Maximum Load Bearing Capacity Research Articles

Three‐dimensional finite element simulation of fracture propagation in rock specimens with pre‐existing fissure(s) under compression and their strength analysis

SummaryA FORTRAN program, consistent with the commercially available finite element (FE) code ABAQUS, is developed based on a three‐dimensional (3D) linear elastic brittle damage constitutive model with two damage criteria. To consider the heterogeneity of rock, the developed FORTRAN program is used to set the stiffness and strength properties of each element of the FE model following a Weibull distribution function. The reliability of the program is assessed against available experimental results for granite cylindrical specimens with a throughgoing, flat and inclined fissure. The calibration procedure of the material parameters is explained in detail, and it is shown that the compressive to tensile strength ratio can have a substantial influence on the failure response of the specimens. Numerical simulations are conducted for models with different levels of heterogeneity. The results show a smaller load bearing capacity for models with less homogeneity, representing gradual coalescence of fully damaged elements forming throughout the models during loading. The maximum load bearing capacity is studied for various combinations of inclination angles of two centrally aligned, throughgoing and flat fissures of equal length embedded in cylindrical models under uniaxial and multiaxial loading conditions. The key role of the compressive to tensile strength ratio is highlighted by repeating certain simulations with a lower compressive to tensile strength ratio. It is proven that the peak loads of the rock models with sufficiently small compressive to tensile strength ratios containing two throughgoing fissures of equal length are similar, provided that the minimum inclination angles of the models are the same. The results are presented and discussed with respect to the existing experimental findings in the literature, suggesting that the numerical model applied in this study can provide useful insight into the failure behaviour of rock‐like materials.

Fatigue Properties of Resistance Spot Welded Dissimilar Interstitial-Free and High Strength Micro-Alloyed Steel Sheets

This study aims to investigate the influence of nugget diameter on tensile-shear and fatigue properties of the dissimilar resistance spot-welded joints of interstitial free and high strength niobium microalloyed steel sheets. The spot-weldings are done at currents of 7 kA and 9 kA at welding time of 300 ms with electrode force of 2.6 kN. Fatigue tests are done at different load amplitudes, considering the maximum tensile-shear load bearing capacity of the joints. The tests are interrupted before the final failure to understand the crack initiation and propagation paths. The study is supplemented by the microstructural and detailed fractographic analyses. The results indicated that the fatigue strength of the spot-welds increased with a decrease in nugget diameter. This could be attributed to the higher microhardness of heat affected zone (HAZ), presence of compressive residual stress and lower variation in thickness reduction on the IF steel side, welded at 7 kA. However, the tensile-shear load bearing capacity of the spot-welds increased with increase in the nugget diameter. The failure of the spot-welded joint under static loading initiates from the HAZ/base metal interface of the IF steel side. Nevertheless, under cyclic loading crack initiates from the notch root at the interface of two sheets lying in the HAZ of IF steel side. Fractographic investigations indicate intergranular fracture features in combination with striations, secondary cracks on the IF steel side under cyclic loading. Fracture surfaces of the specimens failed under static loading shows however, shear dimples on the IF steel side.

Design optimization of roll cage for formula one vehicle by using finite element analysis

In this article, AISI-1020 tubular steel roll cage of a formula one car has been designed and optimized. CATIA software has been employed for designing whereas ANSYS software used for Finite element analysis (FEA). The design of the roll cage has been optimized for maximum load bearing capacity and manoeuvrability conditions. For this purpose, various impact tests have been performed under different conditions in order to determine the level of safety. The effects of different loading conditions on the structural members are studied and discussed. It has been found by the analysis from the front and rear impact tests that less deformation is developed at a higher value of stress. Moreover in case of front rollover and side-impact test, it has been observed that higher stress produces higher deformation. The results show that employed AISI-1020 tubular steel may lead the development of a lighter and safer roll cage design as compared to a conventional Formula-1 roll cage material.

Experimental investigation on the influence of process parameters in Friction stir spot welded dissimilar aluminum alloys

Friction stir spot welding is a solid-state welding process where the joints are formed due to plastic deformation. This technique is economically sound when compared to that of Resistance spot welding. In this research work, the process parameters of friction stir spot welded Al 5754–Al 6061 joined were identified with Response Surface Methodology. The results showed that the tool rotational speed was the most significant parameter that impacted the tensile shear force of the weld joint. The maximum load-bearing capacity of 6.060 kN was obtained at 1000 RPM and 0.04 mm/s. Additionally, the influence of plate position and tool profile on the tensile shear force of the weld joint is also studied. The test result obtained at the optimal welding conditions with respect to the plate position and tool profile showed that both the plate position and tool profile had a significant influence on the load-bearing capacity of the weld joint.

Stabilization on Expansive Soil with Different Sand Layers

Problematic Soil improves by better root growth, water movement, and also by mixing portions of the soil profile, to provide more uniform texture. As a ground improvement technique to improve the strength of problematic soils and this study is carried out to understand the settlement behaviour of layered soils. The soil which is collected was found to be problematic in nature, which is more swelling in nature. The samples of soil are collected the from Mudichur road, Tambaram. The sand used in this study is taken from nearby site and is used to improve the problematic soil by forming a layer of required thickness. The preliminary tests are conducted on the soil samples to determine their properties as per IS standards. After the preliminary test, the plate load tests are performed on the soil with square plate (10 mm x 10mm) in order to know the bearing capacity of soil. The load tests are performed on sand and clay layers with varying thickness of 5cm, 10 cm and 15 cm of sand over clay soil. From the plate load test the load- settlement behaviour of soil layers are studied. It can be conclude that if different layers of sands are provided over Problematic soil then It gets enough Load bearing resistance which can be further gets implemented during Highways constructions. The results says that of 15 cm layer of sand shows maximum load bearing capacity & shown better load – settlement graphs as well.

Restoring Initially Cracked Reinforced Concrete Beams utilizing Carbon Fiber Reinforced Polymer Strips

Carbon fiber reinforced polymer (CFRP) strips are widely used all over the globe as a repair and strengthening material for concrete elements. This paper looks at comparison of numerous methods to rehabilitate concrete beams with the use of CFRP sheet strips. This research work consists of 4 under-reinforced, properly cured RCC beams under two point loading test. One beam was loaded till failure, which was considered the control beam for comparison. Other 3 beams were load till the appearance of initial crack, which normally occurred at third-quarters of failure load and then repaired with different ratios and design of CFRP sheet strips. Afterwards, the repaired beams were loaded again till failure and the results were compared with control beam. Deflections and ultimate load were noted for all concrete beams. It was found out the use of CFRP sheet strips did increase the maximum load bearing capacity of cracked beams, although their behavior was more brittle as compared with control beam.

Optimal Process Parameters to Achieve Maximum Tensile Load Bearing Capacity of Laser Weld Thin Galvanized Steel Sheets

Steels are protected against corrosion through hot-dip galvanization in which material surfaces are coated with molten zinc. Galvanized steel products are reliable in coating life and performance with lower maintenance and repair cost. Welding of such zinc coated steel sheets is of great economic importance in the automotive industries. Many researchers have utilized the S/N ratio transformation while obtaining the optimal solution of several manufacturing processes. However, the additive law in Taguchi technique estimates the deterministic output response from the mean values of the ANOVA table and unable to provide the expected range of the output response. This paper deals with optimal process parameters for achieving maximum tensile load bearing capacity of laser weld thin galvanized steel sheets utilizing the concepts of a modified Taguchi design of experiments. Excepted range of the tensile load bearing capacity is provided for the specified laser process parameters. Empirical relation is developed and validated for the tensile load bearing capacity in terms of the laser process parameters viz., laser power, welding speed and focal point position.

Experimental Characterization of Sandwich Radome for Airborne Applications

Radome is a structural weather proof enclosure that protects radar system from the environment. Radomes are manufactured using composite materials that have low dielectric constant and low loss tangent. The selected materials should have high mechanical strength to withstand aerodynamic and bird impact load conditions. Thus, the design of a radome is always a trade-off between electrical and structural requirements. In the present study, set of Uni-directional (UD) and Bi-directional (BD) glass fabric used as high density face sheet with low density foam ROHACELL 71 Hero grade and Nomex honeycomb as core materials are used to form sandwich radomes. These samples are tested for mechanical performance as per ASTM standards. The maximum load bearing capacity was found higher for the Nomex sandwich with UD face, by 27% than the Rohacell sandwich with UD Face sheet. Nomex sandwich with BD face sheet have higher compressive modulus among other three configurations. The bird impact simulation results show sandwich panel selected is capable of withstanding bird impact load at a velocity of 150 m/s. The measured antenna patterns with and without radome material for frequency range from 2.5 GHz to 4.5 GHz is also discussed.

Using Carbon Fibre Reinforced Polymer Strips for Recuperation of Originally Fissured Concrete Beams

Carbon fiber reinforced polymer (CFRP) strips are widely used all over the globe as a repair and strengthening material for concrete elements. This paper looks at comparison of numerous methods to rehabilitate concrete beams with the use of CFRP sheet strips. This research work consists of 4 under-reinforced, properly cured RCC beams under two point loading test. One beam was loaded till failure which was considered the control beam for comparison. Other 3 beams were load till the appearance of initial crack which normally occurred at third-quarters of failure load and then repaired with different ratios and design of CFRP sheet strips. Afterwards, the repaired beams were loaded again till failure and the results were compared with control beam. Deflections and ultimate load were noted for all concrete beams. It was found out the use of CFRP sheet strips did increase the maximum load bearing capacity of cracked beams although their behavior was more brittle as compared with control beam.

A gradient based model for the mesh-independent damage simulation of layered composite structures

Over the last decades, fiber composite materials have established themselves especially for problems in lightweight construction. In order to use the structure optimally, a precise knowledge of the maximum load-bearing capacity and possible damage to the structure is necessary. For the calculation of damage in fiber composite laminates, various damage models already exist. Classically, these models are applied within the finite element method (FEM). Localization effects occur which lead to a dependence of the results on the used FE-mesh.This paper deals with the gradient extension of free Helmholtz energy using global damage variables to eliminate localization effects.Based on the formulation of the regularized damage model of the single layer, the regularization is transformed into a layered theory for composite shell structures. The associated numerical model within the framework of FEM is explained before the model is illustrated with numerical examples.

Empirical FRP-concrete effective bond length model for externally bonded reinforcement on the grooves

The externally bonded reinforcement on grooves (EBROG) technique has been recently shown to outperform its rival techniques of surface preparation (such as externally bonded reinforcement, EBR) employed to delay the undesirably premature debonding of fiber reinforced polymer (FRP) off the concrete substrate in retrofitted structures. In FRP application, the effective bond length is defined as a length over which the majority of the bond stress is transferred and the maximum load-bearing capacity is obtained. The present study endeavors to develop an original empirical model of the effective bond length of FRP sheets applied on concrete via the EBROG technique. For this purpose, an experimental program is conducted in which 95 specimens prepared through the EBROG and EBR techniques are subjected to the single lap-shear test. The effective bond length is evaluated by analyzing the strain and stress fields on the FRP bond area using the image processing technique of particle image velocimetry (PIV). A model is then developed based on a nonlinear regression analysis along with a probability study performed on the results obtained from the experiments; and the goodness of fit to the data is confirmed. In this model, the effects of groove dimensions, concrete compressive strength, as well as FRP sheet width and stiffness are taken into account. The feasibility of the well-known existing models developed for EBR method was investigated in the EBROG technique and the prediction accuracy was compared with the proposed model.

Load-bearing capacities of ultra-thin occlusal veneers bonded to dentin

ObjectivesTo test whether the load-bearing capacity of occlusal veneers made of ceramic or hybrid materials bonded to dentin does differ from those of porcelain-fused-to metal or lithium disilicate glass ceramic crowns. Material and methodsIn 80 human molars, occlusal tooth substance was removed so that the defects extended into dentin, simulating defects caused by attrition/erosion. Restorations at a standardized thickness of either 0.5 mm or 1.0 mm were digitally designed. For both thicknesses, 4 test groups (n = 10 per group) were defined, each including a different restorative material: “0.5-ZIR”: 0.5 mm thick zirconia (Vita YZ HT); “1.0-ZIR”: 1.0 mm thick zirconia (Vita YZ HT); “0.5-LDC”: 0.5 mm thick lithium disilicate ceramic (IPS e.max Press); “1.0-LDC”: 1.0 mm thick lithium disilicate ceramic (IPS e.max Press); “0.5-HYC”: 0.5 mm thick PICN (Vita Enamic); “1.0-HYC”: 1.0 mm thick PICN (Vita Enamic); “0.5-COC”: 0.5 mm thick tooth shaded resin composite (Lava Ultimate) and “1.0-COC”: 1.0 mm thick tooth shaded resin composite (Lava Ultimate). Consecutively, the specimens were thermo-mechanically aged and then loaded until fracture. The load-bearing capacities (Fmax) between the groups were statistically compared using the Kruskal-Wallis test (p < 0.05) and pairwise group comparison applying the Dunn's method. In addition, the results were compared to those of conventional lithium-disilicate ceramic crowns (“CLD”) and to porcelain-fused to metal crowns (“PFM”). ResultsThe median Finitial values for the 0.5 mm thin restorations were 1′350 N for 0.5-ZIR, 850 N for 0.5-LDC, 1′100 N for 0.5-HYC and 1′950 N for 0.5-COC. With CLD as the control, a significant difference was found between the groups 0.5-COC and 0.5-LDC (KW: p = 0.0124). With PFM as the control, the comparisons between PFM and 0.5-LDC as well as between 0.5-COC and 0.5-LDC were significant (KW: p = 0.0026). Median Fmax values of 2′493 N in the group 0.5-ZIR, 1′165 in the group 0.5-LDC, 2′275 N in the group 0.5-HYC and 2′265 N in the group 0.5-COC were found. The medians of the Finitial values for the 1.0 thick restorations amounted of 2′100 N in 1.0-ZIR, 1′750 N in 1.0-LDC, 2′000 N in 1.0-HYC and 2′300 N in 1.0-COC. Testing the multiple comparisons with Dunn's method no significant differences were found (p > 0.05). The median Fmax values of the 1.0 mm thick restorations were: 2′489 N in the group 1.0-ZIR, 1′864 N in the group 1.0-LDC, 2′485 N in the group 1.0-HYC and 2′479 N in the group 1.0-COC. With CLD as the control group, a significant difference between zirconia and lithium-disilicate was found for the 0.5 (p = 0.0017) and 1.0 mm (p = 0.0320) thick specimens. Comparing the 0.5 mm thick specimens with CLD as the control, a significant difference was found between 0.5-HYC and 0.5-LDC (p = 0.0017). With PFM as the control, the comparison of lithium disilicate and zirconia was statistically significant for both thicknesses (p = 0.0009 for the 0.5 mm thick specimens; p = 0.0074 for the 1.0 mm thick specimens). In addition, with PFM as control group, significant differences were seen between 0.5-LDC and all other groups with restorations in 0.5 mm thickness (p = 0.0017). ConclusionsRegarding their maximum load-bearing capacity, minimally invasive occlusal veneers made of ceramic, hybrid materials or polymeric materials can be applied to correct occlusal tooth wear with exposed dentin and thus replace conventional crown restorations in cases of normally expected intraoral bite forces.

Resistance spot weldability of galvannealed and bare DP600 steel

Resistance spot welding (RSW) of galvannealed and bare dual phase (DP600) steel is a challenging task as it involves the additional complexity of zinc coating layer. This study is focused on optimization of spot welding parameters, viz., welding current and time to achieve maximum load bearing capacity in tensile-shear and coach-peel configurations. Study revealed a minimum critical nugget diameter is needed above which favorable pull-out failure is observed. Critical nugget diameter for pull-out failure is determined to be 4.4 mm. Applicability of different empirical and metallurgical models for determination of critical nugget diameter were assessed. Transition from partial interfacial to pullout failure mode has been explained on the basis of combined effect of increased nugget diameter and micro-mechanism of fracture. It was observed that the there was an increase in nugget diameter and load bearing capacity of the spot welds with an increase in welding current as well as welding time. Best fit equations have been proposed for maximum load bearing capacity as a function of spot welding parameters and nugget diameter. Microstructural evolution and hardness variation across different welding zones have been presented in detail. Redistribution of zinc in different zones of welding has been evaluated using electron probe micro-analysis.

Configuration Optimization for maximum load bearing capacity per unit weight of a Plane Truss using Exhaustive Searching approach

Configuration Optimization for maximum load bearing capacity per unit weight of a Plane Truss using Exhaustive Searching approach

Universal and Nonuniversal Aperture‐to‐Length Scaling of Opening Mode Fractures Developing in a Particle‐Based Lattice Solid Model

AbstractOpening‐mode fractures, such as joints, veins, and dykes, frequently exhibit power‐law aperture‐to‐length scaling, with scaling exponents typically ranging from 0.5 to 2. However, published high quality outcrop data and continuum‐based numerical models indicate that fracture aperture‐to‐length scaling may be nonuniversal, with scaling being superlinear for short fractures and sublinear for long fractures. Here we revisit these published results by means of a particle‐based lattice solid model, which is validated using predictions from linear elasticity and linear elastic fracture mechanics. The triangular lattice model composed of breakable elastic beams, with strengths drawn from a Weibull distribution, is used to investigate the fracture aperture‐to‐length scaling that emerges in a plate subjected to extension. The modeled fracture system evolution is characterized by two stages which are separated by the strain at which peak‐stress occurs. During the pre‐peak‐stress stage, aperture‐to‐length scaling is universal with a power‐law exponent of about one. Shortly after the material has attained its maximum load bearing capacity, which coincides with the formation of a multiple‐segment fracture zone, aperture‐to‐length scaling becomes nonuniversal, with power‐law exponents being consistent with earlier studies. The results presented here confirm that deviation from universal scaling laws is a consequence of fracture interaction. More specifically, the onset of nonuniversal aperture‐to‐length scaling coincides with the formation of a multiple‐segment fracture zone.

Experimental and numerical investigation of sandwich structures with balsa core and hybrid corrugated composite/balsa core under three-point bending using digital image correlation

Sandwich structures are commonly used in automotive, aerospace, and civil infrastructure applications due to their high strength-to-weight and stiffness-to-weight ratios. In the present work, the performance of sandwich structures with aluminum facings and two different types of core, including balsa wood core and hybrid corrugated composite/balsa core subjected to three-point bending, is investigated, both experimentally and numerically. The face sheets are 6061-T6 aluminum alloy and the hybrid core has been made of balsa wood with average density of 125 kg m−3 and E-glass woven fabric, bonded together using epoxy resin. For data acquisition during the tests, a linear variable differential transformer has been placed under the mid-span of the specimens and a digital image correlation technique has been used for monitoring the full-field strain distributions and deflection pattern as well. Continuum damage mechanics has been employed for the finite element model analysis of the three-point bending tests. In order to predict the maximum load-bearing capacity and failure modes, a wood material behavior model for balsa and a combination of Hashin and Puck failure criterion for corrugated composite were imported into ABAQUS/Explicit via VUMAT subroutines. It was found that combining balsa core with corrugated composite results in prevention of catastrophic failure and consequently gradual decrease of load-bearing capacity. Furthermore, the results demonstrate that the hybrid core increases the strength-to-mass density and stiffness-to-mass density ratios by 34.7% and 28.2%, respectively. Numerical findings have been successfully compared to experimental data, which reveals its suitability for parametric analysis of the proposed hybrid core sandwich structure.

Equivalent reinforcement isotropic model for fracture investigation of orthotropic materials

In this research, an efficient mixed mode I/II fracture criterion is developed for fracture investigation of orthotropic materials wherein crack is placed along the fibers. This criterion is developed based on extension of well-known Maximum Tensile Stress (MTS) criterion in conjunction with a novel material model titled as Equivalent Reinforced Isotropic Model (ERIM). In this model, orthotropic material is replaced with an isotropic matrix reinforced with fibers. A comparison between available experimental observations and theoretical estimation implies on capability of developed criterion for predicting both crack propagation direction and fracture instance, wherein the achieved fracture limit curves are also compatible with fracture mechanism of orthotic materials. It is also shown that unlike isotropic materials, fracture toughness of orthotic materials in mode I cannot be introduced as the maximum load bearing capacity and thus new fracture mechanics property, named here as maximum orthotropic fracture toughness in mode I is defined. Optimum angle between crack and fiber direction for maximum load bearing in orthotropic materials is also defined.

Woven collagen biotextiles enable mechanically functional rotator cuff tendon regeneration during repair of segmental tendon defects in vivo.

Despite advancements in surgical techniques and materials for rotator cuff repair procedures, primary repair failures remain common. This study examines the use of electrochemically aligned collagen (ELAC) threads woven into biotextile scaffolds as grafts to repair critical infraspinatus tendon defects in New Zealand White rabbits. Three surgical treatment groups were evaluated: rabbits undergoing direct repair as operative controls, rabbits receiving ELAC scaffolds alone, and rabbits treated with mesenchymal stem cell (MSC)-seeded ELAC scaffolds. In each animal, the intact, contralateral infraspinatus served as an internal positive control. Tendon-bone constructs were harvested after 3 months in vivo and outcome measures included biomechanical testing, histological staining, and immunohistochemical staining. Biomechanical testing revealed that maximum load-bearing capacity was comparable between all groups, while MSC-seeded scaffold repairs exhibited increased stiffness relative to non-seeded scaffold repairs. Histological staining revealed robust collagen deposition around ELAC fibers and increased cellularity within the continuum of woven scaffolds as compared to native tendon. Immunohistochemical staining revealed presence of collagens I and III in all groups, but procollagen I and the tendon-specific marker tenomodulin were only observed in seeded and non-seeded ELAC scaffold repairs. Findings of this pilot study warrant continued investigation of ELAC biotextile scaffolds for repair of critically-sized rotator cuff tendon defects. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1864-1876, 2019.

Ultra-thin occlusal veneers bonded to enamel and made of ceramic or hybrid materials exhibit load-bearing capacities not different from conventional restorations

ObjectivesThe objective of this study was to test whether or not the load-bearing capacity of occlusal veneers bonded to enamel and made of ceramic or hybrid materials does differ from those of porcelain-fused-to-metal or lithium disilicate glass ceramic crowns. Material and methodsIn 80 human molars occlusal enamel was removed without extending into the dentin in order to mimic substance defects caused by attrition. The restorations were digitally designed at a standardized thickness of either 0.5 mm or 1.0 mm. For each thickness, 4 test groups were formed each including a different restorative material: “0.5-ZIR”: 0.5 mm thick zirconia (Vita YZ HT); “1.0-ZIR”: 1.0 mm thick zirconia (Vita YZ HT); “0.5-LDC”: 0.5 mm thick lithium disilicate ceramic (IPS e.max Press); “1.0-LDC”: 1.0 mm thick lithium disilicate ceramic (IPS e.max Press); “0.5-HYC”: 0.5 mm thick PICN (Vita Enamic); “1.0-HYC”: 1.0 mm thick PICN (Vita Enamic); “0.5-COC”: 0.5 mm thick tooth shaded resin composite (Lava Ultimate) and “1.0-COC”: 1.0 mm thick tooth shaded resin composite (Lava ultimate). Each group consists of 10 specimens. Two additional groups of 10 specimens each were used as controls and exhibited conventional crown preparations. In one group the crowns were made of lithium-disilicate ceramic (“CLD”: IPS e.max CAD) and the other group consisted of porcelain-fused to metal crowns (“PFM”). All restorations were cemented onto the prepared teeth following the manufacturer's instruction of the corresponding luting cement. Subsequently, they were thermo-mechanically aged and then loaded until fracture. Load-bearing capacities (Fmax) between the groups were compared applying the Kruskal-Wallis test (p < 0.05) and pairwise group comparisons using the Dunn's method. ResultsMedian values (and quartiles) for the load-bearing capacity amounted to (Fmax) 2′407 (1′670; 2′490) N for the CLD group and to 2′033 (1′869; 2′445) N for the PFM group. For the 0.5 mm thick restorations Fmax reached the highest median value in group 0.5-HYC 2′390 (1′355; 2′490) N, followed by 0.5-COC 2′200 (1′217; 2′492) N and 0.5-LDC 1′692 (1′324; 2′355) N. No results were obtained for group 0.5-ZIR due to the impracticability to fabricate ultra-thin specimens. The distribution of the values for the 1.0 mm thick restorations was 2′489 (2′426; 2′491) N for 1.0-COC, 2′299 (2′156; 2′490) N for 1.0-ZIR, 2′124 (1′245; 2′491) N for 1.0-HYC, and 1′537 (1′245; 1′783) N for 1.0-LDC. The differences of the medians between the test and the control groups did not reach statistical significance for the 0.5 mm thick specimens (KW: p = 0.6952 and p = 0.6986). Within the groups exhibiting 1.0 mm thickness, however, significant different medians were found: 1.0-LDC < 1.0-ZIR and 1.0-LDC < 1.0-COC (KW: p < 0.0209). ConclusionsRegarding their maximum load-bearing capacity, minimally invasive occlusal veneers made of ceramic and hybrid materials can be applied to correct occlusal tooth wear and thus replace conventional crown restorations.

Achieving high mechanical performance in protrusion friction stir spot welding (PFSSW) of DQSK steel compared to other techniques

Protrusion friction spot stir welding (PFSSW) was introduced as a novel method to produce keyhole-free welds of a drawing quality special killed low carbon steel (DQSK). The effects of welding parameters such as tool rotation speed and plunging depth were investigated on the mechanical properties and metallurgical aspects. The sheet/sheet joint interface of the welds produced by PFSSW was visible and non-planar compared to the conventional FSSW method. Microstructure and hardness were affected by dynamic recrystallization and transformation hardening in the stir zone. Hardness value of the stir zone produced by the present work was much lower than that produced by resistance spot welding process due to martensite-free ferritic microstructure in the stir zone. Although all of the welds produced by the present work were failed in interface fracture mode, they exhibited the maximum load bearing capacity compared to other techniques.