermal exposure, the in-plane residual compression in the top-coat (TC) near the TC/thermally grown oxide (TGO) interface increases as the TGO thickens, inducing tensile stresses normal to the interface in the TC close to the undulation crests. A spherical analytical model is used to evaluate this tensile stress, and the result shows that it rises with the TGO growth. This normal tensile stress is the driving force for cracking of TBCs. Cracking parallel to the TGO/TC interface first initiates in the TC near the interface, and then coalesces with the cracks within the TGO and at the bond-coat (BC)/TGO interface, leading to the final delamination. Because TC has a relatively low fracture toughness, the delamination trajectory is primarily in the TC near the TGO/TC interface and along the pathway that contains inter-splat cracks, pores and weak splat boundaries. The results indicate that the large in-plane compressions play a significant role in the cracking evolution of TBCs because they induce normal tensile stress in the TC or at the TGO/BC interface. A cracking pattern dominated by the stress evolution is established in this work and it will provide an informed basis for improving the durability of APS-TBCs.

Numerical investigation of the interaction between hydraulic fractures and natural fractures in porous media based on an enriched FEM

A fully coupled enriched-FEM (XFEM) model is proposed to investigate the interaction between hydraulic fractures and natural fractures in finite 2D porous media. The weak forms of both equilibrium and continuity equations are discretized in an enriched form in the space and by the Newmark scheme in the time domain. The Newton-Raphson method is adopted to solve these discretized equations. To account for the fluid flow in the porous matrix, 2D fluid leakage from the fractures to the matrix is considered by imposing internal flux boundary conditions on the fracture surfaces. A posteriori analysis is carried out to determine the equivalent leak off coefficient of the 1D Carter’s leak off law. The frictional contact of the fracture surface is modeled by the penalty method in the model. The junction ridge function is adopted to describe the weak discontinuities of the pressure field in the elements containing fracture intersection points. A crack initiation criterion based on the average tensile stress along the natural fracture is used to determine whether a hydraulic fracture can cross a natural fracture. The presented model is first validated against the analytical solutions of the KGD model and then several numerical examples are simulated to investigate the effects of the natural fracture properties, treatment parameters, matrix permeability, anisotropy stress and approaching angle on the interaction between hydraulic fractures and natural fractures. The numerical results suggest the acceptable accuracy and robustness of the presented model on modeling fracture interaction behaviors in the presence of fluid leakage into matrix.

Cooperative work of longitudinal slab ballast-less track prestressed concrete simply supported box girder under concrete creep and a temperature gradient

To study the effects of concrete creep and temperature gradients on the cooperative working performance of a longitudinal slab ballast-less track prestressed concrete simply supported box girder system (girder-rail system), a girder-rail system model was established based on the ANSYS software. Then, the deformation of the girder-rail system caused by concrete creep and temperature gradient was studied in addition to the normal stress redistribution of the sliding layer and the normal stress variation of the interface between the cement asphalt mortar (CA mortar) and track slab. The results showed that the mid-span creep camber of the box girder under the girder-rail system was smaller than that of the single box girder, to which a uniform load (converted from the ballast-less track system) was applied. Concrete creep and temperature gradients led to the camber deformation of the ballast-less track, and then caused a redistribution of interlayer stress. At 1500 days, the creep camber of the box girder caused the appearance of a void in the sliding layer close to the end of the box girder (approximately 2 m). Voids appeared in the sliding layers at the middle and edge of the base plate under positive and negative temperature gradients, respectively. Under the creep camber of the box girder, tensile stress at the interface between the CA mortar and track slab appeared at the end of the box girder. This tensile stress appeared at the interface in the middle and edge of the track slab under positive and negative temperature gradients, respectively. Under the effects of creep camber of the box girder and temperature gradient, the maximum normal tensile stress of the interface was 264.8 kPa at day 1500, which was less than the normal cohesive strength of the interface and indicated that there was no interface separation.

Experimental methodology on the serviceability behaviour of reinforced ultra‐high performance fibre reinforced concrete tensile elements

AbstractDesign codes include serviceability limit state (SLS) provisions for stress, crack, and deflection control in concrete structures, which may limit the structural design. When drawing on reinforced ultra‐high performance fibre‐reinforced concrete (R‐UHPFRC), the process of cracking differs significantly from traditional concretes. Thus, it remains unclear whether the traditional provisions are applicable to R‐UHPFRC or should be reviewed. Uniaxial tensile tie test is an excellent option to analyse and review these criteria. This work proposes a novel test methodology to study the behaviour of R‐UHPFRC under serviceability conditions, which lets the study of the global and local deformation behaviour by using different measurement equipment. Two different types of R‐UHPFRC ties with variant fibre content were tested. The global average tensile stress–strain curve, cracking behaviour, number, and width of cracks were obtained. Promising preliminary results admitted that this methodology can be useful to propose design criteria of R‐UHPFRC under SLS.

Environmental, mechanical, and biochemical benefits of water hyacinth (Eichhornia crassipes).

Water hyacinth (WH) has high tolerance in extreme environmental conditions. Here, we examined the potentials of WH (Eichhornia crassipes (Mart) solms) to remove excess nutrients from sewage wastewater. We used four prototypes of water systems: prototypes A (WH + underlay water) and C (WH + sewage water), whereas prototypes B and D were experimental control for A and C, respectively. For prototype A, the percentage removal efficiencies (%Re) for nitrate and phosphate achieved were 75.12 ± 4.22% and 78.90 ± 8.72%, respectively, with a pH increase from 6.29 to 7.69; whereas for prototype C, the values were 54.7 ± 8.11% and 86.10 ± 7.34%, respectively, with a pH decrease from 8.13 to 7.15. For the 3-week retention time, the biomass weight increased in both prototype A (33.26%; [Formula: see text] rate = 15.46g/week) and prototype C (26.43%; [Formula: see text] rate = 12.54g/week). Further, the respective mechanical strength and nutritional values of the WH's fiber and the organic extracts were examined. The air-dried WH stem showed an average tensile stress of 0.04MPa on a load at maximum stress of 137.1N. By comparison, a strand of WH has a tensile strength of 14MPa, inferior to 15, 61, and 400MPa shown by timber, wood, and steel, respectively. However, by knitting, four strands of WH yielded a much-improved tensile strength of 315MPa. Finally, a gas chromatography-mass spectrometer analysis of the plant's extract showed that it contains 35.51% oleic acid, a nutritional extract of high value. Thence, we established a profound economic significance of WH, a macrophyte with latent immense benefits.

Examination of the Delamination of a Stitched Laminated Composite with Experimental and Numerical Analysis Using Mode I Interlaminar

To examine the crack propagation in quasi-brittle materials, cohesive models have been suggested by the works of researcher. They treat the existence of a process zone at the crack tip, with a suitable constitutive law, linking the tensile normal stress T and the relative displacement among the two crack edges. In this paper, we employed the cohesive model which examines the mode I interlaminar fracture into stitched reinforced composite laminates. The test configuration that we used in this study was a stitched reinforced double cantilever beam samples. A bilinear damage-rate-dependent cohesive traction-separation law is implemented to design the woven composite fracture and discrete nonlinear spring elements to characterize the stitches influence, its advantages and disadvantages. A novel macroscopic law adopted from a 1D micromechanical-stitching model is invented to model the stitches effect along the interface. The numerical simulations of double cantilever beam test with the present model present a significant agreement compared to the experimental results.

Buckling of a clamped strip‐like beam with a linear pre‐stress distribution

AbstractA thin linear elastic strip is clamped at both ends and subjected to a linear stress distribution across its width. We use Kirchhoff beam theory to study this problem. If displacements out of the strips own plane are prohibited, the straight configuration remains stable as long as the compression is not too high. With the three‐dimensional spatial description of the rod theory, we find possible buckling modes even in the case of average tensile stresses in the beam. Comparison with shell and beam finite elements shows excellent agreement with the analytical investigation, also with respect to the supercritical behavior.

Presoaking of Semitendinosus Graft With Vancomycin Does Not Alter Its Biomechanical Properties: A Biomechanical In Vitro–Controlled Study Using Graft From Living Donors

To compare the biomechanical properties of human semitendinosus graft presoaked with or without vancomycin under a load to failure tensile test. Thirty semitendinosus grafts harvested during anterior cruciate ligament reconstruction were included. These were dissected equally into 2 halves and subsequently randomly allocated to a vancomycin group and to a control group. A digital caliper was used to precisely measure each samples thickness, length, and width. For the vancomycin group, samples were presoaked in a solution of 5 mg/mL vancomycin for a duration of 10 minutes and the control group samples were presoaked in a physiological serum equally for 10 minutes. Mechanical testing was performed on a universal testing machine (Instron 5566-A) after a preconditioning of 10 cycles of 1 mm extension and a progression of 10 mm/min to failure for each sample. The stress-strain curve was obtained to determine the elastic modulus (Young's modulus), the ultimate tensile stress, the ultimate tensile elongation (UTE) before failure and the elasticity limit. For the control group, the average Young's modulus value was 4.8 ± 0.8, the average UTS was 25.2 ± 5.2 MPa, the average percentage of UTE was 78 ± 17%, and the average elasticity limit value was 17.3 ± 5.3 MPa. For the vancomycin group, the average Young's modulus value was 4.7 ± 0.9, the average ultimate tensile stress was 24.1 ± 6.1 MPa, the average percentage of UTE was 82 ± 14%, and the average elasticity limit value was 18.5 ± 5.9 MPa. No significant difference was observed between the 2 groups for all investigated parameters. Presoaking of human semitendinosus graft with vancomycin does not alter its biomechanical properties. This study demonstrates that vancomycin presoaking used to prevent post-anterior cruciate ligament reconstruction septic arthritis does not affect immediate biomechanical properties of semitendinosus tendons.

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.

Cross-linked PMS/PLA nanofibers with tunable mechanical properties and degradation rate for biomedical applications

Polymeric nanofibers have attracted research attention in recent years for various biomedical applications, including tissue engineering and regenerative medicine. In this work, a series of novel nanofibers based on PMS/PLA with different polymeric weight ratios of 3:2, 1:1, and 2:3 were successfully fabricated by the electrospinning technique. The resultant nanofibers were then cross-linked using high-temperature vacuum oven and sterilized via various methods. The mechanical properties such as elasticity and stiffness, degradation behavior, and cytocompatibility were studied in order to investigate the potential of PMS/PLA nanofibers for tissue engineering applications. The results revealed that by increasing the cross-linking temperature up to 90 °C, PMS/PLA nanofibers maintained their nanostructured features even though there were slight changes in the morphology and diameters of the fibers. The average ultimate tensile stress (σUTS) and Young modulus (E) of the PMS/PLA nanofibers significantly increased with cross-linking temperatures ranging from 2.51 to 3.88 MPa to 6.08–11.07 MPa and from 47.88 to 57.10 MPa to 101.37–142.31 MPa, respectively. The degradation rate of PMS/PLA nanofibers significantly decreased after the cross-linking process. The results also revealed that cross-linked PMS/PLA nanofibers could be safely sterilized without severe damages to fibrous microstructures. The PMS/PLA nanofibers revealed no significant cellular toxicity in in vitro cell culture models. The outcomes suggest that PMS/PLA nanofibers could be effectively fabricated with a range of mechanical properties and degradation rates for tissue engineering applications.