Regions Of High Stress Concentration Research Articles

Application of Deep Learning on Structure Displacement Measurement and Accuracy Analysis

Displacement serves as a crucial indicator in structural health monitoring within civil engineering, with computer vision being a commonly employed tool due to its cost-effectiveness and convenience. This paper introduces a methodology for tracking feature points computed via computer vision techniques SuperPoint and SuperGlue. Two test scenarios are conducted: a bridge loading test characterized by a low uniform stress state, and a tensile strength test marked by a high stress state. However, a notable drawback of this method is the potential misalignment between the survey point (the point under measurement) and the feature point, leading the errors. To address this issue, a fundamental principle for selecting feature points is presented. In the bridge loading test, the displacement of the survey point is recorded, and the influence of misalignment between survey point and feature point on accuracy is analyzed under low-stress uniform conditions. The findings demonstrate the feasibility of this method for field measurements in civil engineering. Subsequently, a tensile strength test is conducted to assess the influence of different feature point selection criteria on accuracy under high-stress conditions. Concurrently, the DIC software Ncorr is applied to analyze the displacement field of feature points near the survey point. The results highlight the significant influence of selecting feature points within regions of high stress concentration on measurement accuracy.

Stress concentration targeted reinforcement using multi-material based 3D printing

Topological engineering (3D printing into complex geometry) has emerged as a pragmatic approach to develop high specific strength (high strength and low density) lightweight structures. These complex lightweight structures fail at high-stress concentration regions, which can be, replaced with soft/tough material using 3D printing. It can improve mechanical properties such as strength, toughness and energy absorption etc. Here, we have developed stress concentration targeted multi-material schwarzite structures by 3D printing technique. The soft (Thermoplastic Polyurethane) material is reinforced at high-stress concentration regions of hard (Polylactic acid) schwarzite structures to enhance the specific yield strength and resilience. The mechanical properties and responses of these structures were then assessed via uniaxial compression tests. The multi-materials 3D printed composite structure shows improved mechanical properties compared to single materials architecture. The specific resilience of composites demonstrates remarkable enhancements, with percentage increases of 204.70 %, 596.50 %, and 1530.99 % observed when compared to hard primitives, and similarly impressive improvements of 182.45 %, 311.64 %, and 477.75 % observed in comparison to hard gyroids. The obtained experimental findings were comprehensively examined and validated with molecular dynamics (MD) simulations. The promising characteristics of these lightweight multi-material-based Schwarzites structures can be utilized in various fields such as energy harvesting devices, protective, safety gears, and aerospace components.

Roadways fracture response under varying dominant blasting frequencies and lateral pressure coefficients

Dominant frequency of blasting waveform attenuates with increasing propagation distance, leading to diverse diffractive effects on a roadway located in different sublevels. To investigate the roadway fracture characteristics in response to varying blasting wave frequencies and geo-stresses. Numerical simulation and experiments were performed by using discrete element methods and acoustic emission (AE) techniques, respectively. Roadway response differences in terms of microcracks propagation regions were primarily investigated, to reveal the relationships between damage-prone regions and the lateral pressure coefficient and blast waveform frequencies. The results showed that the excavation damage zone (EDZ) and the types of microcracks developed are primarily influenced by the principal stress direction. Low-frequencies blast waves contribute significantly to the overall damage to the surrounding rock around the roadway, while high-frequencies blast waves mainly damage the sides of the facing blast. Under the coupling effect of principal stress and blast wave, microcracks are more prone to generate in regions coupling with high-stress concentration regions induced by principal stress and disturbed regions diffracted by blast waves. With the results from this study, the roadway support should consider the difference in damage-prone regions triggered by blasting waves with varying dominant frequencies under different lateral pressure coefficients.

Taking inspiration from medieval architecture: Using catenary arches in place of straight beam as the building block into bending-dominated lattice structures

Regular bending-dominated lattice structures use straight strut elements as the building blocks in their unit cell which is easier to deform under compression. To improve their performance, replacing the straight elements with the curved members of catenary arch geometry is proposed. Two representative cases – body centered cubic and simple cubic are designed, manufactured using AlSi10Mg alloy and tested experimentally in this study with their struts replaced by catenary arches. Numerical simulations were also conducted at the unit cell level to understand the stress development and regions of high stress concentrations. The effect of different heat treatment procedures was also investigated for both test cases. It was observed that the use of catenary elements had opposing effects on the strength of the BCC and SCC lattice structures when compared to their straight element counterparts. The higher nodal connectivity adversely affected the strength and the lattice failure depended highly on the same. The residual stress release heat treatment improved the mechanical properties of the lattice structures while the solution treatment and aging reduced the strength and modulus but substantially increased the compressibility of the lattice structures.

Origami-inspired sandwich structures under low-to-high velocity impacts: A numerical simulation approach

In this study, the ballistic impact performance of sandwich structures with Miura-origami pattern inspired core (MPIC) panels subjected to low-to-high velocity impacts is studied. Sandwich panels with MPIC structure were modeled and finite element analysis was performed using commercially available software LS-DYNA to evaluate their specific energy absorption (SEA) and load-bearing capabilities. A cylindrical indenter (diameter = 10 mm and height = 15 mm) with material property of mild Steel (ρ = 7800 kg/m3) was impacted at three different velocities, i.e., 10 m/s (0.46 J), 50 m/s (11.49 J), 100 m/s (45.95 J) under predefined impact conditions. The obtained results were compared with that of a monolithic solid plate under identical loading conditions and geometrical dimensions. The proposed MPIC design was 93% lighter in weight than the monolithic solid plate. On comparison of stress contours, the monolithic solid plate exhibited regions of high-stress concentration at the impact zone. However, for the MPIC sandwich panel, the stress contour was found to be uniform. For an impact velocity of 100 m/s, the SEA of the MPIC sandwich panel was found to be 1142.6 J/kg, while for the monolithic solid plate, it was obtained as 57.17 J/kg. Eventhough complete penetration of the MPIC sandwich panel occurred for an impact velocity of 100 m/s, the SEA of the MPIC sandwich panels were found to be significantly higher than that of the monolithic solid plate. Since MPIC sandwich panels exhibit enhanced energy dissipation characteristics, they can be an alternative to the conventional monolithic solid plate as light-weight high performance designs for specific applications.

Effect of the in-situ formed CuO additive on the fracture behaviour and failure mechanism of Ag-SnO2 composites

Oxide additives can significantly improve the mechanical properties of ceramic particle-reinforced metal matrix composites. In this study, the fracture behaviour and failure mechanism of the Ag-SnO2 composites without and with in-situ formed CuO additive are investigated using in-situ scanning electron microscope (SEM) and numerical simulation. The results show that the CuO additive significantly enhances the fracture toughness of the Ag-SnO2 composite. The initiation and propagation of secondary cracks near the primary crack tip are effectively inhibited, and large dimples are formed around SnO2 particles. The improvement in the mechanical properties is attributed to the stress concentration relief in the Ag matrix and enhanced interfacial strength. Interface debonding at the sharp corners of the SnO2 particles initiates the formation of cracks in the Ag-SnO2 composite without CuO. The initiated cracks propagate through the high-stress concentration region at an angle of 45° to the loading direction, resulting in a matrix fracture. For the Ag-SnO2 composite with CuO nanoparticles, the propagation rate of the primary cracks reduces significantly, and microcracks are primarily induced near clustered SnO2 particles. Moreover, the damage initiation shifts from the SnO2/Ag interface to the Ag metal matrix with reduced SnO2 particle aggregation in the Ag-SnO2(CuO) composite.

Biomechanical comparison of the undercut thread design versus conventional buttress thread for the lag screw of the dynamic hip screw system.

Objective: To compare the fixation stability of the lag screw with a undercut thread design for the dynamic hip screw (DHS) system versus the lag screw with the conventional buttress thread. Methods: The lag screws with the undercut thread (a flat crest feature, a tip-facing undercut feature) and buttress thread were both manufactured. Fixation stability was investigated using cyclic compressive biomechanical testing on custom osteoporotic femoral head sawbone. The forces required for the same vertical displacement in the two types of lag screw were collected to evaluate the resistance to migration. Varus angle was measured on X-ray images to assess the ability in preventing varus collapse. Finite element analysis (FEA) was performed to analyze the stress and strain distribution at the bone-screw interface of the two types of lag screws. Results: The biomechanical test demonstrated that the force required to achieve the same vertical displacement of the lag screw with the undercut thread was significantly larger than the lag screw with conventional buttress thread (p < 0.05). The average varus angles generated by the undercut and buttress threads were 3.38 ± 0.51° and 5.76 ± 0.38°, respectively (p < 0.05). The FEA revealed that the region of high-stress concentration in the bone surrounding the undercut thread was smaller than that surrounding the buttress thread. Conclusion: The proposed DHS system lag screw with the undercut thread had higher migration resistance and superior fixation stability than the lag screw with the conventional buttress thread.

Biomechanical comparison between unilateral and bilateral percutaneous vertebroplasty for osteoporotic vertebral compression fractures: A finite element analysis.

Background and objective: The osteoporotic vertebral compression fracture (OVCF) has an incidence of 7.8/1000 person-years at 55–65 years. At 75 years or older, the incidence increases to 19.6/1000 person-years in females and 5.2–9.3/1000 person-years in males. To solve this problem, percutaneous vertebroplasty (PVP) was developed in recent years and has been widely used in clinical practice to treat OVCF. Are the clinical effects of unilateral percutaneous vertebroplasty (UPVP) and bilateral percutaneous vertebroplasty (BPVP) the same? The purpose of this study was to compare biomechanical differences between UPVP and BPVP using finite element analysis. Materials and methods: The heterogeneous assignment finite element (FE) model of T11-L1 was constructed and validated. A compression fracture of the vertebral body was performed at T12. UPVP and BPVP were simulated by the difference in the distribution of bone cement in T12. Stress distributions and maximum von Mises stresses of vertebrae and intervertebral discs were compared. The rate of change of maximum displacement between UPVP and BPVP was evaluated. Results: There were no obvious high-stress concentration regions on the anterior and middle columns of the T12 vertebral body in BPVP. Compared with UPVP, the maximum stress on T11 in BPVP was lower under left/right lateral bending, and the maximum stress on L1 was lower under all loading conditions. For the T12-L1 intervertebral disc, the maximum stress of BPVP was less than that of UPVP. The maximum displacement of T12 after BPVP was less than that after UPVP under the six loading conditions. Conclusion: BPVP could balance the stress of the vertebral body, reduce the maximum stress of the intervertebral disc, and offer advantages in terms of stability compared with UPVP. In summary, BPVP could reduce the incidence of postoperative complications and provide promising clinical effects for patients.

The Modeling of the Fracture of Three-Phase Ceramic Composite

In the present study, elastic and strength properties of three-phase Al2O3–ZrB2–SiC composite are investigated based on numerical modeling. Representative volume element (RVE) consisting of Al2O3 matrix, pores, and ZrB2 and SiC inclusions is built based on the experimental data. The uniaxial tension loading of the RVE model under plane strain conditions is considered. The relations of an isotropic elastic-plastic medium with the Drucker–Prager yield criterion are used as constitutive equations. The determination of the effective mechanical properties of the composite is based on the analysis of numerical averaged stress-strain curves. The simulation results demonstrate that the cracks nucleate in the regions of high stress concentration caused by the pore shape. The alumina matrix fractures due to the criterion based on the tensile pressure, while the fracture of inclusions occurs when the criterion based on the accumulated inelastic strain is fulfilled. The influence of the fraction of SiC inclusions on the effective elastic properties of the composite material was studied. It was shown that the elastic moduli weakly depend on the increase of SiC volume fraction in the considered range from 0 % to 34 %.

Structure-mechanical property relations of nanoporous two-dimensional gallium selenide

We apply molecular dynamics simulations to investigate the mechanical properties and atomistic deformation mechanisms of nanoporous gallium selenide (NPGS) nanosheets under uniaxial tension. The NPGS membranes structure–mechanical property correlation is investigated, especially the influences of temperature, neck width, pore shape, relative density, pore size, and strain rate. This work analyses the structural progression, initiation, fracture, brittle failure, Young’s modulus, ultimate strength, fracture strain, material toughness, and critical energy release rate. In most tensile cases, crack initiates at high-stress concentration regions such as pore edges or pore corners. The crack propagates in the perpendicular with tension direction and especially prefers to spread in the zigzag directions of membranes. We also find that the increasing temperature improves the atom kinetic energy, accelerating the fracture process and significantly reducing the material mechanical properties. The relative density is a particular essential parameter to determine material mechanical properties. Likewise, the size effect of neck width indicates both material characteristics, including “smaller is tougher” and “smaller is stronger”. Pore shape, notably diamond-pore, influences the stress distribution and stress absorption due to different tensile neck widths, leading to different mechanical responses, especially the material toughness. However, some material mechanical parameters were not much affected by some symmetrical pore shapes and strain rates. Remarkably, the stress distribution in the loading direction notably decreases the material mechanical performance. We also estimate the function between material mechanical properties and relative density or neck width as scaling laws to predict the mechanical properties of the NPGS nanosheets. The study results in an additional emphasis on mechanical behaviors and potentially expedites the promising applications of NPGS membranes.

Hydrodynamic analysis of an underwater glider wing using ANSYS fluent as an investigation tool

The analysis of the hydrodynamic behavior of the modified trailing edge of an underwater glider wing was conducted using ANSYS Fluent 18.1. The procedure was carried out using the computational fluid dynamics (CFD) approach. A standard four digits NACA0016 aerofoil profile was selected while the geometry points were extracted from NACA online aerofoil generator using Solidworks, which enabled the creation of the 3D wing profile. Since the focus of the study is more toward hydrodynamic behavior or the influence of the modified round trailing edge as opposed to the normal sharp trailing edge, coefficient of lift (CL), coefficient of drag (Cd), coefficient of pressure (Cp) and the drag polar (Cd/CL) are very crucial parameters and have an influence on the accuracy of the results. The results showed lift and drag coefficient are a function of the angle of attack (AOA) and free stream velocities. The investigation showed the optimal design point of the AOA of 12° at the corresponding speed of 0.26 m/s. The critical AOA matched with the optimal design point of 12°. The results also showed that Cp is higher closer to the fuselage and therefore explains why more structural rigidity must be provided in this region of high stress concentration. The drag and lift curve corresponded to the typical wing characteristics of the published experiment data regardless of the operating conditions.

Method of Evaluating Residual Stresses in the Product Material

The method of evaluating the level of residual surface stresses in the products without the loss of their integrity at elastoplastic strains and under static and cyclic loading by scattering of hardness characteristics is proposed. Residual surface stress levels are assessed not by absolute hardness values but by the state of material structure. Its homogeneity coefficient in the Weibull distribution, characterizing the scattering of large-scale hardness data, was taken as a calculated structure damage parameter and evaluated by the LM-hardness method based on direct multiple independent hardness measurements. The estimation of residual stresses is built upon the correlation relation between the material structure damage and residual stresses. By comparing the measured parameters of structure homogeneity, charactering their damage level in the region of residual stresses, with the structure parameter in the region free from them, their level is determined. In the absence of such a region, residual stresses are evaluated by comparing the homogeneity parameter of the product element in their region with that of a reference sample made of the same material and subject to the same operating loads as the examined product. The product quality can be estimated by the regions of high residual stress concentrations, comparing the parameters obtained in its different characteristic sections. Correlation relations, determining the values of residual stresses, are found from preliminary experimental tests of the material specimens by constructing the structural parameter – stress diagram at a preset loading step. The structure parameter is measured by scattering its large-scale hardness measurements.

Micromechanical damage behavior of fiber-reinforced composites under transverse loading including fiber-matrix debonding and matrix cracks

This paper examines the micromechanical damage behavior of carbon-epoxy composite using representative volume elements (RVEs). An algorithm is developed to generate random distributions of fibers in the RVE, and it is possible to create a fiber distribution with high fiber volume fractions. Fiber-matrix debonding and matrix crack are considered as the dominant damage modes. The fiber material is considered linear elastic and Drucker–Prager’s plastic criterion coupled with progressive damage behavior is assumed for matrix material. Moreover, cohesive elements are considered to model fiber-matrix debonding. The effects of different parameters such as fiber volume fraction, random fiber distribution, normal radii distribution, various cohesive parameters, and minimum fiber neighboring spacing on the overall damage behavior of the RVE, mostly the regime beyond the peak stress, are described in detail. It is concluded that due to the high-stress concentration regions, smaller elements are needed to analyze the high fiber volume fractions RVEs accurately. The peak stress and the corresponding strain are insensitive to microstructural randomness. Furthermore, the RVEs’ final failure strain is highly dependent on different fiber arrangements layouts. Since the RVEs are under transverse strain, normal cohesive strength is the dominant cohesive zone parameter that has a significant role in the damage behavior of RVEs. It is shown that minimum fiber neighboring spacing affects the strain in which matrix crack initiates.

Variations in the distribution of local strain energy within different realizations of a representative volume element

Numerical simulations are used to study the variations in microscopic fields between different random realizations of representative volume elements (RVE) with the same macroscopic properties. We focus on the strain energy of the matrix in unidirectional fiber composites with Neo-Hookean components, considering linear and non-linear applied loading. The simulations show significant variations in the strain energy between different realizations of the RVEs, particularly for the regions of high strain and stress concentrations that often govern damage and failure initiation. Results show a strong dependence on the volume fraction, minimum fiber distance and RVE size, as well as poor correlation between the local and the global response, which is characterized using the homogenized stiffness. In the case of non-linear loading, the rearrangement of the microstructure results in even lower correlation with the macroscopic response, as well as very strong variations according to the loading direction. We also show very poor correlation between the response in the linear and non-linear regimes for the same RVE.

Case Studies of Rock Bursts in Tectonic Areas with Facies Change

Although tectonic areas with facies change (i.e., variation of coal seam thickness, coal seam dip angle, or coal quality) are one of the three major geological structures that induce rock bursts, case studies of rock bursts in these tectonic structures are rare. The main objective of this study is to illustrate this issue and provide case studies that may inspire future research. Based on several typical cases of rock bursts induced by tectonic areas with facies change, the conditions conducive for these bursts are introduced and investigated in detail. Subsequently, numerical simulation is performed, showing that stress concentration exists in regions with variable coal seam thicknesses or dip angle. When stoping or tunnelling approaches this region, the peak stress increases rapidly. Thus, the burst occurs via a mechanism involving the superposition of high in-situ stress from tectonic areas with facies change and abutment pressure from stoping or tunnelling, leading to high stress concentration. Strategies for mitigating rock bursts are also provided. Rock bursts induced by tectonic areas with facies change can be mitigated by avoiding regions of high tectonic stress concentration and reducing mining induced stress.

Shear-Strength Capacity Assessment of Corroded Reinforced Concrete Beam-Column Joints

AbstractBeam-column joints are regions of high inelastic stress concentration in reinforced concrete (RC) frames. Evidence of the vulnerability of the joints to damage during earthquakes is witness...

Influence of Fe content on the damage mechanism in A319 aluminum alloy: Tensile tests and digital image correlation

In order to study the role of Fe content on the damage mechanisms of Al–Si–Cu alloy on a microstructural level, a Digital Image Correlation (DIC) method has been developed and performed on two Al–Si–Cu alloys: a high-Fe alloy (0.1wt.% Fe) and a low-Fe alloy (0.8wt.% Fe). Tensile tests on flat specimens have been performed, and a Questar long distance microscope has been used for the in-situ observation during tensile tests. The field measurements allow to identify and track the development and localization of deformation, and the fracture surfaces of the tensile specimens are analyzed using Scanning Electron Microscopy and Energy-Dispersive X-ray spectrometry (SEM-EDX) to identify the damage mechanisms. The results show that crack initiation occurs through the fracture of hard inclusions, i.e. Si particles, iron-intermetallics and Al2Cu particles in the high stress concentration region. Cracks often propagate through the fracture of hard inclusions rather than by their decohesion from the matrix.

Investigation of PDC Cutter Interface Geometry Using 3D FEM Modelling

Polycrystalline Diamond Compact (PDC) cutters have been popularly used in recent times due to their resistance against mechanical and thermal wear. This paper was focused on interface geometries between the substrate and the diamond table. Various types of interfaces were designed, to investigate how different interface geometries influence distribution of stress and strain under shear loading. The interface geometries examined in this paper included castle interface, dent interface, honeycomb interface and chase interface. Parallel to the interface, shear loading was applied to the top of diamond table to mimic the shear loading component from the rock cutting. To apply the shear loading, two locations were considered for each of the geometries. These locations differed depending on the interface features. Stress and strain distribution and values across different interface geometries were analysed with the aid of 3D Finite Element Method (FEM). The numerical simulations indicated that stress and strain magnitudes and distribution patterns varied in relation to different geometries. Some substrates showed relatively lower plastic strain representing higher durability of the geometries. Concentration of stress and strain distribution showed the areas where one could expect weakness. It also implies that rotating the PDC cutter assemblies around their cylindrical axis helps avoiding fatigue of interface elements in regions of high stress concentration; and thus, preventing premature failure of interface elements.

Inversion of stress field evolution consisting of static and dynamic stresses by microseismic velocity tomography

In order to reveal the stress precursors of the “3.15” rockburst disaster that occurred in the No. 1 working face of Junde coal mine, the combined stress field inversion including static and dynamic stresses was conducted by using P-wave velocity tomography, and the static high-stress concentration regions were further designated. Simultaneously, the evolution of dynamic stress generated by seven periodical caving events of primary roof was analyzed, and the fracturing characteristics were described in detail. Ultimately, the stress precursors of the “3.15” rockburst for early warning were clearly revealed. The main conclusions are as follows: (1) the micro-fissures inside coal and rock mass produce the significant reflection and refraction on the propagation of microseismic (MS) waves, and thus P-wave overall characterizes with lower velocity and higher velocity gradient; (2) after the slightly fracturing of primary roof on March 9, 2013, the maximum stress concentration factor suddenly rises to 20. This sign can be viewed as an early warning precursor of rockburst; (3) until March 12, 2013, the large-scale micro-fractures begin to form inside primary roof, and thus the corresponding high velocity gradient regions are generated. This phenomenon can be regarded as an effective precursor of macroscopic fracturing of primary roof; and (4) before the “3.15″ rockburst, the scope of P-wave velocity gradient in the No. 1 working face does not change significantly. The above findings may put forward a certain reference for accurately warning the stress precursors of rockburst by P-wave velocity tomography.

EBSD characterization of shear band formation in aluminum armor alloys

The shear-compression behavior of four commercial aluminum armor alloys, 2139, 2519, 5083, and 7039, that exhibit enhanced resistance to high-strain-rate deformation, were evaluated using a Split Hopkinson Pressure Bar. Each of the alloys was found to exhibit a characteristic critical equivalent strain beyond which plastic collapse of the material occurred. Microstructural changes were systematically quantified as a function of equivalent strain using electron backscatter diffraction along with the effects of crystallographic orientation, secondary particles, and solid solution strengthening on the accumulation of localized strain within the microstructure. The onset of the plastic collapse was determined to correlate with an equivalent strain where nominally all of the grains within the microstructure exhibited characteristics associated with adiabatic shear band formation. The rapid decline of the flow stress during plastic collapse was found to be enhanced by grain fragmentation and refinement in regions of high stress concentrations. Results from this study suggest that improvements in the performance of these Al armor alloys may potentially be achieved through careful control of their processing, in particular with respect to their texturing and the dispersion of secondary particles in the microstructure.