Regions Of Stress Concentration Research Articles

Design improvements to enhance mechanical performance of a locking compression plate as a biodegradable implant plate: a finite element analysis

Mg alloy is one of the most suitable biodegradable materials for making modern LCP. This is due to the osseointegration property, low elastic modulus, the presence in the human bone, and the excellent biodegradable nature. But it lacks much-needed strength compared to conventional (Ti, SS alloys) implants due to low strength of biodegradable (Mg, Zn alloys) materials. The problem can be solved by either biodegradable material development or by design improvement of existing LCP. Improving the design is a better way to improve the LCP. This paper aims to improve the design of existing LCP through the addition of features and their implications by analysing the stress distribution across the plates for improved biodegradable implant mechanical performance. Various designs have been developed and each has certain advantages over conventional LCP which ACT and 4PBT have been demonstrated via the FEM. They are best suited for femur bone fracture treatment replacing conventional metal alloys LCP. The CTLCP, SLCP, and SELCP have improved performance at stress concentration regions while STLCP especially has 36.74% less stress generation than conventional LCP along with excellent biodegradable performance. The designs are discussed in detail to analyse the effect of added features in conventional LCP.

Wear and abnormal fracture failure mechanisms of alloy teeth in TBM insert tooth disc cutters

Insert tooth disc cutters are among the commonly used cutters in TBMs (Tunnel Boring Machines). However, due to the sharpness, protrusion, and small contact area between the alloy teeth and rock, these cutters are prone to uneven loading and stress concentration. This makes the alloy teeth susceptible to abnormal failure modes such as chipping, breakage, and detachment during operation. To improve the compatibility of insert tooth disc cutters with rock, this study investigates the wear and failure mechanisms of these cutters. In an analysis of failed disc cutters, it was found that 53% of the alloy teeth had failed, with breakage and chipping accounting for the highest proportions, at 37% and 15%, respectively. The study proceeded by characterizing the microscopic wear morphology of both the cutter ring matrix and the alloy teeth. The results revealed that the wear of alloy teeth is characterized by shallow surface scratches and pits caused by abrasive, adhesive, and fatigue wear. In contrast, the matrix of the cutter ring exhibited plowing grooves formed primarily by abrasive and adhesive wear. Furthermore, a finite element model (FEM) of the rock-breaking process was established and validated against experimental data to analyze the stress distribution and surface contact pressure of the alloy teeth during rock cutting. Simulation results indicated significant impact phenomena as the alloy teeth penetrate the rock, which reduces their service life. Both spherical and wedge-shaped teeth exhibited noticeable stress concentration and uneven loading, with the regions of stress concentration closely aligning with the areas where chipping occurred. This correlation confirms that the primary causes of tooth chipping are stress concentration and uneven loading. This research provides valuable insights for the selection and optimized design of insert tooth disc cutters in TBM applications.

Three-Dimensional Numerical Analysis of Seismic Response of Steel Frame–Core Wall Structure with Basement Considering Soil–Structure Interaction Effects

In recent years, numerous studies highlighted the crucial role of the soil–structure interaction (SSI) in the seismic performance of basement structures. However, there remains a limited understanding of how this interaction affects buildings with basement structures under varying site conditions. Based on the three-dimensional (3D) numerical analysis method, the influence of the SSI on the seismic response of high-rise steel frame–core wall (SFCW) structures situated on shallow-box foundations were investigated in this study. To further investigate the effects of the SSI and site conditions, three types of soil profiles—soft, medium, and hard—were considered, along with a fixed-foundation model. The results were compared in terms of the maximum lateral displacement, inter-story drift ratio (IDR), acceleration amplification coefficient, and tensile damage for the SFCW structure under different site conditions, with both fixed-base and shallow-box foundation configurations. The findings highlight that the site conditions significantly affected the seismic performance of the SFCW structure, particularly in the soft soil, which increased the lateral deflection and inter-story drift. Moreover, compared with non-pulse-like ground motion, pulse-like ground motion resulted in a higher acceleration amplification coefficient and greater structural response in the SFCW structure. The RC core wall–basement slab junction was a critical region of stress concentration that exhibited a high sensitivity to the site conditions. Additionally, the maximum IDRs showed a more significant variation at incidence angles between 20 and 30 degrees, with a more pronounced effect at a seismic input intensity of 0.3 g than at 0.2 g.

Thermo-mechanical coupling characteristics of the shearer’s guiding shoe during the friction

The reliability and longevity of the guiding shoe are crucial for the proper functioning of coal mining machines. The heavy wear of the sliding surface under thermal stress coupling is the primary factor influencing the service life of the guiding shoe. To reveal the heat flow distribution patterns and the thermo-stress coupling mechanisms of the guiding surface, a thermo-mechanical coupling model of the guiding shoe and the pin row is established. The transient thermodynamic behavior of the guiding shoe under different load and speed conditions is studied using the coupled temp-displacement analysis method in Abaqus. The results indicate that the overall temperature of the guiding shoe friction surface experiences a rapid increase during the initial running-in phase, followed by a progressively slower temperature increase over time. Temperature and stress concentration regions on the friction surface primarily localize at the corners of the shoe groove, and the distribution of temperature and stress shows a strong coupling. Furthermore, elevated traction speed and mechanical load exacerbate the thermo-elastic instability of the guiding shoe, consequently augmenting thermal stress on the friction surface. The increase in support load results in significant thermal shock on the lower area of the left side of the guiding shoe. The research provides a reference for exploring the fatigue failure and wear mechanisms of the guiding shoe while considering thermal effects.

Crack coalescence and failure behaviors in slate specimens containing a circular cavity and a pre-existing flaw pair under uniaxial compression

The flaws (fractures) widely existing in rock mass pose a threat on the stability of many underground cavities. This study aims at investigating the failure process of a cavity affected by adjacent flaws. A number of slate specimens containing a circular cavity and a pre-existing flaw pair were tested under uniaxial compression. Varied flaw configurations were obtained by changing the flaw inclination angle with respect to horizontal and the spacing between flaw pair and cavity. Three main types of cracks emanated from the pre-existing flaw tips, and played a dominant role in the failure process of cavity, comprising primary wing cracks (tensile cracks) and two types of secondary cracks (quasi-coplanar shear cracks and oblique shear cracks). The initiation and propagation of these cracks were highly dependent on the flaw pair configurations. When the pre-existing flaw pairs were non-parallel to the loading direction, (1) mostly, coalescence occurred both in the tensile and compressive stress concentration regions around cavity; (2) in most cases, the quasi-coplanar and oblique shear cracks were the predominant cracks leading to the coalescence between the compressive stress concentration regions of cavity and the pre-existing flaw pair tips. When the pre-existing flaws were parallel to the loading direction, the combination of inclined shear cracks and tensile cracks or inclined shear cracks only dominated the failure of cavity. The initiation angles of wing cracks, quasi-coplanar shear cracks and oblique shear cracks agreed well with the theoretical predictions by the maximum tangential strain criterion (MTSN), Mohr-Coulomb criterion (M−C) and maximum shear stress criterion (MSS), respectively.

Physics-informed neural networks for V-notch stress intensity factor calculation

This paper proposes a physics-informed neural networks (PINNs) based approach for elastic structures with a V-notch, by which the displacement field, stress field as well as the V-notch stress intensity factor (NSIF) can be obtained through artificial neural networks. A PINN model is established for V-notch structures, integrating physical information into a deep neural network to ensure adherence to physical laws while fitting observational data. Subsequently, an adaptive local sampling strategy for V-notch structures is adopted, generating locally dense Gaussian points sampling around regions of stress concentration. Based on this, a sequential PINNs approach for V-notch structures is then established to calculate the NSIF for V-notch structures with arbitrary notch angles. Finally, the effectiveness of the proposed method is validated through three numerical examples. The results demonstrate the method can accurately predict the NSIFs for V-notch structures across a spectrum of opening angles. Compared to the traditional data-driven method, the proposed method is able to more effectively compute the NSIF of V-notch structures due to the integration of physical information and observational data.

A peridynamic-based reconstruction and analysis method for short-fiber reinforced composites

Abstract As the complex microstructure, predicting the effective elastic properties and damage mechanisms of Short-Fiber Reinforced Composites (SFRC) continues to pose a challenge. This study presents a new reconstruction and analysis method based on PeriDynamics (PD) for SFRC. The reconstruction of the surface profiles of short-fibers obtained from Micro-CT (Micro-Computed Tomography) scanning resulted in a PD computational model that accurately reflects the actual microstructure of SFRC. The results predicted the effective elastic modulus of SFRC while fiber volume fraction and distribution have impact. Micro-cracks emerge at stress concentration regions near the fiber-matrix-fiber interfaces between two adjacent fibers, and with increasing load, these cracks gradually propagate, interact, and merge with each other. Eventually, major cracks form, leading to material failure.

Cyclic frictional response of rough rock joints under shear disturbances: Laboratory experiment and numerical simulation

The cyclic frictional response of rock joints under shear disturbances is critical for understanding the stability and durability of rock engineering structures. Laboratory experiments and numerical simulations were conducted to examine the effects of varying cyclic shear displacement amplitudes, frequencies, and cycle numbers on the macroscopic and microscopic shear characteristics of rough rock joints. The experimental results reveal significant differences in shear strength between the first few cycle and subsequent cycles during the cyclic shear process. As the number of shear cycles increases, the asperities on the contact surface gradually sustain damage, leading to a reduction in normal displacement. During cyclic shear, the peak shear load exhibits a two-stage variation with the number of cycles: an initial sharp decline followed by a gradual increase as the cycles proceed. The peak shear strength shows no obvious pattern under different shear displacement amplitudes and frequencies in the early stages of cyclic shear. As cyclic shear progresses, the peak shear strength decreases with increasing shear displacement amplitude but increases with higher shear frequency. Numerical simulations indicate that significant plastic deformation and shear wear occur on the joint surface during the initial cycles. The growth of the wear area is primarily concentrated in regions of stress concentration. Additionally, the simulations reveal that the volume of shear wear increase nonlinearly with the number of cycles. This research provides new insights into the cyclic shear behavior of rough rock joints and offers valuable references for engineering applications.

Experiment and prediction of the strain-range dependent ultra-low-cycle fatigue based on micromechanical cyclic void growth model

Under severe seismic action, the local stress concentration region in steel structures is prone to the ultra-low-cycle fatigue (ULCF) under high triaxiality and irregular cyclic deformation with intensively varying strain amplitudes. It emphasizes the necessity of the jointed effects of the stress triaxiality and strain range incorporated in the ULCF life prediction. Given the limited relevant studies in terms of the underlying micro-mechanisms, this paper focuses on experimental and modeling studies of the combined effects of stress triaxiality and strain range on the ULCF failure, based on Gurson-Tvergaard-Needleman (GTN) microvoid evolution theories. Monotonic tensile tests on three types of notched round bars suggest that fracture strain decreases with increasing triaxiality. Cyclic tests on two types of notched bars under various strain ranges confirm the combined effects of stress triaxiality and strain range. Given a specific triaxiality, the ULCF damage accumulation rate increases linearly as the tensile plastic strain range ramps up. For the same tensile plastic strain range, higher triaxiality results in a greater damage accumulation rate. In the modeling studies, the consistency of the GTN and uncoupled damage models has been proven in terms of ULCF failure of structural steel. Based on GTN theories, a new micromechanical cyclic void growth model (GCVGM) is proposed, considering the detailed processes of void nucleation, growth, and coalescence under monotonic and cyclic loadings. Moreover, the joint effects of stress triaxiality and strain range can be explicitly described within a unified framework, without additional empirical assumptions. Based on experimental and simulation results, the proposed GCVGM shows significant advantages over conventional models in accurately predicting ULCF failure under various loading protocols, with low average errors of 2.73 % and −0.91 % for two types of notched bar specimens, respectively.

Enhanced mechanical properties and atomic-scale mechanisms of ferroelastic domain switching for GdNbO4-La2Zr2O7 materials

Optimization of mechanical properties in La2Zr2O7 (LZO) ceramics, composites and coatings is an on-going requirement for their practical application. Herein, the contribution of monoclinic (La, Gd)NbO4 (m-LGNO) enhancement of fracture toughness by ∼56% reveals its capability to be a prominent toughening agent. Due to the ferroelastic nature of LGNO, ferroelastic switching takes place within the stress concentrated regions, giving rise to significant strain energy relaxation. Atomic-scale evidence reveals that ferroelastic 94°/86° domain switching can occur, yielding merged 94° domains and newly formed 86° domains. The relevant strains induced by ferroelastic domain switching are quantified up to 8.06% and 6.20% in shear and normal strain, respectively. Such domain switching strains highlight their contribution to accommodate external mechanical loading for the 50 mol% GNO-LZO composite. The results indicate that the unique ferroelastic nature and 94°/86° ferroelastic domain switching in m-LGNO cooperatively provide a significant toughening effect.

Design optimization of lightweight automotive seatback through additive manufacturing compression overmolding of metal polymer composites

With the growing demand for enhanced automotive fuel efficiency and environmental sustainability, there is a need for lightweighting automotive components through innovative design and manufacturing processes. This study leverages a combination of numerical iterative design optimization and hybrid additive manufacturing–compression molding (AM-CM) technique for metal polymer composites to lightweight an automotive seatback. The AM-CM process enables robust mechanical interlocking between metals and composites, boasting high stiffness and strength with low overall density. Replacing metallic components with such metal polymer composites allows for comparable mechanical performance while significantly reducing the overall weight. First, the automotive seatback design space is reduced to critical load carrying regions using topology optimization and high stress concentration areas are identified using finite element analysis. Next, a lightweight metal polymer subcomponent is designed for a high stress concentration region. The full seatback frame with spatially heterogeneous material-specific design is then iteratively optimized to enable enhanced stiffness with minimal weight. Overall, the automotive seatback frame designed with location-specific metal, polymer, and metal polymer composite materials weighs 20% less than the metal-only design while exhibiting similar stiffness.

Evaluation of the Impact of Stress Distribution on Polyurethane Trileaflet Heart Valve Leaflets in the Open Configuration by Employing Numerical Simulation

It is costly and time-consuming to design and manufacture functional polyurethane heart valve prototypes, to evaluate and comprehend their hemodynamic behaviour. To enhance the rapid and effective design of replacement heart valves, to meet the minimum criteria of FDA and ISO regulations and specifications, and to reduce the length of required clinical testing, computational fluid dynamics (CFD) and finite element analysis (FEA) were used. The results revealed that when the flexibility of the stent was taken into consideration with a uniform leaflet thickness, stress concentration regions that were present close to the commissural attachment were greatly diminished. Furthermore, it was found that the stress on the leaflets was directly impacted by the effect of reducing the post height on both rigid and flexible stents. When varying the leaflet thickness was considered, the high-stress distribution close to the commissures appeared to reduce at thicker leaflet regions. However, thicker leaflets may result in a stiffer valve with a corresponding increase in pressure drop. It was concluded that a leaflet with predefined varying thickness may be a better option.

The effect of Fe solute atom on interface structure and deformation behavior of Cu/FexNi1-x layered composites by molecular dynamics

Molecular dynamics investigated the effect of Fe solute atom on interface structure and deformation behavior of Cu/FexNi1-x layered composites. Ultimate stress first increases, then decreases, and then increases again with the increase of Fe content. When Fe content is between 20 % and 30 %, ultimate stress reaches the maximum value, which is 15.2 % higher than that of Cu/Ni. As the Fe content increases, stress concentration region on interface shifts from Cu layer to FexNi1-x layer, then to Cu layer, initial dislocation nucleation source on interface transfers from triangular node on Cu side to misfit dislocation line on FexNi1-x side, then to strip region on Cu side, and plastic deformation mechanism of FexNi1-x layer changes from slip of leading and trailing dislocations to slip of partial dislocations, then to slip of perfect dislocations. When Fe content is low, dislocation density rapidly increases to its peak, then decreases, and finally fluctuates around certain value, especially in the Fe30Ni70 layer where the dislocation density decreases to very low value, and interface morphology presents wavy. However, when Fe content is high, dislocation density slowly increases to its peak and then fluctuates around the peak, and interface morphology presents flat. Shear strain width of interface region decreases as Fe content increases, which indicates the interface of Cu/FexNi1-x with low Fe content has good plastic harmonized deformation ability.

Crack growth in sandwich-structured foam core graphite epoxy laminate composite using a phase-field modelling approach

The laminated sandwich composites have wide structure-making applications in the automotive and aviation fields due to their lightweight and superior flexural rigidity properties. Making grooves or holes to assemble more than one structure induces crack discontinuities near the stress concentration region in these sandwich structures. The present work examines the effect of crack discontinuities on the mechanical performance and failure process of the sandwich structures under different loading conditions. Phase field method (PFM) has been presented and implemented using in-house developed MATLAB code. The effect of holes, multiple cracks, number of cores, and loading conditions are analyzed for the mechanical and fracture behavior of the structure. Load-carrying capacity, threshold displacement value for crack initiation, crack propagation trajectory, and energy absorption capacity are compared for various crack discontinuities under different loading conditions. Approximately 35% increase in load carrying capacity is observed in equivalent multiple core sandwich structures.

Study on the tribological performance at the interface between a steel wire rope and groove during a twisting process

In actual use, a steel wire rope is often stretched and twisted around a groove, increasing the risks of contact fatigue, friction and wear at the rope-groove interface under a long-term service condition. With the consideration of influence factors such as the nonlinear contact and wear between the rope and groove, the tribological performance at the rope-groove interface during a twisting process is analyzed in this study. A winding rope-groove model is first established in order to obtain the contact and sliding solutions at the interface between the rope and groove, which are then used as the load conditions of a simplified local model that is built for wear solution using a modified Archard's wear theory. Based on the finite element simulation software ABAQUS, the ALE adaptive mesh technology and UMESHMOTION subroutine secondary development are adopted to analyze the evolutions of wear topography and contact behavior between the rope and the groove. The results show that the twisting movement of the steel wire rope around the groove causes an interfacial wear between them. The wear scars occur on the outside wire of the steel wire rope and the bottom area of the groove, and the wear scar on the groove is smaller but deeper. A ring-shaped region of stress concentration happens near the edge of wear region. As the wear process proceeds, the depths and dimensions of the wear scars increase, while the contact pressure decreases. The contact performance and wear change dramatically at the beginning of wear process and tend to be stable subsequently. An increment of lay angle of the outside wire aggravates the wear and contact between the steel wire rope and the groove.

Effect of laser texturing and thermomechanical joining parameters on bond strength of steel-flax fiber reinforced vitrimer composites

The study examines laser texturing's impact on metal-composite hybrid joint mechanics formed via heat compression. It focuses on sustainable composite fabrication, utilizing flax fibers and a recyclable vitrimer resin known for dynamic covalent bond exchange capabilities, enhancing recyclability, repairability, and reshaping. Simulated heating conditions determined optimal bonding between the composite and laser-textured surfaces, considering the glass transition temperature for minimum temperature and time requirements. Deviations from initial heat pressing conditions (135 °C, 0.6 MPa, 5 min) reduced bonding strength, underscoring parameter sensitivity. Cross-tensional tests under varied laser texturing conditions, supported by microscopic examinations, revealed optimal strength (1680 N) with a 150 μm hatch distance and 9 repetitions, ensuring consistent ablation volume and time. Supplementary ANSYS simulations pinpointed stress concentration regions in cross-tensional joints, guiding adjustments in laser texturing within the region of interest to assess mechanical properties. The hybrid cross-tensional and lap shear joints were also reconnected after each fracture via heat compression, allowing for the evaluation of degradation in bonding strength over each cycle.

Visualization of crack generation of vulcanized butadiene rubber under uniaxial elongation by atomic force microscopy nanomechanics

Crack resistance performance by oxidation must be considered in rubber product development because cracks are the starting point for fracture. When rubber is stretched extensively, mechanical stresses can break apart its molecular chains, generating radicals and promoting mechanochemical oxidation. This reaction is one of the causes of cracking. However, it is not fully understood how cracks are formed in vulcanized rubber with an inhomogeneous crosslinking structure. Atomic force microscopy (AFM) nanomechanics has been utilized to observe vulcanized butadiene rubber in an elongated state. It was shown that crack generation is related to mechanochemical oxidation, and that the cracks could be clearly visualized as stress-concentrated regions at the nanoscale. Additionally, crack formation is accelerated with increasing elongation of the rubber. This demonstrates that AFM nanomechanics is an effective tool for observation of the generation of cracks associated with mechanochemical oxidation in rubber materials.

Composite strengthening via stress-concentration regions softening: The proof of concept with Schwarzites and Schwarzynes inspired multi-material additive manufacturing

Inspired by nature, porous graded topological structures based on carbon, like Schwarzites and Schwartzynes, exhibit a distinctive radial-gradient distribution of pores. The pores are strategically arranged in two patterns: small pores at the centre and larger pores in the outer region (ψ), and larger pores at the centre with smaller pores in the outer region (Ω). This type of topological engineering, with its unique deformation behaviour, makes these structures highly suitable for engineering applications requiring high energy absorption. However, the existence of stress-concentration regions within the porous graded structures leads to premature structural failure during uni-axial compression. To enhance the mechanical properties of such porous graded structures, this study proposes a strategy of tailoring their pores' deformation characteristics by replacing the stress concentration regions with soft/flexible materials. The selective reinforcing two (ψ2) and three layers (Ω3) soft material enhances the specific yield strength of the multi-material composite by 187.27 % and 230.22 %, respectively compared to the respective porous soft structures. Specific resilience is heightened by 289.93 % and 323.82 % for multi-material composite ψ2 and Ω3, w.r.t the respective porous hard structure(ψ0′ and Ω0,). Our results present a unique strategy for improving the structural performance of the porous graded structures by tailoring the deformation characteristics. Engineered multi-material-based advanced composites, resulting from this approach, exhibit significant potential for applications requiring energy absorption without failure.

Mechanism of radial chain rockbursts in a deep granite TBM tunnel under the influence of weak band

Radial chain rockbursts (RCRs) in deep-buried TBM tunnels have prolonged durations and can pose significant safety risks. Further research is needed to deepen our understanding of the mechanisms of recurrence of rockbursts under the influence of structure plane. In this study, the geological characteristics, occurrence characteristics, microseismic (MS) activity laws, and rock mass fracture mechanism of several RCRs influenced by weak band were summarized to reveal the mechanism of recurrence of RCRs. Research shows that under the influence of weak band, (1) RCRs tends to occur in the area where the dip angle is large, and the strike intersects with the tunnel direction at a large angle and forms a small angle with the maximum principal stress. The width of the weak band typically ranges from 0.01 to 1 m, which is positively correlated with the final depth of rockburst pit. The strength of the weak band is relatively “soft” compared to the surrounding bedrock. (2) The depth of each rockburst pit in RCRs gradually decreases, the time interval between adjacent rockbursts gradually increases, and the maximum thickness of rock block in each rockburst gradually increases. (3) The maximum MS energy of MS events and the maximum apparent stress gradually decreased in the development process of RCRs. The region of stress concentration gradually extended to deeper zone, and the distance difference between stress concentration region and sidewall during each rockburst occurrence stage gradually decreased. (4) The effect of weak band on RCRs attributes to the excavation induced local stress concentration near the weak band, and the interface between the weak band and surrounding rock controls the boundary of the rockburst body. The “chain effect” of RCRs mainly shows that the promotion effect of the previous rockburst on the subsequent rockburst, by promoting the stress and rock fracture transferring to the deep zone, and the proportion of shear fractures increases.

Study of hydraulic cutting as a method to prevent coal burst disasters

This study explores the causes of coal bursts in the Xinzhou Kiln Mine, identifying key factors such as residual pillars, hard coal seams and/or roofs, stress concentration due to complex geological structures, and the stress distribution characteristics of the primary rock. A significant finding is that hydraulic cutting not only diminishes and redistributes the stress concentration region inside the coal seam but also mitigates the burst potential of the coal-rock mass, fundamentally reducing the likelihood of coal bursts. By taking Face No. 8937 in Xinzhou Kiln Mine as the test object, a coal burst prevention test was performed using hydraulic cutting. In combination with theoretical analysis and numerical simulation, the mechanism of hydraulic cutting for preventing coal burst was discussed, and reasonable cutting parameters were established. Onsite monitoring revealed that hydraulic cutting disrupts the integrity of the coal-rock mass, releases internal stress, and increases its water content, thereby weakening its burst tendency. Additionally, the deformation and fracturing of the cutting slots and the closure of boreholes shifted the stress concentration from the coal seam to deeper areas and to the two ribs. Post-cutting observations showed a significant reduction in both the frequency and impact energy of coal bursts; there was also a noticeable increase in the convergence of the roadway in the cutting area compared to non-cutting areas. Furthermore, displacement of the roof and floor increased by 78.9 % and that of the two ribs increased by 47.4 % after cutting, preventing the coal-rock mass from accumulating high stress. In conclusion, hydraulic cutting is a promising method for effectively preventing coal bursts and enhancing the safety of mining operations.