Cyclic Tensile Loading Research Articles

Investigating the birth-related caudal maternal pelvic floor muscle injury: The consequences of low cycle fatigue damage

One of the major causes of pelvic organ prolapse is pelvic muscle injury sustained during a vaginal delivery. The most common site of this injury is where the pubovisceral muscle takes origin from the pubic bone. We hypothesized that it is possible for low-cycle material fatigue to occur at the origin of the pubovisceral muscle under the large repetitive loads associated with pushing during the second stage of a difficult labor. The main goal was to test if the origin of the pubovisceral muscle accumulates material damage under sub-maximal cyclic tensile loading and identify any microscopic evidence of such damage. Twenty origins of the ishiococcygeous muscle (homologous to the pubovisceral muscle in women) were dissected from female sheep pelvises. Four specimens were stretched to failure to characterize the failure properties of the specimens. Thirteen specimens were then subjected to relaxation and subsequent fatigue tests, while three specimens remained as untested controls. Histology was performed to check for microscopic damage accumulation. The fatigue stress-time curves showed continuous stress softening, a sign of material damage accumulation. Histology confirmed the presence of accumulated microdamage in the form of kinked muscle fibers and muscle fiber disruption in the areas with higher deformation, namely in the muscle near the musculotendinous junction. The origin of ovine ishiococcygeous muscle can accumulate damage under sub-maximal repetitive loading. The damage appears in the muscle near the musculotendinous junction and was sufficient to negatively affect the macroscopic mechanical properties of the specimens.

The Influence of Loading Paths on Mechanical Behavior and Microstructure of Mn18Cr18N Austenitic Stainless Steel

The mechanical behavior of Mn18Cr18N steel along different loading paths was investigated at room temperature. In compression–tensile loading paths, the strain hardening behavior depends on subsequent tensile loading directions. When the subsequent loading axis coincides with the previous loading axis, the strain hardening path coincides with the strain hardening path in previous strain stage. When the subsequent loading axis changed, the subsequent strain hardening rate is remarkable greater than that in the previous strain hardening stage. The tensile ductility is different along different loading paths. In consecutive compression–tensile loading paths, the tensile ductility increased first and then decreased. Dislocation rearrangement caused good ductility during the tensile loading. In non-consecutive compression–tensile loading paths, the tensile ductility decreased gradually. Dislocation multiplication occurred rapidly during the subsequent tensile loading. Stress hardening is remarkable during compression–tensile consecutive cyclic loading when the strain amplitude is greater than 0.01. The maximum tensile stress can be reached up to 1549.6 MPa at 3 cycles with 0.15 strain amplitude, which is an increase of 395.4 MPa compared to the simple tensile loading. During complex loading paths, dislocation configurations and the substructures not only depend on the accumulated strains but also on the loading paths.

A quantitative study on temperature variation of rubber under steady state uniaxial tensile cyclic loading

Rubber materials under cyclic mechanical loading show special properties compared to other materials. This research aims to quantitatively clarify the relationship between cyclic deformation and temperature variation of carbon black filled styrene-butadiene rubber (SBR) under steady state condition after the rubber is accommodated enough both mechanically and thermally. A dumbbell specimen was subjected to uniaxial cyclic tension at various loading conditions. Temperature variation on the gauge zone surface of the specimen was measured by infrared thermography. In addition to the experiment, the temperature variation of the specimen was also predicted theoretically. The prediction is composed of three parts. The first part shows a three-elements model to reproduce the mechanical behavior with considering residual strain and stress softening. The material parameters are determined to match the experimental data at each loading condition. The second part predicts the temperature variation under adiabatic condition by considering three factors: isentropic elastic, entropic elastic and viscous dissipation effects. Third, a correction scheme is proposed to consider the heat transfer between the specimen and the surrounding air or others. As a result, the temperature amplitude and phase difference between temperature and strain are predicted. The predicted results were compared with the experimental data. It is confirmed that the predicted results are in good agreement with ones obtained by the infrared thermography. Furthermore, the phase difference between temperature and strain is about 180∘ at the small deformation area (isentropic elastic effect dominated) while it is almost about 0∘ at large deformation area (entropic elastic effect dominated). In addition to this, there exists a phase transition area between these two areas. It is concluded that the proposed method is a good way to provide quantitative information of the temperature variation of rubber materials subjected to uniaxial cyclic loading under steady state.

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.

Determination of surface mechanical property and residual stress stability for shot-peened SAF2507 duplex stainless steel by in situ X-ray diffraction stress analysis

In this study, SAF2507 duplex (austenite–ferrite) stainless steel was processed by shot peening. The depth–profile variations of the stress state and work hardening in the shot-peened layer were investigated by X-ray diffraction and microhardness tests. The evolutions of surface morphology and microstructure were investigated using scanning and transmission electron microscopy. The stress–strain relations of the shot-peened surface and surface residual stress relaxation caused by cyclic stresses were experimentally determined by in situ X-ray diffraction stress analysis combined with tensile tests. Results showed that shot peening (SP) has induced severe plastic deformation in the surface layer, with the attendant work hardening and high compressive residual stresses (CRS). Nevertheless, there were incompatibilities in plastic deformation between the phases, and more property improvements represented by higher CRS, peak breadth and microhardness were conferred into austenitic phases. SP notably enhanced the surface yield strength of this two-phase alloy. The surface yield strength σ0.2 of ferrite and austenite were around 780 and 1100MPa after SP, which were 59% and 104% respectively higher than that of the untreated surface. The surface stress relaxation under cyclic tensile loadings consisted of a two-stage process. The surface residual stresses relaxed dramatically within the first cycle (N=1), then decreased linearly with the logarithm of loading cycles (N>1). The more severely deformed microstructures in austenite resulted in higher surface yield strength and contributed to higher cyclic stability of residual stress.

Nonlinear Lamb wave analysis for microdefect identification in mechanical structural health assessment

Abstract In order to study the application of ultrasonic Lamb wave in the detection of defective plates, a nonlinear Lamb wave detection system was established. The system was used to detect aluminum alloy plates with different depth cracks and aluminum alloy plates with different tensile load cycles. The acquired time domain waveforms are analyzed by Fast Fourier Transform (FFT), and the influence of two kinds of defects on the nonlinear effects of Lamb waves is obtained. The test results show that for crack defects, the deepening of the defects will increase the ultrasonic nonlinear effect of the test piece. When the crack depth exceeds 4 mm, the non-linear effect of crack defects does not increase. For fatigue crack defects, the occurrence of crack defects will also exacerbate the nonlinear effect of the test piece, but when the test piece is fatigue fractured, its macro defects have a smaller effect on nonlinearity.

Experimental study on seismic behavior of mortise-tenon joints reinforced with shape memory alloy

This article presents the results of a study on seismic behavior of mortise-tenon joints of traditional Chinese timber-frame structures reinforced with shape memory alloy (SMA) wires. A monotonic tensile test and a cyclic tensile loading test of the SMA and material tests of wood were carried out. Three full-scale straight-tenon joints reinforced with a different number of SMA wires and one unreinforced contrast joint were subjected to low-cycle reversed loading tests. Seismic behavior of joints such as failure modes, hysteretic and skeleton curves, bending capacities and stiffness degradation, energy dissipation, resetting abilities and deformation capacities were obtained. The results show that the amount of tenon pullout of joints reinforced with SMA wires is reduced. SMA wires provide continuous bending moments and stiffness during the resetting process of joints. The bending capacities and initial stiffness of the reinforced joints are improved. SMA wires provide stable energy dissipation, damping performance and resetting abilities for joints and reduce residual deformation. As the number of SMA wires increases, the bending capacities, initial stiffness, energy dissipation, and self-resetting abilities will be further enhanced. And there are good deformation capacities in reinforced joints.

Effect of plasticity on superelasticity and hysteretic dissipation of NiTi shape memory alloy

This paper experimentally investigates the effect of plastic deformation on superelasticity and hysteretic dissipation of NiTi shape memory alloy (SMA). First, NiTi SMA wires were stretched at an extremely high stress to explore the plastic yielding and fracture mechanism. Results show that plastic yielding and fracture took place at stresses of 1260 MPa and 1550 MPa, due to the formations and mergers of the dislocation slipping bands. Then, the SMA wires were plastically treated at different stresses near the plastic yield limit. Finally, the specimens after “plastic treatment” were subjected to cyclic tensile loading to estimate the effect of the plastic deformation on the material features such as superelasticity, hysteretic dissipation, residual deformation, temperature variation. Results show that most of the material features degraded with the increasing magnitude of plasticity except the residual deformation. From the physical view of point, the plasticity-induced internal stress field facilitates the formation of martensite variants and obstructs the reverse phase transformation from martensite variants to their parent austenite phase.

Volumetric assessment of fatigue damage in a SiCf/SiC ceramic matrix composite via in situ X-ray computed tomography

To enhance the understanding of matrix cracking and damage progression on the macroscopic scale, within a 0/90° fibre reinforced SiCf/SiC ceramic matrix composite (CMC), X-ray computed tomography (XCT) imaging and analysis have been performed in conjunction with a commercially available in-situ mechanical loading device. CMC test coupons were subjected to tensile cyclic loads and inspected using XCT without removal from the tensile loading device. Attempts to measure and quantify the resulting damage using volumetric image analysis techniques are presented, by characterising the crack network from XCT images acquired at both the maximum and minimum load condition during selected fatigue cycles. The XCT detection of significant crack development within the first loading half-cycle shows good agreement with cumulative acoustic emission energy data recorded under similar test conditions. The results are seen as an important step towards correlating the damage behaviour detected via different NDE and health monitoring techniques.

Bridging chains mediate nonlinear mechanics of polymer nanocomposites under cyclic deformation

Elastomer-based nanocomposites, mixtures of elastomeric rubber with hard nanoparticles, generally exhibit strain stiffening under large strains while also showing strain softening at low strain during large cyclic deformations due to the Mullins Effect. Numerous studies have documented the Mullins effect over the last 50 years, and many models have been developed to explain (and predict) the Mullins effect as it is closely related to material failure. Even with this rich history, relatively few studies have connected experimentally measured changes in nanocomposite chain structure with nonlinear strain hardening and nanofiller dispersion. In this work, we quantify the strain hardening mechanics, and chain anisotropy in situ in silica-filled acrylonitrile butadiene rubber (NBR) nanocomposites under cyclic tensile loading. Macroscopic strain hardening and molecular chain anisotropy increased after the first loading cycle, as a strong Mullins effect appeared, for nanocomposites with sufficient filler volume fraction. In composites with low filler content, we observed little increase in strain hardening or chain anisotropy and a barely-visible Mullins effect. Our results provide strong experimental support that chain delamination from the filler surface is related to the Mullins effect in nanocomposite materials.

Self-heating behavior during cyclic loadings of 316L stainless steel specimens manufactured or repaired by Directed Energy Deposition

The purpose of this article is to assess a self-heating testing method for the characterization of fatigue properties of single-track thickness additively manufactured specimens. It also evaluates the impact of the microstructure orientation with respect to the loading direction on the dissipative behavior and the initiation of microcracks. The 316L stainless steel specimens under scrutiny were manufactured by Directed Energy Deposition in two configurations: (i) fully printed specimens (2 orientations) and (ii) repaired specimens. The paper first presents a morphologic and crystallographic texture analysis and second, a series of self-heating tests under cyclic loading. The microstructural analysis revealed elongated grains with their sizes, shapes and preferred orientations controlled by process parameters. The self-heating measurements under cyclic tensile loading proved that the dissipation estimation through infrared measurements can be performed on small scale, thin specimens. The self-heating curves could successfully be represented by the Munier model. Moreover, several links between the printing parameters and self-heating results could be established. For example, a smaller vertical increment between successively deposited layers leads to higher mean endurance limits in all configurations. Repaired specimens had a lower mean endurance limit when compared with fully printed or conventionally manufactured substrate specimens. Finally, anisotropy was highlighted during these cyclic tests: specimens loaded orthogonally to the printing direction (PD) showed higher fatigue limits when compared with the ones tested along the PD. Additionally, post-mortem observations revealed characteristic microcracking patterns initiated during the self-heating experiments. Loading along the printing direction induced a classical dominating crack, whereas orthogonal loading generated a network of microcracks along the printing direction. This suggests that the damage, such as void opening, where concentrated at the interlayers. Additionally these damage patterns can be correlated with patterns of plasticity at the grains scale observed in a previous study.

Effect of heat-treatment on the microstructure and fatigue properties of lamellar γ-TiAl alloyed with Nb, Mo and/or C

In this study, the effect of the heat-treatment was investigated on five different γ-TiAl compositions alloyed with 7 at.% of Nb and varying content of Mo and C. Mechanical properties of as-received and heat-treated alloys were assessed using tensile and symmetrical tension-compression cyclic loading at room temperature and 750 °C. Scanning electron microscopy, electron back-scatter and X-ray powder diffraction, as well as high-resolution scanning transmission electron microscopy, were used to characterize microstructural changes induced by the heat-treatments. Modification of lamellar substructure in terms of a significant decrease of lamellar spacing directly affects the mobility of dislocations. Together with the change in the phase composition of the alloys, it is the key mechanism leading to the improvement of the ultimate tensile stress, fracture plastic strain as well as higher cyclic strength. It also increases the cumulative plastic strain in cyclic loading both at ambient and elevated temperatures.

Experimental investigation of fatigue behavior for adhesively-bonded GFRP/steel joints

The fatigue behavior of an adhesively bonded glass fiber-reinforced polymer (GFRP)/steel double-lap joint (DLJ) under cyclic tensile loading with load ratio R = 0.1 was experimentally studied. Results in terms of failure mode, F-N curve, stiffness degradation law, crack initiation and propagation laws were obtained. Linear and nonlinear models of stiffness degradation and a mathematical model of the crack growth rate were developed for the adhesive GFRP/steel DLJ under fatigue loading. The fatigue performance of adhesive GFRP/steel DLJ was compared with that of adhesive GFRP/GFRP DLJ to identify the differences between these behaviors. The results demonstrated that the stiffness degradation law of the adhesive GFRP/steel DLJ can be objectively and accurately characterized by the nonlinear stiffness degradation model in terms of the equivalent shear stiffness. The crack initiation life and the ratio between the crack initiation life and fatigue life increased with the deceasing maximum applied load. The fatigue life of the GFRP/steel DLJ was more sensitive to the variation in the maximum applied load compared with that of the GFRP/GFRP DLJ. Moreover, the decaying rate of stiffness and the interfacial crack propagation rate for the GFRP/steel DLJ under fatigue loading were larger than those for the GFRP/GFRP DLJ.

Effect of carbonyl iron powder incorporation on the piezoresistive sensing characteristics of CNT-based polymeric sensor

The electrical and piezoresistive sensing characteristics of polymeric composites incorporating carbon nanotube (CNT) and carbonyl iron powder (CIP) were investigated in this study. A novel manufacturing method was introduced to effectively and uniformly disperse CNT and CIP into polymeric composites. Five different CNT proportions and three different CIP proportions were considered to explore the synergistic effects of CNT and CIP incorporation on the electrical and the piezoresistive sensing characteristics of the composites. Piezoresistive sensing characteristics (e.g., electrical resistance changes, time-based peak shifts, R-square values) of the composites were observed, and the effect of the magnetization on their piezoresistive sensing characteristics was also examined. The incorporation of CIP into CNT-embedded polymeric composites was shown to improve the piezoresistive sensing characteristics of the polymeric composites under cyclic tensile strain loads.

Investigation on the uniaxial ratchetting and fatigue failure behaviors of silicone seal adhesive bonded butt-joints under tensile and torsional cyclic loading

In order to investigate the uniaxial ratchetting behaviors and fatigue failure of silicone seal adhesive bonded hollow cylinder butt-joints under uniaxial tensile and torsional cyclic loading, the effects of stress amplitude, mean stress, cycle time and loading history on the ratchetting strain, ratchetting strain rate and fatigue life were discussed respectively. The experimental results show that ratchetting strain appeared in both tensile and torsional cyclic loading. The ratchetting strain of tensile cycle evolved in three stages, while that of torsion cycle evolved in two stages. Furthermore, the effect of uniaxial tensile cycle on ratchetting strain is greater than that of uniaxial torsion cycle, and the fatigue life of torsion cycle is higher than that of tensile cycle. The stress amplitude, mean stress and cycle time have influence on the ratchetting strain, ratchetting strain rate and fatigue life of the adhesively bonded butt-joints. The ratchetting strain and ratchetting strain rate increase, and the fatigue life decreases with the increase of stress amplitude and mean stress, or the decrease of cycle time. In addition, it is also found that silicone seal adhesive bonded butt-joint has a strong memory of loading history for the stress amplitude. Prior stress cycle with higher stress amplitude restrains the ratchetting strain in subsequent cycle with lower stress amplitude.

Feasibility of Evaluating Acoustoelastic Coefficient of Concrete under Tensile Stress with One-Sided Ultrasonic Method

In this paper, an experimental study on the feasibility of evaluating acoustoelastic coefficient of concrete with one-sided ultrasonic pulse method under tensile stress is conducted. Tensile load cycles are imposed on prismatic concrete specimens and ultrasonic wave velocities are measured simultaneously. Acoustoelastic coefficients are obtained by linear fit of the test results and compared to correlate results in literature. The feasibility of evaluating acoustoelastic coefficient of concrete with one-sided ultrasonic method under tensile stress is discussed.

A Comparison of Adjuvant Techniques on Setting Time of Octyl-2-Cyanoacrylate (DERMABOND Advanced)

Octyl-2-cyanoacrylate is a topical skin adhesive (TSA) that has gained popularity over the last decade for wound and incisional wound closure. TSAs have been used with or without suture when closing lacerations or operative incisions. One brand of octyl-2-cyanoacrylate, DERMABOND, was shown to have high wound bursting strength and tensile force, large number of normal tensile loading cycles to failure, long time to failure, and short setting time. Many intraoperative methods have been used by surgical staff in an effort to reduce curing time (ie, time for the tissue adhesive to set), including waving a hand or towels over the incision or bringing the operating room lights into closer proximity to the wound. Two investigators applied the TSA to their own volar forearms and measured the time to complete dryness in the operative room. A total of 112 applications of DERMABOND was performed and recorded at 1 mm TSA thickness (n=56) and at 2 mm TSA thickness (n=56). Mean drying times from each group and subgroup were calculated and compared using student’s t test and multivariate analysis. We found that no adjuvant methods commonly used in the operating room to speed up drying times were effective. If DERMABOND is utilized for wounds and surgical closure, we recommend applying only a thin layer utilizing the small applicator for more expeditious setting times and cost-effectiveness.

Determining effective crack lengths from electrical measurements in polymer-supported thin films

Although it is evident that the formation of multiple through-thickness cracks in polymer-supported thin films leads to an increase of the electrical resistance, the attempts to quantify the dependence of resistance growth only based on the induced crack density have not yet been successful. In this paper a recently developed relationship, representing the resistance growth as a two-variable polynomial function of crack density and crack length, is utilized to analyze the crack patterns induced by monotonic and cyclic tensile loading of 250 nm thick Cu films with a 10 nm Cr adhesion layer on polyimide. It is demonstrated that by knowing the in-situ resistance during deformation and post-mortem linear density of induced cracks, it is possible to extract the effective crack lengths, a parameter which is often ignored during experimental characterization of the damage induced through mechanical loading. The described algorithm is not only much more cost-effective in comparison to time-consuming in-situ microscopy methods, it also reflects the reliability of the whole sample rather than of only selected surface areas.

A new analytical approach for stiffness loss modelling of asphalt mixtures under cyclic indirect tensile loadings

In this study, the indirect tension mode of loading was used to investigate the fatigue behavior of both modified and unmodified asphalt mixtures. Experimental data were analyzed by studying the evolution of the stiffness modulus with the number of cycles. A new analytical approach was introduced to model the variation of the material stiffness and determine different phases of testing. The material response under the selected mode of loading was then characterized based on a damage parameter that refers to the quasi-stationary stage of testing. Moreover, the damage parameter, normalized by a specific stiffness value, was used to provide a general fatigue law where the fatigue life of materials is determined independently from mixture composition. Results prove that good correlations can be established.

Synergistic effects of interface slip and fiber fracture on stress-dependent mechanical hysteresis of SiC/SiC minicomposites

ABSTRACT In this paper, the synergistic effects of interface slip and fiber fracture on stress-dependent mechanical hysteresis of SiC/SiC ceramic-matrix minicomposites (mini-CMCs) are investigated. Upon cyclic loading/unloading, the relative slip between the fiber and the matrix, and the fracture fiber affect the hysteresis behavior of mini-CMCs. The micro-stress field of the damaged mini-CMCs is obtained through shear-lag analysis, and cyclic loading/unloading hysteresis strain is related with the stress level, interface slip, and broken fiber. The effects of constituent properties and internal damage state on cyclic loading/unloading interface slip and hysteresis loops of SiC/SiC minicomposite are analyzed. The experimental matrix cracking density, stress-dependent mechanical hysteresis and interface slip of Hi-NicalonTM, Hi-NicalonTM Type S, and TyrannoTM ZMI SiC/SiC minicomposites are predicted. The interface debonding and slip range, and mechanical hysteresis loops of SiC/SiC minicomposites are affected by the stress level, constituent properties of the fiber volume, interface properties, and damage state of matrix cracking and broken fiber subjected to cyclic tensile loading.