Cyclic Axial Tension Research Articles

Capacity Change of Piles in Loess under Cyclic Axial Tension or Compression Load

Capacity Change of Piles in Loess under Cyclic Axial Tension or Compression Load

Seismic Behaviour of CFST Space Intersecting Nodes in an Oblique Mesh

The design of intersecting nodes in high-rise oblique mesh structures is a critical issue. The existing research on the intersecting nodes of oblique meshes mainly focuses on plane intersecting nodes and monotonic axial compression loads. The plane intersecting nodes cannot consider the contribution of the node’s out-of-plane angle and floor beam to the node’s out-of-plane stiffness in actual structures. In this paper, numerical analysis using ABAQUS was conducted to investigate the mechanical performance of space intersecting nodes of oblique meshes (OMSIN) under cyclic axial tension and compression loads, to provide a reference for the engineering application of oblique mesh structures in seismic regions. Six parameters were considered: the space intersecting angle, the plane angle symmetry coefficient, the plane intersecting angle, the out-of-plane constraint restraint, the steel content of the cross-section, and the concrete strength. The study showed that changes in the thickness of the steel tube wall are unfavourable for the uniform transmission of stress. Increasing the space intersecting angle significantly weakened the seismic performance, and the space angle affects the failure mode of the node. Asymmetric arrangements of the upper and lower plane angles caused nonlinear development of out-of-plane. The ultimate load and overall compressive stiffness of the specimen were positively correlated with the plane angle, and vertical constraints should be applied to the node position of components with plane angles greater than or equal to 70°. The out-of-plane constraint was a key factor affecting the seismic performance of the node, and it was proportional to the ultimate load of the component. In structural design, if the aim is to improve the mechanical performance of the component by increasing the steel content, more enormous out-of-plane constraints should be set to control plane external displacement strictly. The concrete strength is proportional to the ultimate axial load and axial stiffness, and its influence on the mechanical performance in the axial tension direction is not significant. Finally, a dimensionless skeleton curve model of the node was established. The existing formula for the bearing capacity of CFST columns was fitted to obtain the calculation formula for the axial yield and ultimate load of the OMSIN under cyclic loads.

TAK-242 treatment and its effect on mechanical properties and gene expression associated with IVD degeneration in SPARC-null mice

Intervertebral disc (IVD) degeneration is accompanied by mechanical and gene expression changes to IVDs. SPARC-null mice display accelerated IVD degeneration, and treatment with (toll-like receptor 4 (TLR4) inhibitor) TAK-242 decreases proinflammatory cytokines and pain. This study examined if chronic TAK-242 treatment impacts mechanical properties and gene expression associated with IVD degeneration in SPARC-null mice. Male and female SPARC-null and WT mice aged 7-9 months were given intraperitoneal injections with TAK-242 or an equivalent saline vehicle for 8 weeks (3x/per week, M-W-F). L2-L5 spinal segments were tested in cyclic axial tension andcompression. Gene expression analysis (RT-qPCR) was performed on male IVD tissues using Qiagen RT2 PCR arrays. SPARC-null mice had decreased NZ length (p = 0.001) and increased NZ stiffness (p < 0.001) compared to WT mice. NZ length was not impacted by TAK-242 treatment (p = 0.967) despite increased hysteresis energy (p = 0.024). Tensile stiffness was greater in SPARC-null mice (p = 0.018), and compressive (p < 0.001) stiffness was reduced from TAK-242 treatment in WT but not SPARC-null mice (p = 0.391). Gene expression analysis found upregulation of 13 ECM and 5 inflammatory genes in SPARC-null mice, and downregulation of 2 inflammatory genes after TAK-242 treatment. TAK-242 had limited impacts on SPARC-null mechanical properties and did not attenuate NZ mechanical changes associated with IVD degeneration. Expression analysis revealed an increase in ECM and inflammatory gene expression in SPARCnull mice with a reduction in inflammatory expression due to TAK-242 treatment. This study provides insight into the role of TLR4 in SPARC-null mediated IVD degeneration.

Mixed mode surface crack growth in aluminium alloys under complex stress state

In this study fatigue crack growth tests were carried out on hollow cylindrical specimens, made of D16T and B95AT aluminum alloys (analogue of 2024 and 7075 aluminum), with initial external semi-elliptical surface cracks and undergoing complex stress state. The crack growth behavior of aforementioned materials was studied under cyclic axial tension, pure torsion and combined tension+torsion fatigue loading. Optical microscope measurements and the crack mouth opening displacement (CMOD) method were respectively used to monitor crack length and calculate crack depth. The experimental crack front positions were highlighted by using a beach mark procedure during the tests. The stress strain field along the crack front of semi-elliptical cracks in the cylindrical hollow specimens was assessed by Finite Element Method (FEM) analysis. The stress intensity factors (SIFs) were calculated by the 3D M-integral approach and the distributions of equivalent elastic SIFs along the crack front were used for crack growth rate assessment under mixed mode conditions. As a result, the fracture resistance parameters of aluminum alloys under complex stress state were presented. The simulation of cracks propagation turned out to be consistent with experimental results.

Mechanical Consequence of Induced Intervertebral Disc Degeneration in the SPARC-Null Mouse.

Intervertebral disc (IVD) degeneration is associated with low back pain (LBP) and accompanied by mechanical changes to the spine. Secreted protein acidic and rich in cysteine (SPARC) is a protein that contributes to the functioning and maintenance of the extracellular matrix. SPARC-null mice display accelerated IVD degeneration and pain-associated behaviors. This study examined if SPARC-null mice also display altered spine mechanics as compared to wild-type (WT) mice. Lumbar spines from SPARC-null (n = 36) and WT (n = 18) mice aged 14-25 months were subjected to cyclic axial tension and compression to determine neutral zone (NZ) length and stiffness. Three separate mechanical tests were completed for each spine to determine the effect of the number of IVDs tested in series (one versus two versus three IVDs). SPARC-null spine NZs were both stiffer (p < 0.001) and smaller in length (p < 0.001) than WT spines. There was an effect of the number of IVDs tested in series for NZ length but not NZ stiffness when collapsed across condition (SPARC-null and WT). Correlation analysis revealed a weak negative correlation (r = -0.24) between age and NZ length in SPARC-null mice and a weak positive correlation (r = 0.30) between age and NZ stiffness in WT mice. In conclusion, SPARC-null mice had stiffer and smaller NZs than WT mice, regardless of the number of IVDs in series being tested. The increased stiffness of these IVDs likely influences mobility at these spinal joints thereby potentially contributing to low back pain.

Damage mechanisms and failure analysis of high-strength eutectoid and duplex stainless steel wires subjected to static and cyclic axial tension loading under transverse compressive loads

Multi-wire strands used in a wide range of structural applications are designed to withstand high axial and cyclic tensile loads, but they can also be subjected to permanent or accidental transverse loads that might alter their tensile and fatigue behavior. In this context, the paper presents, respectively, a comparative experimental analysis involving two types of high-strength cold-drawn wires made of conventional eutectoid steel and an advanced lean duplex stainless steel. The same empirical fracture criterion was found to predict the tensile bearing capacity as a function of the applied transverse load in the two wires. The fatigue endurance required by the standards in force for prestressing steel wires when free from transverse loads are satisfied by the two wire types even under transverse loads as high as 40% of their tensile strength. The analysis of the failure mechanisms reveals consistent macroscopic and microscopic differences between the wires, which result from the local biaxiality of stress state and from the microstructural alteration induced by the transverse load when large plastic deformation occurs.

Effect of voids on the crack formation in a [45/−45/0]s laminate under cyclic axial tension

In the present work, the influence of manufacturing induced voids on damage mechanisms at the microscopic scale was analysed on [45/−45/0]s laminates subjected to tension fatigue loading. Microscopic observations of the top surface of the 45° ply revealed that the first event of damage at the microscopic scale was the initiation of multiple micro-cracks in the matrix between the fibres, located preferentially in correspondence of the voids in that layer. The subsequent coalescence of these micro-cracks gave rise to the formation of a crack propagating in the 45° fibres direction. This is qualitatively the same scenario observed in void-free specimens in a recent work by the authors, thus confirming that the same crack initiation criterion can be applied in the absence and presence of voids. In addition, the micro-scale damage is shown to evolve faster and therefore off-axis cracks to initiate earlier and in a larger quantity in the presence of voids.

Fatigue Surface Crack Growth in Aluminum Alloys under Different Temperatures

The variation of crack growth behavior is studied under cyclic axial tension fatigue loading for the different temperatures conditions. The subject for studies is cylindrical hollow specimens of B95 and D16 aluminum alloys with semi-elliptical surface cracks. By experimental studies for considered temperature conditions the relations between the crack sizes on the free surface of specimen, crack opening displacements (COD), crack growth rate and aspect ratio were obtained. These relationships are useful for automation of experimental studies of surface crack growth. For the same specimen configuration and the different crack front position as a function of cyclic tension loading and temperatures conditions, the following constraint parameters were analyzed, namely, the non-singular T-stress, Tz -factor and the stress triaxiality parameter h in the 3D series of elastic-plastic computations. The governing parameter of the elastic-plastic stress fields In-factor distributions along various crack fronts was also determined from numerical calculations. The plastic stress intensity factor (SIF) approach was applied to the fatigue crack growth on the free surface of the hollow specimens as well as the deepest point of the semi-elliptical surface crack front. As result principal particularities of the fatigue surface crack growth rate as a function of temperature conditions are established.

Surface crack growth in cylindrical hollow specimen subject to tension and torsion

The subject for studies is an aluminium cylindrical hollow specimen with external axial and part circumferential semi-elliptical surface crack undergoing fatigue loads. Both the optical microscope measurements and the crack opening displacement (COD) method are used to monitor and calculate both crack depth and crack length during the tests. The variation of crack growth behaviour is studied under cyclic axial tension, pure torsion and combined tension+torsion fatigue loading. For the particular surface flaw geometries considered, the elastic and plastic in-plane and out-of-plane constraint parameters, as well as the governing parameter for stress fields in the form of In-integral and plastic stress intensity factor, are obtained as a function of the aspect ratio, dimensionless crack length and crack depth. The combined effect of tension and torsion loading and initial surface flaw orientation on the crack growth for two type of aluminium alloys is made explicit. The experimental and numerical results of the present study provided the opportunity to explore the suggestion that fatigue crack propagation may be governed more strongly by the plastic stress intensity factor rather than the magnitude of the elastic SIFs alone. One advantage of the plastic SIF is its sensitivity to combined loading due to accounting for the plastic properties of the material.

内圧を受ける配管の繰返し軸方向引張圧縮によるラチェット変形解析(保全・設備診断技術,&lt;特集&gt;第13回動力・エネルギー技術シンポジウム)

内圧を受ける配管の繰返し軸方向引張圧縮によるラチェット変形解析(保全・設備診断技術,&lt;特集&gt;第13回動力・エネルギー技術シンポジウム)

A202 内圧を受ける配管の繰返し軸方向引張圧縮によるラチェット変形解析(材料強度評価-1,OS-6 保全・設備診断技術(3),一般講演,地球温暖化防止と動力エネルギー技術)

A202 内圧を受ける配管の繰返し軸方向引張圧縮によるラチェット変形解析(材料強度評価-1,OS-6 保全・設備診断技術(3),一般講演,地球温暖化防止と動力エネルギー技術)

Investigation of service failures of steel music wire

An investigation of a number of service failures of the hard steel strings of plucked musical instruments is reported. All the failed strings were found to contain transverse fatigue cracks, mostly located near the end of the vibrating length (e.g. at the “bridge” of the instrument) and extending to about one third of the section thickness. One wire had corroded severely before failing in fatigue. Final failure occurred by ductile fracture. An analysis of the service stresses showed that the strings are subjected to high mean tensile stresses resulting principally from elastoplastic bending opposite the failure location. It is shown that a small cyclic axial tension arises from repeated plucking during playing and this can lead to fatigue initiation and propagation over a large proportion of the wire cross section. Neither surface nor bulk defects, wear nor contact stresses were found to be factors of importance in the cases examined, contrary to some speculation.

Strength of Cylindrical Specimens Subjected to Laser Hardening along the Generator and a Spiral Path

We have shown that the path of a continuous CO2-laser beam over the cylindrical surface of specimens in the course of their hardening substantially affects the strength of steels in cyclic axial tension and bending with torsion. Hardening on a spiral path ensures higher mechanical parameters as compared with that along the generator of the cylindrical surface.

超細粒鋼（ＳＵＦ鋼）における疲労微小き裂の発生と初期伝ぱのＡＦＭ観察

Steel plates produced by an advanced thermo-mechanical control process have two regions: the ultrafinegrained surface layer with the average grain size of less than 2μm and the intermediate region with medium-sized grains. Smooth specimens made of ultrafine-grained and medium-grained regions were fatigued under cyclic axial tension compression at room temperature. The effect of the microstructure on the initiation and the early propagation of small fatigue cracks were investigated by observing the images of specimen surfaces replicated on plastic sheets by atomic force microscopy. In the medium-grained specimens, the fatigue cracks initiated from the simple slip lines. In the ultrafine-grained specimens, complex slip deformation in the shape of irregularities of the specimen surface was observed prior to the initiation of fatigue cracks. The fatigue cracks were nucleated at the grain boundary between the grains containing the complex slip deformation. The crack propagation rate in the ultrafine-grained specimens decreases because of the grain-boundary blocking and crack deflection in an early stage of the propagation.

超細粒鋼（ＳＵＦ鋼）における疲労き裂伝ぱにおよぼす微視組織の影響

Steel plates with surface layers having ultrafine-grained microstructure, called SUF steel, exhibit excellent crack arrestability against brittle crack propagation by forming shear-lips at the surface layers. Although SUF steels have been proven to possess superior fatigue properties as well, the mechanism of the improvement in fatigue properties is not fully understood. In this study, smooth specimens and single-edge-notched specimens were prepared from the ultrafine-grained surface layer and the medium-grained mid-thickness region in the LT and LS directions. The specimens were fatigued under cyclic axial tension compression at room temperature. The effects of the microstructures on the fatigue limits and crack propagation behavior were investigated.The crack propagatiom rate, when compared at the same stress intensity range, was the lowest in the ultrafinegrained LS specimen. The threshold value of the stress intensity range in the ultrafine-grained LS specimen was higher than that in the medium-grained LS specimen, indicating that the ultrafine-grained specimen exhibited not only higher fatigue limits but also superior crack arrestability against long fatigue cracks. The higher crack arrestabiliy in the ultrafine-grained spesimen is attributed to bifurcation of fatigue cracks.

758 超細粒鋼(SUF 鋼)における疲労き裂発生過程のナノスケール観察

Ultrafine-grained specimens with the average grain size of less than 2μm and medium-grained specimens were prepared from steel plates produced by an advanced thermo-mechanical control process. The smooth specimens were fatigued under cyclic axial tension compression at room temperature and the crack initiation and early propagation behaviors were investigated by atomic force microscopy. In the medium-grained specimens, the fatigue cracks initiated from the simple slip lines. On the other hand, in the ultrafine-grained specimens, complex slip deformation was formed in the vicinity of grain boundaries prior to the initiation of fatigue cracks. The fatigue cracks were nucleated at the grain boundary between the grains with the complex slip deformation. The crack propagation rate in the early stage decreases because of the grain-boundary blocking and crack deflection in the ultrafine-grained specimens.

反応焼結ＴｉＡｌ金属間化合物の長い疲労き裂および切欠き底からの微小疲労き裂伝ぱ挙動

Smooth and notched specimens of reactive-sintered Ti-45at%Al-1.6at%Mn intermetallic compound with lamellar and equiaxed γ microstructures were fatigued under cyclic axial tension compression at room temperature. The effect of microstructures on the crack propagation behavior was investigated in comparison with cast Ti-47.2at%Al with larger grain size.Fatigue crack paths were tortuous in the lamellar microstructure in contrast to the straight crack paths in the equiaxed γ microstructure. In comparison with cast TiAl, reactive-sintered TiAl exhibited higher crack propagation rates when compared at the same stress intensity range. The values of stress intensity range at threshold were greater in cast TiAl. Those threshold values had a tendency to increase with the roughness of the fracture surface. The rate of increase in crack opening stress intensity factor at threshold with non-propagating crack length was smaller than that of cast TiAl. Predicted fatigue limits for crack initiation and propagation based on the fatigue-crackgrowth resistance-curve method were in agreement with the experimental results. The fatigue limits of notched specimens were smaller than those of cast TiAl in spite of the superior mechanical properties of reactive-sintered TiAl.

金属間化合物ＴｉＡｌにおける切欠き底微小疲労き裂の伝ぱ挙動

Single-edge-notched specimens of an intermetallic compound TiAl were fatigued under cyclic axial tension compression. The effect of microstructure on the propagation behavior of short fatigue cracks formed at the notch root was investigated. The crack length was measured with the AC potential method and the development of crack closure with crack extension was measured through the compliance method. The crack path is tortuous in lamellagrains, while straight in gamma-grains. When compared at the same non-propagating crack length, the crack opening stress intensity factor at the threshold increases with increasing lamella volume fraction. The relation between the crack propagation rate and the effective stress intensity range for short cracks was identical to that for long cracks. The resistance-curve method was used to predict the fatigue strength of notched specimens. The predicted values of the fatigue limits for crack initiation and for fracture, and the non-propagating crack length agreed well with the experimental results.

Overlay models for structural analysis under cyclic loading

The behaviour of structural elements subjected to cyclic loading conditions is described by overlay models and simulated using standard finite element programs. The material model is established by parallel connection of several finite elements, each describing elasto-plastic material behaviour with kinematic or isotropic hardening and sharing the same geometrical position. The death or birth option, respectively, is used to simulate the yielding condition with a higher and lower yielding stress. A method estimating the material parameters is discussed. Results found by using ADINA 6.0 for the analysis of a cylindrical structural element under cyclic axial tension are presented. The effect of locally varying material parameters is discussed.