Changes In Stress Distribution Research Articles

Deterioration of the fixation segment's stress distribution and the strength reduction of screw holding position together cause screw loosening in ALSR fixed OLIF patients with poor BMD.

The vertebral body’s Hounsfield unit (HU) value can credibly reflect patients’ bone mineral density (BMD). Given that poor bone-screw integration initially triggers screw loosening and regional differences in BMD and strength in the vertebral body exist, HU in screw holding planes should better predict screw loosening. According to the stress shielding effect, the stress distribution changes in the fixation segment with BMD reduction should be related to screw loosening, but this has not been identified. We retrospectively collected the radiographic and demographic data of 56 patients treated by single-level oblique lumbar interbody fusion (OLIF) with anterior lateral single rod (ALSR) screw fixation. BMD was identified by measuring HU values in vertebral bodies and screw holding planes. Regression analyses identified independent risk factors for cranial and caudal screw loosening separately. Meanwhile, OLIF with ALSR fixation was numerically simulated; the elastic modulus of bony structures was adjusted to simulate different grades of BMD reduction. Stress distribution changes were judged by computing stress distribution in screws, bone-screw interfaces, and cancellous bones in the fixation segment. The results showed that HU reduction in vertebral bodies and screw holding planes were independent risk factors for screw loosening. The predictive performance of screw holding plane HU is better than the mean HU of vertebral bodies. Cranial screws suffer a higher risk of screw loosening, but HU was not significantly different between cranial and caudal sides. The poor BMD led to stress concentrations on both the screw and bone-screw interfaces. Biomechanical deterioration was more severe in the cranial screws than in the caudal screws. Additionally, lower stress can also be observed in fixation segments’ cancellous bone. Therefore, a higher proportion of ALSR load transmission triggers stress concentration on the screw and bone-screw interfaces in patients with poor BMD. This, together with decreased bony strength in the screw holding position, contributes to screw loosening in osteoporotic patients biomechanically. The trajectory optimization of ALSR screws based on preoperative HU measurement and regular anti-osteoporosis therapy may effectively reduce the risk of screw loosening.

Effects of Electroshock Treatment on Residual Stress and the Geometric Dimensions of Components Fabricated with Wire Arc Additive Manufacturing

In wire arc additive manufacturing, residual stress is generated from a nonuniform thermal distribution, resulting in the fabricated component demonstrating large deformation. This study explored the effects of electroshock treatment (EST) on the residual stress and geometric dimensions of additive manufacturing components. A special and innovative stress frame was built with wire arc additive manufacturing, on which the EST was conducted. Changes in the residual stress, geometric dimensions, temperature, microstructure, and dislocation distribution on the stress frame during processing were investigated. According to the experimental results, it was concluded that the dislocation density decreased and that the distribution was more homogeneous after EST, which was affected by electron wind force. Finally, the residual stress was reduced, and the geometric dimensions were improved on the substrate.

A patient-cohort study of numerical analysis on sacroiliac joint stress distribution in pre- and post-operative hip dysplasia

In acetabular dysplasia, the cartilaginous roof on the acetabular side does not fully cover the femoral head, which may lead to abnormal stress distribution in both the femoral head and pelvis. These stress changes may have implications to the adjacent sacroiliac joint (SIJ). The SIJ has a minimal range of motion and is closely coupled to the adjacent spine and pelvis. In consequence, the SIJ may react sensitively to changes in stress distribution at the acetabulum, with hypermobility-induced pain. The purpose of this study was to investigate the stress distribution of the SIJ in acetabular dysplasia, and to gain insight into the cause and mechanisms of hypermobility-induced pain at the SIJ. Finite element models of pre- and postoperative pelves of four patients with acetabular dysplasia were created and analyzed in double leg standing positions. The preoperative models were relatively inflare, the sacral nutation movement, SIJ cartilage equivalent stress, and the load on the surrounding ligaments decreased with increased posterior acetabular coverage. Acetabular morphology was shown to affect the SIJ, and improvement of the posterior acetabular coverage may help normalize load transmission of the pelvis and thus improve the stress environment of the SIJ in acetabular dysplasia.

Infrared Radiation Characterization of Damaged Coal Rupture Based on Stress Distribution and Energy.

As coal mine production enters the deep mining stage, the impact of coal and rock dynamic hazards is becoming more and more significant. And the coal and rock containing initial damage such as fractures are more susceptible to destabilization damage by disturbance. So, this paper takes coal containing macro-crack with different inclination angles as the research object and uses the RMT-150B rock mechanics system to carry out uniaxial loading rupture tests on the specimens. On this basis, the changes in infrared radiation on the surface are observed using an infrared thermal imaging camera, and it is analyzed and studied according to the stress distribution and energy change of the specimens. The results show that the strain ratio at crack closure after bearing the coal gradually increases with the increase in the macro-crack inclination. When the inclination angle is 0° < α < 90°, there are obvious low-temperature bands on the upper and lower sides after macro-crack closure. The variance of the infrared thermal image of the specimen can reflect its infrared radiation information more effectively and has a good correspondence with the stress–strain curve. With the increase in the specimen macro-crack inclination angle, the linear change of VIRT is more obvious, the rate of change gradually increases, and the inclination angle is the maximum at 90°. The accumulated elastic strain energy Ue is the main source of energy for the sudden change in infrared radiation generated during the bursting process that occurs when the specimen is damaged, and Ue is linearly and positively correlated with the change in infrared radiation in front of the specimen peak. These will provide some experimental basis and theoretical guidance for the use of infrared radiation precursor characteristics to warn the damaged coal–rock dynamic disaster.

Phase-Field Model of Hydride Blister Growth Kinetics on Zirconium Surface

The precipitation of zirconium hydride blisters on the surface of zirconium alloy cladding destroys the integrity of the material and leads to material failure, which has serious potential safety hazards. To study the corrosion kinetics of zirconium hydride blisters, we established a phase-field model coupled with anisotropic elastic, which can reflect the microstructure evolution process of zirconium hydride blisters. The model studies the natural growth of hydride blister and the structural evolution process after applying radial stress and discusses the corrosion characteristics, stress distribution, and displacement changes. Zirconium hydride blisters tend to be semi-ellipsoidal in natural growth. Applying radial outward stress will promote the growth of blisters and aggravate the harm of corrosion. The stress state changes with applying stress, which affects the elastic driving force, resulting in the change of blister morphology. This work is helpful to understand the corrosion kinetic mechanism of hydride blisters.

Improving the Stability of a Hemipelvic Prosthesis Based on Bone Mineral Density Screw Channel and Prosthesis Optimization Design.

In pelvic reconstruction surgery, the hemipelvic prosthesis can cause significant changes in stress distribution due to its high stiffness, and its solid structure is not suitable for osseointegration. The purpose of this study was to identify a novel bone mineral density screw channel and design the structure of the prosthesis so as to improve the distribution of stress, promote bone growth, and enhance the biomechanical properties of the prosthesis. The mechanical characteristics of bone mineral density screw and traditional screw were compared by finite element analysis method, and redesigned by topology optimization. The direction of the newly proposed screw channel was the posterolateral entrance of the auricular surface, ending at the contralateral sacral cape. Compared to the original group, the maximum stress of the optimized prosthesis was decreased by 24.39%, the maximum stress of the sacrum in the optimized group was decreased by 27.23%, and the average strain energy density of the sacrum in the optimized group was increased by 8.43%. On the surface of screw and connecting plate, the area with micromotion more than 28 μm is reduced by 12.17%. On the screw surface, the area with micromotion more than 28 μm is reduced by 22.9%. The newly determined screw channel and optimized prosthesis design can effectively improve the biomechanical properties of a prosthesis and the microenvironment of osseointegration. This method can provide a reference for the fixation of prostheses in clinical pelvic reconstruction.

Microscale Changes in Microstructure and Stress Distribution in Duplex Stainless Steel Caused by Plastic Deformation

Microscale Changes in Microstructure and Stress Distribution in Duplex Stainless Steel Caused by Plastic Deformation

Experimental and numerical studies of fatigue behavior of Ti6Al4V alloy treated by laser shock peening

Laser shock peening (LSP) is applied as the laser surface treatment technology to improve the fatigue resistance of aircraft parts with complex geometric features. In this paper, the effects of laser energy inputs on residual stresses and fatigue properties for hole-structured specimens of Ti6Al4V alloy treated by LSP are studied. Changes of residual stress distributions, fatigue behaviors and fracture morphologies are analyzed with different laser-induced shock pressures. The results show the fatigue life is prolonged by 137% compared with the untreated specimens due to the introduction of compressive residual stresses. The sectional observations of fatigue fracture morphology show the inwards movement of fatigue crack initiation positions and the complexity of fracture cracks after LSP treatment. The simulation results confirm that the fatigue life with different laser energy inputs depends strongly on the three-dimensional stress distribution around the hole. Among them, high surface compressive stresses and deep stress affected layers play a decisive role in improving fatigue life. The results in this study broaden the knowledge of fatigue behavior and explore engineering potentials of improved fatigue life for complex industrial specimens.

Numerical Modeling and Investigation of Fault-Induced Water Inrush Hazard under Different Mining Advancing Directions

Evaluations of the risk of fault-induced water inrush hazard is an important issue for mining engineering applications. According to the characteristics of the seam floor during mining advancing, a mechanical model of fault activation is built to obtain the equations of normal stress and shear stress on the surface of fault, as well as the mechanics criterion of fault activation. Furthermore, using FLAC3D numerical software, the stress variation on the surface of fault under two different mining advancing directions are numerically simulated, and the distribution characteristics of the plastic failure zone of the roof and floor near the fault are obtained. The results show that: (1) When mining advances from the hanging wall, the normal stress increases more greatly than that from the foot wall, the shear stress distribution changes drastically with a large peak, and it is more likely to cause fault activation. (2) When mining advances from the hanging wall and approaches the fault, the normal stress and shear stress within the fault first increases, and then decreases suddenly. When mining advances from the foot wall, the normal stress and shear stress increases constantly, and the fault zone stays in the compaction state where the hanging wall and foot wall are squeezed together, which is unfavorable for water inrush hazard. (3) When mining advances from the hanging wall, the deep-seated fault under the floor is damaged first, and the plastic failure zone of the floor increases obviously. When mining advances from the foot wall, the shallow fault under the floor is damaged first, and the plastic failure zone of roof increases obviously. (4) For a water-conducting fault, the waterproof coal pillar size of the mining advancing from the hanging wall should be larger than that from the foot wall. (5) The in-situ monitoring results are in agreement with the simulation results, which proves the effectiveness of the simulation.

Determinants of fracture type in the proximal femur: Biomechanical study of fresh frozen cadavers and finite element models.

Proximal femur fractures are usually categorized as either a cervical or trochanteric fracture, but the relationship between fracture type and fall direction is not clear. By cadaveric mechanical testing and finite element analysis (FEA), the aims of this research were to verify the factors that define the proximal femur fracture type and to clarify the change in stress distribution based on fall direction. From fresh frozen cadavers, we obtained 26 proximal femora including ten pairs of 20 femora. We conducted quasi-static compression tests in two fall patterns (lateral and posterolateral), and identified the fracture type. We then examined the relationship between fracture type and the following explanatory variables: age, sex, neck shaft angle, femoral neck length, bone mineral density (cervical and trochanteric), and fall direction. In addition, for the ten pairs of femurs, the effect of fall direction on fracture type was examined by comparing the left and right sides. In addition, we generated the proximal femur finite element (FE) models from computed tomography data to simulate and verify the change of external force in different fall directions. In mechanical tests, only fall direction was found to have a significant relationship with fracture type (p=0.0227). The posterolateral fall group had a significantly higher incidence of trochanteric fractures than lateral fall group (p=0.0325). According to FEA, the equivalent stress in the lateral fall was found to be more concentrated in the cervical area than in the posterolateral fall. In proximal femur fractures, fall direction was significantly associated with fracture type; in particular, trochanteric fractures were more likely to occur following a posterolateral fall than a lateral fall.

Eddy Current Mapping Technology for Residual Stress and Surface Hardness Evaluation in Laser Hardened Steels

Laser quenching can achieve surface hardening with narrow heat affected zone while without affecting the surface roughness of the material. Therefore, the laser quenching technique is increasingly applied for surface hardening in key components such as precision gear, guide rail, etc. Phase transformation and thermal diffusion occur in the process of laser quenching, resulting in change of microstructures and residual stress distribution in the surface layer material. To evaluate the quality of the laser-hardened material of 45and 30Cr steel, eddy current mapping technology is employed in this study to characterize the residual stress and surface hardness. First, C-scan eddy current inspection was performed to the laser hardened region. The mapping results of the impedance parameters clearly show the boundary between the hardened zone and the matrix. Second, X-ray diffraction system and Vickers hardness tester were alternatively used to analyze the distribution of surface hardness and residual stress. Third, the correlation between the individual eddy current parameter and the surface hardness (or residual stress) is investigated by simple linear regression tool. The impedance amplitude demonstrates good linear dependencies on both the surface hardness and residual stress. Therefore, the proposed eddy current mapping technology is capable of mapping the distribution of surface hardness (related with microstructures) or the residual stress in laser hardened ferromagnetic components.

A hydrodynamic model for analyzing the closure stresses in the wellbore strengthening problem

AbstractThe problem of creating unwanted fractures while drilling ultradeep wells is mitigated with the application of wellbore strengthening techniques. Despite the numerous applications, an open question remains about the efficiency of the loss of circulation materials (LCM) and its implications on the closure stress distribution change during plugging. This work investigates the effects on the stress field before and after plugging along the fracture extension axis by introducing a hydrodynamic plug. With the hydrodynamic plug, fluid flow is constrained by pressure conditions at specific locations in the fracture simulating the LCM. Three different scenarios were considered. First, the efficiency of the bridge is simulated by varying the pressure drop. Second, the location of the bridge inside the fracture and finally a nearly packed fracture. The models are fully coupled and were solved with the finite element method in impermeable and permeable hard rocks. We find that for high‐efficiency bridges, narrower fracture profiles are predicted, which causes the induced closure stresses to increase significantly. On the other hand, when the bridge is close and near the wellbore area, the fracture profiles are maintained wide and narrow when it is nearest to the tip. The predicted fracture geometry induces higher closure stresses when the plug is near the well and slightly reduces when it is near the tip. Finally, the pressure profile resulting from the packed fracture significantly affects the fracture dimensions, resulting in narrower fracture, however resulting in a smooth variation of induced closure stresses with high magnitude comparable to the stresses at the state of propagation. The diffusion occurring in the permeable case creates back‐stresses that appear to have an additive contribution to the induced closure stresses. This underlines the significance of diffusion on the induced coupled closure stresses for large fractures while performing wellbore strengthening methodologies.

Somethings About Biological Prostheses

Finite element models of the female biofidel were developed using a specific combination of segmentation with computed tomography and solid modeling tools capable of representing bone physiology and structural behavior. This biofidel finite element (FEM) model is used to evaluate the change in the physiological distribution of stress in the femoral prosthesis and to evaluate the new design criteria for biopsy. Biomimetics, biomechanics, and tissue engineering are three multidisciplinary fields that have been considered in this research to achieve the goal of improving the reliability of prosthetic implants. The authors took these studies to gather the untapped potential of such advanced materials and design technologies by developing finite models of Biofidel elements capable of correctly mimicking the biomechanical behavior of the femur. The new remodeling of the tetrahedral elements was performed in 3Matic looking for the congruence of the node at the bone-implant interfaces, where the material was defined for the new configuration of the finite elements. The evaluation of the mechanical properties was made taking into account the mechanical characteristics of the cortical and trabecular bone. For biomechanical integration of the implant, a custom material with an improved combination of strength and rigidity that matches the bone should be used. This greater biomechanical compatibility will avoid weakening the implant and increase lifespan, avoiding additional surgery for revision and allowing good biological integration (bone growth). Innovative biomimetic materials for tissue engineering based on hydrophilic polymers were developed by our research group and presented attractive physical, biological, and mechanical properties for biomedical applications. For use with metal prostheses, the authors have developed a hybrid biocompatible material, extremely biocompatible, based on hydrophilic chemicals and hydroxy-ethyl-methacrylate type. The structural metal composition of the new prostheses will be made of titanium alloys using additive technology based on melting thin layers of titanium powder (about 50 microns) on each other until the desired component is obtained (sandwich method). Then, the biomaterial and osteoconductive nanostructured material developed in our previous studies can cover the titanium structural prosthetic skeleton. These hybrid biological prostheses, which are made using synthetic materials capable of inducing the growth of biological networks and structural steel scaffolding, may favor the emergence of new classes of orthopedic hybrids in the medical field. The new hybrid bio-prosthesis could drastically reduce protection against stress while providing an advantageous improvement in the life of the prosthesis compared to traditional solutions. Recovering optimal joint functionality will improve the patient's quality of life, which perceives a significant reduction in the risk of the new surgery. The requirement to predict potential structural changes that could be induced by improper use of biologically compatible prostheses in bone structure and morphology has forced our studies to evaluate fictitious models that could be considered for efficient bone distribution and orthotropic behavior.

Towards understanding the ploughing friction mechanism in ultrasonic assisted grinding with single grain

Despite the widespread use of ultrasonic vibration in machining (i.e., grinding) due to friction reduction, the friction mechanism at the tool-workpiece contact is still unclear. Most of the explanations focus on the kinematic analysis, but few attempts have been made to understand the deformation process of the tool-workpiece contact under ultrasonic vibration. This work presents a novel prediction model to calculate the ploughing friction coefficient with the two-dimensional ultrasonic vibration assistance (imposed transverse vibration and additional normal vibration). Considering the ploughed surface generation, the actual contact area and the distribution of friction stress could be predicted. Particularly, the instantaneous contact area with a complex motion path was solved by generating the ploughed surface and calculating the overlapping area of the particle geometry engaged with the generated groove. Experimental results agree well with the predicted results. In addition to the deflection of resultant velocity, the friction reduction is also attributed to the change in friction stress distribution due to three special contact states. This research can deepen the understanding of tool-workpiece friction reduction mechanism in ultrasonic assisted grinding and might provide an important reference for studying other ultrasonic assisted machining processes.

Asymptomatic foot and ankle structural injuries: a 3D imaging and finite element analysis of elite fencers

BackgroundFencing is a highly asymmetrical combat sport, that imposes high mechanical demands over repeated exposures on the musculoskeletal structures, a primary cause of injuries in fencers. However, there are limited epidemiological studies on the structural injuries of the foot and ankle in fencers. This study aimed to investigate foot and ankle structural injuries, and explore how metatarsophalangeal joint structural changes may affect the mechanisms of foot and ankle injuries in asymptomatic fencers.Methods3D images of foot and ankle morphology using computed tomography were obtained from ten elite fencers. We then constructed finite element models of the first metatarsophalangeal joint in the foot of their trail legs. The validated models were used to simulate stress distribution changes from different ankle joint angles during lunging.ResultsThe findings showed that stress distribution changes at the medial and lateral sesamoid may have caused sesamoid fractures, and that habitual and concentrated stress on the metatarsal bones might have flattened the sesamoid groove. This process may damage the integrity of the first metatarsophalangeal joint, and consequently affect the efficiency of the windlass mechanism in fencers. During lunging, different ankle joint angles of the trail foot increased the total stress difference of the medial and lateral foot, and thus influenced the lunging quality and its stability.ConclusionsOur findings revealed that the asymmetric nature of fencing might have caused asymptomatic foot and ankle structural injuries, and finite element analysis results indicated that this might increase the incidence of the serious injuries if unattended. Regular computed tomography examination should be introduced to monitor elite fencers’ lower limb alterations, permitting unique angle adjustments in the trail foot without sacrificing technical or physiologic properties based on the exam results and reduce the lower limb injury risk.

Influence of neighbouring tube expansion on the residual stress of tubesheet with single-row holes

Abstract 1 The expansion joint is a commonly used method of connection tube and tubesheet in the pressure vessel industry. This paper established the rationality of the numerical simulation method by comparing with the analytical model. On this basis, the effect of neighbouring tube expansion on the residual stress of tubesheet with single-row holes was investigated, as well as the effect of the cyclic joint temperature changes on the tubesheet stress amplitude. Finally, preliminary work was conducted to determine the fatigue life of pressure vessels considering expansion factors. The results indicated that as the model was extended from one hole to 10 holes, the maximum and average stresses of each hole increased gradually and stabilized at a limit value when the model reached 10 holes, and the maximum and average stress in the expanded cases were approximately 13% and 10% higher than those in the unexpanded case, respectively. Residual stress results will lead to the change of stress distribution and the increase of stress amplitude, and then affect the fatigue life of the pressure vessel equipment. •Multilinear kinematic hardening model are used to exhibits the Bauschinger effect. •Numerical simulation method is validated by the analytical model. •Expansion process has a great influence on the stress level of the tube holes. •Residual stress leads to a significant change of tubesheet stress distribution. •Residual stress increases the stress amplitude and affects fatigue life.

The Role Of The Acromioclavicular And Coracoclavicular Ligaments In Shoulder Motion Using A Three-Dimensional Finite Element Model

The aim was to develop a three-dimensional (3D) finite element model (FEM) of the acromioclavicular (AC) joint, which can be used in the future for the dynamic study of reconstruction techniques. The secondary objectives were to analyze stress distribution, strain, geometric and length change in the coracoclavicular (CC) and AC ligaments and to determine spatial relationships of the AC during shoulder motion.

Discussion on the manuscript entitled “Thermal residual stress in a functionally graded material system” by K. S. Ravichandran, Materials Science and Engineering A, 201(1–2), pp. 269-276

In the article entitled “Thermal residual stress in a functionally graded material system”, a strip element made of a combination of Al2O3 ceramic and Ni metal was considered as a functionally graded material to obtain the general expressions for thermal residual stresses. The results showed that the stress distribution changes continuously as the volume fraction of the ceramic varies according to a power function. However, an incorrect term for bending stiffness was used in this expression. In addition, the expression for the residual stress term, which is resulted from the uniform elongation of the strip fibers, should not be used to calculate the reactive bending moment. It must be obtained from the nonuniform distribution of thermal strain across the thickness. In this study, the derivation of the final expression for the thermal residual stress in a functionally graded strip element by the strain suppression method is discussed.

Dynamically Tunable Dry Adhesion through a Subsurface Thin Layer with Tunable Stiffness

AbstractRecently, a novel concept to realize dynamically tunable dry adhesion via subsurface stiffness modulation (SSM) in a composite core–shell structure has been introduced and demonstrated for gripping and release of objects. Here, a variant form of the composite core–shell design is proposed to significantly improve the performance of dynamically tunable dry adhesion in terms of activation time and activation voltage. Specifically, composite pillars with an embedded microfluidic channel filled with a low melting point alloy (LMPA) are fabricated, and the adhesion of the pillars is characterized as a function of LMPA state: either melted or solid. The effects of the thickness and in‐plane pattern of the LMPA channel, as well as the depth at which it is embedded on tunable adhesion are investigated. Experiments show that the effective adhesion strength can be reduced up to 50%, equivalent to a 2× change in dry adhesion when the LMPA is melted. Finite element analysis of the stress distribution change under SSM shows that the experimentally observed tunable adhesion is primarily due to stiffness change close to the interface. In addition, two technology demonstrations of composite pillars picking and releasing objects with fast activation (≈1 s) and low activation voltages (≈1 V) are included.

Cycle deformation enabled controllable mechanical polarity of bulk metallic glasses

Tuning anisotropy in bulk metallic glasses, ideally isotropic, is of practical interest in optimizing properties and of fundamental interest in understanding the amorphous structure and its instability. By employing the quasi-elastic asymmetric mechanical cycling method, we effectively induce the polarized plastic response of a model bulk metallic glass, without damaging the sample or introducing significant annealing or rejuvenation effects. Moreover, the polarized anelastic limit can be well controlled by regulating the amplitude of mechanical cycling. Through the atomic-level analysis of nonaffine displacement, it is found that the asymmetric cycling can only exhaust the plastic atomic rearrangements, and the survived anelastic rearrangements govern the anelastic limit of the training direction. While usual structural indicators are not sensitive probes for the induced anisotropy, the changes in local yield stress distributions capture the polarization well. This polarized plastic response of metallic glasses is originated from the plastic-event-exhaustion induced asymmetry of local potential energy surface, rather than the frozen-in anelastic strain. Our study is of fundamental importance, which furthers our understanding of the mechanical deformation of metallic glasses and sheds some light on the prospects for improved properties through induced anisotropy.