Axial Tension Compression Research Articles

The effects of CNT type, alignment and dopants on piezoresistance in CNT fibres

Carbon nanotube fibres (CNTF) are piezoresistive, hence heralded as deformation sensors in applications ranging from flexible touch sensors to artificial skins and robotics. This work studies the piezoresistive behaviour of a wide range of CNT fibres from different sources, processing routes and microstructures. It provides a unifying view of the factors controlling piezoresistance in CNT fibres and related nanocarbon networks. We clarify the role of alignment and concentration of dopants and the constituent CNT type, demonstrating that the origin of piezoresistance in aligned fibres is the direct deformation of the constituent nanotubes, therefore, it is governed by the bulk modulus and thus the degree of CNT alignment. Doping through intercalation, which does not affect modulus or CNT separation, is detrimental to piezoresistive sensing, reducing the gauge factor proportionally to its decrease in resistivity. Aligned fibres show a quasi-linear piezoresistive response, with a positive change in resistance for all deformation modes applied: axial tension, axial or transverse compression. The axial gauge factor is shown to be proportional to fibre Young's modulus, with values of 2–9 for fibres spun from aerogels and above 30 for undoped fibres spun from liquid crystal solutions, respectively. Piezoresistance is attributed to the formation of internal barriers for conduction between metallic regions, which arise from the heterogeneous stress distribution along individual CNTs inherent in shear lag-type stress transfer. Commercial multifilament CNT yarns with a high degree of alignment and a format amenable for integration in large structures have demonstrated the piezoresistive gauge factors of 4 and sufficient sensitivity at strains below 1 % suitable for structural health monitoring of engineering structural composites.

Performance analysis of vertical smart isolator based on magnetorheological elastomer

ABSTRACT As one of the field-dependent smart materials whose stiffness and damping properties can change instantaneously and reversibly, magnetorheological elastomer (MRE) has been extensively utilized on base isolation for vibration reduction. However, most previous studies have focused on the shear dynamic performance of MRE isolators, and there are few reports on the vertical extrusion performance of basic isolators within construction equipment. In this paper, MRE materials with strong bearing capacity and suitable vertical stiffness were fabricated by comprehensively considering the selection of raw materials, particle ratio, and sample size. The tension-compression viscoelasticity of the prepared MRE under varying magnetic fields and strain amplitudes was experimentally evaluated using an MRE axial MR testing system. Eventually, a single-degree-of-freedom dynamic test rig for vibration isolation of equipment in buildings, which integrates a vertical isolator with MRE as the core component, was constructed to perform a series of experimental investigations on the alterable frequency vibration capability of the designed MRE vertical isolator. The test results reveal that the controllable stiffness-damping properties of the prepared MRE in the axial tension-compression mode can enable the developed vertical isolator to exhibit superior frequency shifting and vibration attenuating characteristics in structural vibration.

Cyclic behaviour of circular CFT-SG columns under axial tension-compression: Novel FE modelling and design methods

The ultra-high concrete-filled steel tubular (CFT) power transmission tower is popularly applied in engineering practice, which may be under a typical cyclic axial tension-compression loading condition due to the dynamic wind load. Nonetheless, the CFT columns of the tower may be accompanied by significant gap defects due to the influence of structural feature, material property, and service environment. Hence, to figure out the performance of circular CFT columns with spherical-cap gaps (CFT-SG) subjected to cyclic axial tension-compression, this paper investigates a constitutive relationship for the gapped core concrete, which is verified by several existing experiments. A novel numerical modelling approach for simulating the irregular cross-section of the circular CFT-SG columns under cyclic axial load was following established based on the triangulation method and code programming. The influence of important parameters such as gap ratio, material strength, and diameter to thickness ratio on the hysteresis characteristics, load-bearing capacity, elastic stiffness, energy dissipation and ductility of circular CFT-SG columns under cyclic axial tension-compression force is studied. Moreover, the restoring force model of the circular CFT-SG columns under cyclic axial tension-compression is finally presented. Research results declare that the compressive bearing capacity, stiffness, ductility, and energy dissipation of circular CFT-SG columns under cyclic axial tension-compression are gradually weakened with the increment in the gap ratio. The numerical modelling approach and restoring force model proposed in this article can accurately evaluate the hysteresis performance of circular CFT-SG columns subjected to cyclic axial tension-compression.

Numerical Simulation Study on the Constitutive Model of Fully-Graded Concrete Based on Statistical Damage Theory

A statistical damage model (SDM) of fully-graded concrete was created using statistical damage theory, based on the mechanical properties of axial tension and axial compression of the material. The SDM considers two damage modes, fracture and yield, and explains the intrinsic connection between the mesoscopic damage evolution mechanism and the macroscopic nonlinear mechanical behavior of fully-graded concrete. The artificial bee colony (ABC) algorithm was used to obtain the optimal parameter combination through an intelligent search of parameters εa, εh, εb and H in the constitutive model by taking the test data as the target value, and the sum of the squares of the differences between the target value and the predicted value as the objective function. The SDM numerical simulation model of fully-graded concrete is proposed by compiling subroutines in FORTRAN by constructing two modules of data model and damage analysis. The numerical results under uniaxial and biaxial forces are in agreement with the experimental results, which verifies the accuracy of the program. The model also analyzes the characteristics of mesoscopic damage evolution and predicts the mechanical properties under triaxial forces. The results show that the proposed numerical simulation model can reflect the salient features for fully-graded concrete under uniaxial, biaxial and triaxial loading conditions, and the evolution law of mesoscopic parameters. Therefore, the proposed model serves as a basis for the refined finite element analysis of hydraulic fully-graded concrete structures and reveals the mesoscopic damage mechanism of concrete under different load environments.

Natural Frequency and Modes of the Longitudinal and Torsional Vibrations in the Bars with Variable Cross Section

The paper is focused on the problem of natural frequencies and modes determination based on perturbation theory for longitudinal and torsional vibrations in bars with variable cross section. The mechanical properties and cross section geometry of the bar are changing small from the average value with regard to longitudinal coordinate. Based on the theory of small perturbations the analytical solution is obtained for natural frequencies and modes of the stationary harmonic vibrations in bars. The efficiency of the proposed method is supported by comparison and good agreement of the obtain results with a sharp solution for a given cross section profiles. It was established that the approximate solution is working good up to the ratio 2.5–3 between maximum and minimum diameter of cross section. The results of numerical simulations are aimed to estimate the geometry and elastic behavior of the metallic specimens for very high cycle fatigue experimental investigation under axial tension-compression and torsion loadings. The piezoelectric fatigue testing system and procedure is based on stationary vibration excitation in the metallic specimen at the first mode natural frequency.

Features of the Internal Force Factors Distribution in Reinforced Concrete Piles of Complex Cross Section under the Influence of a Transverse Load

Bar reinforced concrete structures, which include piles, in real working conditions perceive a whole range of internal force factors. Axial tension-compression forces, bending moments and shear forces are the most commonly perceived internal force factors. Of particular interest is the effect on the cross section of the shear force. If a complex curly shape is replaced by elementary form, then the calculation is not difficult. However, when calculating the composite cross section, there is no unambiguous solution. In accordance with the adopted regulatory documentation, it is necessary to accept only a main part, while discarding the surrounding areas. It is important to study the configuration of the shape of a complex section for the perception of a shear force. The purpose of the work was to refine the account of the entire complex section using numerical simulation by the finite element method, analytical calculations and small-scale experiments. Determination of further practical application of the obtained results on real structures was also the goal of the study. The parameters of the distribution of shear force between the main rib and flanges were obtained by numerical analysis and small-scale experiments. Numerical models of rectangular and tee cross sections beams have been developed. Analytical dependences were studied and full-scale tests of reinforced concrete beams of various sections were carried out. It has been established that when taking into account the work of the entire cross-section, the bearing capacity of concrete for the action of a shear force is 20% greater than when calculating only the main section without taking into account the shelves.

New neural network-based algorithm for predicting fatigue life of aluminum alloys in terms of machining parameters

Various classification of aluminum alloys is one of the most common applied materials in transportation industries due to the specific mechanical and material properties. Body of vehicles, including cars, ships, and airplanes, are constantly exposed to different cyclic loads that lead to surface damage and finally, fatigue failure occurs by crack growth. Therefore, the quality of the machined surface has a direct effect on the fatigue life of the products. In this regard, the most important source of surface roughness is the choice of machining parameters. To understand it, turning operations were performed on 2xxx and 7xxx series aluminum alloys considering different values of process parameters. For any series of aluminums, 189 high-cycle fatigue testing specimens were prepared, and experiments were performed by axial tension–compression fatigue test machine in 7 levels of stress (all tests were repeated three times and the mean failure cycles were reported as the fatigue life). Next, an Artificial Neural Network (ANN) based on the Back Propagation (BP) error algorithm was developed to predict fatigue life of Al alloys which are machined with different conditions. To this end, the parameters considered as input variables to the neural network structure include the Yield Strength (YS) and Ultimate Tensile Strength (UTS) to identify the aluminum series, as well as the process parameters such as cutting depth (d), rotational speed (R), and feed speed (V). In addition, the applied cyclic stress (S) to specimen was considered as input. Furthermore, surface roughness (Z) and number of cycles to failure (N) were considered as ANN output. The comparison of the obtained results from ANN predicting with the experimental values indicates that this approach was tuned finely. Eventually, the presented model can be a suitable alternative to perform fatigue tests with high costs and time-consuming.‌‌ Also, the most effective machining parameter on the surface roughness and fatigue limit was reported.

Experimental study on the mechanical response of metro shield tunnels obliquely crossing ground fissures

Whether the shield tunnel can be adopted to cross the ground fissure is an important issue in the field of metro construction in Xi'an, China. To study this issue, the model test and numerical simulation on a metro shield tunnel that obliquely crosses a ground fissure were carried out. The lining internal force, segment deformation and failure characteristics under the action of ground fissure dislocation were investigated. The results show that the shield tunnel obliquely crossing ground fissure exhibits three-dimensional deformation of axial bending, horizontal local torsion, and axial tension–compression, if the ground fissure dislocation takes place. The segments near ground fissure present uneven vertical dislocation, horizontal slight deflection, and axial tilt. The lining is in bias pressure state, and cracks around segment bolts nearby the vault and inverted arch of shield tunnel when the actual ground fissure dislocation reaches 24 cm. The deformation and failure of shield tunnel obliquely intersecting with the ground fissure is in the torsional-shear mode, which affects the 8 rings in the hanging wall and the 5 rings in the footwall respectively, and these segments need to be strengthened. Also, some countermeasures and suggestions are proposed to deal with the adverse impacts of ground fissure on metro shield tunnel.

Application of Probabilistic Approach to Investigate Influence of Details in Time History of Temperature Changes on the HCF Life of Integrated Bridge Steel Piles Installed on Water

This research estimates the high-cycle fatigue (HCF) life of integrated concrete bridge installed on water due to temperature changes. To this end, CATIA software was used to geometrically model of a real-scale bridge. Next, thermal–structural coupling analysis was performed by finite element (FE) simulation in ANSYS WORKBENCH software. The comparison technique with experimental data was used to validate the simulation. Afterward, thermal analysis was performed due to air temperature changes in different modes, including the average monthly temperature changes (large variations) as well as the maximum and minimum monthly temperature changes (small variations). The results showed that the most changes in deck length and subsequent maximum deviation in the upper part of steel piles were related to the three warm seasons in the presence of the water. Eventually, a probabilistic approach was employed to find variable amplitude fatigue lifetime of the component based on the number of annual loading blocks. To achieve the high-accuracy response, the effective parameters of the proposed probabilistic approach, including order of Fourier series and the stress range, were optimized automatically. In addition, to obtain HCF behavior of raw material, axial tension–compression fatigue tests were performed on the standard specimens fabricated from steel piles. The results revealed that considering small variations in the calculation of structural fatigue life led to a 550% reduction in life compared to structural analysis due to large variations. In addition, the obtained results were compared with the finite element results.

Mechanical Behavior of Concrete-filled Steel Tubular Space Intersecting Nodes in High-rise Oblique Diagrid Tube Structures

In recent years, the researches on concrete-filled steel tubular (CFST) intersecting nodes mainly focused on the plane intersecting nodes, while that on space intersecting nodes with off-plane angles was relatively less. In this study, the nonlinear analyses of CFST space intersecting node models established in ABAQUS were performed under the monotonic axial compression and reciprocal axial tension-compression loads, respectively. The stress distributions of steel tubes and core concrete were analyzed, and the hysteresis characteristics and stiffness degradation of the node were studied. The in-plane angle, off-plane angle, out-of-plane constraint effect, steel tube diameter-to-thickness ratio, and core concrete strength were used as control parameters to analyze their effects on the mechanical behavior of the nodes. The results show that the bearing capacity of the nodes meets the design requirements, the hysteresis loop is full, the initial stiffness is large and the stiffness degrades slowly. The off-plane angle, out-of-plane constraint effect, steel tube diameter-thickness ratio and core concrete strength have significant effects on the bearing capacity and lateral stiffness of the nodes. In order to reduce the adverse effect of out-of-plane displacement, the space intersecting nodes in practical engineering can use reinforced floor beams or prestressd cables to impose out-of-plane constraint, and the recommended value of out-of-plane constraint effect is 10–30 kN/mm.

Ex vivo biomechanical evaluation of Acute lumbar endplate injury and comparison to annulus fibrosus injury in a rat model

Back pain is often associated with intervertebral disc (IVD) degeneration, and IVD degeneration phenotypes are commonly characterized by annulus fibrosus (AF)-driven and endplate (EP)-driven phenotypes. Few studies of EP injury exist in animal models, even though clinical studies show EP lesions are strongly associated with IVD pathology and pain. This project established an ex-vivo rat lumbar EP injury model and characterized effects of EP injury on motion segment biomechanical properties, as compared to AF injury, a common way of inducing IVD degeneration. Lumbar motion segments (39 total vertebra-IVD-vertebra sections) assigned to Intact (L1/L2), AF injury and EP injury (L3/L4 and L5/L6 randomly selected), and biomechanically tested in axial tension-compression, stress-relaxation and torsional testing in pre-injury and post-injury conditions using a repeated-measures design. EP injury involved superior vertebra endplate puncture transcorporeally and obliquely. AF injury involved mid-line punctures anterior and bilaterally. Axial ROM, tensile stiffness, hysteresis, and neutral zone stiffness were significantly affected by EP injury but not AF injury. Torque range, torsional stiffness and torsional neutral zone stiffness were significantly affected by AF injury but not EP injury. Stress-relaxation fast time constant was decreased for EP injury. EP and AF injuries induced distinct biomechanical changes in lumbar motion segments with EP injury having the largest impact on axial biomechanical properties and AF injury most prominently affecting torsional properties. This study deepens the understanding of biomechanical mechanism of EP-driven low back pain and provides methods and biomechanical characterization for future in vivo studies.

Study on isothermal fatigue life prediction model of a new type hot stamping die steel 4Cr2Mo2V

In this paper, the isothermal fatigue behavior and life of 4Cr2Mo2V steel for new hot stamping die were studied. Axial tension compression symmetric fatigue tests with different strains were carried out at 300 ℃. When the half strain amplitude was from 0.3% to 0.9%, the response stress continued to soften, and the decline rate of response stress gradually increased, but when the half strain amplitude was 0.9%, the material would fail early. Used Coffin-Manson (C-M), Basquin-Coffin-Manson (BCM) and original Ostergren models to predict the life, the prediction effect was not good. Box-Cox variable transformation was carried out on the cycle life, and then the modified Ostergren model could accurately predict the life. The life prediction model was also established by fitting the response stress curve, but the appropriate d value needs to be set to accurately simulate the life.

Nonlinear deformations of a cylindrical pipe with pre-stressed thin coatings

The paper presents an exact solution for the problem of large deformations of torsion, axial tension–compression, and radial expansion or shrinkage of an elastic hollow circular cylinder equipped with pre-stressed elastic coatings. Surface coatings are modeled using the six-parameter nonlinear shell theory. The constitutive material of the cylinder is described by a three-dimensional nonlinear model of the isotropic incompressible body of the general form. Special boundary conditions describe the interaction of this material with thin coatings on the inner and outer surface of the pipe. Based on the solution obtained, numerical calculations were performed on the effect of preliminary stresses in coatings on the stress–strain state of a cylindrical pipe.

Examination of Longitudinal Seismic Vulnerability of Shield Tunnels Utilizing Incremental Dynamic Analysis

In order to study the longitudinal seismic capacity of shield tunnels, this work applies the structural seismic vulnerability analysis, based on incremental dynamic analysis (IDA), to a shield tunnel and explores the ground motion intensity measure suitable for the shield tunnel in different site types. The failure probability of the structure at each earthquake intensity is calculated by combining the probabilistic seismic demand model with the limits on the engineering demand parameters to establish the seismic vulnerability curve of the structure. The results indicate that the peak ground velocity (PGV) is the ground motion intensity measure suitable for the longitudinal seismic performance of the shield tunnel. The site type has the most profound influence on the extent of the longitudinal damage to the shield tunnel, and site type IV is the most dangerous under an earthquake. Further, the tunnel has stronger seismic resistance in the elastoplastic stage. The low-grade bolts between the rings damage more severely than the high-grade bolts. A tunnel with either a great depth of burial or a large cross section is more dangerous than the one with either a small depth of burial or a small cross section. The risk of the axial tension-compression failure of the shield tunnel is higher than that of the horizontal transverse shear failure.

Geometrical modeling and mechanical behavior analysis of Nb3Sn Rutherford cable

The energy upgrade of the Large Hadron Collider and Future Circular Collider propose new requirement that the magnetic field of accelerate magnets is up to 16 T. Nb3Sn Rutherford cables are used in magnet design for such high level magnetic field. Rutherford cables must undergo complex stress conditions owing to the extreme magnetic environment and complicated cabling process which often leads to mechanical instability. In this study, a three-dimensional model is established and analyzed to better understand the mechanical behavior of Rutherford cables subjected to different loading conditions during the cabling process. A rapid approach to construct the geometry of a Rutherford cable is first presented, followed by an analysis of its mechanical behavior under axial tension, cyclic tension and transverse compression conditions. Instability behaviors, such as “pop-out” and “cross-over”, are investigated. The results show that the friction coefficient, laying angle and core play important roles in the cable mechanical performance. For better mechanical stability of the strands in Rutherford cables, it is recommended to select a higher friction value among the strands and a laying angle between 74° and 78° for non-cored cable, whereas a larger laying angle is suggested for copper-cored cable.

Experimental and numerical studies of an axial tension-compression corrugated steel plate damper

Metallic dampers are widely used due to their satisfactory plastic energy dissipation, low price and convenient installation. In this study, an axial tension and compression corrugated steel plate damper (ATCCSPD) was proposed. According to the mechanical properties of the ATCCSPD, low-frequency cyclic loading tests and numerical verification of seven ATCCSPD specimens were designed and performed. Additionally, the test phenomena and failure modes of the ATCCSPD specimens were analysed, and seismic performance indices such as the hysteretic curve, skeleton curve, ductility and energy dissipation were obtained. Then, the impacts of the thickness of the corrugated web, the aspect ratio and the thickness of the flange on the seismic behaviour of the ATCCSPD specimens were investigated. The results demonstrated that the seven ATCCSPD specimens exhibited satisfactory ductility and energy dissipation capacity, and the hysteretic curves were stable and full. Overall, the ATCCSPD specimens exhibited axial tension and compression deformation, while the internal corrugated web exhibited pure shear deformation during the loading process. The web thickness and aspect ratio were the main factors affecting the bearing capacity and energy dissipation of the ATCCSPD specimens. The finite element software ABAQUS was used to simulate the ATCCSPD specimens, and shear damage was added to the nonlinear kinematic hardening constitutive model of steel, which could effectively simulate the failure process of the corresponding part after cracks formed in the ATCCSPD specimens. Finally, combined with the test results and the numerical results, the shear bearing capacity formula of the corrugated webs was fitted; then, the formula for calculating the tensile (compressive) bearing capacity of the ATCCSPD specimens was obtained by the superposition principle. By comparing the calculation results with the test results, it was found that the proposed formula was conservative and, hence, suitable for engineering applications.

Experimental Study on the Effect of Freeze‐Thaw Cycles on Axial Tension and Compression Performance of Concrete after Complete Carbonization

The effect of freeze‐thaw cycles on the axial tension and axial compression properties of completely carbonized concrete are investigated in this study. Three grade concrete specimens (C30, C40, and C45) were fabricated. The freeze‐thaw cycle test was carried out on the completely carbonized specimens, followed by axial tension and axial compression tests. The results show that completed carbonization increases the axial tensile peak stress of C30, C40, and C45 concrete specimens by 8.7%, 9.7%, and, 12.1%, respectively. The peak axial tension strain increased by 1.9%, 7.2%, and 9.6%, respectively. The peak axial compressive stress increased by 10.5%, 19.1%, and 24.1%, respectively. The peak axial compressive strain decreased by 13.7%, 14.1%, and 14.3%, respectively. With the increase of freeze‐thaw cycles, the peak stress of tensile stress, peak strain, and compressive stress of concrete decrease continuously. The peak strain of compressive strain increases. The lower the strength grade of concrete, the faster the decline rate of stress and strain. According to the data changes of peak stress and peak strain at different times of freeze thaw after carbonization, the stress‐strain curve fitting formula for concrete under freeze‐thaw cycles after complete carbonization is put forward, which has a good coincidence with the experimental result.

Ex-vivo biomechanics of repaired rat intervertebral discs using genipin crosslinked fibrin adhesive hydrogel

Microdiscectomy is the current standard surgical treatment for intervertebral disc (IVD) herniation, however annulus fibrosus (AF) defects remain unrepaired which can alter IVD biomechanical properties and lead to reherniation, IVD degeneration and recurrent back pain. Genipin-crosslinked fibrin (FibGen) hydrogel is an injectable AF sealant previously shown to partially restore IVD motion segment biomechanical properties. A small animal model of herniation and repair is needed to evaluate repair potential for early-stage screening of IVD repair strategies prior to more costly large animal and eventual human studies. This study developed an ex-vivo rat caudal IVD herniation model and characterized torsional, axial tension–compression and stress relaxation biomechanical properties before and after herniation injury with or without repair using FibGen. Injury group involved an annular defect followed by removal of nucleus pulposus tissue to simulate a severe herniation while Repaired group involved FibGen injection. Injury significantly altered axial range of motion, neutral zone, torsional stiffness, torque range and stress-relaxation biomechanical parameters compared to Intact. FibGen repair restored the stress-relaxation parameters including effective hydraulic permeability indicating it effectively sealed the IVD defect, and there was a trend for improved tensile stiffness and axial neutral zone length. This study demonstrated a model for studying IVD herniation injury and repair strategies using rat caudal IVDs ex-vivo and demonstrated FibGen sealed IVDs to restore water retention and IVD pressurization. This ex-vivo small animal model may be modified for future in-vivo studies to screen IVD repair strategies using FibGen and other IVD repair biomaterials as an augment to additional large animal and human IVD testing.

Very High Cycle Fatigue Behavior of Additively Manufactured 316L Stainless Steel.

The present paper is focused on an experimental study of the damage-to-failure mechanism of additively manufactured 316L stainless steel specimens subjected to very high cycle fatigue (VHCF) loading. Ultrasonic axial tension-compression tests were carried out on specimens for up to 109 cycles, and fracture surface analysis was performed. A fine granular area (FGA) surrounding internal defects was observed and formed a “fish-eye” fracture type. Nonmetallic inclusions and the lack of fusion within the fracture surfaces that were observed with SEM were assumed to be sources of damage initiation and growth of the FGAs. The characteristic diameter of the FGAs was ≈500 μm on the fracture surface and were induced by nonmetallic inclusions; this characteristic diameter was the same as that for the fracture surface induced by a lack of fusion. Fracture surfaces corresponding to the high cycle fatigue (HCF) regime were discussed as well to emphasize damage features related to the VHCF regime.

Mechano-geometrical skeletal muscle fibre characterisation under cyclic and relaxation loading

In the present work, mechano-geometrical characterisations of skeletal muscle fibres in two different deformation states, namely, axial tension and axial compression, were realised. In both cases, cyclic and relaxation tests were performed. Additionally, the changes in the volume of the fibres during deformation were recorded to obtain more detailed information about the muscle fibre load transfer mechanisms. To the best of the authors’ knowledge, the present experimental investigation of the mechanical and geometrical characteristics of muscle fibres provides a novel comprehensive data set that can be used to obtain a better understanding of muscle fibre load transfer mechanisms and to construct meaningful models. In the present study, it is shown that muscle fibres exhibit incompressibility (5% volume decrease at maximum deformation) under tension and that this feature is more pronounced under compression loading (37% volume decrease at maximum deformation). These findings are particularly interesting and lead to a further understanding of load transfer mechanisms and to the development of new modelling strategies.