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Background: Polymers in practical applications often face diverse torsional loads, such as polymeric gears, couplings, scaffolds, etc. Meanwhile, additive manufacturing enables the creation of intricate geometries for specific needs and its application to fabricate various component parts has grown exponentially. Nevertheless, research on cyclic and reversed cyclic torsional loading of additively-manufactured polymers is very limited. Objective: Mechanical characterization of monotonic, cyclic, and reversed cyclic torsion in polylactic acid (PLA), PLA Premium, and PLA Tough materials. Methods: Specimens were 3D-printed with a 0° build orientation using an extrusion technique and two infill orientation angles (± 45° and 0°/90°). Specimens were subjected to underwent monotonic, cyclic, and reversed cyclic torsion until failure. Results: Regardless of material type, ductile fracture governed the behavior under monotonic loading and brittle failure under cyclic and reversed cyclic loadings. Specimens with a ± 45° infill orientation outperformed their 0°/90° counterparts across all materials, with PLA Premium exhibiting superior performance compared to PLA and PLA Tough. Importantly, it was demonstrated that the previously-proposed multilinear idealized shear stress-shear strain curve, developed for monotonic loading of 15 different polymers, also applies to the envelope curves of cyclic and reversed cyclic loading in PLA-based polymers. Thus, it is useful as material model input for numerical simulation purposes. [ABSTRACT FROM AUTHOR]

The influence of strain amplitude on deformation mechanisms and cracking modes during cyclic torsion of the AZ31 magnesium (Mg) alloy was quantitatively investigated via EBSD‐SEM characterization. At 0.42% strain amplitude, basal slip was the dominated deformation mechanism throughout the entire fatigue life. At 1.732% strain amplitude, the activation of deformation mechanisms was featured by the periodic transition: tension twinning + basal slip (during counterclockwise torsion) then detwinning + tension twinning + basal slip (during reverse torsion). Moreover, cracking along slip traces (ST) and tension twins (TTW) were the primary cracking modes at 0.42% and 1.732% strain amplitude, respectively. ST cracking and TTW cracking preferentially appeared in soft‐oriented grains for basal slip and tension twinning, respectively. The underlying mechanisms governing the activation of various deformation mechanisms, cracking modes, and cyclic stress–strain responses were systematically discussed. Highlights: At 0.42% strain amplitude, basal slip was the dominated deformation mechanism.At 1.732% strain amplitude, twinning–detwinning exhibited higher activity.Cracking modes exhibited high dependency on the strain amplitude.Transgranular cracks were prone to occur in soft grains for twinning/basal slip. [ABSTRACT FROM AUTHOR]

A multiphase‐gradient‐structured medium‐Mn steel with dislocation/stacking fault (SF) density gradient, austenite fraction gradient, and grain size gradient is designed and fabricated by cyclic torsion. It exhibits higher yield strength (YS) (942 MPa), ultimate tensile strength (1295 MPa), and tensile toughness (290 mJ mm−3) than its homogeneous counterpart (672, 1273 MPa, and 278 mJ mm−3, respectively). High‐density‐interlaced SFs are generated at the surface region because of the change in strain path and stress state during cyclic torsion. These massive interactive SFs promote the persistent martensite transformation of the retained austenite in the surface region within the entire uniform strain range. Therefore, in addition to the central layer, the surface region in the gradient structures provides strong strain hardening. Moreover, the continuous martensite transformation in the surface region allows the gradient structure to be retained even after tensile failure, which is beneficial for improving the heterogeneous‐deformation‐induced (HDI) hardening of the gradient‐structured sample during tensile deformation. Thus, the combination of active and persistent transformation‐induced plasticity effect and HDI hardening contributes to its excellent tensile toughness and ductility. Quantitative analysis indicates that HDI strengthening and dislocation strengthening play a dominant role in the sample's ultrahigh YS. [ABSTRACT FROM AUTHOR]

This study explores the effect of adding 3 wt.% Y to pure magnesium (Mg) on its mechanical behavior under cyclic torsional loadings at room temperature. The research examines deformation and cracking modes in both pure Mg and Mg‐3Y samples. Deformation modes are monitored using quasi‐in‐situ EBSD observations coupled with slip trace analysis. The findings reveal that basal slip dominates the cyclic deformation throughout the fatigue life of the pure Mg sample, while both basal and pyramidal slip dominate the cyclic deformation in the Mg‐3Y sample. Intergranular cracking is the primary cracking mode for both samples under cyclic torsional loadings. Basal and pyramidal slip persistent slip band (PSB) cracking serves as a primary transgranular cracking mode in the pure Mg and Mg‐3Y samples, respectively. The study also investigates the underlying mechanism governing the activity of various deformation modes, cracking modes, and mechanical behavior. Highlights: Under cyclic torsional loadings, the Mg‐3Y sample exhibited enhanced activity of nonbasal slip.Intergranular cracking was a dominant cracking mode for the pure Mg and Mg‐3Y samples under cyclic torsional loadings.Basal slip and pyramidal slip PSB cracking was a primary transgranular cracking mode in the pure Mg sample and Mg‐3Y sample, respectively.The increased activity of nonbasal slip in the Mg‐3Y sample is possibly responsible for its longer fatigue life. [ABSTRACT FROM AUTHOR]

• Fracture surface analysis is conducted on the failed specimens using a scanning electron microscope. • The influence of overload on the torsional fatigue life and pre-torsion fatigue on the tensile strength. • Estimation of the fatigue zone and residual zone size. This study presents the outcomes of experimental research designed to explore the effects of plastic deformation on the tensile strength and torsional fatigue life of the CuSn7Zn4Pb7 bronze alloy. The primary objective was to understand how plastic deformation impacts these critical mechanical properties of the alloy. The study aimed to determine the nature of damages and attempt to systematise them. Various combinations of loads and material microstructure play a decisive role in the propagation of fatigue cracks. Therefore, in the study, the microstructure of the analysed material, the determination of its chemical composition, and its compliance with relevant material standards were presented. Additionally, microscopic images of fracture surfaces, along with fatigue crack analysis and determining the presence of the fatigue and residual zones, were provided. [ABSTRACT FROM AUTHOR]

Inclusion-initiated fracture in high-strength spring steel is studied for axial and torsion very high cycle fatigue (VHCF) loading at load ratios of R = −1, 0.1 and 0.35. Ultrasonic S-N tests are performed with SWOSC-V steel featuring intentionally increased numbers and sizes of non-metallic inclusions. The fatigue limit for axial and torsion loading is considered the threshold for mode I cracks starting at internal inclusions. The influence of inclusion size and Vickers hardness on cyclic strength is well predicted with Murakami and Endo's a r e a parameter model. In the presence of similarly sized inclusions, stress biaxiality is considered by a ratio of torsion to axial fatigue strength of 0.86. Load ratio sensitivity is accounted for by the factor ((1 − R)/2)α, with α being 0.41 for axial and 0.55 for torsion loading. VHCF properties under torsion loading cannot appropriately be deduced from axial data. In contrast to axial loading, the defect sensitivity for torsion loading increases significantly with superimposed static mean load, and no inclusion-initiated fracture is found at R = −1. Size effects and the stress gradient effective under torsion loading are considered to explain smaller crack initiating inclusions found in torsion ultrasonic fatigue tests. [ABSTRACT FROM AUTHOR]

The influence of mean shear stress on torsion very high cycle fatigue (VHCF) for internal inclusion‐initiated fracture is investigated. Ultrasonic torsion fatigue tests are performed at load ratios R = −1, 0.1, and 0.35 with high‐strength spring steel SWOSC‐V featuring an increased number of nonmetallic inclusions. Based on Murakami and Endo's area parameter model, an equation predicting the torsion fatigue limit in the presence of detrimental defects is rendered. Stress biaxiality is considered using a ratio of torsion to axial fatigue strength of τa/σa = 0.86. Considering the load ratio sensitivity according to ([1 − R]/2)α, the value for α is experimentally determined to be 0.550. A fine granular area (FGA) is generated at an artificial surface defect in a fully reversed cyclic torsion test in vacuum. Measured growth rates in the FGA were 10−14–10−12 m/cycle, and the formation of the FGA consumed 98% of the VHCF lifetime. [ABSTRACT FROM AUTHOR]

Cyclic torsion tests are performed on micron-scale copper wires with and without surface passivation to study the role of the higher-order condition in the plastic behavior of thin wires under non-proportional loading. A typical strengthening size effect is observed in the symmetric cycles. More obvious strength enhancement exists in the torsional response of passivated copper wires. An unusual Bauschinger effect is found during the loading-unloading cycles, which is more pronounced in passivated wires. The finite element implementation based on Gudmundson's strain gradient plasticity theory is developed for wire torsion to characterize the observed size-dependent phenomena. The higher-order boundary conditions are introduced to simulate the passivated surface. The predicted radial distributions of plastic strain, stress components, and geometrically necessary dislocation density for the passivated and unpassivated wires are given and compared. This work provides a reasonable basis for understanding the role of higher-order conditions of strain gradient plasticity. • Cyclic torsion tests are performed on micron-scale passivated copper wires. • More pronounced unusual Bauchinger effects exist in passivated wires. • The finite element model is developed based on strain gradients theory. • Passivation effects are predicted by introducing higher-order conditions. [ABSTRACT FROM AUTHOR]

The cyclic torsion was carried out on the extruded AZ31 magnesium alloy rods at room temperature by using a computer controlled torsion testing machine. The texture of initial extruded magnesium alloy rods was measured by the XRD technique, which displays a typical basal texture. The mechanical properties during deformation were measured, and the microstructure and texture feature after torsion were analyzed by the EBSD. Meanwhile, the effect of cyclic torsion on mechanical properties of magnesium alloy rods was also investigated. The results show that the symmetrical stress-strain hysteresis curves are obtained during the cyclic torsion of magnesium alloy rods, revealing that sliding is the dominant deformation mode during former torsions, moreover, the stress peak values of the hysteresis curves present an increasing first and then decreasing trend with the increase of cycle period, which is dominated by work hardening and internal micro-crack propagation. The stress peak forms at the 4th cycle under conditions of 60ånd 90°maximum torsion angles, respectively. Amounts of extension twinning bands formed within grains after torsion of magnesium alloy rods, c-axis of grains is rotated to the axial direction of bars caused by the activation of twinning. Mechanical properties of twisted magnesium alloy rods tested by computer controlled universal testing machine show that the compression yielding strength of magnesium alloy bars is increased by the cyclic torsion, the value of which is increased from about 100MPa before torsion to about 200MPa after torsion at most.

Inclusion-initiated fracture in high-strength spring steel is studied for axial and torsion very high cycle fatigue (VHCF) loading at load ratios of R = −1, 0.1 and 0.35. Ultrasonic S-N tests are performed with SWOSC-V steel featuring intentionally increased numbers and sizes of non-metallic inclusions. The fatigue limit for axial and torsion loading is considered the threshold for mode I cracks starting at internal inclusions. The influence of inclusion size and Vickers hardness on cyclic strength is well predicted with Murakami and Endo’s area parameter model. In the presence of similarly sized inclusions, stress biaxiality is considered by a ratio of torsion to axial fatigue strength of 0.86. Load ratio sensitivity is accounted for by the factor ((1 − R)/2)α, with α being 0.41 for axial and 0.55 for torsion loading. VHCF properties under torsion loading cannot appropriately be deduced from axial data. In contrast to axial loading, the defect sensitivity for torsion loading increases significantly with superimposed static mean load, and no inclusion-initiated fracture is found at R = −1. Size effects and the stress gradient effective under torsion loading are considered to explain smaller crack initiating inclusions found in torsion ultrasonic fatigue tests.

Multiaxial stress states frequently occur in technical components and, due to the multitude of possible load situations and variations in behaviour of different materials, are to date not fully predictable. This is particularly the case when loads lie in the plastic range, when strain accumulation, hardening and softening play a decisive role for the material reaction. This study therefore aims at adding to the understanding of material behaviour under complex load conditions. Fatigue tests conducted under cyclic torsional angles (5°, 7.5°, 10° and 15°), with superimposed axial static compression loads (250 MPa and 350 MPa), were carried out using smooth specimens at room temperature. A high nitrogen alloyed austenitic stainless steel (nickel free), was employed to determine not only the number of cycles to failure but particularly to aid in the understanding of the mechanical material reaction to the multiaxial stresses as well as modes of crack formation and growth. Experimental test results indicate that strain hardening occurs under the compressive strain, while at the same time cyclic softening is observable in the torsional shear stresses. Furthermore, the cracks’ nature is unusual with multiple branching and presence of cracks perpendicular in direction to the surface cracks, indicative of the varying multiaxial stress states across the samples’ cross section as cross slip is activated in different directions. In addition, it is believed that the static compressive stress facilitated the Stage I (mode II) crack to change direction from the axial direction to a plane perpendicular to the specimen’s axis.

Copyright of Rare Metal Materials & Engineering is the property of Northwest Institute for Nonferrous Metal Research and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this work, the evaluation of the growth of cracks in specimens of square cross section requested by symmetrical cyclic torsion moments was performed. The specimens were manufactured from AISI 1015. A pre-crack was machined on one side to induce the crack growth. The crack length with the increase in the number of cycles was measured by means of penetrating liquids method. By means of the Finite Element Method, the stress - strain state of the specimens was simulated. The displacements in the tip of the crack were determined to apply the technique of the Crack Tip Opening Displacements to calculate the Stress Intensity Factor. The calculated Stress Intensity Factor was related to the dimensions of the specimen and the size of the crack to propose an equation for the shape function. A Paris's Law in mode of failure III was proposed. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Highlights • Ultrasonic torsion fatigue tests at positive load ratios are described. • Inclusion initiated fracture is found for cyclic torsion at positive load ratios. • Exclusively surface fracture is found for fully reversed cyclic torsion. • Load ratio influences the cyclic torsion HCF and VHCF strength or spring steel. • Interface fracture at aluminates and fracture of MnS inclusions initiated cracks. Abstract The influence of inclusions on cyclic torsion very high cycle fatigue (VHCF) is studied at different load ratios. Testing material is a high-strength spring steel, which was prepared based on the SWOSC–V composition with intentionally increased number and size of inclusions. Ultrasonic torsion fatigue tests were performed at load ratios R = –1, R = 0.1 and R = 0.35 with shot peened specimens. All specimens that were cycled at R = 0.1 or R = 0.35 and failed above 108 cycles showed crack initiation at internal aluminate or MnS inclusions. Interface failures between particles and metallic matrix generate cracks at aluminate inclusions, which predominantly grow in mode I. MnS inclusions have an elongated shape oriented in the specimens' length direction. Shearing of the MnS inclusions generates initial mode II/mode III cracks, which subsequently branch to mode I cracks. All specimens cycled at R = –1 showed surface crack initiation without inclusions, irrespective of lifetime. S–N curves are shifted towards lower shear stress amplitudes with increasing load ratio, indicating a pronounced mean stress influence on cyclic torsion strength. [ABSTRACT FROM AUTHOR]

Combining hetero-structure and TRIP effect can be a feasible approach to enhancing the strength-ductility synergy. Here, varied gradient microstructures with gradual increase in dislocation density with or without martensite content from the center to the surface were constructed in a commercial austenitic stainless steel with strong TRIP effect by cyclic torsion (CT) processes. These designed gradient microstructures resulted in excellent strength-ductility synergies, for example, after CT processing with 20° torsion angle, the yield strength was enhanced 2.7 times, while 78% of the uniform elongation and 121% of the static toughness was achieved, compared to its CG counterpart. The high yield strength was caused by the introduced dislocations and the additional hetero-deformation induced (HDI) strengthening (>350 MPa) due to the mechanical incompatibility between different zones. The high ductility and toughness originated from the unexpectedly continuous work hardening from the soft center to the hard surface. Amazingly, the work hardening provided by the hard surface zones outperformed that by the soft central zones during the middle and late tensile deformation. The multiple-stage activation of stack faults, continuous γ → α′ martensitic transformation (i.e., TRIP effect), mechanical nanotwinning and Lomer-Cottrell locks combined with the HDI work-hardening devoted to the significantly enhanced work hardening capacity of the hard surface zones. This study provides a strategy of combining the gradient dislocation microstructure and TRIP effect to develop advanced metallic materials with high strength and ductility/toughness. [ABSTRACT FROM AUTHOR]

• Cyclic torsion of Mg alloy is studied by experiment and crystal plasticity model. • Deformation mechanism is revealed by active operation modes, TVF, internal stress. • "Butterfly" shaped axial strain-shear strain curve is led by twinning-detwinning. • Gradient twin structure could be regulated in Mg alloy through cyclic torsion. This work investigated the cyclic torsional behaviors of extruded AZ61A Mg alloy tubes through experiments and simulations. To capture the Bauschinger effect, the elastic viscoplastic self-consistent model with the twinning and detwinning scheme, together with a torsion-specific finite element approach was improved by adding a back-stress. A unique Swift effect with the "butterfly" shape was observed and reasonably reproduced by our model. Furthermore, the relative activities of deformation mechanisms, internal stress distributions, and twin volume fraction distributions under cyclic torsion were discussed. The findings could be beneficial to the design, manufacturing, and service of Mg alloys, particularly under cyclic torsion. [ABSTRACT FROM AUTHOR]

Based on a quasi-static test on six concrete-filled double skin steel tube columns subject to cyclic pure torsion, the torsion behavior of concrete-filled double skin steel tube columns with various section types, hollow ratios and steel ratios was studied. The failure modes, torsion-rotation angle hysteretic curves and strain distribution law of concrete-filled double skin steel tube columns under reversed cyclic loading are obtained. The test results show that the hysteretic curves of concrete-filled double skin steel tube columns under pure torsion are plump. The unloading stiffness was close to the initial elastic stiffness. The good energy dissipation capacity of concrete-filled double skin steel tube columns can be observed. Under a cyclic torsion moment, the torsion-resistance capacity of circular concrete-filled double skin steel tube columns was better than that of square and rectangular concrete-filled double skin steel tube columns. With the same thickness of the inner steel tube and the same section size and shape, the hollow ratio of concrete-filled double skin steel tube columns has little effect on the cyclic torsion behavior. [ABSTRACT FROM AUTHOR]

Cold forming is usually associated with the "work hardening" of the material being formed. The work hardening behavior of metals subject to complex processing paths is different from that in monotonic deformation. The results show that, after some initial hardening, there is a possibility that further deformation will cause softening in the material ("work softening"). Recent work showed that cyclic torsion applied to drawn products causes changes in the subsequent tensile behavior of low carbon steel, and that the effect will depend on the previous "history" of the material. For annealed samples, the cyclic torsion leads to an increase in the yield strength, but does not affect the tensile strength and elongation. For the case of previously drawn bars, the cyclic deformation caused a decrease in the yield and tensile strength and an increase in the total elongation. The present paper discusses the dislocation structure changes associated with different strain paths in mild steel.

Although the material property and structural behavior of recycled aggregate concrete (RAC) have been widely investigated, the research on seismic performance of RAC members under cyclic torsion is still very limited. In this paper, the failure mode, hysteresis loop, strain of steel reinforcement, principal strain of concrete, energy dissipation capacity, skeleton curve, deterioration of stiffness and ductility factor of RAC beams and natural aggregate concrete (NAC) beams under cyclic torsion were compared and investigated. The results indicate that although both the RAC and NAC torsional beams present a torsional failure mode with spiral cracks, the cracks of RAC beams are larger than that of NAC beams. The hysteresis loop shape and corresponding inflection points of NAC and RAC torsional beams are very similar, but the energy dissipation capacity and ductility factor of RAC torsional beams are about 20% and 7% higher than those of NAC beams, respectively. The use of RAC in cyclic torsional beams does not bring apparent influence on the deterioration of stiffness, but the bearing capacity of RAC torsional beams is lower than that of NAC beams. [ABSTRACT FROM AUTHOR]

The very high cycle fatigue (VHCF) properties of shot-peened VDSiCr spring steel have been investigated with the ultrasonic fatigue testing method. Fatigue behaviour under cyclic torsion and cyclic tension loading at load ratios between R = −1 and R = 0.5 is compared. For 90% of the VHCF failures under axial loading, fractured grain boundaries or inclusions in the interior of the material act as crack starters. In contrast, the initial crack is produced by cyclic shear in the interior or, less frequently, at the surface for more than 90% of the VHCF failures under torsional loading. The crack path deflects from mode II/mode III to mode I at the border of the initiating shear area. The change of crack path correlates to a stress intensity factor range for a crack loaded in shear mode of Δ K τ,ISA = 5.6 ± 0.5 MPam 1/2 for load ratio R = 0.1 and Δ K τ,ISA = 3.8 ± 0.4 MPam 1/2 for R = 0.35, respectively. Residual stresses due to shot-peening are stable during VHCF axial loading while they are reduced during VHCF torsional loading. [ABSTRACT FROM AUTHOR]

An approach to the analysis of the limit state and the fatigue life of simplest structural members subject to a combination of inphase cyclic tension/compression and cyclic torsion or a combination of cyclic bending and cyclic torsion is proposed. The solution is constructed using a limit-state model that relates the fatigue strengths in terms of a power transcendental function. The calculated results are validated experimentally for solid prismatic rods and thin-walled tubes subject to fatigue failure [ABSTRACT FROM AUTHOR]

Accurate and approximate alternatives of limiting state models for isotropic metallic materials under symmetrical cyclic bending-torsional loading are proposed. In the accurate models, the relation between the peak amplitudes of normal and tangential stresses is preset with exponential transcendental functions. The approximate alternatives were obtained from the accurate models by series expansion of transcendental functions reduced to two and three terms. The models were experimentally verified with limiting state calculation problems for solid cylindrical and thinwalled tubular specimens. The proposed models are compared with classical fracture criteria-based ones. [ABSTRACT FROM AUTHOR]

Cyclic torsion fatigue tests with superimposed static torsion loads are performed with VDSiCr spring steel with shot-peened surface in the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regime. Fatigue properties are investigated at load ratios R = 0.1, R = 0.35 and R = 0.5 up to limiting lifetimes of 5 × 10 9 cycles with a newly developed ultrasonic torsion testing method. Increasing the load ratio reduces the shear stress amplitude that the material can withstand without failure. Fatigue cracks are initiated at the surface in the HCF regime. In the VHCF regime, cracks are preferentially initiated internally in the matrix, below the surface layer with compression residual stresses, and less frequently at the surface. Cyclic and mean shear stresses with 50% survival probability in the VHCF regime are presented in a Haigh diagram. Linear line approximation delivers a mean stress sensitivity of M = 0.33 for load ratios between R = −1 and R = 0.5. [ABSTRACT FROM AUTHOR]

Turbo generator shafts are often subjected to cyclic torsion resulting in formation of large longitudinal cracks as well as circumferential cracks. The presence of these cracks could greatly impact the shaft resonance frequencies. In this paper, dynamic response of a shaft with longitudinal and circumferential cracks is investigated through a comprehen-sive analytical study. The longitudinally cracked section of the shaft was modeled as an uncracked shaft with reduced torsional rigidity. Torsional rigidity correction factor (i.e., the ratio of torsional rigidity of the cracked shaft to that of the uncracked shaft) was obtained from finite element analysis and was shown to be only a function of crack depth to the shaft radius. The resonance frequency and frictional energy loss of a shaft with a longitudinal crack were found little affected by the presence of the crack as long as the crack depth was less than 20% of the shaft radius even if the entire shaft is cracked longi-tudinally. Moreover, we showed that the longitudinal crack location could be more con-veniently identified by monitoring the slope of the torsional response along the shaft. The circumferential crack was modeled as a torsional spring with a torsional damping. The torsion spring and damping constants were obtained using fracture mechanics. For a shaft with both a longitudinal crack and a circumferential crack, the resonance frequency was governed by the longitudinal crack when the circumferential crack depth was less than 30% of the shaft radius. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mechanical Engineering the National Technical University of Ukraine 'Kyiv Polytechnic Institute' is the property of National Technical University of Ukraine KPI and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The problem of fatigue endurance calculation for solid cylindrical and thin-walled tubular specimens from isotropic metallic materials under combined symmetrical cyclic tensile-compressive and torsional loading is solved. The solution is based on the nonlinear model of limiting state, describing the relation between the peak amplitudes of cycle stresses in the form of the exponential transcendental function. [ABSTRACT FROM AUTHOR]

Abstract: Circumferentially notched bars of austenitic stainless steel, SUS316L, and carbon steel, SGV410, with three different notch-tip radii were fatigued under cyclic torsion without and with static tension. The torsional fatigue life of SUS316L was found to increase with increasing stress concentration under the same nominal shear stress amplitude. Electrical potential monitoring revealed that the crack initiation life decreased with increasing stress concentration, while the crack propagation life increased. This anomalous notch-strengthening effect was ascribed to the larger retardation of fatigue crack propagation by sliding contacts of fracture surfaces. The superposition of static tension on cyclic torsion causes notch weakening. The notch-strengthening effect in torsional fatigue was not found in carbon steels, SGV410. The difference in the crack path of small cracks near notch root between stainless steel and carbon steel gives rise to the difference in the notch effect in torsional fatigue. The factory-roof shape observed on fracture surfaces of SUS316L became finer with higher stress amplitude and for sharper notches. The superposition of static tension makes the factory-roof shape less evident. Under higher stresses, the fracture surface was smeared to be flat. The fracture surfaces of SGV410 became smoother with increasing stress amplitude and notch acuity. The three-dimensional feature of fracture surfaces clearly showed the difference of the topography of fracture surfaces. The topographic feature was closely related to the amount of retardation of crack propagation due to the sliding contact of fracture surfaces. [Copyright &y& Elsevier]

Very high cycle fatigue (VHCF) properties of VDSiCr spring steel are investigated with ultrasonic equipment under fully reversed cyclic torsion loading and under cyclic axial loading at load ratios R = -1, R = 0.1 and R = 0.5. Shot-peened specimens with surface finish similar to valve springs in combustion engines are tested until limiting lifetimes of 1010 cycles. Under cyclic torsion loading, specimens either fail below 106 cycles with crack initiation at the surface or they do not fail. Under cyclic axial loading, failures above 109 cycles were found for all load ratios with crack initiation at the surface or at internal inclusions. Ratio of mean endurance limit (50% failure probability at 1010 cycles) under fully reversed cyclic torsion and cyclic tension-compression loading is 0.86. Cyclic torsion loading slightly below the endurance limit leads to cyclic softening first followed by cyclic hardening whereas cyclic stability is found for tension-compression loading. Cyclic torsion reduces surface compression stresses whereas they are hardly affected by cyclic tension-compression loading. Mean endurance limit at 1010 cycles for R = 0.1 is 61% of the endurance stress amplitude at load ratio R = -1, and for R = 0.5 it is 44% of the tension-compression endurance limit. Endurance limits for cyclic torsion and cyclic tension-compression loading are comparable, if effective stress amplitude is used that considers cyclic normal stresses and residual compression stresses at the surface. [ABSTRACT FROM AUTHOR]

Circular concrete members were reinforced with a conventional single spiral and a new confinement technique consisting of two opposing spirals (cross spirals). Eighteen members were studied under pure reverse cyclic torsional loading to investigate advantages of the new confinement technique. Cross spirals allow improved strength and ductility or increased spiral spacing to aid concrete aggregate passage during construction. Members with conventional single-spiral and new cross-spiral reinforcement schemes were constructed using identical methods and materials. All members had diameters of 200 mm (8 in.); lengths of 1000, 800, 600, and 400 mm (39, 32, 24, and 16 in.); and spiral spacings varying from 25 to 90 mm (1 to 3.5 in.). Results from cross-spiral members are compared with those of single-spiral members to evaluate the performance of the new cross-spiral confinement technique. [ABSTRACT FROM AUTHOR]

Abstract: Technological metal forming processes of extrusion, forging and rolling with imposed cyclic torsion or shear deformation are of engineering interest in view of their advantages with respect to monotonic loading processes. The present work is aimed at the analysis of an axisymmetric extrusion process assisted by cyclic torsion, which can be induced by a cyclically rotating die with a specified rotation amplitude and frequency. The material is assumed to be rigid-perfectly plastic and the upper-bound analysis for a kinematically admissible flow field is presented. The field parameters are specified from the condition of minimum plastic dissipation. The evolution of the extrusion force and torsional moment is studied and the corresponding plastic flow field is specified, with process control parameters such as the ratio of extrusion and rotation rates, and the amplitude of die rotation. For increasing rotation frequency, it is shown that localization of plastic flow occurs in the bottom zone close to the rotating die. The analysis allows for specification of process control parameters and their relation to extrusion force, torsional moment, and the associated plastic dissipation for varying reduction ratios. [Copyright &y& Elsevier]

Abstract: The typical slip patterns and dislocation substructures of polycrystalline copper under cyclic torsion were experimentally investigated. The cyclic stress–strain curve of the material consisted of three regions, resembling those of single crystal copper oriented for single slip. During the formation of persistent slip bands, cross slip bands between primary slip bands were often observed. Under cyclic torsion at a high shear strain amplitude, cross slip between slip bands of each slip system was an important process for the collapse of dislocation tangles into dislocation cell walls. During the transient stage of the formation of dislocation cells, the stress amplitude was inversely proportional to the average diameter of dislocation cells. This relationship is identical to that between the saturated stress magnitude and the corresponding dislocation cell size. The formation of typical dislocation patterns in copper under cyclic loading is closely associated with cross slip of screw dislocations. [Copyright &y& Elsevier]

Abstract: Ultrasonic equipment is described which is used to perform cyclic torsion and cyclic tension–compression fatigue experiments with the aluminium alloy 2024-T351 in the high and very high cycle fatigue regime. Displacement amplitude of one specimen’s end and cyclic resonance frequency are measured and controlled in closed-loop electronic circuits, and the specimens are loaded in pulse-pause sequences to prevent heating. Theoretical considerations and the practical realisation of a load train to perform ultrasonic torsion fatigue tests are presented. Cyclic torsion and cyclic tension–compression endurance data of 2024-T351 are compared using Mises equivalent stresses. At same equivalent stresses, numbers of cycles necessary to create cracks with minimum length 300μm in cyclic torsion were 2–10 times higher than lifetimes in tension–compression tests. Crack initiation and propagation in cyclic torsion is in the directions of maximum shear stresses whereas fracture surface at crack initiation location produced by cyclic tension–compression is perpendicular to the principal stress. One direction of maximum shear (specimen’s length direction) is preferred, and circumferential fatigue cracks develop and propagate at significantly greater numbers of torsion load cycles. [Copyright &y& Elsevier]

The formation mechanism of the factory-roof pattern in a circumferential notched specimen was examined. To achieve observation of the material's cracks internally, plastic material, that was acrylic, was used for the test. Cyclic torsional tests were performed with and without application of static tension. A factory-roof pattern was formed in the fracture surface when cyclic torsion tests were conducted with static tension. Formation of the factory-roof pattern was found to be dependent on testing conditions. When such a pattern was formed, many small cracks were initiated by shear mode, followed by their coalescence. The new cracks' initiation at the front of the shear mode cracks could be one of the reasons for the coalescence, After the coalescence and branching of cracks, the cracks grew under the control of the maximum principal stress criterion. This behavior was examined by direct observation of the cracks. The final fracture pattern showed the initiation of many shear-mode cracks and their succeeding coalescence. From those observations, we considered the formation of a factory-roof pattern model. [ABSTRACT FROM AUTHOR]

Abstract: Fatigue tests of crack propagation from a circular notch in thin-walled tubular specimens made of low-carbon steel were performed under cyclic uniaxial tension-compression, and combined loading of cyclic torsion with and without superposed static and cyclic axial loading. The propagation path of fatigue cracks followed the plane on which the total range of the normal stress including the compressive component of the stress was maximum for the cases of combined mode loading as well as uniaxial loading. For all cases examined, when compared at the same stress intensity range, the propagation rate became faster than that predicted from the crack propagation law obtained for carbon steels under uniaxial loading in small-scale yielding condition. Even when compared at the same value of the effective stress intensity range, the crack propagation rate was faster,because of excessive plasticity ahead of the fatigue crack. The J-integral range determined from the relation between load and displacement was proved to be an appropriate parameter for crack propagation with excessive plasticity. The J-integral range was correlated to the stress amplitude and the crack length for each loading condition. [Copyright &y& Elsevier]

Abstract: Strain softening effects have been previously observed in drawn low carbon steel bars as a result of cyclic torsion experiments. In this paper, the substructural aspects related to the phenomenon have been investigated. Single pass drawn bars were subjected to a quarter, to a half, to a full torsion cycle and to 10 such cycles. Transmission electron microscopy revealed the development of extended microbands crossing the former dislocation arrangement of the drawn metal, which evolves to a rectangular shaped subgrains structure as torsion deformation is conducted. [Copyright &y& Elsevier]