Reduce Stress Concentration Research Articles

Significantly enhanced fatigue resistance and mechanisms of hypoeutectic Al-Si composite calibrated using trace in-situ nanocrystals

Fatigue resistance under extreme stress conditions is an important indicator to evaluate industrial application potential of Al-Si-Mg alloys, but their fatigue resistance is inherently weakened by large grain size, long-needle Si phases and coarse precipitates. This work reports significantly optimized microstructure configuration and fatigue resistance of hypoeutectic Al-Si composite optimized by the nanocrystallization products of a NiNbTi metallic glass. It was proved the in-situ NiTi (B2) nanocrystals can serve as the heterogeneous nucleation sites of α-Al and β-Mg2Si and the growth retarder of eutectic Si. Particularly, the optimized composite exhibited nearly 5 times and 6 times longer fatigue life than the unoptimized alloy at 120 MPa (60 Hz) and 240 MPa (20 Hz), respectively. The fatigue strength (N = 107) was increased by 21.7 % and 25.9 % at 60 Hz and 20 Hz, respectively. The α-Al refinement enhanced the resistance to fatigue crack initiation. The refinement and spheroidization of eutectic Si phases reduced stress concentration. Also, the austenite-martensite phase transformation of NiTi afforded more energy for precipitation. Refined β-Mg2Si and β'' phases were facilitated to interact with dislocations, improving the resistance to dislocation slip during cyclic strain through the dislocation shearing effect. This work provides a theoretical basis for the future development of Al-Si alloys and composites with excellent fatigue resistance for expanding their industrial application scope.

Комп’ютерне моделювання впливу кільцевих включень на концентрацію напружень в тонких циліндричних і конічних оболонках з круговими отворами

Shell structures are used in various industries, such the aerospace industry, the oil and gas industry, power engineering, mechanical engineering, construction, etc. Due to their design or manufacturing features, their integrity may be disrupted by the presence of various openings, around which local stresses develop. Finding ways to reduce stress concentrations around openings is an important problem in deformable solid mechanics. This paper presents the results of a computer simulation and a finite-element analysis of the stress and strain field of thin-walled cylindrical and truncated conical shells with circular openings in the presence of annular inclusions around them made of a material whose properties differ from the main material of the shells. The effect of the elastic modulus of an inclusion and its geometric parameters on the stress and strain concentration in the vicinity of the openings was studied. Several inclusion materials and inclusion widths were considered. An annular inclusion made of a homogeneous material and located in the shell plane was considered. Stress and strain intensity distributions in the local stress concentration zones were calculated. A comparative analysis of the results obtained for cylindrical and conical shells was carried out. The study showed that the presence of a “soft” homogeneous annular inclusion makes it possible to reduce the stress concentration around the opening by ~13–35% depending on the inclusion width and elastic modulus both for a cylindrical and a conical shell. Certain combinations of the geometric and mechanical parameters of the inclusion give rise to a “mechanical” effect, which consists in shifting the stress concentration zone from the opening edge to the inclusion – shell material interface. For conical shells, due to their geometric features, a “conical” effect occurs: the stresses increase not only in the vicinity of the opening-weakened zone, but also near the cone basis.

Design of functionally graded material to reduce stress concentration around semicircular notches for Inplane tensile and bending loads

Design of functionally graded material to reduce stress concentration around semicircular notches for Inplane tensile and bending loads

Static behavior of ribbed folded plate roof under vertical uniform load—Experimental study and meshfree method analysis

SummaryFolded plate roofs are widely used in building roofs due to their light weight and high stiffness. However, traditional folded plate roofs are often limited in application due to insufficient stiffness under the current trend of pursuing larger‐span roofs. Ribbed folded plate roofs can effectively solve this problem because ribs not only increase the stiffness of the roof and reduce stress concentration, but they are also easy to be formed into various shapes to meet different needs for buildings. Therefore, the detailed analysis was carried out on a reinforced concrete ribbed folded plate roof (RCRFR) under the vertical uniform load to investigate its static behavior. The bearing capacity, failure mode, load–displacement relationship, and strain variation were obtained through the test. Additionally, based on the finite element (FE) method, not only a comparison was conducted between RCRFR and reinforced concrete ribless folded plate roof (RCLFR), but the influence of material nonlinearity and geometric nonlinearity on the structure was also investigated. Moreover, the bending characteristics of RCRFR under design load were analyzed based on the reproducing kernel particle method. The experimental results showed that this structure had good mechanical properties within the design load. In the overload stage, the concrete on the underside of the structure was severely damaged. Furthermore, the yielding of the ribbed plate's reinforcing bars caused the increased vertical deformation difference between the ribbed plate and the top chord, and the ribbed plate and the central ridge beam. Eventually, the failure of the anchorage of the ribbed plate's reinforcing bars anchored in the central ridge beam and the top chord led to the loss of structural load‐bearing capacity. The FE analysis results demonstrated that ribs enhance the stiffness of the structure, with material nonlinearity having the primary impact and geometric nonlinearity exerting a secondary effect. The meshfree method analysis was in concordance with the experimental results as well as those of the FE analysis.

Proximal femoral bionic nail-a novel internal fixation system for the treatment of femoral neck fractures: a finite element analysis.

Introduction: Currently, cannulated screws (CSs) and dynamic hip screws (DHSs) are widely used for the treatment of femoral neck fractures, but the postoperative complications associated with these internal fixations remain high. In response to this challenge, our team proposes a new approach involving triangular-supported fixation and the development of the proximal femoral bionic nail (PFBN). The primary objective of this study is to investigate the biomechanical differences among CSs, DHSs, and the PFBN in their capacity to stabilize femoral neck fractures. Methods: A normal proximal femur model was constructed according to the CT data of a normal healthy adult. A femoral neck fracture model was constructed and fixed with CSs, DHSs, and the PFBN to simulate the fracture fixation model. Abaqus 6.14 software was used to compare the biomechanical characters of the three fracture fixation models. Results: The maximum stresses and displacements of the normal proximal femur were 45.35MPa and 2.83mm, respectively. Under axial loading, the PFBN was more effective than DHSs and CSs in improving the stress concentration of the internal fixation and reducing the peak values of von Mises stress, maximum principal stress, and minimum principal stress. The PFBN fixation model exhibits superior overall and fracture section stability in comparison to both the DHS fixation model and the CS fixation model under axial loading. Notably, the maximum stress and peak displacement of the PFBN and bone were lower than those of the DHS and CS fixation models under bending and torsional loading. Conclusion: The PFBN shows considerable improvement in reducing stress concentration, propagating stress, and enhancing the overall stability in the femoral neck fracture fixation model compared to DHSs and CSs. These enhancements more closely correspond to the tissue structure and biomechanical characteristics of the proximal femur, demonstrating that the PFBN has great potential for therapeutic purposes in treating femoral neck fractures.

Comparison of local, gradient-enhanced and integral form of continuum damage approaches to strain localization in fiber reinforced composites

Structures often have inserts and notches that cause stress concentration and consequent reduction in the load bearing capacity. The literature on numerical implementation of continuum damage mechanics (CDM) has generally focused on using local theories of damage. However, their use to analyze deformations of notched laminates that are prone to strain localization can cause numerical convergence issues that can be alleviated by employing a non-local theory. There are a few studies using a non-local damage theory for fiber-reinforced polymeric composites (FRPCs) and even fewer for strain localization in FRPCs. The non-local theories employ an equivalent (or effective or von Mises) strain often used in metal plasticity while most theories for studying failure of FRPCs use individual strain/stress components. Here, we compare predictions from local and nonlocal CDM approaches that are effective in studying strain localization in FRPCs. For the local approach, we employ a rate-dependent evolution relation. For the non-local approach, we either compute damage at a point as the weighted sum of damage at its neighbors that introduces a length scale into the problem, or employ a gradient-enhanced approach that also introduces a length scale. It is shown that numerical predictions from both the rate-dependent and the non-local theory alleviate to different degrees sensitivity of results to the finite element mesh used and the strain localization issues. Of these, a local rate-type approach is more convenient and cost effective.

Influence of the combined additions Mn, Cr or Ni on the formation of dispersoids and mechanical properties of Al–Mg–Si–Cu alloys

The effect of individual and combined additions of different transition metals (TMs), Mn, Cr, and Ni, on the precipitation of dispersoids and the final mechanical properties of Al–Mg–Si–Cu alloys was systematically studied by scanning electron microscopy, transmission electron microscopy and tensile testing. The various TM additions examined are found to induce notably different dispersoid precipitation behaviors. The combined addition of Mn, Cr produces the highest number density of dispersoids among the three TM-added alloys examined, due to the incorporation of Cr promoting the precipitation of the α-Al(Mn, Cr, Fe)Si dispersoid. By contrast, the combined addition of Mn, Ni slightly suppresses the precipitation of the α-Al(Mn, Ni, Fe)Si dispersoid compared with individual Mn addition. The presence of a fine dispersoid microstructure can moderately increase the strength, and strongly increase the elongation, especially for the case of the combined Mn, Cr added alloy, where the elongation is increased almost threefold compared with the base alloy. An excellent strength-elongation combination, with an ultimate tensile strength of 421.9 ± 2.2 MPa and an elongation of 18.2 ± 3.6, is achieved for this alloy. This property is superior to most reported 6xxx alloys. The main reasons for this result are the presence of a high number density of dispersoids promoting grain refinement, providing high Orowan hardening, and reducing stress concentration on the grain boundary. The findings of this work are expected to provide guidance for developing new Al–Mg–Si–Cu alloys with excellent comprehensive mechanical properties.

Effect of boundary conditions on energy harvesting of a flow-induced snapping sheet at low Reynolds number

Recent studies on the snap-through motion of elastic sheets have attracted intense interest in energy-harvesting applications. However, the effect of boundary conditions (BCs) on energy extraction performance still remains an open question. In this study, we explored the snapping dynamics and energy-harvesting characteristics of the buckled sheet at various conditions using fluid–structure interaction simulations at a Reynolds number Re = 100. It was found that the front boundary condition (BC) dramatically affects the sheet's snapping dynamics, e.g., the pinned or relatively soft front BC triggers the sheet's instability easily and thus boasts the collection of potential energy. In the snap-through oscillation state, a stiffer rear BC results in a larger improvement in the sheet's energy collection compared with a minor effect of front BC. Meanwhile, the enhancement can also be achieved by adjusting the rear rotational spring stiffness up to 1.125 × 10−4, after which it remains nearly constant, as observed in the case of EI* = 0.004. This introduction of an elastic BC with krs* = 1.125 × 10−4 not only efficiently enhances energy extraction but significantly reduces stress concentration and, as a result, greatly prolongs the sheet's fatigue durability, especially for the stiffer sheet with EI* = 0.004. The effect of three other governing parameters, including the length ratio ΔL*, sheet's bending stiffness EI*, and mass ratio m*, on the sheet's energy-harvesting performance were also explored. The result shows that increasing ΔL* and EI* could improve the total energy harvested, primarily by enhancing the elastic potential energy, particularly in the aft half of the sheet. In contrast, increasing m* mainly enhances the kinetic energy collected by the sheet's central portion, thus improving the total energy-extracting performance. This study provides an in-depth insight into the dynamics of a buckled sheet under various BCs, which may offer some guidance on the optimization of relevant energy harvesters.

Analysis of the influence of fillet geometry on stress concentration in keyway by the finite element method

Machines play a pivotal role in the modern world, as they streamline various activities by virtue of their capacity to convert energy, such as transforming electrical energy into mechanical energy. In this context, the mechanical shaft assumes significant importance, as it enables the transmission of power to a wide range of applications. Being a solid component, the shaft is subjected to mechanical stresses, and the keyway groove, present in the shaft, is a feature that exacerbates stress concentrations in its geometry, which is undesirable as it increases the risk of failure due to rupture. Therefore, this research aimed to investigate the influence of the keyway groove geometry on stress concentration in shafts under bending loads, using simulations based on the finite element method. The study compares elliptical keyways with circular keyways and assesses how variations in parameters impact stress concentration, employing the Ansys tool for the analysis. The results demonstrate that slight modifications in the keyway groove geometry can significantly reduce stress concentrations, thereby contributing to the optimized design of mechanical components and providing valuable insights for engineers working in this field.

Effect of surface texture spacing on interface heat transfer and tensile property of laser‐welded steel/CFRTP joint

AbstractMetal‐polymer hybrid joints can contribute to weight reduction and have potential use in transportation industries. In this work, laser texturing was used to enhance bonding strength of laser‐welded 304 stainless steel/carbon fiber reinforced thermoplastics (CFRTP) joint. The tight relationship between surface texture spacing and porosity characteristic as well as tensile property of joint was systematically investigated. The temperature field distribution during welding process was simulated and the mechanism of porosity suppression depending on grid spacing was discussed. The result showed that the number of pores at cross‐section decreased first and then rose with the increase of micro‐structure spacing, which corresponded to the variation trend of bonding strength and was inconsistent with the evolution of connecting area. The joint achieved the minimum porosity defect and reached maximum fracture load of 2594 N when the grid spacing was 1.2 mm, while the maximum joint width of 9.28 mm was obtained when 0.4 mm spacing was adopted, indicating that the joint quality rather than mechanical interlocking governed the mechanical property of joint. Appropriate interface contact conductance (TCC) related to texture spacing could optimize the interface heat dissipation rate, and was the key factor to efficiently control the shrinkage porosity. The TCC of small or large grid spacing was too high or too small, resulting in failure of the heat transfer path through the interface to metal during cooling process. Moreover, the proper texture spacing improved the uniformity of joint strain distribution in tensile‐shear testing, which benefited joint strength.Highlights Laser‐textured grid pattern spacing affected number and distribution of pores. Heat dissipation rate varied with various spacing at joint interface. 1.2 mm spacing texture reduced stress concentration during tensile process.

Significantly enhanced reversibility and mechanical stability in grain-oriented MnNiGe-based smart materials

Materials that undergo a magnetostructural transition (MST) usually exhibit fascinating magnetoresponsive properties, making them an important class of smart materials. However, practical application of this class of smart materials has been hindered by structural degradation as well as large irreversibility of the MST during consecutive thermal and field cycles. Here we report a significant improvement of the reversibility and mechanical stability in grain-oriented MnNiGe-based alloys that were fabricated using a directional solidification method. The preferred grain orientation enables synergistic deformations between neighboring grains during the MST, leading to a substantial reduction in the transition-induced stress concentration. As a result, in situ and ex situ microscopic observations demonstrate a good mechanical stability of the textured alloys across the MST, in strong contrast to conventional MM'X (M, M’ = Mn, Fe, Co, Ni; X = Si, Ge) materials with randomly-oriented grains. The detailed transition stages of the MST have also been observed at the microscopic scale, and are reported for the first time in the MM'X family. Besides, a low thermal hysteresis (ΔThys) of ∼ 4 K was obtained in the textured alloys, which is the lowest ΔThys in the MM'X material family. Textured MnNiGe-based alloys show a large reversible isothermal entropy change (≥ 35.9 Jkg−1K−1) in a 5 T field change, which is the highest among typical magnetocaloric materials. Consequently, this work provides a promising strategy for enhancing the cyclic stability of materials with a MST, which may boost their practical applications in solid-state refrigerators, energy harvesters and high-precision actuators.

Biomechanical evaluation of three implants for treating unstable femoral intertrochanteric fractures: finite element analysis in axial, bending and torsion loads.

Purpose: How to effectively enhance the mechanical stability of intramedullary implants for unstable femoral intertrochanteric fractures (UFIFs) is challenging. The authors developed a new implant for managing such patients. Our aim was to enhance the whole mechanical stability of internal devices through increasing antirotation and medial support. We expected to reduce stress concentration in implants. Each implant was compared to proximal femoral nail antirotation (PFNA) via finite element method. Methods: Adult AO/OTA 31-A2.3 fracture models were constructed, and then the new intramedullary system (NIS), PFNA, InterTan nail models were assembled. We simulated three different kinds of load cases, including axial, bending, and torsion loads. For further comparison of PFNA and the NIS, finite element analysis (FEA) was repeated for five times under axial loads of 2100N. Two types of displacement and stress distribution were assessed. Results: Findings showed that the NIS had the best mechanical stability under axial, bending, and torsion load conditions compared to PFNA and InterTan. It could be seen that the NIS displayed the best properties with respect to maximal displacement while PFNA showed the worst properties for the same parameter in axial loads of 2100N. In terms of maximal stress, also the NIS exhibited the best properties while PFNA showed the worst properties in axial loads of 2100N. For bending and torsion load cases, it displayed a similar trend with that of axial loads. Moreover, under axial loads of 2100N, the difference between the PFNA group and the NIS group was statistically significant (p < 0.05). Conclusion: The new intramedullary system exhibited more uniform stress distribution and better biomechanical properties compared to the PFNA and InterTan. This might provide a new and efficacious device for managing unstable femoral intertrochanteric fractures.

Correlational fractal characteristics and damage progression of granite with different grain sizes based on acoustic emission monitoring

Mineral grain size caused by the geological diagenetic process is one of the fundamental reasons leading to the differences in rock mechanical behaviors, which brings challenges to the stability of underground engineering, especially in rock masses with continuous grain size changes. This study conducted uniaxial compression tests on granite samples obtained from the same invaded anticline with different grain sizes. During the tests, the acoustic emission (AE) signals were acquired synchronously. The correlation between damage evolution and AE data was then studied by frequency-spectrum analysis, fractal theory methods, and G-P algorithms. The mechanism of grain size effect on granite failure evolution was discussed. The results reveal that as the grain size increases, the strength and the elastic modulus decrease while the plastic deformation characteristic is enhanced. Grain size also affects the frequency distribution of AE signals and its time-varying characteristics. With the increase in grain size, the proportion of high-frequency signals declines during loading. The fractal dimension value of dominant frequency during loading fluctuates within the range from 0.5 to 2.25 and generally shows an overall ‘rise-fall-rise-fall’ mode. In addition, as the grain size increases from fine-grained to medium-grained, the fractal dimension changes from an increasing to a decreasing trend earlier in the compaction and elastic stages. Especially in coarse-grained samples, after a brief increase, the fractal dimension decreases continuously until approaching the overall failure. The frequency domain characteristics and correlation fractal variation of granites reflect the damage and crack evolution inside the rock sample. More scattered and unordered micro-cracks generated in samples with finer grains facilitate the dispersion of applied stress and the reduction of local stress concentration, resulting in higher strength and stiffness of the sample.

Microstructure-strengthening correlation of 2219 Al alloy subjected to ultrasonic melt treatment, hot rolling and heat treatment

Improving strength while retaining good ductility is crucial for expanding the application of 2219 Al alloy. In this study, refined microstructure, excellent strength and ductility were obtained for the 2219 Al alloy under the combined effects of ultrasonic melt treatment (UMT), hot rolling and T6 heat treatment (HRT6). The mean grain size declined from 664.2 μm to 194.9 μm for the as-cast 2219 Al alloy after 240s UMT, with a refining efficiency of 70.7 %. Meanwhile, the Cu content in Al matrix was increased by 41.7 %, and the area fraction of reticular eutectic structure was accordingly lessened by 64.5 %. The nucleation of θʹʹ/θʹ-Al2Cu phase was actuated owing to the increased Cu content in Al matrix, resulting in more dispersive θʹʹ/θʹ-Al2Cu precipitates in the HRT6 alloy with UMT. Besides, the recrystallization was encouraged because the boundaries of refined as-cast grains provided more favorable nucleation sites, and the increased dispersive θʹʹ/θʹ-Al2Cu precipitates would inhibits the grain boundary merging during HRT6. Thus, the average dimension of the recrystallized grains was decreased to the lowest value of 71.3 μm in the HRT6 alloy with 240s UMT. Meanwhile, the ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) were enhanced to 456.2 MPa, 307.0 MPa and 16.7 %, and precipitation strengthening contributed the most to the YS enhancement. The improved ductility was mainly due to the increased deformation capacity induced by the refined grains and reduced stress concentration caused by the dispersive θʹʹ/θʹ-Al2Cu particles.

Seismic performance of a novel hemisphere-based rocking hinge realizing self-centering damage-free bridge system

The rocking column with post-tensioned (PT) strands is shown able to provide satisfactory self-centering capacity for bridge systems after earthquakes. However, local damage to concrete at the rocking interface and consequent losses of PT force may occur during ground motions. To minimize the local damage and facilitate the construction procedure, this paper proposes a novel hemisphere-based rocking hinge (HRH) at the rocking interface. For the columns with the proposed HRH, self-centering capacity is provided by PT strands, and energy dissipation is supplied by oval-shaped metal dampers. Hemispheres are adopted to achieve pre-determined rotation center, as well as reduce stress concentration and avoid local damage to the rocking interface. The construction of the HRH is first described, followed by an analytical model characterizing the hysterical behavior of the column with this HRH. The analytical model is then numerically validated using models developed by both the Abaqus and the OpenSees softwares. Accordingly, a design procedure is presented for columns utilizing this HRH, achieving damage-free and self-centering seismic performance. Finally, the HRH is implemented in an illustrative bridge, and its efficiency is verified by comparing the seismic responses with the conventional RC bridge. Results show that the HRH bridge possesses an excellent self-centering capacity and is able to maintain operational even after a major earthquake.

Failure behavior and crashworthiness characteristic of repaired composites‐metal hybrid tubes by acoustic emission

AbstractIn this study, the transverse indentation test was applied to simulate the damage caused by impact to the carbon fiber‐reinforced plastics (CFRP)/Al hybrid tube, and composites patch repair technology was used to repair the hybrid tube with different damage degrees. The effects of width and ply‐number of the patch on failure behavior and crashworthiness under axial load were investigated. It was concluded that the technology can effectively reduce stress concentration around the indentation and then improve compressive strength. Increasing the ply‐number of the patch can mitigate the failure mode of med‐length collapse of the hybrid tube and can effectively improve the crashworthiness indicators. The optimal repair strategy increased energy absorption by 54.02% and mean crushing force by 53.66%. However, the improvement of failure behavior by the ply‐number is limited by patch width. Acoustic emission and infrared thermography technologies were used to further analyze the damage characteristics and damage evolution of the hybrid tubes in pre‐crushing stage. It was found that the crushing form of the middle collapse tended to produce a more intense acoustic emission response and higher temperature change than that of the end crushing. In engineering practice, it provides a valuable reference for the reasonable repair of composite tubular structures and their hybrid structures.Highlights Composite repair technology is used for the repair of CFRP/Al hybrid tubes. The effects of ply‐number and width of patch on repair quality are studied. The technology can effectively improve residual crashworthiness of structure. The improvement of failure behavior by ply‐number is limited by patch width. The damage behavior of various crushing forms can be revealed by AE and IR.

Shape-locking in architected materials through 3D printed magnetically activated joints

Shape morphing is the ability of objects to adapt to different shapes and reduce stress concentrations through increased contact area. This is a common trait of natural and engineered objects and has several applications in, among others, soft robotics and orthopedic implants. Shape morphing is achieved through flexible materials or rigid components with either kinematic or compliant joints. An additional step, namely shape locking, is needed for sustained load support. Activation of a locking mechanism can be done with any energy, among which magnetism is one. Here, we present the implementation of a magnetic locking mechanism for kinematically deformable metamaterial structures that maintain shape and support loads upon locking. The structure consists of 3D printed rigid magnetic and non-magnetic components connected by hinges. We created several prototypes of the proposed designs using two additive manufacturing methods (i.e., material extrusion and multi-material jetting) and demonstrated its application in a closed-loop grid for arbitrary shapes. Moreover, we characterized the performance of the prototypes using mechanical tests and multibody kinematic system simulations. This work highlights the viability of the locking concept and provides design considerations for future applications. Further improvement and optimizations are needed for increased efficiency and effectiveness.

An Automated Parametric Surface Patch-Based Construction Method for Smooth Lattice Structures with Irregular Topologies

Additive manufacturing enables the realization of complex component designs that cannot be achieved with conventional processes, such as the integration of cellular structures, such as lattice structures, for weight reduction. To include lattice structures in component designs, an automated algorithm compatible with conventional CAD that is able to handle various lattice topologies as well as variable local shape parameters such as strut radii is required. Smooth node transitions are desired due to their advantages in terms of reduced stress concentrations and improved fatigue performance. The surface patch-based algorithm developed in this work is able to solidify given lattice frames to smooth lattice structures without manual construction steps. The algorithm requires only a few seconds of sketching time for each node and favours parallelisation. Automated special-case workarounds as well as fallback mechanisms are considered for non-standard inputs. The algorithm is demonstrated on irregular lattice topologies and applied for the construction of a lattice infill of an aircraft component that was additively manufactured.

Enhancing the mechanical stability of restored teeth with interfacial cracks: Finite element analysis

ObjectivesThis study aims to enhance the mechanical stability of restored molar teeth with class II occlusal-distal (OD) cavities. We seek to achieve this goal through a comprehensive investigation of three primary factors: (1) the choice of restoration material properties, (2) internal cavity geometries, and (3) the impact of double-layered restoration configurations. MethodsTo achieve our objectives, we initiated by creating two-dimensional (2D) models of restored teeth featuring class II OD cavities, utilizing scanned and segmented images of maxillary molar teeth. We drew 2D profiles of dentine and enamel, which were then imported into finite element analysis (FEA) software. To explore various cavity geometries, we implemented a total of thirteen different designs, encompassing straight, oblique, grooved, curved, and double-layered configurations. We utilized a semi-circular stone to simulate the application of contact load on the restored tooth. We applied identical boundary conditions and contact loading across all models. To assign material properties, we developed a Python code, enabling the automatic assignment of seven elastic moduli ranging from 2 GPa to 26 GPa to the restoration materials. Meanwhile, constant material properties were assigned to the enamel and dentine. In total, we conducted 133 FEA simulations to comprehensively analyse the effects of the aforementioned factors on the strength and performance of restored molar teeth. ResultsOur analysis revealed two key factors significantly influencing the mechanical resistance of treated teeth, particularly in the presence of a crack or debonding: (1) the marginal geometry of the OD cavity and (2) the elastic modulus of the restorative material. However, altering the internal cavity angle and implementing a double-layered restoration did not significantly influence the restored tooth's overall strength and performance in the face of crack or debonding situations. SignificanceThe findings of this study have substantial implications for designing and restoring class II OD cavities to enhance resistance to cracks or debonding. The use of curved marginal geometries in restoration design can significantly improve fracture resistance, with double-curved geometries reducing stress concentrations by approximately 43% compared to straight cavities. These results offer valuable guidance for strengthening the structural integrity of restored teeth, calling for further experimental investigations to explore practical applications and benefits.

Bearing performance and damage characteristics of rein‐infused thermoplastic 3D woven composites bolted joints

AbstractThis paper presents a comprehensive study on the single‐bolt single‐shear (SBSS) and double‐bolt single‐shear (DBSS) lap joint performance of resin‐infused thermoplastic 3D fiber‐reinforced composite (FRC) in on‐axis ( and ) and off‐axis () configurations. The bearing performance and failure mechanisms are compared with thermoset 3D‐FRC. The resin‐infused thermoplastic 3D‐FRC bolted joint shows improved bearing performance in terms of higher ultimate bearing strength, stiffness loss strength, and reduced damage severity than its thermoset counterpart. Additionally, this paper presents a detailed study on the intermediate and final failure mechanisms, obtained from scanning electron microscopy of the interrupted and ultimate bearing tests, to understand damage progression in SBSS and BDSS lap joints at the submicron level. The major damage characteristics of a thermoplastic 3D‐FRC bolted joint include plastic deformation and plastic kinking at the hole front tip, which improve the bearing capacity and reduce stress concentration, damage severity, and its deleterious effects.Highlights Single‐bolt and double‐bolt joint performances of 3D woven composites Failure investigation of different joint configurations and fiber orientations Effect of matrix toughness on the bearing performance of 3D woven composites Progressive damage development and failure modes of 3D woven composite joints.