Axial Loading Conditions Research Articles

The influence of thickness/grain size ratio in microforming through crystal plasticity

Microscale forming operations have become popular due to miniaturisation which focuses on micro scale design and manufacturing of devices, components and parts, e.g. in RF-MEMS. In such processes when the component dimension becomes comparable with the grain size, considerable size effect is observed. Recent experimental studies on micron sized sheet specimens have shown that the ratio between thickness (t) and grain size (d) has a significant influence on the mechanical behavior of materials which cannot be explained merely with the intrinsic (grain) size effect. Even though the grain sizes are similar, remarkable differences in mechanical response is obtained for cases with different thicknesses. In this context the aim of the current study is to address this extrinsic type size effect through crystal plasticity simulations. A series of local crystal plasticity finite element simulations are conducted for different values of t/d ratio in tensile specimens. Different granular morphologies of polycrystalline samples are generated using Voronoi tessellation and tested under axial loading conditions. The macroscopic influence of varying t/d ratio is studied in detail and compared with the experimental findings in the literature.

Analysis of optimum stacking sequence of GFRP composite laminate under axial loading condition

Composites' popularity/use in the aerospace, automobile, and defense industries has lately expanded because to its cheaper production costs, light weight, higher fracture toughness, low thermal expansion, corrosion resistance, and better control over thermo-mechanical properties. Because of their fiber orientations, FRC have a strong anisotropic mechanical response. Present work is aimed in shaping the most favorable stacking sequence of the GFRP composite laminate under axial loading situations; these orientations create a variety of failure modes, which are more complex. The studies used MATLAB and simulation methods (ANSYS) to evaluate stress, strain, and deformation values in order to better understands and predict the behavior of GFRP Composite laminates with various unidirectional fiber orientations under plane stress conditions.

Model of thermomechanical behavior of a shock-absorbing unit

Modern industries use structures that should meet strict requirements for dynamic characteristics specified in many branches, such as aviation, military, instrument–making, automotive, etc. The fulfillment of these requirements is associated, in particular, with the use of the damping systems of structures, the operation of which is determined by a complex of nonlinear processes (contact interaction, dry friction, large deformations, etc.), thus making the task of constructing their mathematical models relevant. The currently used approaches to modeling these systems do not fully take into account the nonlinear effects intrinsic to the above processes, or require significant computational resources, and may also require a large number of experiments. The purpose of this study is to construct and identify a model of deformation of a shock absorber, taking into account friction, temperature, viscoelastic and hyperelastic behavior of the material and to determine the following integral thermomechanical characteristics of a shock absorber under various loading conditions: a shock absorber response to displacement, the amount of heat released during one deformation cycle, the magnitude of the friction force. At the first stage, a model of visco-hyperelastic behavior of a material is constructed and its parameters are calculated based on the real experiment data. The hyperelastic characteristics were determined using the results of free tension-compression and constrained compression tests, and the parameters of the viscoelastic model were found in the harmonic load and variable temperature experiments. Then, a finite element model of the damper is constructed using the ANSYS software package and the parameters of friction due to contact interaction are determined by making comparison with the results of deformation tests of the shock absorber under the conditions of axial and transverse loading. At the last stage, the constructed model is used to evaluate the thermomechanical behavior of the shock absorber under cyclic deformation, which is also realized during vibration. As a result, the dependencies of viscous and dry friction energy released during one deformation cycle on the friction coefficient, velocity and temperature are obtained.

Effect of Implant Design on Stress Distribution: A Finite Element Study.

Implant design and biomaterial composition are contributing factors in stress distribution throughout the implant body and the surrounding bone. The aim of this study was to evaluate the pattern of stress distribution using four different implant systems based on finite element analysis. This study was conducted using a cone beam computed tomography scan and four implant systems (ITI, SPI, 3i, and IDCAM); mandibular and implant models were constructed by a computer-aided design software (CATIA). Stress distribution under axial, mesio-distal, and combination static loading was assessed using finite element analysis in ABAQUS. The maximum von Mises stress value in dental implants was recorded for IDCAMs and IDCAMm implants considering all types of loading directions; however, these implant models showed the least stress distribution in the surrounding bone. The maximum stress occurred using combination followed by axial and mesio-distal loading. The stress distribution was concentrated, in all designs, at the level of the most coronal portion of the cortical bone. Within the limitations of the present study, it could be assumed that implant design may affect the distribution of stress in the implant body, and it could be used as a strategy to reduce stress concentration in the surrounding bone.

An in vitro investigation of the fracture strength of root-filled - posterior teeth restored with polymer full-coverage crowns

Objectives: To investigate, by an in vitro study, the fracture strength of root-filled teeth restored with polyetheretherketone (PEEK) full-coverage crowns.Materials and Methods: Two single-rooted maxillary second premolar Typodont teeth were prepared according to the standardized preparation guidelines for two different full-coverage crown restorations: computer-aided design/computer-aided manufacturing monolithic lithium disilicate crowns (E.max) for the control samples and machine pressed monolithic PEEK crowns for the test samples. Teeth were duplicated in a polyurethane-based resin, with properties analogous to human dentin; n = 5 for each category. Replicas were embedded in polyurethane-based resin material using a retaining copper ring, with a simulated 200-μ periodontal ligament. Subsequently, all samples received orthograde root canal treatment using standardized preparation and obturation techniques. Crowns were cemented with resin-modified glass ionomer cement using a standardized cementation force. All teeth were subjected to a monotonic, axial static load of 2500 N to the point of fracture.Results: All control group samples displayed failure as a combined crown/tooth fracture. The crowns in the test group samples (PEEK) did not fracture under the experimental loads. Under the maximum loads, the crowns exhibited plastic deformation visible as an indentation created on the occlusal surface. Subsurface cohesive damage of the interface cement was noted. T-test showed that the resistance to fracture of the test group compared to the control group was highly significant (P < 0.001).Conclusions: Within the limitations of this study, PEEK crowns help preserve the remaining tooth structure and provide more predictable protection when compared to E.max crowns. They demonstrate failure by surface deformation and subsurface cohesive damage to the interface cement layer. It is unknown if this failure mode would occur under normal masticatory loads.

Lateral Impact Response of Elliptical Hollow and Partially Concrete-Filled Cold-Formed Steel Columns Under Static Axial Compression Load

In recent years, the use of partially concrete-filled steel tubular (PCFST) columns has been considered due to their cost-effectiveness and reduction of structural weight in bridge piers and building columns. One of the critical discussions about these columns is their impact resistance. In this article, the dynamic response of hollow and PCFST columns with elliptical cross-section under simultaneous loading of static axial compressive load and lateral impact load is presented using finite element modeling in ABAQUS software (FEA). To ensure the accuracy of the numerical modeling, the analysis results are compared with the results of previous works. The effects of different parameters such as impact velocity, the height of the impact location, the impact direction, the impact block mass, the size and shape of the impact block are investigated in this paper. The results of the numerical analysis showed that the partially filled specimens had better performance than the hollow specimens. The changes in impact direction and impact block mass parameters have a significant effect on the failure of the columns, especially when they are under high impact velocity. Changing the impact velocity significantly affects the impact resistance of specimens. However, the size and shape of the impact block did not have a significant effect on the displacement of the column against the impact loading.

Dynamic Mechanical Characteristics of Impact Rock under the Combined Action of Different Constant Temperatures and Static and Dynamic Loads

The complex mechanical environment of deep coal and rock masses leads to obvious changes on their dynamic mechanical properties. However, there are few reports on the dynamic mechanical properties of rocks under the combined action of medium temperature (normal temperature ∼100°C) and static and dynamic loads. In this paper, a dynamic load and temperature combined action Hopkinson pressure bar experimental system is used to experimentally study the impact type of a fine sandstone under temperature conditions of 18°C, 40°C, 60°C, 80°C, and 100°C, an axial static load of 3 MPa, a gas chamber pressure of 0.06 MPa, and a constant temperature time of 4 h. The dynamic characteristics of the change law of the fine sandstone and the energy dissipation characteristics of the load process are analyzed, and the characteristic law of the fine sandstone surface response is analyzed using digital image correlation technology. Our results indicate the following. (1) Under conditions in which the other experimental conditions remain unchanged, the dynamic stress-strain of the fine sandstone presents a bimodal shape with a “rebound” phenomenon. Increasing temperature causes the peak strength of the fine sandstone to increase; however, the relative strength can increase or decrease. The relative increase in the strength is 1.14 MPa (°C) when the temperature increases from 40°C to 60°C, 0.15 MPa (°C) when the temperature increases from 60°C to 80°C, and 0.62 MPa (°C) when the temperature increases from 80°C to 100°C. (2) The digital image correlation results show that, under the action of a dynamic load stress wave, the fine sandstone experiences a displacement vector change on the sample surface; furthermore, under the combined action of the temperature and dynamic and static loads, the fine sandstone experiences macroscopic shear failure. The surface strain in the propagation direction of the stress wave is obviously higher and can even reach values of more than 10 times that of the strain in other directions. (3) From the perspective of energy dissipation, the incident energy, reflected energy, and dissipated energy of the fine sandstone under an impact load have the same change law. After being affected by a dynamic load, the energy rapidly increases to a certain value and then remains relatively stable. The transmitted energy is relatively small and can be approximated as a horizontal line. As the temperature increases, the incident energy, reflected energy, and dissipated energy tend to first decrease and then increase, and most of the incident energy in the fine sandstone is dissipated in the form of reflected waves.

A new concept for improving the structural resilience of lap-welded steel pipeline joints

Lap-welded steel joints are widely used in steel pipelines for water transmission, and their structural resistance is essential for safeguarding pipeline integrity and functionality after severe earthquakes or other geohazards. These pipelines are thin-walled with a diameter-to-thickness ratio ranging between 100 and 240 and are susceptible to buckling. The present paper is part of a longtime research project on the structural performance of lap-welded steel pipeline joints subjected to severe inelastic deformations, motivated by the need of pipeline safety in geohazards areas. The work described in the present paper focuses on the mechanical behavior, analysis, and design of a new seismic resistant lap-welded joint which was developed to improve the structural performance of lap-welded steel pipelines. Analysis consists of extensive finite element simulations, supported by a series of special-purpose full-scale experiments, on the mechanical response of the new lap-welded joints subjected to severe structural (axial and bending) loading conditions. The proposed joint consists of the standard lap weld configuration, enhanced by a small geometric projection introduced at a specific location near the field-applied fillet weld. The numerical and experimental results demonstrate that under severe compressive loading, this enhancement of the standard lap-welded joint results in consistent and preferential buckling of the steel pipe cylinder and not the lap-welded joint. The proposed joint effectively allows for the steel pipeline resistance to not be limited by the compression capacity of the standard lap-welded joint and offers an efficient, reliable, and economical solution for lap-welded joints in steel water pipelines constructed in geohazard areas.

Numerical Analysis of Failure Mode of Micropile in Cohesive Soil

In this paper, fnite element was used to study the behavior of micropile. The model was developed using PLAXIS 3D foundation program. Micropiles are tested by the static axial load testing of individual piles. In the FE-analysis the pile is assumed to be linear elastic and for the subsoil is assumed as Mohr-Coulomb model. The model was developed to simulate the micropiles type A where the grouting is applied by gravity. This modeliscompared with the results of the pile load test. A good agreement was obtained with the experimental results. Finally the failure pattern was investigated.

Response of pile group adjacent to a slope crest under static axial loading

Response of pile group adjacent to a slope crest under static axial loading

Dynamic behaviour and failure mechanism of coal subjected to coupled water-static-dynamic loads

The stability of a coal pillar dam in a coal mine underground reservoir is affected by water pressure, static geo-stress, and coal mine earthquakes. Thus, it is essential to accurately evaluate the dynamic behaviour of coal under coupled water-static-dynamic loads to reasonably design a coal pillar dam. In this study, an innovative test system was developed based on a split Hopkinson pressure bar (SHPB) device, and a series of impact tests of coal under the coupled action of impact load, static axial preloading, and water pressure were performed with this system. The effects of coupled water-static-dynamic loads on mechanical behaviours, including strength and deformation characteristics, failure mode, and energy dissipation of the coal samples were systematically investigated. Results showed that the dynamic deformation process of the coal samples can be divided into three stages: linear elastic deformation stage, crack unstable propagation stage, and post-peak failure stage. Impact and higher axial static loads were the two negative factors that made the coal samples more prone to damage. In contrast, the presence of water pressure positively affected the sample, which improved the dynamic strength and reduced the failure strain of the sample. Energy dissipation characteristics showed that water pressure enhanced the energy utilisation efficiency of the sample. Furthermore, the microcosmic mechanism of free water protecting coal from the fractures was also examined.

Fire damaged ultra-high performance concrete (UHPC) under coupled axial static and impact loading

The load bearing structural components such as columns could experience axial static loads during the service life. High temperature induced by fire would have a significant detrimental impact on the mechanical properties of concrete materials. The structure could be severely damaged as the column was simultaneously loaded by other impact loads. In this study, the behavior of fire damaged ultra-high performance concrete (UHPC) with a compressive strength of 128.3 MPa under coupled axial static and impact loading was studied. UHPC specimens were heated to the target temperatures (250, 500 and 750 °C) in an electric furnace and then naturally cooled down to room temperature. The results demonstrated that the P-wave velocity and compressive strength of the heated-cooled treatment UHPC degraded significantly as the target temperature exceeded 250 °C. The impact tests were then conducted on the heated-cooled treatment UHPC specimens with axial static compression. The experimental results indicated that the axial static compression could enhance the dynamic mechanical properties such as compressive strength and elastic modulus in the elastic phase and weaken the dynamic mechanical properties in the plastic phase. In addition, the dynamic increase factor (DIF) of UHPC exhibited an increase with the temperature. The UHPC specimen could withstand a temperature of 250 °C, but lost most of its strength at temperatures of 500 and 750 °C. Thus, the axially loaded static force accelerated the failure of the specimen after being heated to above 250 °C.

Deformation Mode and Energy Absorption Analysis of Bi-Tubular Corrugated Crash Box Structure

In this research, the characteristic of crash box with bi-tubular corrugated structure are numerically examined under axial loading condition. The crash box characteristic were observed in the compression test of aluminum alloy (AA6061) using ANSYS software. The comparation were carried out on two geometrical types, namely: ordinary corrugated tube (OCT) and bi-tubular corrugated tube (BCT). The result showed that comparing both of crash box structure exhibit the Simultaneous crush mode (S-mode) deformation. The force-displacement present a stable diagram without any fluctuation. BCT structure resulted 71% energy absorption capacity increment compared to OCT structure. The highest energy absorbed by BCT structure was 10.8 kJ. There are no significant specific energy absorption different between the specimen and the highest SEA occurat OCT structure with 31.281 kJ kg-1.

Optimization and modeling of axial strength of concrete-filled double skin steel tubular columns using response surface and neural-network methods

The main objective of this study is to optimize and model the ultimate strength of axially loaded concrete-filled double skin steel tubular (CFDST) composite columns having a circular hollow section . By performing the multi-objective optimization analysis through the response surface methodology (RSM), an ultimate strength-based optimal design solution for CFDST composite columns was proposed. Besides, artificial neural networks (ANN) together with RSM techniques were used to develop design formulations that can be involved in the prediction of the ultimate axial strength of such types of composite columns. An experiment data repository compiled from the studies available in the literature was used in both optimization and modeling analysis. The aim of the optimization was to achieve the optimum values for the design parameters based on the maximum capacity. However, in the modeling, attaining a design formula having an accurate and reliable prediction performance was the purpose. Furthermore, a verification study in which the developed models were compared with the modified design formulas of the AISC and Eurocode 4 and some existing models proposed by the researchers was carried out. It was observed that the generated models gave a good estimation capability with a considerably high R-squared value and fewer errors. After statistically analyzing the outputs of the models, it was proved that the models proposed in the current study yielded more reliable, accurate, and consistent prediction performance than the existing formulas. Besides, it was indicated the optimization analysis has a desirability value of 0.942, meaning an almost perfect optimization. • The CFDST composite columns were optimized based on ultimate strength. • The ultimate strength-based modeling of the CFDST columns was carried out. • The axial loading condition was considered in the modeling. • Reliable and accurate numerical models were developed. • Optimum properties for the CFDST column with the CHS were achieved.

Unified fatigue life prediction of bolts with different sizes and lengths under various axial loading conditions

Bolts tend to show different fatigue behavior with respect to the size or shape of a bolt and the level of preload though it is the same material. This makes it difficult to predict the fatigue life of bolts. In this study, a novel method to construct a unified stress-life (S-N) curve was proposed for the three different bolts with different sizes and lengths subjected to various external axial loading conditions and preloads, ranging from 44 % to 88% of the ultimate tensile stress. A total of 133 experiments for 46 different fatigue conditions were conducted and finite element analysis was also performed to calculate multiaxial stress components at the root of the thread. The fatigue characteristics of the bolts were investigated depending on various loading conditions, and the life prediction performance with fitted S-N curves was compared with respect to four mean stress correction models. The unified S-N curve showed high accuracy in life prediction; 15 % mean absolute error without exceeding ± 50 % for finite life loading conditions.

A built-up type horizontally corrugated steel plate shear wall with a special shape

A built-up type specially shaped corrugated steel shear wall (BS-CSSW) that can be concealed within enclosure walls was proposed for applications in residential buildings. Quasi-static tests were performed on two specially shaped corrugated steel shear wall specimens (S-CSSW and BS-CSSW) and refined finite element simulations were conducted. With the verified modeling method, a parametric study was performed on BS-CSSWs with different wall configurations and interior column positions. The results indicated that the corrugated shear plates in the S-CSSW underwent premature elastic buckling, thus leading to a sudden drop in strength upon buckling and low strength levels after buckling. Shear panels in the BS-CSSW successfully entered the shear yielding mode and remained in a stable in-plane shearing state until reaching 2% drift. The BS-CSSW had higher elastic and plastic strength levels, better ductility, slower stiffness reduction, lower out-of-plane plate deformation and a wider hysteretic relationship than those of the S-CSSW. The position of the interior columns primarily influenced the slenderness of the side and interior corrugated panels and affected the strength development modes. The BS-CSSWs had separate bearing modes between lateral loads and axial loads and could withstand high axial load conditions with little influence on shear strengths.

Natural frequencies and vibration modes of tank's protective capacitance with weld defects under axial static load

The natural frequencies and vibration modes of tank's protective capacitance with welded joints defects under axial static load are determined in order to construct a diagnostic model and monitor of the welded joints defects propagation. Computer simulation of capacitance dynamic behavior using the computer finite element analysis system NASTRAN was performed. The design model in the form of a cylindrical thin-walled shell with allowance for belts from weld rolled sheet was built. Weld defects as two through horizontal cracks located in the welds between the first and second shell belts were presented. The crack width was equaled to the rolled sheets diameter. For assessing the effect of crack propagation on the shell dynamic characteristics the crack length increased until a single continuous crack. The defects in the form of through cracks allowed to generalize different weld defects types and predict the shell critical state. Determination of capacitance natural frequencies and vibration modes under axial static load was performed in two stages. At the first stage, the capacitance stress-strain state in a nonlinear formulation was investigated and a total stiffness matrix (linear and geometric) was formed. The nonlinear static problem as a finite element approximation of the Lagrange possible displacements principle was formulated. The Newton-Raphson stepwise loading method (Nonlinear Static) was used. The natural frequencies and vibration modes were determined by by the Lanczos method (Param Modes) on solving the eigenvalue problem. The effect of weld defects and axial static action on the capacitance dynamic characteristics was evaluated. The results showed that the presence of cracks and an their length increase reduced the values of the natural frequencies. The static action of an axial compressive load on a thin shell wall can both reduce and increase its rigidity, thereby changing its natural frequency and vibration modes. According to the authors, consideration of such a load should be present in the dynamic calculations of thin shells, especially under stochastic loads (wind, seismic, etc.).

Buckling behaviors of thin-walled cylindrical shells under localized axial compression loads, Part 2: Numerical study

In the second part of this series paper, a high-fidelity finite element model was established first to systematically study the buckling behaviors of thin-walled cylindrical shell subjected to localized axial compression load. By comparing with the experimental results, the feasibility and accuracy of the present FE model were validated. Then, the buckling mechanism, failure mode and load carrying capacity of cylindrical shell under localized axial compression load were thoroughly discussed and elucidated. Finally, some key factors that affect the buckling behaviors of cylindrical shells were carefully investigated, including material yield strength, the amplitude and topography of initial geometric imperfections, and the location of localized axial compression load along shell circumference. Results indicated that the distribution scope of localized axial compression load, shell material yield strength and the amplitude of initial geometric imperfections play a dominant role in the buckling behaviors of cylindrical shell under localized axial compression loads. The experimental and numerical investigations carried out in this research work can be regarded as a systematic attempt to study the buckling problems of thin-walled cylindrical shell structures under the more complex and practical axial load conditions. The results and conclusions obtained from this paper can also provide some guides for the design and application of thin-walled cylindrical shell in actual engineering.

The effect of commercial herbal toothpastes on dental wear: a comparative evaluation by Optical coherence tomography

The purpose of this study was to compare the tooth wear in function of the use of different commercial herbal toothpastes through the analysis of Optical Coherence Tomography (OCT). Twenty bovine teeth were obtained and distributed in 4 groups (n = 5) according to the dentifrice used: G1: Captive Nature (Chamomile, Xylitol, Juá and Salvia); G2: Suavetex Content (Turmeric); G3: Colgate Triple Action (positive control); G4: distilled water (negative control). The samples were painted in the half of the fragment with nail polish so that only half of the fragment was brushed. The simulated brushing (20,000 cycles) was performed with linear movements, under static axial load of 200g and speed of 4.5 cycles per second. After this step, an analysis was performed through OCT and and the images obtained were evaluated to identify possible changes in the specimen surface. According to the qualitative analysis of the OCT images, enamel wear was not observed, since all measurements were null. Regarding the evaluation of dentin, surface wear was observed in all groups except G4, but G3 had the highest number of samples with surface wear around 21.32%. All dentifrices had abrasive wear on the dentin surface to a greater or lesser extent, but there was no wear on the enamel surface.

Applicability of Concrete–Steel Composite Piles for Offshore Wind Foundations

Offshore wind-turbine support structures are largely made of steel since steel monopiles have accounted for the majority of installations in the last decade. As turbines become bigger, steel structures have led to an exponential increase in material and installation costs. From this point of view, the use of concrete for future support structures has been initiated. In this study, concrete–steel composite piles have been investigated. A pre-tensioned high strength concrete pile was placed in the lower part, mainly to support the axial load, and a steel pile in the upper part to resist the lateral load. A mechanical joint was adapted to connect the two different types of piles. Static axial, dynamic axial, and lateral load tests were performed to evaluate the load-displacement response of the composite pile, verify the integrity of the mechanical joint, and investigate its potential application to offshore wind foundations. This paper focused on the load-displacement response and the connection integrity; in particular, it investigated the lateral load-displacement response by comparing it to the results of beam-spring analysis. Based on the results from the field tests, a site-specific lateral load-displacement curve was suggested, and the connection integrity was verified.