Changes In Stress Values Research Articles

Effect of Scratching and Bending Degree on the Residual Stress of the 7055 Aluminum Alloy Plate

This study investigated the effects of scratches and bending on the surface stress of aluminum alloy plates with varying thicknesses. The purpose of this study was to provide guidance for surface stress testing of plates with different thicknesses. The “birth and death” element method was used to simulate the generation of surface scratches, while the stress field under the pre-stretched state was obtained through the displacement of one end of the board by 2.5%. The X-ray residual stress analyzer (μ-x360 s) was used to experimentally characterize the stress level on the surface of the plate. The research results showed that the residual stress level near the scratches decreases significantly, while the surface stress level of the plate decreases significantly after bending. The changes in stress values with increasing bending degree for plates of different thicknesses showed that the thicker the plate, the greater the tensile effect on the surface of the plate, resulting in smaller compressive stress. The longitudinal non-uniformity of the plates with different thicknesses was also analyzed, and it was found that the testing error of stress testing results was within ±5 MPa. In conclusion, this study provides useful guidance for the accurate measurement of surface stress on aluminum alloy plates of varying thicknesses, considering the effects of scratches, and bending.

Finite element analysis of the cervical spine and soft tissue of the neck at different flexion angles

Aim: This study aims to investigate the impact of von Mises stress distribution on the cervical spine and soft tissue of the neck at different flexion angles of 0°, 15°, 30°, 45°, and 60°. Materials and Methods: Finite element analysis of the neck's cervical spine and soft tissue was performed separately in Ansys Discovery Live software, a possible approach for simulating the mechanical behavior of the neck. Three-dimensional (3D) models were created in 3D Max software and static structural analyses of soft tissues were performed in ANSYS by using the Finite Element Method. The maximum stress distributions of the cervical spine in cervical vertebra bodies at different flexion angles were analyzed at the lowest and highest stress values of 0° and 30°, respectively. For the intervertebral contact surfaces, the lowest and highest stress values were determined at 0° and 45°, respectively. Results: The value of stress showed a linear increase with increasing flexion angles in the soft tissue of the neck. The observation that the stress values obtained at different flexion angles were arbitrarily in either positive or negative directions when compared to the upright posture suggests that the effect of neck flexion on stress distribution in the cervical spine is complex and multifactorial. The change in stress values in the soft tissue of the neck was always positive and linear with increasing flexion angles. Conclusion: People who work with technological devices are prone to a musculoskeletal disorder associated with forward flexion of the neck, and individuals are encouraged to adopt a neck flexion angle between 0° and 15°. This finding could help guide the development of strategies to reduce the risk of neck injury or damage in different postures.

Effect of the strength of steel sheets and wires on residual stress of thin steel sheet lap-fillet GMA weld joint

Weld residual stress of the lap fillet GMA welding joints which was performed using two strength grades of steel sheets and two strength grades of welding wires were measured. In addition, to consider the effects of steel sheet strength and weld metal strength on welding residual stress, thermal elastoplastic analysis using FEM was carried out for the experiments. As a result of the analysis using the temperature history of the heat-affected zone as a fitting parameter, the residual stress distributions near the toe were in agreement with the measurement in the FE analysis. Comparing the residual stress distributions in the direction perpendicular to the weld line on the weld metal surface near the toe, which is the occurring point of fatigue cracks in the FE analysis results, with the same steel sheet, the higher the weld metal strength the smaller the tensile residual stress. And comparing with the same wire, the higher the steel sheet strength the higher the tensile residual stress. The reason for the former is that when using high-strength wire, cooling transformation occurs at a lower temperature than using low-strength wire. As a result, it is considered that the tensile residual stress was effectively reduced by causing transformation expansion while the surrounding strength was high. The reason for the latter is considered to be that each stress value changes based on the yield stress of the steel sheet and weld metal because the plastic strain continues to occur in each direction until transformation occurs after welding. It was considered that the larger the ratio of the hardness of the weld metal to the base metal, the smaller the ratio of the residual stress of the weld metal near the toe to the yield stress.

Seismic inversion constrained by stress value changes

ABSTRACT Seismic inversion is an effective way to get stress distribution of rock in coal mine, but its usage is still limited by multi-solution problem in practice. As seismometers can only be deployed in limited areas in underground coal mine, it is impossible to solve multi-solution problem by adding more seismometers, thus, we propose a new seismic inversion method which introduces stress value changes as constraint to solve this problem. Numerical experiments show that the new method can reduce the mean distance between inversion results and true wave velocity distributions by about 11.5%, reduce the variance of the distances by about 91%, reduce the mean distance between inversion results and frequency-domain-truncated true wave velocity distributions by about 30.6% and reduce the variance of the distances by about 84.1%. These results indicate that the new method proposed in this paper can reduce the non-uniqueness of solutions in seismic inversion and improve the reliability and stability of seismic inversion.

Studies on the stress and thermal properties of Mo/B4C and MoxC1-x/B4C multilayers

A comparative study of Mo/B4C and MoxC1-x/B4C multilayers deposited by DC magnetron sputtering technology was presented in this paper. Using a homemade real-time stress measure instrument, the stress of two kinds of multilayers was investigated. Characterizations of the multilayers before and after annealing were performed by grazing incident and at-wavelength near-normal incident x-ray reflectivity. Experimental results show that after replacing Mo by MoxC1-x, MoxC1-x/B4C multilayers obtain relatively smaller compressive stress compared with Mo/B4C multilayers. The corresponding stress value changes from −0.99 GPa to −0.36 Gpa. MoxC1-x/B4C multilayers have also proven to have better thermal stability up to 600 °C. After repeatedly annealing from 100 °C to 600 °C, Mo/B4C multilayers had a ∼2% decrease in near-normal incident reflectivity, while MoxC1-x/B4C multilayers had a smaller 1.4% loss of reflectivity and a higher stability temperature.

Study on Flow Field and Rotor Safety Characteristics of MSPs Based on Flow Thermo-Coupling

In order to obtain the structural intensity under the operation conditions of MSP (molten salt pump), the rotor component of MSP is taken as the research object. In this paper, the influence of material properties change on the structural performance of MSP at different temperatures is analyzed. The stress distribution and strain distribution of MSP rotor components under different loads are investigated, and the intensity calculation of MSP rotor system is carried out to explore whether it meets the intensity requirements under high temperature operation, which lays a foundation for the high temperature test of MSP. The results show that the maximum deformation position of the blade working face appears at the outer edge of the impeller. When the fluid-structure coupling is applied, the blade strain law and the strain law during thermo-coupling are similar. The effect of the temperature field on the degree of blade deformation is not significant, provided that other factors remain the same. The position where the impeller equivalent stress is the largest is mainly concentrated in the area where the blade is in contact with the front and rear cover plates at the outlet of the impeller. Different degrees of stress concentration occur in the area where the blade is in contact with the impeller hub. The distribution law of the equivalent stress on the surface of the impeller cover plate is that the equivalent stress value changes periodically along the circumferential direction of the impeller, and the number of change cycles is equal to the number of impeller blades. This study can provide a reference for the structural design of MSPs.

Investigation on effect of geometric, material and load parameters on strength of composites with cutouts

Composite applications require presence of multiple holes for mechanical fasteners or cutouts in laminates. Unlike isotropic materials, composite materials experience change in stress values due to different parameters such as geometric, material and loading parameters. The present study is devoted to primarily determine whether geometric or material parameters have dominant influence on strength of composite laminates. Computational study using ABAQUS CAE software is employed for the analyses. Results reveal that geometric parameters have much significant influence on stress concentration factor and thereby the strength of composite laminates, when compared to material parameters. An elliptical cutout is seen to have comparatively more adverse effect on strength of laminate, when compared with other cutout shapes. Further, effect of load parameters - in-plane tension, compression and shear, is also studied. However, no significant effect was evidenced in stress concentration factor due to load parameters.

Investigation on effect of geometric, material and load parameters on strength of composites with cutouts

Composite applications require presence of multiple holes for mechanical fasteners or cutouts in laminates. Unlike isotropic materials, composite materials experience change in stress values due to different parameters such as geometric, material and loading parameters. The present study is devoted to primarily determine whether geometric or material parameters have dominant influence on strength of composite laminates. Computational study using ABAQUS CAE software is employed for the analyses. Results reveal that geometric parameters have much significant influence on stress concentration factor and thereby the strength of composite laminates, when compared to material parameters. An elliptical cutout is seen to have comparatively more adverse effect on strength of laminate, when compared with other cutout shapes. Further, effect of load parameters - in-plane tension, compression and shear, is also studied. However, no significant effect was evidenced in stress concentration factor due to load parameters.

Multiscale Mechanical Evaluation of Human Supraspinatus Tendon Under Shear Loading After Glycosaminoglycan Reduction.

Proteoglycans (PGs) are broadly distributed within many soft tissues and, among other roles, often contribute to mechanical properties. Although PGs, consisting of a core protein and glycosaminoglycan (GAG) sidechains, were once hypothesized to regulate stress/strain transfer between collagen fibrils and help support load in tendon, several studies have reported no changes to tensile mechanics after GAG depletion. Since GAGs are known to help sustain nontensile loading in other tissues, we hypothesized that GAGs might help support shear loading in human supraspinatus tendon (SST), a commonly injured tendon which functions in a complex multiaxial loading environment. Therefore, the objective of this study was to determine whether GAGs contribute to the response of SST to shear, specifically in terms of multiscale mechanical properties and mechanisms of microscale matrix deformation. Results showed that chondroitinase ABC (ChABC) treatment digested GAGs in SST while not disrupting collagen fibers. Peak and equilibrium shear stresses decreased only slightly after ChABC treatment and were not significantly different from pretreatment values. Reduced stress ratios were computed and shown to be slightly greater after ChABC treatment compared to phosphate-buffered saline (PBS) incubation without enzyme, suggesting that these relatively small changes in stress values were not due strictly to tissue swelling. Microscale deformations were also not different after ChABC treatment. This study demonstrates that GAGs possibly play a minor role in contributing to the mechanical behavior of SST in shear, but are not a key tissue constituent to regulate shear mechanics.

Stability Analysis of the AC Filter Capacitor Structure

In the UHV DC transmission engineering, mechanical strength and reliability of the capacitor structure is the premise to resist natural disasters such as earthquake or fierce wind. However, there are some unreasonable design problems or phenomena in which the structural strength and stiffness can not meet the structural stability requirements. In this paper, by using Solid Works software, the solid models of the capacitor structure with tilting layer and without tilting one are presented respectively at first. And then, the dynamic simulations of the structure are carried out by means of finite element method, that’s the numerical simulation software WORKBENCH module in ANSYS and meanwhile the stress value changes of some models are compared and discussed. At last, the results show that the stability of the structure with sloping layers is no better than the one without sloping layers. This paper provides some references for designing the capacitor structure with good stability and low production cost.

Finite Element Analysis of the Influence of Implant Inclination on Stress Distribution in Mandibular Overdentures

The purpose of this finite element study was to evaluate the influence of implant inclination on the stress pattern in the bone surrounding the implants that support mandibular overdentures. The models used in this study were 3-implant-supported mandibular overdentures with a bar-and-clip attachment system. Each model was modified according to the distal implant inclination (0 and 20°). A unilateral vertical load was applied unilaterally to the first molar and first premolar of the overdenture, and the stress distribution in the bone was analyzed. Implant inclination decreased the stress distribution pattern in bone surrounding the implants when the load was applied on the molar site, but when applied at the premolar site, similar stress value changes were not found. Within the limitation of this study, it seems that the inclination of splinted implants in mandibular overdentures does not have any adverse effect on stress distribution pattern values around the implant.

Behavioural Modelling of Corundum under the Effect of Porosity Rate

Corundum, which is a form of Alumina, is used to manufacture various components and mechanical, electrical and electronics parts. Known for its relatively high hardness, its other characteristics depend on the porosity rate that varies depending on the manufacturing process. One of the characteristics to consider is the tensile stress value changes in a standard test to failure as a function of applied force and porosity rate. In this study, for a better understanding of the effect of the two parameters, we used the statistical method of design of experiments that makes it possible to establish a mathematical model of the response, by which explains the effect of the two parameters in isolation from each other, then their effect simultaneously. Consequently, we can explain the mechanical behaviour of the porous corundum, with curves and graphs, and optimize the final result.

In-situ stress measurements and stress distribution characteristics in underground coal mines in China

The theory, equipment and method of hydraulic fracturing stress measurement used in underground coal mine roadways in China are presented. A quality assurance system and a quality ranking scheme were developed for hydraulic fracturing stress measurements under specific conditions encountered in Chinese underground coal mines. During the last 8 years, a total of 204 hydraulic fracturing stress measurement campaigns have been carried out in 49 coal mines within 13 Chinese coal districts. The test sites which are located in sub-horizontal, inclined and steeply dipping coal measures range in depth from 69.2 m to 1 283 m. Each stress data record was assigned a quality between A and E according to a proposed data quality ranking scheme. A total of 97 stress data records of A and B quality were used to investigate the distribution characteristics of in-situ stresses within the coal districts. Generally, in-situ stresses increase with depth. In shallow coal mines, the rate of increase in horizontal stresses with depth is greater than the rate of increase of vertical stress. With increasing depth the rate of increase in horizontal stresses decreases. A considerable scatter in the in-situ stress test data may be due to distinct differences in both the strength and deformation moduli of strata located in varying geological environments and different coal districts. In addition, large folds and faults often result in a change in orientation of the maximum horizontal stress, and in distinct changes in stress values. Three types of stress field distribution have been noted with σ H > σ h > σ v found mainly in relatively shallow coal mines (< 400 m), the σ H > σ v > σ h type in moderately deep coal mines (400–600 m), and the σ v > σ H > σ h type predominantly in moderately deep to deep coal mines. The ratio of the maximum horizontal principal stresses to vertical stress is usually between 0.5 and 2.0 in the coal districts.

Residual stress characterization of polycrystalline 3C-SiC films on Si(100) deposited from methylsilane

Polycrystalline 3C-SiC thin films are deposited on 100 mm Si(100) wafers via low pressure chemical vapor deposition from the precursor methylsilane in the temperature range of 700–850 °C. Residual stress, strain, and strain gradient are characterized as functions of deposition pressure, temperature, and dichlorosilane as an additional silicon source. By optimizing the deposition parameters, the residual stress is found to decrease from 1377±10 to 196±19 MPa. The low stress film exhibits a strain of 3.4×10−4, corresponding to Young’s modulus of 455 GPa, and strain gradient of −8×10−4 μm−1. The analysis suggests that the change in stress values is due to a combination of effects, in particular, thermal mismatch, grain size effect, and chemical composition.

Experimental observation and numerical analysis of cracking phenomena in adjoining Vickers indentations on glass surface

Generation and propagation of radial cracks around two adjoining Vickers indentations on soda-lime glass were dynamically observed by means of a newly developed apparatus. In particular, it was remarked how the separation distance between two indentations influenced the probability of crack nucleation and propagation. The stress distribution in the region surrounding the adjoining indentations was analyzed with a three-dimensional finite element analysis. It is shown that the induced stress is strongly influenced by the preexisting stress made by the neighboring indentation. These stress field interactions results in change of the severity of the stress value especially in the region between the adjoining indentations. The interacted stress value changes with the separation distance. The analytical result is able to explain the experimental observations.

Design and development of a new acetabular cup prosthesis

Historically, the main objective of Total Hip Replacements (THR) was to relieve pain and increase quality of life in the elderly and not normally intended for young active patients. With the current trend of performing THR on younger patients, the requirement is not only the increased longevity of the prosthesis but also increased performance for more strenuous activities. The acetabular cup design has far more impact on long-term survival of the THR than the femoral component. Optimising the acetabular cup produces a complex problem where the individual design factors have massive impact on the system. Changes in stress values, even caused by initial primary fixation during the operation, can result in stresses being transferred unfavourably. For optimisation of the acetabular cup, the properties of the natural hip must be retained by minimising both remodelling and bone resorption. This work has produced a novel acetabular cup prostheses with a ceramic on ceramic bearing surface that should last longer and perform better, thus reducing the necessity for costly and debilitating revisions. In addition, the use of the proposed novel anatomically orientated mechanical testing methods gives fast results and can also allow further insight into fatigue of alumina bearing couples in THR.

Establishment of the three-dimensional finite element model of the first permanent mandibular molar and its stress analysis

To establish more rational three dimensional finite element model (FEM) of the first permanent mandibular molar and to study the internal stress distribution. The FEM was applied to analyze the stress distribution of the first permanent mandibular molar under various loading conditions. Under all five loading conditions, the maximum von-Mises stress and compressive stress in enamel were larger than that in dentin, and the tensile stress in enamel was smaller than that in dentin. When vertical force and buccal-lingual oblique force were loaded, the stresses in the enamel and dentin were minimum; when lingual-buccal oblique force was loaded, the stresses were maximum; the stresses were mainly distributed at cervical region, furcation and apical area of the mesial-lingual root canal wall. The stress value changes and stress distribution in the enamel and dentin were closely related with the direction of the occlusion force.

The effectiveness of a new algorithm on a three-dimensional finite element model construction of bone trabeculae in implant biomechanics.

More validity of finite element analysis (FEA) in implant biomechanics requires element downsizing. However, excess downsizing needs computer memory and calculation time. To evaluate the effectiveness of a new algorithm established for more valid FEA model construction without downsizing, three-dimensional FEA bone trabeculae models with different element sizes (300, 150 and 75 micron) were constructed. Four algorithms of stepwise (1 to 4 ranks) assignment of Young's modulus accorded with bone volume in the individual cubic element was used and then stress distribution against vertical loading was analysed. The model with 300 micron element size, with 4 ranks of Young's moduli accorded with bone volume in each element presented similar stress distribution to the model with the 75 micron element size. These results show that the new algorithm was effective, and the use of the 300 micron element for bone trabeculae representation was proposed, without critical changes in stress values and for possible savings on computer memory and calculation time in the laboratory.

Cretaceous‐Early Eocene Tectonic Stress Field in China1

Abstract The Cretaceous‐early Eocene tectonic stress field in China was reconstructed using the data of 369 large‐and medium‐scale flexural folds and 157 joint sets. It was found that the maximum compressive principal stress axis in eastern China dips 32 ° NE (nearly horizontal), and strikes SW 212 °, whereas that in western China dips 15 ° NE (also nearly horizontal) and trends SW 195 °. The estimation of the dip angles of fold limbs and the palaeotectonic stress values indicates that there was a tendency of gradual weakening of tectonism from southwestern to northeastern China in the Cretaceous‐early Eocene. At the depth of 2‐3 km, the differential stress value changes from 183 MPa in Tibet to 100 MPa in North and East China.The authors consider that the tectonic stress of this period was related to the north‐northeastward movement and push of the Indian‐Australian plate.