Stress Distribution Research Articles

A two-step dynamic FEM-FELA approach for seismic slope stability assessment

AbstractThe determination of the factor of safety (FoS) of slopes during seismic excitation can be complex if the relevant effects of pore water pressure accumulation, nonlinear material response and variable shear strength are duly accounted for. A rational two-step approach to tackle this task based on a hydro-mechanically coupled dynamic simulation and finite element limit analyses is henceforth introduced. To ensure accurate transfer of the hydro-mechanical soil state, a mapping concept is presented, accounting for spatial distributions of stresses, excess pore water pressures, inertial forces and shear strength. The proposed approach is compared to limit equilibrium method (LEM) for the case of a large-scale water-saturated open cast mine slope subjected to seismic loading. In comparison with LEM, the new approach to assess seismic slope stability proves to be simpler in its implementation and straightforward, which could be an important asset for practitioners.

Vehicle Collision Analysis of the Reinforced Concrete Barriers Installed on Bridges Using Node-Independent Model

This paper focuses on improving vehicle collision simulations using finite element analysis (FEA) to examine interactions between reinforced concrete barriers and bridge decks. Three scenarios are explored: treating the barrier as a rigid body, analyzing reinforcement with a fixed base, and including the bridge deck’s cantilever portion beneath the barrier. Except for the rigid body model, a node-independent approach models the complex interactions between reinforcement and concrete in barriers on the bridge deck. This study evaluates barrier strength, occupant risk, and post-collision vehicle safety. Strength is assessed by examining stress in reinforcement and concrete, while occupant risk is measured using Theoretical Head Impact Velocity (THIV) and Post-impact Head Deceleration (PHD). Vehicle trajectory during collisions is also analyzed for stability. The results show significant differences in stress distribution and failure patterns when the bridge deck is considered compared to scenarios without it. Occupant risk evaluations suggest more flexible responses when the bridge deck is included. However, vehicle trajectory post-collision showed no significant differences across scenarios. These findings indicate that modeling efficiency varies based on evaluation criteria, suggesting a more realistic and effective approach for assessing barriers on bridges.

Residual Stress Homogenization of Hybrid Implants

Objectives: Hybrid implants commonly exhibit decreased corrosion resistance and fatigue due to differences in compressive residual stresses between the smooth and rough surfaces. The main objective of this study was to investigate the influence of an annealing heat treatment to reduce the residual stresses in hybrid implants. Methodology: Commercially pure titanium (CpTi) bars were heat-treated at 800 °C and different annealing times. Optical microscopy was used to analyze the resulting grain growth kinetics. Diffractometry was used to measure residual stress after heat treatment, corrosion resistance by open circuit potential (EOCP), corrosion potentials (ECORR), and corrosion currents (ICORR) of heat-treated samples, as well as fatigue behavior by creep testing. The von Mises distribution and the resulting microstrains in heat-treated hybrid implants and in cortical and trabecular bone were assessed by finite element analysis. The results of treated hybrid implants were compared to those of untreated hybrid implants and hybrid implants with a rough surface (shot-blasted). Results: The proposed heat treatment (800 °C for 30 min, followed by quenching in water at 20 °C) could successfully homogenize the residual stress difference between the two surfaces of the hybrid implant (−20.2 MPa). It provides better fatigue behavior and corrosion resistance (p ˂ 0.05, ANOVA). Stress distribution was significantly improved in the trabecular bone. Heat-treated hybrid implants performed worse than implants with a rough surface. Clinical significance: Annealing heat treatment can be used to improve the mechanical properties and corrosion resistance of hybrid surface implants by homogenizing residual stresses.

Biomechanical effects of FNS on femoral neck fractures based on different reduction quality: finite element analysis.

The femoral neck system (FNS) has been extensively studied and applied for the treatment of young patients with femoral neck fractures. The purpose of this study was to explore the biomechanical impact variations in reduction qualities on femoral neck fractures, considering factors such as tip-apex distance, the positioning of the bolt in the cortical corridor of the femoral neck, and bone mineral density. A randomly selected volunteer was recruited, whose clinical data on the femur were collected to establish finite element models for positive reduction, anatomical reduction, and negative reduction respectively. Based on the constructed models, different scenarios were established by varying the tip-apex distance, bone mineral density, and positioning of the bolt in the cortical corridor of the femoral neck. Under a vertical load of 2100N, the displacement and Von Mises stress (VMS) distribution of each group of models were evaluated through simulation testing. Under a load of 2100N, the maximum VMS values of the femoral neck system and femoral head was recorded during negative reduction, 968.85MPa and 80.09MPa respectively. In addition, factors influencing the negative reduction of FNS and the femoral head were identified to be the tip-apex distance > 10mm, the presence of osteoporosis, and the bolt positioned in the lower-middle to the third part of the cortical corridor of the femoral neck. The displacement and stress of negative reduction were greater than those of positive reduction and anatomical reduction when the tip-apex distance > 10mm, and the bolt was situated in the lower-middle to the third part of the cortical corridor of the femoral neck, and in the presence of osteoporosis. This means that we recommend positive repositioning over negative repositioning when anatomical repositioning is not clinically feasible.

A comparative evaluation of the displacement and stress distribution of Kilroy spring, ballista spring and temporary anchorage devices during traction of palatally impacted canine using a 3 dimensional finite element analysis

The above study comprises a comparative evaluation of the displacement and stress distribution of Kilroy spring, Ballista spring and Temporary anchorage devices during traction of palatally impacted canine using a 3 dimensional finite element analysis. Palatally impacted canine is a common phenomenon occuring in around 8% of individuals. The Finite Element Analysis/Finite Element method (FEA/FEM) is the most intricate and dependable study that significantly revolutionized the world of dentistry and biomechanical research. Stresses and displacements can be precisely located using this type of numerical analysis. The orthodontist can better comprehend the physiological reactions that take place within the dentoalveolar complex because of the quantitative information it gives them. A Cone Beam Computed Tomography (CBCT)scan of the maxilla was obtained from a patient who reported to the Department of Orthodontics and Dentofacial Orthopaedics after he satisfied the inclusion and exclusion criterion. Finite element 3-D models of Kilroy spring, Ballista spring, Cantilever spring, miniscrew, lingual button, 0.022-inch-slot brackets, 0.019x0.025-inch SS archwire, stainless steel bands with molar tubes were constructed using a three-dimensional computer-aided design program (SolidWorks 2017; Solid Works K.K., Tokyo, Japan). All these components were imported and individually assembled in the ANSYS Software (Version 2021 R2, ANSYS, Canonsburg, Pa) and stress analysis was carried out. On the basis of this study following conclusion were drawn: The maximum amount of impacted canine displacement, with initial simulation, wasobserved with Kilroy spring followed by Ballista spring and miniscrew assisted Cantilever spring and the maximum amount of displacement of adjacent teeth i.e. lateral incisor and 1st premolar is observed with Ballista spring followed by kilroy spring and miniscrew assisted Cantilever spring. Furthurmore stress concentration on the canine is highest in case of ballista spring followed by Kilroy spring and miniscrew assisted Cantilever spring. Over all, miniscrew assisted Cantilever spring can be an efficient treatment option for traction of a palatally impacted canine.

Stress-strain state of implant-supported restorations in tooth replacement

Background: Dental implant therapy may be associated with breakage and deformation of implant-supported restorations, necessitating an assessment of their stress-strain state when applying a load. Aim: To compare the stress-strain state of implants with their respective fixed restorations in tooth replacement. Materials and Methods: A 3D mathematical model of the posterior mandible with three missing teeth was used to assess the stress-strain state for the following dental restoration options: three implant-supported crowns; a two-implant-supported bridge; or a bridge supported by tooth and implant. A 150 N load was applied to the central part of a restoration in both vertical and oblique directions to compare maximum stress values and their distribution. Results: Oblique load was found to have a negative impact on stress intensity and distribution (471.7 MPa vs 90.7 MPa with vertical load for three implants). The most heavily loaded parts of restorations were identified: the border of the crown and the implant connection zone. A homogeneous stress distribution from a bridge to the two supporting implants was observed, along with a decrease in stress when using a bridge rather than three implant-supported crowns (160.0 MPa vs 16.1 MPa). In contrast, the load on the supporting implant increased when a bridge supported by tooth and implant was used (1,053.5 MPa with oblique load). Conclusion: Compared to three implants replacing three missing teeth, a two-implant-supported bridge decreases stress on the implants and their respective restoration. Replacing one supporting implant with a tooth increases stress on the implant to the ultimate strength of titanium alloy in the abutment.

Mixed FEM implementation of three-point bending of the beam with an edge crack within strain gradient elasticity theory

AbstractThis paper considers the problem of symmetrical three-point bending of a prismatic beam with an edge crack. The solution is obtained by the mixed finite element method within the simplified Toupin–Mindlin strain gradient elasticity theory. A mixed variational formulation of the boundary value problem for displacements–strains–stresses and their gradients is applied, simplifying the choice of approximating functions. The concept of energy balance is adopted to calculate the energy release rate with a virtual increase in crack length. The increment of the potential energy of an elastic body is determined by accounting for the strain and stress gradient contribution. Numerical calculations were performed using a quasi-uniform triangular mesh of the cross-type. The mesh refinement was applied in the vicinity of the crack tip, at the concentrated support, and the point of application of the transverse force, and uniform mesh partitioning was utilized in the rest of the beam. The fine-mesh analysis was carried out on the successively condensed meshes in the stress concentration domain for different values of the length scale parameter. The crack opening displacements and the distribution of strains and Cauchy stresses for various values of the length scale parameter are presented. An increase in this parameter increases the stiffness of the crack, which leads to a decrease in the crack opening displacements and a smooth closure of its faces at the crack tip. In addition, accounting for the scale parameter reduces the calculated values of strains and stresses near the crack tip. Based on the energy balance criterion, local fracture parameters such as the release rate of elastic energy at the crack tip and the stress intensity factor are determined for different values of the mesh step. The numerical calculations indicate the convergence of the obtained approximations. The main feature of solutions, which includes the strain gradient contribution, is the decrease in the values of the calculated parameters associated with the fracture energy compared to the classical elasticity theory.

Influence of micro-milling machining parameters on residual stresses in alumina bioceramics-a three-dimensional finite element simulation study.

The formation and distribution of residual stress during the micro-milling process significantly affect the crack resistance and service life of alumina bioceramics. This study aims to optimize the surface residual stress distribution by adjusting machining parameters, thereby improving the machining quality of alumina ceramics. A three-dimensional finite element model of alumina bioceramics was developed, and numerical simulations were conducted to analyze the effects of feed per tooth, cutting depth, and spindle speed on temperature and residual stress. The study further explores the patterns of residual stress variation. The results show that both surface temperature and residual tensile stress exhibit systematic trends with parameter changes. Specifically, surface residual tensile stress increases with cutting depth initially but decreases sharply once the cutting depth exceeds 25 μm. Residual tensile stress increases with spindle speed, reaching its peak at 21,000 r/min before stabilizing. Additionally, the residual tensile stress rises with feed per tooth at first but gradually declines when the value exceeds 25 μm/z. This research reveals the mechanisms by which micro-milling parameters influence surface temperature and residual stress in alumina bioceramics, providing theoretical guidance for optimizing micro-milling processes. The findings can also be extended to the micro-milling of other hard-to-machine materials, offering broad engineering application potential.

Effect of Laser Power on Weld Formability and Residual Stress of Unequal Thickness 410 Ferritic Stainless Steel/RCL540 Low-Carbon Alloy Steel

In this paper, the butt joint of unequal thickness 410 ferritic stainless steel and RCL540 low-carbon alloy steel sheets are realized by laser welding. The effects of different laser powers on weld formability, mechanical properties, and residual stress in the welding process are investigated. It is observed that with increasing laser power, the heat accumulates at the bottom of the molten pool and weld metal, causing the ratios of upper and lower melt widths to decrease. The tensile test results show that all specimens fractured in the weak zone of the base metal on the stainless steel side at 10 mm from the weld seam. The residual stress distributions of the specimens are calculated using ABAQUS 2022 software and compared with the measurements of the blind-hole method. It is found that the stainless steel side produces tensile stresses, with the power increase offset by compressive stresses in the base metal. When the laser power is 1200 W, the welded joint has the best weld formability and mechanical properties and the least residual stress. The upper and lower melt width ratio is 1.17, the maximum microhardness of the weld metal is 374.7 HV, the maximum test force and tensile strength are 5617.5 N and 468.12 MPa, respectively, and the minimum values of the transverse and longitudinal stresses are −45.8 MPa and −106.4 MPa, respectively.

ANGLED DENTAL IMPLANTS: IMPLICATIONS FOR CLINICAL PRACTICE AND BIOMECHANICAL CONSIDERATIONS

Angled dental implants have emerged as an effective solution in clinical settings where the placement of straight implants is constrained by unfavorable bone positions or the presence of adjacent anatomical structures. The angulation of implants significantly influences stress distribution around the implant, impacting its stability and longevity. Research highlights that the direction of applied loads is critical, as angled implants can generate greater bending and shear forces compared to straight implants, potentially leading to stress concentrations in surrounding bone. Finite element analysis (FEA) is commonly used to model these conditions, offering insights into stress zones and predicting potential failure areas. Bone quality plays a vital role in how implants respond to applied forces, with denser bones effectively dissipating forces while more porous bones are at higher risk of resorption and integration failure. Studies indicate that excessive stresses on angled implants can lead to bone resorption, compromising long-term stability. Therefore, careful consideration of implant angulation, connection type, bone quality, and thorough surgical planning is essential. Recent studies, including those investigating the effects of implant design and bone density on stress distribution, have demonstrated that varying implant threads and angulated abutments affect the stresses experienced by surrounding bone and implants. The findings emphasize the need for appropriate implant selection and a detailed assessment of bone anatomy and patient-specific clinical conditions. By incorporating advanced technologies like FEA, clinicians can enhance their understanding of biomechanical interactions, ultimately leading to improved clinical outcomes and patient satisfaction. Continuous education and the implementation of best practices in dentistry remain vital for the successful application of angled dental implants.

A new biomechanical approach to cranial suture function: the role of contact elements in linear and nonlinear models

Abstract Understanding cranial sutures and how they relieve and dissipate stress is essential to assess their role in cranial biomechanics and to develop highly accurate predictive models. This involves examining how ontogeny affects cranial sutures, as well as their morphology and function, and how these changes through time may impact essential biomechanical loadings such as chewing or direct biting. In this work, we study the cranial sutures of Crocodylus niloticus in detail using contact elements under finite element analysis. Contact elements permit the creation of a physical relationship between two bones that are in contact and even the configuration of these relationships, for example, in terms of movement or flexibility. The definition of bone contacts may require linear and/or nonlinear computational solutions to attain higher accuracy. Herein, skull geometry is tested to determine how bones may be altered by different types of contacts under various conditions. As predicted, the absence of sutures or cranial kinesis leads to a reduction in stress distribution across the skull, whereas sutures and cranial kinesis help the skull relieve stress and prevent certain bones from sustaining high stress levels. The type of contact used in individual sutures has a significant effect on model outcomes. Additionally, feeding behaviors significantly impact cranial biomechanics, reflecting the influence of other variables that may be applied to the models. As highlighted by the results, in order to obtain accurate results when analyzing fossil taxa, the nature of the cranial sutures should be taken into account. Therefore, developing predictive models based on living taxa is invaluable, because it facilitates the study of extinct taxa for which there is a lack of information on the fibrous joints due to poor or no preservation in the fossil record.

Component‐section transverse‐pressure effect on internal damage and failure mode of post‐installed rebar

AbstractA post‐installed rebar (PIR) is commonly used to establish structural connections between new components and existing structures, such as structural member extensions or concrete layer overlays in the construction/strengthening/retrofitting of buildings or bridges. In joint connections, the anchored PIR system always bears a non‐negligible compression in the component section, which is derived from the loads and self‐weight and has a confinement effect on the anchorage zone. However, excessive pressure can result in the fracture of the adhesive component, thereby leading to brittle failure in the PIR system. Owing to the important role of the adhesive component in the PIR system, this study is focused on the internal damage to the PIR system, and the effect of transverse pressure on the failure modes is investigated. This study comprises an experimental investigation of the failures of a PIR system under transverse pressure and a description of the internal damages based on the test results. Finally, an elastic analysis was established to explain the internal cracking and investigate the stress distribution in the PIR system. The tests on 34 pull‐out specimens showed two typical failures for the PIR system under transverse pressure (adhesive–rebar [A–R] interface failure and adhesive fracture failure). The A–R interface failure resulted from the shearing failure in the adhesive component, while the adhesive fracture failure resulted from the propagation of longitudinal and transverse cracks. The elastic analysis indicated that cracking in the concrete and adhesive component was dominated by circumferential stress, and the rebar rib direction and adhesive component thickness had a significant influence on the stress distribution. Based on this, some suggestions for anchorage design were made.

Micro-Scale Fracture Characteristics of Emulsified Asphalt Cold Recycled Mixture Based on Discrete Element Method

Asphalt pavement often experiences structural failure due to repeated vehicle loading. The discrete element method (DEM) model was established based on the semicircle bending test (SCB) to investigate the fracture damage mechanism of emulsified asphalt cold recycled mixture (CRME) under loading. The micro-mechanical parameters of CRME were determined through a reliable validation process using the uniaxial compression static creep test. The microscopic fracture characteristics of CRME were investigated through the load-displacement curve, stress distribution, and force chain distribution. The fracture energy was used as the evaluation index to analyze the influence of prefabricated notch length and aggregate gradation on the fracture performance of CRME. The results indicate that the emulsified asphalt mortar-aggregate interface was the critical weak position of the mixture fracture; the failure of the tension chain was the main destructional form of the SCB test. The development of cracks affected the stress concentration phenomenon and stress concentration level of the mixture. Fine-grained mixture exhibited crack resistance. The number and length of cracks were affected by gradation. As the prefabricated notch length increased, the influence gradually diminished. The research results could provide theoretical and data support for the design of CRME.

Study of the residual stress distribution in SiCp/Al composites under thermal cycling conditions

In this study, a three-dimensional random representative volume element model was constructed using the finite element method combined with Python script to investigate the residual stress distribution in SiCp/Al composites with varying volume fractions, particle shapes, and particle size under thermal cycling conditions. The model has two different particle morphologies: spheres and irregular polygons. The results show that the irregular polygonal SiC particles exhibit higher residual stresses than spherical particles before and after thermal cycling due to their complex load transfer pathways and higher stress concentration at particle corners, which makes them more consistent with the characterization of SiCp/Al composites under practical application conditions. As the volume fraction of SiC particles increases, the particle spacing decreases, hindering the release of thermal stresses through plastic deformation. Notably, the relief rate of residual stress reached 53% in the 12 vol% SiCp/Al composites, with the stress decreasing from 698 MPa to 328 MPa after 50 thermal cycles. In contrast, the reduction rate for 18 vol% composites is only 13% after thermal cycling. Furthermore, compared to larger particles (7.3 µm, 8.9 µm), the smaller particles (4.3 µm, 5.9 µm) exhibit a more uniform stress distribution and lower thermal stresses before and after thermal cycling. Consequently, our work provides a significant theoretical basis for the design and application of SiCp/Al composites, especially for the application of materials under extreme temperature changes.

Steady-State Inverse-Temperature Crystallization Enabling Low Defect Perovskite Single Crystal and Efficient X-Ray Detectors.

Organic-inorganic halide perovskite single crystals (SCs) have shown great potential in radiation detection applications due to their large radiation stopping power and excellent carrier transport properties. The spatial-confined inverse-temperature crystallization (ITC) method has been widely adopted to obtain large-sized SCs. However, they usually face the problems of uneven stress distribution and high defect density due to the limited crystal growth space and varied growth rate with the increase in temperature, making it difficult to fabricate highly sensitive and stable radiation detectors. In this study, the steady-state inverse-temperature crystallization method (SS-ITC) is developed to regulate the growth process of SCs by controlling the growth speed precisely to achieve a constant rate of growth as the temperature increases. Compared with the conventional ITC-grown samples, the lattice spacing of SCs prepared by the SS-ITC method is reduced by 1.2% due to tensile stress relaxation, resulting in a lower defect density of 7.93×109cm-3 and a remarkable uniformity over a large area. As a result, the co-planar X-ray detectors based on these high-quality SCs exhibit a high sensitivity of 1.67×105 µC Gyair -1cm-2, representing the best performing MAPbBr3-based X-ray detectors reported to date.

Critical length parameter of HDPE and its use in fatigue lifetime predictions

The contribution describes the fatigue lifetime predictions of polyethylene notched specimens based on the theory of critical distance. The approach uses the line method, which averages the axial stress over the critical distance. The critical distance is determined from experimental data of Cracked Round Bar (CRB) specimens and specimens with a model notch. From these two sets of experimental fatigue data and corresponding axial stress distributions, the critical distance is determined. The critical distance depends on the number of cycles to failure and notch radius. For this reason, the critical distance is modified by the ratio of stress concentration factors and the modified distance is used for fatigue lifetime predictions of notched specimens with various notch radii. Using this approach significant savings in testing time can be achieved. CRB fatigue tests are commonly used tests for ranking PE pipe grades and are easily available. Adding the fatigue tests of notched specimens with a model notch, the critical parameter can be found, and fatigue lifetime predictions of various notches can be calculated.

A New Multi-Axial Functional Stress Analysis Assessing the Longevity of a Ti-6Al-4V Dental Implant Abutment Screw

This study investigates the impact of tightening torque (preload) and the friction coefficient on stress generation and fatigue resistance of a Ti-6Al-4V abutment screw with an internal hexagonal connection under dynamic multi-axial masticatory loads in high-cycle fatigue (HCF) conditions. A three-dimensional model of the implant–abutment assembly was simulated using ANSYS Workbench 16.2 computer aided engineering software with chewing forces ranging from 300 N to 1000 N, evaluated over 1.35 × 107 cycles, simulating 15 years of service. Results indicate that the healthy range of normal to maximal mastication forces (300–550 N) preserved the screw’s structural integrity, while higher loads (≥800 N) exceeded the Ti-6Al-4V alloy’s yield strength, indicating a risk of plastic deformation under extreme conditions. Stress peaked near the end of the occluding phase (206.5 ms), marking a critical temporal point for fatigue accumulation. Optimizing the friction coefficient (0.5 µ) and preload management improved stress distribution, minimized fatigue damage, and ensured joint stability. Masticatory forces up to 550 N were well within the abutment screw’s capacity to sustain extended service life and maintain its elastic behavior.

Inclusion of Muscle Forces Affects Finite Element Prediction of Compression Screw Pullout but Not Fatigue Failure in a Custom Pelvic Implant

Custom implants used for pelvic reconstruction in pelvic sarcoma surgery face a high complication rate due to mechanical failures of fixation screws. Consequently, patient-specific finite element (FE) models have been employed to analyze custom pelvic implant durability. However, muscle forces have often been omitted from FE studies of the post-operative pelvis with a custom implant, despite the lack of evidence that this omission has minimal impact on predicted bone, implant, and fixation screw stress distributions. This study investigated the influence of muscle forces on FE predictions of fixation screw pullout and fatigue failure in a custom pelvic implant. Specifically, FE analyses were conducted using a patient-specific FE model loaded with seven sets of personalized muscle and hip joint contact force loading conditions estimated using a personalized neuromusculoskeletal (NMS) model. Predictions of fixation screw pullout and fatigue failure—quantified by simulated screw axial forces and von Mises stresses, respectively—were compared between analyses with and without personalized muscle forces. The study found that muscle forces had a considerable influence on predicted screw pullout but not fatigue failure. However, it remains unclear whether including or excluding muscle forces would yield more conservative predictions of screw failures. Furthermore, while the effect of muscle forces on predicted screw failures was location-dependent for cortical screws, no clear location dependency was observed for cancellous screws. These findings support the combined use of patient-specific FE and NMS models, including loading from muscle forces, when predicting screw pullout but not fatigue failure in custom pelvic implants.

Investigation of co-seismic stress and aftershock distribution along the Sumatra–Andaman subduction zone

AbstractThis study aimed to investigate co-seismic stress and aftershock distribution along the Sumatra–Andaman subduction zone (SASZ). The fault parameters of six major earthquakes with an M ≥ 7 that occurred during 2010–2022 along the SASZ, were utilized to determine the Coulomb stress change using numerical modeling techniques calculated on the receiver faults with similar focal mechanisms of the mainshock, strike-slip, thrust, and normal faulting, respectively. The earthquake events were then classified to analyze the aftershocks of major earthquakes in the area. These aftershocks were mapped in order to determine the relationship between the aftershock distribution and the areas of increased or decreased stress. The relationship between the co-seismic stress and distribution of aftershocks in the SASZ was found to mainly depend on the focal mechanism of major earthquakes and the type of receiver fault used for calculation. After a major earthquake in the SASZ, there are two possible patterns that most aftershocks will be generated from in the areas of increased stress. First, a major earthquake is a type of thrust fault calculated on the receiver fault using the focal mechanism of the mainshock. Second, a major earthquake is a type of strike-slip fault calculated on the receiver fault with an optimum-oriented strike-slip fault. This relationship is likely to represent the specific pattern of the seismotectonic stress in the SASZ that can be used to evaluate the risk areas of aftershocks after a major earthquake has occurred. Furthermore, two earthquake events with large magnitudes were generated following the respective major earthquake in the SASZ that were located around the areas of increased stress, indicating that these two earthquake events were likely triggered in areas of increased stress following the respective major earthquake. Therefore, this study concluded that after a major earthquake occurrence in the SASZ, the areas of increased stress have a higher risk of generating both a large number of aftershocks and a new large-magnitude mainshock event. The investigation of co-seismic stress is very important to estimate areas of increased stress after a major earthquake, as this can be useful for monitoring both earthquake and tsunami hazards in the area.

WASTE EGGSHELL AND SAWDUST AS REINFORCEMENTS FOR SUSTAINABLE POLYESTER COMPOSITES: MECHANICAL CHARACTERIZATION AND ENVIRONMENTAL DURABILITY ASSESSMENT

This research endeavor undertakes an experimental investigation into the bending and tensile properties of polyester composites reinforced with waste eggshell powder and sawdust particles at 35 wt.%. Valorizing these waste materials as reinforcements contributes to sustainable practices, waste minimization, and environmental pollution mitigation. Composite samples were fabricated using hand lay-up and compression molding techniques. The effects of environmental exposure to water, acidic, and basic media immersion on the mechanical performance were evaluated to assess durability. Experimental characterization through tensile and three-point bending tests determined mechanical properties, stress-strain behavior, and failure mechanisms. Additionally, finite element analysis (FEA) simulations complemented the experiments by providing insights into stress distributions, deformations, and potential failure initiation sites within the composites under flexural loading. The computational models accurately captured the reinforcing effects of the waste materials and the degradation induced by environmental exposure, validating the experimental trends. Incorporating waste natural fibers significantly enhanced polyester's bending strength by 140% (sawdust) and 75% (eggshell), and tensile strength by 13% (sawdust) and 10% (eggshell). However, environmental exposure degraded properties to varying extents, with water immersion reducing tensile strength by 63% (sawdust) and 3% (eggshell), and flexural strength by 63% (sawdust) and 3% (eggshell). The acidic medium caused 58% (sawdust) and 23% (eggshell) reductions in tensile strength, and similar flexural strength degradations. Strikingly, the basic medium decreased eggshell composite tensile strength by 170% and flexural strength by 6%, while sawdust composite strengths declined by 44%.