Axial Loading Conditions Research Articles

Permeability Evolution of Fractured Rock Subjected to Cyclic Axial Load Conditions

Permeability experiments on saw-cut fractured rock subjected to cyclic axial load conditions were conducted on the MTS815 rock mechanics testing system. The influence of the frequency and amplitude of cyclic axial forces on axial displacement and permeability evolution of fractured rock was experimentally investigated. Results show that the increasing frequency under the same amplitude of axial load leads to a reduction in axial displacement, but a drop followed by an increase in permeability, while the permeability values oscillated sharply under high amplitude of cyclic loads, which can be attributed to the production of gouge materials. Besides, the increase in axial displacement roughly contributed to the permeability reduction, and excessive amplitude of cyclic load posed limited boost to the permeability enhancement. By comparing with the quasistatic function, we found that it did not completely correspond to the trend of the permeability evolution subjected to cyclic axial forces, and sensitivity coefficients evolving with frequency and amplitude should be considered. A new function of the permeability evolution subjected to the amplitude and frequency of cyclic axial forces was derived and verified by the experimental data. This study suggests that small amplitude and high frequency of dynamic forces have the potential for enhancing the permeability of fracture and triggering the disaster of fractured rock.

Conductivity performance evaluation of fractures filled with proppant of different sizes in shale with LBM-DEM

This paper proposes a coupled discrete element method (DEM) and lattice Boltzmann method (LBM) to compute the conductivity of fractures filled with proppant in shale as a function of the closure pressure. The particle discrete element was applied to model proppant-shale interaction process under variable closure stress, and the pore-scale simulation was carried out by LBM to model gas flow in the reconstructed digitised model (the deformed proppant-filled fractures). The laboratory bench-scale experiments were conducted in support of the numerical modeling examining the proppant embedment into the shale as a function of closure stress and measuring the conductivity of proppant-filled fractures as the proppant embedment experiments were conducted under different axial load conditions. The numerical results calculated by LBM-DEM were validated by a calibration test and the laboratory bench-scale experiments, and an agreement was achieved between them, indicating the effectiveness of this proposed method. [Received: June 28, 2017; Accepted: February 1, 2018].

Influence of Bioactive, Resin and Glass Ionomer luting cements on the fracture loads of dentin bonded ceramic crowns.

Objective:To investigate the failure loads of dentin bonded all-ceramic crowns when luted with Bioactive, resin and glass ionomer cements (GIC) in an in-vitro setting.Methods:This study was conducted at King Saud University, Saudi Arabia, from Nov.2018 to March 2019. In this study, 60 premolar teeth were prepared for dentin-bonded ceramic crowns. Lithium disilicate ceramic crowns fabricated using CAD-CAM technique were cemented to teeth using Bioactive (ACITVA), Resin (Nexus 3 Gen) and GIC (Ketac Cem- Maxicap). Half of the bonded specimens in each group were thermocycled (50000 cycles), however the remaining half were not aged (n=10). Fracture loads of bonded crowns were assessed by exposing them to static axial occlusal loads (1mm/min) using a round ended metal probe in a Universal testing machine. Means and standard deviations among the study groups were compared with ANOVA and Tukey-Kramer multiple comparisons test.Results:Highest failure loads were observed in resin group without ageing (thermocycling) (689.13±89.41 N), however, the lowest loads were observed in GIC specimens with ageing (243.16±49.03 N). Among non-aged samples, failure loads for Bioactive (480.30±47.26 N) group were less than Resin (689.13±89.41 N) samples but higher than GIC (307.51±45.29 N) specimens respectively. Among the aged specimens, Bioactive (404.42±60.43 N) showed significantly higher failure loads than GIC (243.16±49.03 N), however lower failure loads than Resin (582.33±95.95 N) samples.Conclusions:Dentin boned crowns with resin cementation showed higher failure loads than Bioactive and GIC luted crowns. Crowns luted with Bioactive cement showed acceptable failure loads for use as restoration on anterior teeth.

ТЕОРЕТИЧЕСКИЕ ОСНОВЫ ДИАГРАММНОГО МЕТОДА РАСЧЁТА СТЕРЖНЕВЫХ ЭЛЕМЕНТОВ ИЗ АРМИРОВАННОГО БЕТОНА

At the present stage of development, the diagram method for calculating rod elements made of reinforced concrete has a number of disadvantages, which is due to the lack of a single holistic theory. The paper attempts to lay its foundations. For this purpose, the most General structure of the theory is developed, and a three-level computational model is proposed, hierarchically built on the principle of discretization of the computational scheme: level 1 - "element" - design model of the rod, built according to the well-known rules of construction mechanics; level 2 – "cross" – enhanced non-linear (discrete) deformation model, adopted by SP 63.13330 with some significant clarification of the author; level 3 – material – analysis model of standard samples of concrete and rebar subject to action of the axial compressive or tensile static short-term load or under static short-time load, pure shear (to describe proposed Jenny more deformation curve of concrete). A detailed algorithm for the relationship of models at all three levels is described.

Evaluation of axial crashworthiness performance of composite wrapped metallic circular tubular structures

Recently, most of the metallic vehicle structures have been substituted by innovative composite materials owing to its light-weight and better energy absorbing capability. Generally, the traditional metallic tubes deforms in progressive buckling mode whereas the composite tubes in catastrophic fracture mode. The combination of the metal with the composite materials can signify a better level of crashworthiness characteristics. In this context, crashworthiness performance of composite wrapped metallic circular tubular structures was examined experimentally under axial quasi-static loading conditions in the current study. The crushing mechanism and deformation history of the tested samples were presented and discussed. In addition, the influence of composite fabrics on the deformation profiles has also been defined. The experimental outcomes obtained revealed that the proposed composite wrapped metal tubes exhibit better energy absorbing capability in terms of controlled crushing mechanism and reduction of initial peak crushing force. These tubes could be applied as energy absorbing crashworthiness structures in automobile applications. [Copyright information to be updated in production process]

Comparative study of friction stir welding process and its variables

The Friction Stir Welding (FSW) process is an attractive material combined technique for similar and different alloys without material losses. The legend Wayne Thomas is the father of the FSW technique. At 1991 the material joining process was initiated and filed patents by the TWI Welding Institute in the UK. Initially, the FSW process was utilized to fabricate dissimilar weld joints. This material joining technique provides enormous advantages in aluminium alloy related components. The friction stir welding process has become a major material combining process without using the additional filler material. During material joining, the process does not release any type of gases and fumes. This material joining technique is a solid-state joining process and which is an environment-friendly. The solid-state joining process is utilized with a non-consumable rotating tool while joining two similar and dissimilar metals. This article looks, at an overview of friction stir welding process and variables such as tool revolving rate, tool travelling speed, different pin profiles, tool tilt angle, and axial loading conditions for joining of material joints. These FSW process variables, decide the quality of weld joints. Recently worldwide, more than 135 licenses have been filed for the FSW process. In the routine process, several new techniques and applications are being developed in the material joining process. A massive joining process (FSW) is recently widely utilized in the area of various applications like aeronautical, shipbuilding, rail manufacturing industries, especially for aluminium-related weld joints. In addition to the applications of FSW, various aspects and a number of key troubles are also discussed.

Dynamic Characteristics of Deep Dolomite Under One-Dimensional Static and Dynamic Loads

The failure characteristics of rock subjected to impact disturbance under one-dimensional static axial compression are helpful for studying the problems of pillar instability and rock burst in deep, high geostress surrounding rock under blasting disturbances. Improved split Hopkinson pressure bar equipment was used for one-dimensional dynamic–static combined impact tests of deep-seated dolomite specimens under axial compression levels of 0, 12, 24, and 36 MPa. The experimental results demonstrate that the dolomite specimens exhibit strong brittleness. The dynamic strength always maintains a strong positive correlation with the strain rate when the axial compression is fixed; when the strain rate is close, the dynamic elasticity modulus and peak strength of the specimens first increase and then decrease with the increase in axial compression, and the peak value appears at 24 MPa. The impact resistance of specimens can be enhanced when the axial compression is 12 or 24 MPa, but when it increases to 36 MPa, the damage inside the specimen begins to cause damage to the dynamic rock strength. Prior to the rock macroscopic failure, the axial static load changes the rock structure state, and it can store strain energy or cause irreversible damage.

Numerical Modeling of the Behavior of a Pile Foundation under Axial Load with Ansys

This paper studies the behavior of an isolated pile under static axial load and aims to analyze this type of foundation taking into account the soil-structure interaction. The implemented approach is a finite element analysis of a numerical behavior model of the soil-pile system, with emphasis on the behavioral parametric study of the system. A three-dimensional numerical model taking into account the geometric, mechanical and geotechnical parameters of the soil was used for modeling on Ansys using finite element method (FEM). This allowed us to study the influence of soil behavior (elastic or elastoplastic perfect) on the response of the pile under axial load. The study also shows that the increase of the soil reaction module gives rise to a dome effect or a much more pronounced thrust in the elastoplastic domain at a certain depth. The study also shows an increase of the reaction module of the soil mass with the depth and consequently a decrease of the deformations.

Dynamic mechanical characteristics and fracture mechanism of gas-bearing coal based on SHPB experiments

To investigate the dynamic characteristics and fracture mechanisms of gas-bearing coal samples, a split Hopkinson pressure bar experimental system (SHPB-GAS) was built, using which dynamic impact experiments of gas-bearing coal were performed. Stress wave signals were collected and processed to analyze changes in strain characteristics with time. Relationships between dynamic strength, failure strain, and various factors such as axial static load, confining pressure, gas pressure, and impact load were analyzed. Our results show that dynamic strength and failure strain increased with the increase of confining pressure and impact load, but decreased with the increase of axial static load and gas pressure. Furthermore, evolution of dynamic cracks and failure mode of gas-bearing coal were analyzed, with the results indicating that samples presented axial tension fracture under the combination loading (axial static load, confining pressure, gas pressure and impact load). The effects of these four factors on the fracture evolution in coal samples were then discussed. Under these conditions, the fracture mechanism of gas-bearing coal was investigated and the effects of shear stress and normal stress on the fracture surface were illustrated. Our findings show that gas flow over the coal surface will increase shear stress along the fracture surface, in turn inducing coal fracture.

Mechanical response to tensile stress of a composite material reinforced with sugar cane fibers

Composite materials reinforced with organic fibers have attracted great interest in the area of mechanical engineering in recent decades due to the wide variety of industrial applications where these materials can be used, and the low impact on the environment, compared with traditional materials. In this work, experimental and numerical tests are carried out to investigate the mechanical response to a tensile load of a composite material with an epoxy matrix, reinforced with sugar cane fibers. Mechanical tests under the ASTM standard for tensile loads were performed. Then, a numerical model to investigate the mechanical response of the composite is done by finite element analysis. Results indicate that this composite material has good performance under axial loading conditions, and can be used for structural applications.

Mechanical performance of AH joints and influence on the stability behaviour of single-layer cylindrical shells

Abstract Previous studies on the mechanical performance of AH (assembled hub) joints mainly focused on the axial capacity and the bending capacity of the joint system. However, the joint system in latticed shells is subjected to combined axial forces and bending moments in practice. In this paper, the mechanical performance of joints under eccentric load is investigated experimentally and numerically. The eccentric bearing capacity, as well as the failure mechanism of the novel joint system, are derived and compared with the axial loading and pure bending conditions. The correlation curve with 95% guaranteed rate is determined by non-linear regression analysis. On this basis, a combined non-linear spring model is established to simulate the mechanical performance of joints in single-layer cylindrical shells for stability analysis. The results indicate that for orthogonal type cylindrical latticed shells with diagonals or crossed cables, the stability reduction factor can reach a range of up to 0.8 to 0.96. However, for cylindrical latticed shells with lamella grids or three-way grids, the stability reduction factor is less than 0.62. This situation can be improved by strengthening the joint system or reducing the intersection angles of members. When the intersection angle decreases from 90° to 60°, the stability reduction factors of lamella shells will increase by 34%–47%. This means that cylindrical shells with AH joints have sufficient stability to meet engineering requirements by rational design.

Periprosthetic bone response to axial loading following TKR

PurposeThe purpose of this paper is to investigate by means of finite element analysis (FEA), the effect of polyethylene insert thickness and implant material, under axial loading following TKA.Design/methodology/approachThe 3D geometric model of bone was processed using the CT scan data by MIMICS (3matic Inc.), package. Implant components were 3D scanned and subsequently 3D modeled using ANSYS Spaceclaim and meshed in Hypermesh (Altair Hyperworks). The assembled, meshed bone-implant model was then input to ABAQUS for FE simulations, considering axial loading.FindingsPolyethylene insert thickness was found to have very little or no significance (p>0.05) on the mechanical performance, namely, stress, strain and stress shielding of bone-implant system. Implant material was found to have a very significant effect (p<0.05) on the performance parameters and greatly reduced the high stress zones up to 60 percent on the tibial flange region and periprosthetic region of tibia.Originality/valueVery few FEA studies have been done considering a full bone with heterogeneous material properties, to save computational time. Moreover, four different polyethylene insert thickness with a metal-backed and all-poly tibial tray was considered as the variables affecting the bone-implant system response, under static axial loading. The authors believe that considering a full bone shall lead to more precise outcomes, in terms of the response of bone-implant system, namely, stress, strains and stress shielding in the periprosthetic region, to loading.

Synthesis and Electrochemical Characterization of Silk Fibroin Micro/Nano Particles

In this study, the dynamic instability of three-layered cylindrical shells containing a functionally graded (FG) interlayer subjected to static and time dependent periodic axial compressive loads are investigated. The governing relations, modified Donnell type dynamic stability and deformation compatibility equations are derived. The governing equations are reduced Mathieu–Hill equation by using Galerkin׳s method and the expressions for boundaries of unstable regions of three-layered cylindrical shell with an FG interlayer are found. Finally, the effects of variations of volume fractions of FG interlayer and shell characteristics on the magnitudes of boundaries of unstable regions are studied numerically.

Auxeticity effect on crushing characteristics of auxetic foam-filled square tubes under axial loading

Abstract This paper treats energy absorption and crushing characteristics of auxetic foam-filled square-section tubes under axial loading condition. The influence of auxeticity effect on the structural collapse was experimentally investigated to quantify the interaction effect between Poisson's ratios of foam (ranging from −0.31– 0.03) and square tube walls under quasi-static and dynamic loadings. The validated computer simulation technique was employed to conduct a series of parametric study in order to evaluate the influence of tube parameters on the energy absorption responses. It is evident that negative Poisson ratio effectively influences the crushing response and energy absorption capability of auxetic foam-filled square tubes. Moreover, it was found that increasing the auxeticity level of foam filler enhances crashworthiness performance of foam-filled structures under both quasi-static and dynamic loading conditions. The primary outcome of this study is a design guideline for the use of auxetic foam in different ranges of Poisson's ratio as a core for an energy absorber device where impact loading is expected.

Numerical and Experimental Study on Deficient Short Steel Tubes Strengthened with CFRP Under Compression

In view of development and repair costs, support of structures is imperative. Several factors, for example, design and calculation errors, absence of appropriate installation, change of structures application, exhaustion, seismic tremor, fire and natural conditions diminish their strength. In such cases, structures have need of rehabilitation and restoration to achieve their original performance. One of the most up to date materials for retrofitting is carbon fiber reinforced polymer (CFRP) that can provide an amount of restriction to postpone buckling of thin steel walls. This paper provides a numerical and experimental investigation on CFRP strengthened short steel tubes with initial horizontal and vertical deficiency under compression. Ten square and circular specimens were tested to study effects of the following parameters: (1) position of deficiency, horizontal or vertical; (2) tube shape, square or circular; (3) CFRP strengthening. In the experiments, axial static loading was gradually applied and for the numerical study three-dimensional (3D) static nonlinear analysis method using ABAQUS software was performed. The results show that deficiency reduces load-bearing capacity of steel columns and the impact of horizontal deficiency is higher than the impact of vertical deficiency, in both square and circular tubes. Use of CFRP materials for strengthening of short steel columns with initial deficiency indicates that fibers play a considerable role on increasing load bearing capacity, reducing stress at the damage location, preventing deformation caused by deficiency and delaying local buckling. Both numerical and experimental outcomes are in good agreement, which underlines the accuracy of the models adopted.

Effect of Parameters on the Mechanical Behavior of Core Strands: Experimental, Numerical and Statistical Study

The cables are widely used in mechanical, electrical and civil engineering applications, as they are flexible and highly resistant. In this paper, the behavior of the elastic limit of straight central core strands is studied. In this study, we focus on the elastic limit’s behavior of straight central core strands. That is, we investigate 27 cores with different configurations. They generally consist of 7 wires (1+6) belonging to wire ropes of type 19x7 subjected to static axial loads. The numerical study is performed using finite element method (FEM). The main results are compared with experimental data. Finally, to determinate the impact of three parameters: the basic material constituting the strands, the winding angle of wires and the diameter of strands on the yield strength of the core strands, we apply a design of experiments (DOE) analysis by YATES’ method.

Ratcheting assessment of pressurized pipelines under cyclic axial loading: Experimental and numerical investigations

The present study aimed to study ratcheting strains of pressurized stainless steel (UNS S32750) pipes with cyclic axial loading conditions. To this aim, some experiments were performed for the tubes involving cyclic axial loading under internal pressure. All specimens were analyzed with a finite element code. Ohno-Wang hardening model was employed in numerical analysis to calculate the ratcheting of the tubes. By using this hardening model, all predicted ratcheting results were consistent with those of the experimental ones. In this study, the effect of pre-compressed strain, internal pressure and stress amplitude were evaluated experimentally and the numerical results were compared with the results. Finally, the tubes collapsed at about the same strain level as it did under monotonic loading. The number of cycles to collapse and the ratcheting strain rate of the pressurized pipelines depend on the different parameters such as cyclic loading parameters, pre-strain and internal pressure. The results show that an increase of pre-strain, internal pressure and cyclic loading parameters leads to increase ratcheting strain rate of pipelines in both axial and circumferential directions.

Discontinuous slow crack growth modeling of semi-elliptical surface crack in high density polyethylene using crack layer theory

Surface flaws in structural materials are most likely to be generated during service time. One of the most general shapes of surface flaws is the semi-elliptical surface crack. Frequently, the slow crack growth (SCG) of a crack has been fitted based on the conventional Paris–Erdogan relationship. However, in the case of engineering plastics, which generally reveal a severe unrecoverable damage zone at the crack tip, the conventional Paris–Erdogan relationship is not appropriate to describe the SCG of a crack. Especially, SCG kinetics of some engineering polymers such as high-density polyethylene (HDPE) affect the SCG characteristics, i.e. non-conventional discontinuous SCG behavior, which cannot be simulated by conventional Paris–Erdogan relationship. It is known that the crack layer (CL) theory, which deals with driving forces of crack and process zone (PZ) together, can be a good mathematical model to simulate such SCG behavior. In this study, the discontinuous SCG of a semi-elliptical surface flaw in HDPE plate under cyclic tensile stress was simulated using the CL theory. Although the CL theory has the advantage of simulating the discontinuous SCG of HDPE accurately, until now the applications have been concentrated on one-dimensional slow crack growth. In this paper, the CL model for two-dimensional surface crack growth for axial and bending loading conditions was developed for the first time. The proposed model is validated with actual test results, and the role of some key CL parameters on discontinuous SCG behavior of a semi-elliptical surface flaw is investigated by intensive parametric studies.

Numerical analyses on seismic behavior of helical concrete columns

This paper presents the behavior of the helical reinforced concrete columns (HCC) subjected to horizontal 2D seismic motion excitation combined with the static axial load. Helical concrete columns are new types of elements which arose in the new twisted buildings, providing a special geometry by twisting the top section by an angle (ϕ), furthermore, offsetting the top section by a considerable distance respecting to the bottom section. In order to study seismic behavior of the HCC under a seismic load of the short period using finite element software, numerical simulation is carried out in this paper using ANSYS V 18.1 software. A brief comparison of the HCC behavior was made between different cases of conventional reinforcement in the longitudinal and transverse directions, as well as the different twisting angles (ϕ) of column sections. The comparison illustrated that all columns response with giving the same mode shapes of vibration in the modal analysis with different values of natural frequencies and relative amplitude deformations. However, the difference be very noticeable when changing the section size of the columns comparably with changing the twisting angles of the section, where increasing the section size of HCC from 250 mm to 400 mm cause increase the natural frequency by 55.4% for second mode shape, while it cause decreasing the relative amplitude response of HCC by 52.5% for sixth mode shape. The transient analysis of the six types of HCC excited by horizontal 2D seismic motion indicates the tendency of HCC to increase its responses, like twisting and buckling deformations. The deform shape-time history of 6 HCC demonstrated that with increasing (shear stress path section distance) S of HCC column which depends up on (ϕ value), the top section would have less stresses.

Axial behavior of tapered piles using cavity expansion theory

This paper presents a procedure for evaluating the load–displacement behavior of tapered piles under static axial compressive loads. The response of tapered piles under elastic phase is evaluated using nonlinear load transfer method, whereas the increase in stresses due to slippage at the soil–pile interface is obtained from a developed drained cylindrical cavity expansion solution based on a nonlinear stress–dilatancy relationship. The governing differential equation is solved using the differential quadrature element method. The methodology is validated using two reported experimental model testing of the tapered pile in cohesive–frictional soil and soft soil. A comparative analysis between the different nonlinear load transfer models is also carried out. Further, the effect of the heterogeneity of the soil properties along the length of the pile on the axial response of the tapered pile is studied.