Stress Distribution Research Articles

A novel hybrid boundary element for polygonal holes with rounded corners in two-dimensional anisotropic elastic solids

A novel hybrid boundary element is developed for polygonal holes in finite anisotropic elastic plates based on two different special fundamental solutions for holes. Since these special fundamental solutions satisfy traction-free condition along the hole's boundary, there is no mesh required on the boundary of polygonal holes. Various types of polygonal holes with rounded corners, such as triangles, rhombuses, ovals, pentagons, are considered by adding proper perturbation to an elliptical hole. The developed hybrid element is a mixture of two special boundary elements: one is based on the special fundamental solution derived through nonconformal mapping and the other is based on the solution derived through perturbation technique with conformal mapping. The special boundary element methods are combined through submodeling technique. First, the global model is solved using the perturbation solution. Then, using the displacements obtained from global model, an auxiliary submodel is set up and the results are evaluated with the nonconformal solution. The present method is compared and validated with conventional boundary element method and finite element method. The effect of hole curvature, material anisotropy, and loading condition on the stress distribution around the hole is presented.

Viscoelastic-adhesive modeling of hybrid adhesively bonded double-lap joints: analytical and numerical studies

ABSTRACT There are a limited number of studies examining the viscoelastic and viscoplastic behavior of adhesive joints. If there is more than one adhesive in the overlap region, the problem becomes more complex and viscoelastic modeling of the overlap region becomes difficult. There is no study in the literature that covers such a bonding (overlap) scheme and examines the viscoelastic behavior of the double lap joint (DLJ). In this study, the effect of viscoelasticity of polymeric adhesives on shear stress and strain distributions in the hybrid-adhesive layer of a DLJ is studied. Maxwell-Wiechert (MW) viscoelastic material model is used to define the viscoelastic behavior of the adhesives. Analytical and finite element (FE) results are compared for both mono- and hybrid-adhesive joints under the step load. Good matches are observed between the analytical and numerical results. Four different hybrid-adhesive joints with different combinations of the adherend thicknesses are investigated by considering only the analytical method. In order to investigate the effect of the loading type on the viscoelastic behavior, step and ramp loads were applied to the joint separately. It is observed that applying the ramp load to the hybrid-adhesive joints affects the shear stresses occurred at the ends of the overlap more than the mono-adhesive joints.

Stress-related discrete variable topology optimization with handling non-physical stress concentrations

The accuracy of stress calculation with a fixed mesh significantly affects the stress-based topology optimization, due to potential non-physical stress concentrations in voxel-based topology descriptions. This paper proposes a novel problem-independent machine learning enhanced high-precision stress calculation method (PIML-HPSCM) to address this challenge. As an immersed analysis method, PIML-HPSCM combines the high efficiency of fixed mesh with the accuracy of body-fitted mesh, without complex integration schemes of other immersed methods. PIML-HPSCM utilizes the extended multiscale finite element method to depict the material heterogeneity within high-resolution boundary elements. The accurate stress field can then be calculated conveniently by establishing stress evaluation matrices of high-resolution boundary elements. Moreover, the PIML is independent of problem settings and is applicable for various problems with the same governing equation type. Invoking the offline-trained neural network online can enhance stress calculation efficiency by 10–20 times. The stress-based discrete variable topology optimization, which naturally avoids singular stress phenomenon, is efficiently addressed by the sequential approximate integer programming method with PIML-HPSCM. Results from 2D and 3D examples demonstrate that the stresses calculated by PIML-HPSCM are consistent with those by body-fitted mesh, and optimized designs effectively eliminate stress concentrations of initial designs and have uniform stress distributions.

High aspect ratio cellulose nanofibrils with low crystallinity for strong and tough films

Cellulose nanofibril (CNF) films with both high strength and high toughness are attractive for applications in energy, packaging, and flexible electronics. However, simultaneously achieving these mechanical properties remains a significant challenge. Herein, a multiscale structural optimization strategy is proposed to prepare high aspect ratio CNFs with reduced crystallinity for strong and tough films. Carboxymethylation coupled with mild mechanical disintegration is employed to modulate the multiscale structure of CNFs. The as-prepared CNFs feature an aspect ratio of >800 and a crystallinity of <60 %. The film prepared using CNFs with a high aspect ratio (~1100) and reduced crystallinity (~54 %) exhibits a tensile strength of 229.9 ± 9.9 MPa and toughness of 22.2 ± 1.4 MJ/m3. The underlying mechanism for balancing these mechanical properties is unveiled. The high aspect ratio of the CNFs facilitates the transfer and distribution of local stress, thus endowing the corresponding film with high strength and toughness. Moreover, the low crystallinity of the CNFs permits the movement of the cellulose chains in the amorphous regions, thereby dissipating energy and finally increasing the film toughness. This work introduces an innovative and straightforward method for producing strong and tough CNF films, paving the way for their broader applications.

Research on the migration law of aggregate particles in the compaction process of asphalt mixture based on discrete element method

Asphalt mixture compaction is among the key technologies in asphalt pavement construction, but the effect of asphalt mixture mixing quality on mixture compaction performance is still unclear. This research aimed to develop an asphalt mixture compaction model by discrete element simulation and verify it by compaction degree. Asphalt mixture compaction process was simulated and the effect of asphalt mixture workability on the stress, migration law and void distribution properties of aggregate particles during compaction process was investigated. The obtained results showed that the developed asphalt mixture compaction model was reasonable and correct. The more uniform the asphalt mixture is mixed, the smaller the average force on the aggregates, the aggregate particle migration velocity, and the aggregate particle displacement during the compaction of the asphalt mixture. Under the same conditions, increasing the mixing temperature from 140℃ to 180℃ increased the average velocity of the aggregates in the asphalt mixture by 92 %. It also decreased the voids in the compacted mixture specimens. At the same time, under the action of edge effect, void distribution at the center of compacted specimen was small, void distribution around the specimen was high, and void distribution along specimen compaction force direction was also high.

Analysis of the effect of aggregate type on the dynamic behaviour of concrete

This paper focuses on how different aggregate types affect the dynamic response of concrete. While Split Hopkinson Pressure Bar (SHPB) is commonly used to assess dynamic behaviour through the dynamic increase factor (DIF), the specific influence of aggregate type, a major component of concrete, remains unclear. This influence is investigated using fast Fourier transform analysis of strain signals. Two different types of aggregates, sandstone and schist, with distinct geological origins and mineral compositions, are used to examine this effect. Energy analysis is performed to understand how aggregate type affects energy absorption. The fineness modulus of fractured specimens is also determined which allow the comparison of post-fracture grain sizes. A crucial link between aggregate type and dynamic response of concrete is observed. Stiffer aggregates lead to stiffer concrete, which influence the frequency of energy responsible for damage initiation. At lower strain rates, concrete with stiffer aggregates absorbs lower-frequency energy. However, as strain rate increases, the frequency of absorbed energy becomes more dependent on the extent of damage within the aggregates themselves. The type of aggregate also significantly affects the size distribution of the fractured material. To analyse the stress distribution under dynamic loading, numerical simulations are carried out. These simulations showed that the maximum stress in concrete is related to the stiffness of the aggregate.

Effect of pile driving induced ground vibrations and stress distribution to close settlements: a case study

The pile method, applied in the foundational operations of construction to enhance soil-bearing capacity, is utilized in locations with insufficient soil support. Its purpose is to reinforce the foundation and improve soil stability before constructing a structure. In this study, vibrations occurring during the application of Vibrex-type piles for foundation reinforcement in a construction project located in the Konak district of Izmir Province were measured at various distances from the measurement points. The study further explored the influence of pile application on soil stability, considering the geomechanical properties of the site’s soil structure. The analysis of the study’s graph indicates that stress and vibration velocity remains at optimal levels, suggesting favorable working conditions.

Experimental and numerical investigation on residual stress of 316L SS treated by different laser shock peening parameters

316 L stainless steel has excellent mechanical properties, but fracture occurs when working in some extreme environments for a long time. As one of the important surface treatment technologies, laser shock peening (LSP) can improve the mechanical properties by inducing compressive residual stress (CRS) within the material, and has been widely used in a variety of fields due to its outstanding capabilities. Since LSP produces significant CRS, the influence of different laser parameters on the residual stress distribution of 316 L stainless steel was studied by numerical simulation, and verified by experiments. The results reveals that with the increase of laser energy, the residual stress in the surface and depth direction of the material increases firstly and then decreases gradually; three LSP cycles were performed on the same material, and it was found that the surface CRS within material had only a slight increase with three LSP cycles compared to the one with two LSP cycles, indicating that the CRS had reached the saturation; the effect of LSP on the residual stress of materials under different spot shapes was also studied, which indicates that the square spot can achieve better strengthening effect for multi-point LSP. Furthermore, the reasons for the improvement of mechanical properties were analyzed through microstructure observation.

Enhanced orthopedic implant design for transfemoral amputation incorporating a honeycomb structure technology

After lower limb amputation, the primary challenge is to facilitate the patient’s adoption of a prosthetic limb seamlessly, without encountering complications or discomfort. Elevated stress levels within the residual limb, experienced when wearing the socket and while standing or walking, contribute to patient discomfort. As an initial step in this study, we developed a finite element model of above-knee amputation. Additionally, we designed a prototype orthopedic implant composed of several parts, with the lower section featuring a honeycomb structure aimed at absorbing and diminishing stresses at the interface of the residual limb and prosthetic. In this study, finite element models with and without orthopedic implants were analyzed to assess the feasibility and impact of incorporating a honeycomb structure within the implants on stress distribution, particularly at the stump-prosthetic interface. Models with honeycomb-structured implants, at varying densities, showed a reduction in interface stress to approximately 2.15e-2 MPa and 2.01e-2 MPa, compared to 4.5e-2 MPa in model without honeycomb structure in the implant and 7.97e-2 MPa in models without any implants.

Parameters affecting performance of fully instrumented model testing of strip footings on geocell-reinforced soils

A thorough study was conducted to assess the performance of the strip footing reinforced with geocells in sand, focusing on understanding the enhancement effects and geocell reinforcement mechanisms. Critical factors such as geocell modulus, height, soil relative density and load eccentricity were examined through fully instrumented model tests. Measurements included surface displacement profiles, strains on the geocell layer, subsurface pressure distribution and other relevant parameters. Results revealed that the strip footing on geocell-reinforced sand beds exhibited better performance compared to those on unreinforced soil, characterized by increased load-carrying capacity and reduced settlements. Notably, stiffer geocells improved performance significantly, with a 40% higher modulus enhancing the bearing pressure by up to 25%, due to better confinement and anchorage effects. Conversely, geocells with a lower modulus demonstrated more effective vertical stress distribution. Furthermore, increased geocell height moderately enhanced footing performance by improving confinement, although wall buckling under eccentric loading limited major gains. Dense soils under centric loading exhibited up to a 20% better improvement in bearing pressure than loose soils due to higher strain mobilization within the geocell layer. These findings highlight the crucial role of geocell and soil properties, as well as loading conditions, in optimizing reinforcement effects for strip footings.

Impact of weak interlayer characteristics on the mechanical behavior and failure modes of cemented tailings backfill: A study on thickness, strength, and dip angle

The mechanical properties of cemented tailings backfill (CTB) are crucial for managing ground pressure and sustaining mine productivity. However, multiple fillings often result in weak interlayers (WI) within the backfill, compromising its stability. This study investigates the mechanical behavior and failure modes of composite cemented tailings backfill (CCTB) with different WI characteristics—thickness (ranging from 0 mm to 30 mm), strength (cement-tailings ratio from 1:4 to 1:20), and dip angle (from 0° to 9°)—after 28 days of curing through uniaxial compression tests. Regression and error analysis methods were employed to establish the relationships between WI physical characteristics and CCTB mechanical properties. Additionally, the inherent mechanisms of mechanical strength deterioration in CCTB containing WI were discussed based on experimental and simulation results of CCTB failure modes. The results found that the uniaxial compressive strength (UCS) and elastic modulus (E) of CTB decrease with lower cement content, while the peak strength strain (PSS) increases. Incorporating WIs weakens CCTB, reducing UCS and E, and increasing PSS. Regression analysis combined with error analysis revealed that WI thickness has an exponential relationship with UCS, E, and PSS. As WI thickness increases, reduction coefficients for UCS and E rise significantly, exacerbated by the WI’s diminished strength. The WI’s dip angle significantly affects CCTB’s mechanical behavior, disrupting stress distribution and load transfer, resulting in heightened stress concentrations and structural weakening. COMSOL simulations corroborated these experimental findings, providing deeper insights into stress distribution and failure mechanisms within the CCTB structure. These findings aim to provide a theoretical basis for mitigating the impact of WI characteristics on the stability and load-bearing capacity of CCTB in future mining operations.

Failure analysis of CFRP/Al single lap adhesive joint with enhancing porous metal foam insert

Cohesive failure is one of the main causes of adhesive bonding failure. The enhanced method and mechanism for adhesive signify a critical research issue for better adhesive joint design. This study proposes using a porous metal foam insert adhesive to enhance the carbon fiber reinforced polymer/aluminum single lap joint. In particular, stress distribution and failure locations of joints with and without insert were compared by simulation modeling. The insert of the Cu-foam, Fe-foam, and Ni-foam, compared to no insert, increased the shear strength of the bonded joint by 32.23 %, 36.66 %, and 66.82 %, respectively. Compared to no insert, the crack propagation of the joint with a metal foam insert was changed from the cross-section of the adhesive layer to the plane of the foam insert. The highest strength of the adhesive joint with the Ni-foam insert was further analyzed to determine fatigue behavior compared with pure adhesive joint under different stress levels. Compared to no insert, the fatigue life increased highly, and the crack path was prolonged.

Dislocation structures and residual stresses in duplex stainless steel fabricated by laser powder bed fusion with 430 and 316L powders

The duplex stainless steel is fabricated using laser powder bed fusion (LPBF), with raw materials prepared by mechanically mixing 430 and 316 L powders in a 1:1 mass ratio. The as-built alloys exhibit good overall mechanical properties, and theoretical strength calculations are performed based on the flow strength model. Uniquely, the distribution of dislocations, residual stresses, and strain accommodation mechanisms are investigated using electron backscattered diffraction and transmission electron microscopy. The results show that the microstructure of the as-built alloys is predominantly ferritic phase, with an austenitic phase content of approximately 4 %. The ultimate tensile strength is 938 ± 4 MPa and the elongation is 19 ± 0.58 %. The as-built alloys possess high dislocation densities, with the dislocation density in the ferritic phases being higher than in the austenitic phases. In particular, austenitic phases present barely any local misorientation and minimal rotations within grains, stacking faults are introduced to accommodate the solidification strains. However, ferritic phases exhibit a high dislocations density, with dislocations present on the (101), (011‾) and (211) planes, accommodating solidification strains and cooling stresses through elastoplastic deformation, and building up geometrically necessary dislocations.

Mechanism clarification and mitigation measures of radial deformation induced by girth welding of thin-walled pipes

Girth welding is extensively utilized in connecting pipeline structures. Excessive welding deformation may result in a decrease in ultimate bearing capacity and fatigue life. This research explores the characteristics and underlying mechanics of radial deformation in thin-walled girth welded pipes and proposes mitigation measures. Initially, several 304 stainless steel pipes were joined utilizing four distinct welding procedures. Welding deformation and residual stress distribution were measured using a 3D coordinate measuring machine (CMM) and the Cos α X-ray diffraction (XRD) method, respectively. Subsequently, numerical models were developed to simulate the welding process and verify the accuracy of the fusion zone, residual stress field, and radial deformation in the models. The mechanism of radial deformation was further elucidated based on the inherent strain method. The results show that the direction of radial deformation relies substantially on the hoop plastic strain. Hoop tensile plastic strain corresponds to radial outward deformation, while hoop shrinkage plastic strain corresponds to radial inward deformation. In addition, the influence of axial constraint on the formation process and results of hoop plastic strain, as well as the effect of heating zone width on radial deformation, was studied. Through simulation outcomes, the research suggests employing a regulated heat source method to mitigate radial deformation, which could potentially reduce deformation by 92.8%, offering considerable advantages in deformation mitigation and welding efficiency augmentation.

Combined non-destructive evaluation of the damage precursors in fused silica optics

Combined non-destructive evaluation methods for fused silica’s damage precursors including UV photothermal weak absorption, ultrafast fluorescence, steady-state fluorescence, Raman spectroscopy, and stress distribution, are proposed to explain the damage mechanism from multiple perspectives. The correlation between each non-destructive characterization method and damage behaviors is simultaneously verified, in general, the damage threshold test of R on 1. The results have shown that regions with high photothermal absorption are accompanied by low damage thresholds, because the photothermal conversion process is associated with laser-induced damage. The damage threshold is also lower at locations of bright ultrafast fluorescence signals with a lifetime ranging from 1.2∼3 ns, as ultrafast fluorescence is associated with high densities of defects. A complementary relationship between the distribution of ultrafast fluorescence and the distribution of photothermal absorption signals is constructed. This indicates that the steady-state fluorescence cannot accurately evaluate the precursor’s damage performance. Furthermore, Raman spectroscopy is utilized to identify the structural changes in bond lengths and angles, as well as locations of damages coinciding with stress distribution.

Investigating the influence of graphene coating thickness on Al0.3CoCrFeNi high-entropy alloy using molecular dynamics simulation

Graphene was proven to be an excellent surface-strengthening material. However, there needs to be more literature explaining its strengthening mechanism at the atomic level. This study systematically investigated the surface strengthening mechanism of graphene coating on the Al0.3CoCrFeNi high-entropy alloy (HEA) and the influence of loading-unloading cycles on the formation of internal defects in the material through molecular dynamics (MD) simulations at the atomic level. Research results show that the internal stress concentration in HEA without graphene coating leads to a more considerable residual depth after unloading. With the addition of a graphene coating, the material's stress area increases, effectively alleviating stress concentration and reducing residual depth. Furthermore, the lengths of Lomer-Cottrell dislocation locks and Hirth dislocation locks inside the material increase, enhancing the material's deformation resistance. The more layers of graphene, the larger the stress distribution area and the greater the hardness. Under the same indentation force, the number of HCP structures and amorphous structures inside the material is inversely proportional to the thickness of the graphene layers. In addition, after multiple loading and unloading cycles, the hardness of HEA/GP materials basically remains unchanged, while internal defects increase and residual depth increases.

A Systematic Review of Modeling and Simulation for Precision Diamond Wire Sawing of Monocrystalline Silicon.

Precision processing of monocrystalline silicon presents significant challenges due to its unique crystal structure and chemical properties. Effective modeling and simulation are essential for advancing the understanding of the manufacturing process, optimizing design, and refining production parameters to enhance product quality and performance. This review provides a comprehensive analysis of the modeling and simulation techniques applied in the precision machining of monocrystalline silicon using diamond wire sawing. Firstly, the principles of mathematical analytical model, molecular dynamics, and finite element methods as they relate to monocrystalline silicon processing are outlined. Subsequently, the review explores how mathematical analytical models address force-related issues in this context. Molecular dynamics simulations provide valuable insights into atomic-scale processes, including subsurface damage and stress distribution. The finite element method is utilized to investigate temperature variations and abrasive wear during wire cutting. Furthermore, similarities, differences, and complementarities among these three modeling approaches are examined. Finally, future directions for applying these models to precision machining of monocrystalline silicon are discussed.

Mechanical response and failure mechanism of circular inclusion embedded in brittle materials under dynamic impact

Inclusions are prevalent in both natural and synthetic materials. Gaining a comprehensive understanding of their dynamic response and interaction with the surrounding matrix is essential in fundamental mechanics and engineering applications. This study aims to achieve such understanding through theoretical analysis, experimental investigations, and numerical simulations, focusing on the dynamic destruction of inclusions and the underlying mechanisms. Firstly, the circumferential, radial, and shear stresses around elastic heterogeneous inclusions were derived by the wave function expansion and Duhamel integration methods. Subsequently, a set of experiments on sandstone specimens containing three types of inclusions (plaster, epoxy resin, cement) were conducted utilizing the Split Hopkinson Pressure Bar (SHPB) system in conjunction with high-speed photography and Digital Image Correlation (DIC) techniques to obtain the surface deformation of inclusion specimens. Eventually, a series of Finite Element Method (FEM) numerical simulations adopted suitable materials were also carried out to investigate the fracture process of inclusion and matrix under dynamic impact. The results demonstrate that the stress distributions and fracture mode of matrix and inclusion are highly dependent on the physical and mechanical properties of the inclusions and the surrounding matrix, specifically, density ρ, elastic modulus E, Poisson's ratio v, and strength. With an increase in the E and v, there is a reduction in the concentration of circumferential stress, while the radial and shear stresses experience an increase. The experimental and numerical results corroborated the theoretical findings and indicated that the localized dynamic stress concentrations induced by wave scattering around the inclusions directly dominated both local and overall specimen failure. Due to the dissimilarities in elastic parameters and strength between the inclusion and the matrix, the stress state of the inclusion and the interface is not homogeneous. Under dynamic loading, the weaker inclusion experiences tensile cracking at both ends of the loading, and as the mechanical properties (ρ, E, v, and strength) of the inclusion rise, a transition from tensile- hybrid-shear failure occurs within the inclusion. The findings of this study help us understand the dynamic failure mechanisms of dissimilar inclusions in brittle material.

3D study of dyke-induced asymmetric graben: The 1971 Mt. Etna (Italy) case by structural data and numerical modelling

In this work, we have integrated field data and numerical models to characterise a unique dyke-induced graben system, exposed both in section and plan view, with an unexpected asymmetric fault geometry. This volcanotectonic feature is related to the 1971 eruption of Mt. Etna (southern Italy) and is located near the northern wall of the Valle del Bove, a huge depression carved into the eastern flank of the edifice. A new structural map and quantitative data were obtained from the analysis of aerial stereophotos collected before the onset of the 1971 eruption and after, high-resolution drone-derived models and field surveys carried out in the summer of 2022. In plan view, the graben is 2-km-long and its width ranges 27–143 m from the bottom to the upper part of the section view, with about 82 m of difference in elevation from top to bottom. Graben faults clearly show an asymmetric setting in terms of attitude, with one fault that dips 70° to the south, and the other one that dips 50° to the north. Vertical offset values are greater at higher elevations. We also ran a set of numerical models, aimed at investigating the distribution and orientation of stresses around the inferred dyke tip and in the host rock. The comparison between field data and numerical models suggests a key role of the inclined topography, as shown in section view, in determining the orientation of dyke-induced σ1 and σ3 in the host rock. This, in turn, controls the geometry of the graben faults, resulting in the observed asymmetric setting. Additionally, dyke-induced stress concentrations and vertical offset values support the hypothesis of a downward propagation of the graben faults, from the surface down to the dyke tip.

Steel-concrete-steel sandwich composite cable-pylon anchorage of cable-stayed bridges: horizontal bearing capacity

Steel-concrete-steel sandwich composite cable-pylon is preliminarily applied to bridge engineering due to its excellent mechanical properties and high degree of assembly. However, the stress behavior of the steel-concrete-steel sandwich composite cable-pylon anchorage zone under the strong horizontal component force of the cable force is relatively unknown. In this paper, a 1:4 scaled-down steel-concrete-steel sandwich composite cable-pylon model test under horizontal force is designed and carried out to investigate the strain distribution in inner and outer steel plates, and the horizontal displacements in the pylon wall, and the crack development in the concrete pylon wall. Subsequently, a simplified analysis method is proposed for facilitating the calculation of the load distribution ratios of both steel plates and concrete, and the pylon wall stresses are obtained based on the force method. Furthermore, aiming to improve the problem of excessive stress in the anchorage region of the outer steel plate, the effects of various parameters on the mechanical properties of the anchorage region are investigated through parametric analysis, and the investigated parameters include the diameter of the reinforcement bar, area of the bearing plate, concrete strength, the thicknesses of the steel plate and perfobond ribs. The results indicate that increasing the diameter of the reinforcement bar is insignificant in improving the stress distribution and value of the outer steel plate, and appropriately increasing the bearing area, concrete strength, thicknesses of the steel plate and perfobond ribs can reduce the stress peak value of the outer steel plate, among which changing the thickness of the steel plate and bearing area is the most significant effect. The research results can provide experimental data and theoretical support for the design and optimization of steel-concrete-steel sandwich composite cable-pylon anchorage zones.