Cyclic Tensile Loading Research Articles

Creep of Textile-Reinforced Composite Under Static and Cyclic Loads

The paper considers the creep of a textile-reinforced thermoplastic composite with a glass filler under the action of a combined short-term cyclic and long-term static tensile loads at room temperature. The investigations were carried out on glass-fabric-reinforced polypropylene specimens, which were made by autoclave molding. The creep of the composite was experimentally investigated under a cyclic load at different amplitudes. The creep kernel has been calculated from experimental data according to the Boltzmann superposition principle. Other creep models of materials have been analyzed based on data from a review. The laws governing the short-term creep of polypropylene under the action of a static load have been determined. A behaviorial model of the composite under investigation under the considered conditions is proposed. Numerical calculations have been made with the aid of the proposed model using experimental results taken from other works, and a good agreement between them has been established. The peculiarities of the creep of textile-reinforced polypropylene under the considered conditions have been determined. The range of application of the model has been determined.

Mechanobiology of bone and suture - Results from a pig model.

To compare the morphology and mechanical function of sutures in normal pigs and minipigs to those of Yucatan minipigs, a natural model for midfacial hypoplasia. Research took place at the Department of Orthodontics at the University of Washington and used varying sample sizes of normal-snouted pigs and Yucatan minipigs. Skulls and heads were examined for morphology of the nasofrontal suture using computed tomography and histology. Strain gauge recordings were made of sutural strain during mastication and during cyclic tensile loading of the nasofrontal suture. Sutures in Yucatans had narrower gaps than same-age normal pigs. The nasofrontal suture was simpler in construction and had more active osteoblasts on the bone fronts in Yucatans. The sutural ligament was less well organized, and based on a small sample, masticatory strain appeared to be lower than in normal minipigs. However, sutures were not fused and showed similar strains in response to the cyclic loading procedure. Midfacial hypoplasia in Yucatan pigs has the likely proximate cause of hyperossification. Yet prior to fusion, the sutures appear to be amenable to treatment that would promote their growth rate.

Influence of transversal loading on tensile and fatigue behaviour of high-strength lean duplex stainless steel wires

The research addresses the failure behavior of a high-strength lean duplex stainless steel wire simultaneously subjected to static transversal and static and cyclic axial loadings. Such bi-axial loadings are experienced by the wires when incorporated into strands for structural tendons of cable-stayed systems or prestressing concrete structures. The experiments were made with a specially designed device assuring the control of the locally applied transversal force during the axial loading in simple or cyclic tension of the wire. Thus, a static fracture criterion and fatigue endurance limit locus for the stress range of 200 MPa were found on an empirical basis for the analyzed wires when subjected to biaxial loading. The resulting data were compared with those obtained from identical tests of eutectoid steel wires currently used in prestressing applications. Additionally, scanning electron microscopy was employed to determine how the static transverse loads modify the failure and fatigue damage mechanisms, when combined with static and cyclic tensile loading.

Viscoplastic constitutive modelling of the ratchetting behavior of 35CrMo steel under cyclic uniaxial tensile loading with a wide range of stress amplitude

The rate-dependent ratchetting characteristics of 35CrMo alloy under repeated uniaxial tension considering different stress amplitudes were studied at 500 °C. It is found that the applied stress rate and stress amplitude influence the accumulated plastic deformation greatly. The existing visco-plastic ratchetting constitutive model can well predict those features considering the effect of stress rate, but not so well when the stress amplitude effect is involved, especially for the cases of relatively low stress amplitude. Accordingly, a modified rate-dependent ratchetting constitutive model has been developed, which can well predict the ratchetting deformations in a wide range of stress amplitude and stress rate. Furthermore, the modified rate-dependent ratchetting constitutive model can be used to assess the ratchet boundary of the alloy with relatively high accuracy.

Electrical self-sensing of strain and damage of thermoplastic hierarchical composites subjected to monotonic and cyclic tensile loading

Electrical monitoring of strain and damage in multiscale hierarchical composites comprising unidirectional aramid fibers modified by multiwall carbon nanotubes and polypropylene as matrix is investigated. The key factor for electrical self-sensing in these thermoplastic composites is the formation of a multiwall carbon nanotube network, which is achieved by using two material architectures. In the first architecture, the multiwall carbon nanotubes are dispersed within the polypropylene matrix, while aramid fibers remain unmodified. The second architecture uses also multiwall carbon nanotube-modified polypropylene matrix, but the aramid fibers are also modified by depositing multiwall carbon nanotubes. Under tensile loading, the electrical response is nonlinear with strain ( ε), and the piezoresistive sensitivity was quantified by gage factors corresponding to low ( ε < 0.25%) and high ( ε > 0.3%) strain regimes. Such gage factors were 4.83 (for ε < 0.25%) and 13.2 (for ε > 0.3%) for composites containing multiwall carbon nanotubes only in the polypropylene matrix. The composites containing multiwall carbon nanotubes in the matrix and fibers presented higher piezoresistive sensitivity, with average gage factors of 9.24 ( ε < 0.25%) and 14.0 ( ε > 0.3%). The higher sensitivity to strain and damage for a specific material architecture was also evident during cyclic and constant strain loading programs and is attributed to the preferential localization of multiwall carbon nanotubes in the hierarchical composite.

Mechanical and Cytocompatibility Evaluation of UHMWPE/PCL/Bioglass® Fibrous Composite for Acetabular Labrum Implant.

In this study, a fibrous composite was developed as synthetic graft for labral reconstruction treatment, comprised of ultra-high molecular weight polyethylene (UHMWPE) fabric, ultrafine fibre of polycaprolactone (PCL), and 45S5 Bioglass®. This experiment aimed to examine the mechanical performance and cytocompatibility of the composite. Electrospinning and a slurry dipping technique were applied for composite fabrication. To assess the mechanical performance of UHMWPE, tensile cyclic loading test was carried out. Meanwhile, cytocompatibility of the composite on fibroblastic cells was examined through a viability assay, as well as SEM images to observe cell attachment and proliferation. The mechanical test showed that the UHMWPE fabric had a mean displacement of 1.038 mm after 600 cycles, approximately 4.5 times greater resistance compared to that of natural labrum, based on data obtained from literature. A viability assay demonstrated the predominant occupation of live cells on the material surface, suggesting that the composite was able to provide a viable environment for cell growth. Meanwhile, SEM images exhibited cell adhesion and the formation of cell colonies on the material surface. These results indicated that the UHMWPE/PCL/Bioglass® composite could be a promising material for labrum implants.

Concurrent ratcheting and stress relaxation at the notch root of steel samples undergoing asymmetric tensile loading cycles

AbstractThe current study intends to develop a framework model to assess ratcheting and stress relaxation at the notch root of 1045 steel samples over asymmetric loading cycles. The framework involves the Ahmadzadeh‐Varvani (A‐V) kinematic hardening rule to control ratcheting progress and Neuber rule to accommodate for local stress and strain components at the vicinity of notch root. Plastic strain at notch root was first coupled with its counterpart in the A‐V model to establish a relation between local stress and backstress components. Calculated local stress and strain values at turning points enabled the A‐V model to assess ratcheting strain over each loading cycle. The stepwise drop in stresses at peak‐valley tips of hysteresis loops at the notch root was associated to coupled framework of the A‐V model and Neuber rule through constancy in local strain while ratcheting progressed over each cycle. This relaxed out the local stresses at tips of hysteresis loops to position on Neuber hyperbolic curve. Predicted ratcheting values at notch root of various diameters closely agreed with those of measured in steel samples over stress cycles.

Coupled axial tension-flexure behavior of slender reinforced concrete walls

Reinforced concrete (RC) walls in high-rise buildings, in particular wall piers that form part of a coupled or core wall system, may experience coupled axial tension-flexure loading when subjected to lateral demands. The seismic behavior of RC walls with various axial tensile forces was investigated by quasi-static tests on four RC slender walls subjected to the combined tension and flexure loading. The failure modes, strength and deformation capacity, effective flexural stiffness, and design equations are presented. The failure modes included flexural-sliding failure and flexural failure. The effective flexural stiffness and lateral strength of the walls significantly decreased as the axial tensile forces were increased. The ACI 318-14 and ASCE/SEI 41-13 code provisions overestimated the effective flexural stiffness of RC walls subjected to axial tension. Although equations proposed by Paulay & Priestley and Adebar et al. consider the influence of axial forces, they were not able to accurately predict the effective flexural stiffness of the RC wall specimens subjected to tensile forces. Both sectional analysis using XTRACT and JGJ 3-2010 (China) code equations provided accurate estimation of the flexural yield strength of walls. Finally, both a refined model and simplified equation were proposed to estimate the axial elongation for RC slender walls subjected to axial tensile force and cyclic lateral loading.

Centrifuge modelling of a helical anchor under different cyclic loading conditions in sand

Helical foundations used in transmission towers, wind turbines, solar panel systems and other similar structures must exhibit adequate performance under cyclic loading. Although a number of studies on the cyclic behaviour of helical anchors has increased, the available observations are still incomplete in terms of providing conclusive recommendations for practical applicability. To address this need, cyclic and monotonic axial tensile load tests were conducted on a single-helix model anchor in very dense dry sand in a centrifuge. The cyclic tests were carried out with different load amplitudes and with the number of cycles varying between 1000 and 3000. After the cyclic tests, the post-cyclic tensile capacity was evaluated by way of monotonic loading tests. Two different displacement regimes were observed during cycling, with a noticeable development of cumulative permanent displacements in the first approximately 100 cycles. In most of the tests, a stable cyclic response and a slight reduction in the post-cyclic capacity were observed. Additionally, the effect of the cyclic loading sequence was evaluated by way of two additional tests in which the cyclic loading was applied with different amplitudes in different orders. The results indicated that the order of the cyclic sequences influences the displacement response and the losses in the post-cyclic capacity.

Computational and Experimental Fatigue Analysis of Contoured Spinal Rods

Posterior fixation with contoured rods is an established methodology for the treatment of spinal deformities. Both uniform industrial preforming and intraoperative contouring introduce tensile and compressive plastic deformations, respectively, at the concave and at the convex sides of the rod. The purpose of this study is to develop a validated numerical framework capable of predicting how the fatigue behavior of contoured spinal rods is affected by residual stresses when loaded in lordotic and kyphotic configurations. Established finite element models (FEM) describing static contouring were implemented as a preliminary simulation step and were followed by subsequent cyclical loading steps. The equivalent Sines stress distribution predicted in each configuration was compared to that in straight rods (SR) and related to the corresponding experimental number of cycles to failure. In the straight configuration, the maximum equivalent stress (441 MPa) exceeds the limit curve, as confirmed by experimental rod breakage after around 1.9 × 105 loading cycles. The stresses further increased in the lordotic configuration, where failure was reached within 2.4 × 104 cycles. The maximum equivalent stress was below the limit curve for the kyphotic configuration (640 MPa), for which a run-out of 106 cycles was reached. Microscopy inspection confirmed agreement between numerical predictions and experimental fatigue crack location. The contouring technique (uniform contouring (UC) or French bender (FB)) was not related to any statistically significant difference. Our study demonstrates the key role of residual stresses in altering the mean stress component, superposing to the tensile cyclic load, potentially explaining the higher failure rate of lordotic rods compared to kyphotic ones.

Mechanical durability of solid oxide fuel cell glass-ceramic sealant/steel interconnect joint under thermo-mechanical cycling

A testing method is developed to quantitatively determine the thermo-mechanical cycling life in oxidizing atmosphere for the joint between a solid oxide fuel cell glass-ceramic sealant and a ferritic stainless steel interconnect. Thermo-mechanical cycling tests are performed under cyclic shear or tensile loading in conjunction with cyclic temperature variance between 40 °C and 800 °C. Results reveal thermo-mechanical cycling life under both shear and tensile loadings increases with a decrease in end stress at 800 °C, for a certain end stress at 40 °C. Nevertheless, for a certain end stress at 800 °C, the tensile thermo-mechanical cycling life increases with a decrease in end stress at 40 °C, while the shear thermo-mechanical cycling life is independent of end stress at 40 °C. A difference in fracture pattern is also observed between shear and tensile loadings. For shear loading, fracture mainly takes place along the interface between glass-ceramic sealant and an oxide layer, such as BaCrO4 or Cr2O3. However, for tensile loading, fracture mainly occurs within the glass-ceramic layer, following crack initiation at the interface of Cr2O3/sealant or Cr2O3/BaCrO4.

Effects of self-healing on tensile behavior and air permeability of high strain hardening UHPC

High strain hardening UHPC was expected to be self-healing due to its multiple micro-cracks in tension and the low water-to-binder ratio. The direct tensile tests with the acoustic emission (AE) analysis method and air permeability tests were carried out on high strain hardening UHPC in order to investigate the self-healing behavior under three re-curing conditions (water, 80%RH and 45%RH). Moreover, the cyclic tensile loading was applied to create more severe damage and two re-curing schemes (water and steam) were used to evaluate the self-healing effects. Experimental results show that the direct tensile stress-strain curves of high strain hardening UHPC re-cured in water and 80%RH conditions have the recovery of first cracking strain. New crystals were observed in the micro-cracks after self-healing, whose strength was proved to be lower than that of the intact part. The high strain hardening UHPC can recover 40%-47% of the first cracking strain after 28 days of water re-curing, where new damages characterized by AE sources number were found to generate inside the UHPC matrix. Air permeability test shows a sensitive response to the damage created by the tensile deformation. Steam re-curing method shows more effective and less time consuming for self-healing than water re-curing method.

Novel adhesives for sternal fixation and stabilization: A biomechanical analysis

BackgroundCerclage wires remain the current standard of care following median sternotomy, despite significant complications including dehiscence and infection. This study uses a human cadaveric model to investigate the use of glass polyalkenoate cements formulated from two glasses, A (mole fraction: SiO2:0.48, ZnO:0.36, CaO:0.12, SrO:0.04) and B (mole fraction: SiO2:0.48, ZnO:0.355, CaO:0.06, SrO:0.08, P2O5:0.02, Ta2O5:0.005), to improve wired sternal fixation. MethodsMedian sternotomies were performed on fifteen cadaveric sterna. Fixation was performed with either traditional wire cerclage or adhesive-enhanced wire cerclage; the adhesive based on either Glass A or Glass B. Cyclic tensile loading of 10 N to 100 N was applied. Every 30 cycles, the maximum load was increased by 100 N up to a maximum of 500 N. Two adhered sterna were tested beyond 500 N. Mid-sternal displacement was measured to assess fixation stability. FindingsDisplacement for adhesive-enhanced sternal closures were significantly less (p < 0.05) than standard wire cerclage. There was no significant difference between adhesives. Up to 500 N, no adhesive-enhanced sternum experienced a pathological sternal displacement (>2 mm), while three out of five of traditional wire fixations did. Of the two adhered samples tested beyond 500 N, one showed pathological displacement at 800 N and the other at 1100 N. Failure of adhered sterna appeared to initiate within the trabecular bone rather than in the adhesive. InterpretationThe adhesives were capable of providing immediate bone stability, significantly reducing sternal displacement. In vivo investigations are warranted to determine the effect the adhesives have on bone remodelling.

Optical stereolithography of antifouling zwitterionic hydrogels.

This paper reports the rapid 3D printing of tough (toughness, UT, up to 141.6 kJ m-3), highly solvated (φwater∼ 60 v/o), and antifouling hybrid hydrogels for potential uses in biomedical, smart materials, and sensor applications, using a zwitterionic photochemistry compatible with stereolithography (SLA). A Design of Experiments (DOE) framework was used for systematically investigating the multivariate photochemistry of SLA generally and, specifically, to determine an aqueous SLA system with an additional zwitterionic acrylate, which significantly increases the gelation rate, and the resilience of the resulting hybrid hydrogels relative to an equivalent non-ionic polyacrylamide hydrogel. Specifically, the resulting zwitterionic hybrid hydrogels (Z-gels) can be tuned over a large range of ultimate strains, ca. 0.5 < γult < 5.0, and elastic moduli, ca. 10 < E < 1000 kPa, while also demonstrating a high resilience under cyclic tensile loading. Importantly, unlike traditional chemistry, increasing the elastic modulus of the Z-gels does not necessarily reduce the ultimate strain. Moreover, the Z-gels can be rapidly printed using a desktop commercial SLA 3D printer, with relatively low photoirradiation dosages of visible light (135 to 675 mJ cm-2 per 50-100 μm layer). Compared with the counterpart polyacrylamide hydrogels, the Z-gels have greater antifouling properties and exhibit 58.2% less absorption of bovine serum albumin.

Mechanical Properties of Submicron Glass Fiber Reinforced Vinyl Ester Composite

Vinyl ester (VE) resin inherently has intrinsic brittleness due to its high cross-link density. To improve mechanical performance, micro/nano fillers are widely used to modify this matrix. In present study, glass fiber in submicron scale at low contents was added into VE to prepare submicron composite (sMC). The impact resistance of un-notched sMC degraded with the increase of sGF content while that of notched-sMC remained the unchanged. Flexural properties of sMCs also were the same with that of neat resin. The results of Dynamic mechanical analysis (DMA) test showed the slight increase of storage modulus and the decrease of tan delta value in the case of sMC compared to those of un-filled matrix. However, the Mode I fracture toughness of sMC improved up to 26% and 61% corresponding to 0.3 and 0.6 wt% glass fiber used. The compact tension sample test suggests that there is the delay of crack propagation under tensile cyclic load in resin reinforced by submicron glass fiber. The number of failure cycle enlarged proportionally with the increment of sGF content in matrix.

Transverse load influence on tensile fatigue resistance of high-strength steel wires for structural applications in civil engineering

Cold-drawn duplex stainless steel is an alternative to cold-drawn eutectoid steel to prevent the stress corrosion cracking risk in strands for structural uses as concrete prestressing and strand-tendons of cable stayed bridges. These possible applications create uncertainty concerning the fatigue behaviour of strand wires when subjected to the combined action of cyclic tensile loads and transverse loads that occur at the contact with the other strand wires or at the anchorages, couplers and deviators. This research compares the experimental behaviour of two cold-drawn wire types, manufactured from a lean duplex stainless steel and an eutectoid steel, when simultaneously subjected to transverse static and axial fatigue loads. The results show that the fatigue endurance required by the standards in force for prestressing steel wires, free from transverse loads are maintained by the two wire types even under transverse loads as high as 40% of their tensile strength.

On the fatigue propagation of multiple cracks in friction stir weldments using linear and non-linear models under cyclic tensile loading

In this work, the propagation life of a friction stir-welded sample made of ductile materials is estimated by employing linear elastic fracture mechanics (LEFM) and small-scale yielding (SSY) conditions. The purpose is to demonstrate that by considering the SSY, the prediction of the propagation life of the welded sample can be improved when compared to the traditional LEFM. The process of friction stir welding (FSW) of an AA2024-T3 butt joint is then simulated by using the finite element method. Hence, a thermal analysis of the numerical model is performed, and the calculated temperature field is subsequently subjected to thermo-mechanical analysis. In the latter model, the two defects located in the most critical position, detected experimentally by performing fatigue tests on the same component, are introduced into the model by using the constrained crack faces technique. Furthermore, to enable the thermo-mechanical simulation of the FSW process, temperature-dependent non-linear material properties, material softening, and isotropic hardening are considered. Concerning fatigue crack growth analysis, three simulations of the fatigue crack propagation are performed by using three different propagation laws. The first is performed by considering linear elastic material properties and Vasudevan’s law on fatigue crack propagation; the second is by employing non-linear material properties and Kujawski–Ellyin law; the third takes into account the non-linear material properties and UniGrow law. Thereafter, appropriate constraints and a remote fatigue load are applied to the specimen to allow residual stress redistribution and fatigue crack growth, respectively. The constraint effect is also evaluated by the calculation of the T-stress parameter. Finally, a comparison between the numerical and experimental results is presented; consequently, a better agreement with the case of the non-linear model under the SSY conditions is found.

Investigation of the network topology of vitreous silica during cyclic tensile loading

AbstractIn this paper, we present visco‐plastic effects of vitreous silica. By introducing a stepwise loading‐relaxation procedure, we evaluate a quasi‐static hysteresis and observe permanent plastic deformation. The investigation of the medium‐range order of the sample at various deformation states provides new insights into the changes of the atomistic arrangements caused by the plastification.

Micro‐structure related modelling of ultra‐high‐performance fibre reinforced concrete (UHPFRC) subjected to cyclic tensile loading

AbstractUltra‐high performance concrete with a compressive strength of more than 140 N/mm2 reacts very brittle without the addition of fibres. At designing economical and resource‐efficient building components as well as performance‐optimized materials, the supporting effects of the additional microfibres must be considered. Prospectively, cyclic loading and the fatigue behaviour of high performance materials and slim components will come to the fore. Therefore, the influence of cyclic deterioration on the load bearing capacity of the interface transition zone connecting microfibres and the surrounding concrete surface must be investigated. As part of the DFG Priority Programme 2020, the damage mechanisms and processes regarding the deterioration of UHPFRC subjected to cyclic tensile loading are explored in an Experimental‐Virtual Lab. Using the concepts of elasto‐plasticity and continuum damage mechanics, the material models for the components of the composite material UHPFRC are improved and enhanced to be combined on a mesoscale with the help of a non‐linear bond model. This bond model is discretized by interface elements with curved surfaces in 3D space and describes the interaction of fibres and concrete in the bond zone in terms of adhesion and friction effects. For validation and verification, single and multiple fibre pullout tests are simulated in 3D‐finite element analyses. These FE‐simulations and preliminary findings are supposed to provide the essential basis for future numerical degradation prediction.

Cyclic deformation behaviours of 18Mn3Si2CrNiMo multiphase (martensite/bainite/retained austensite) steel

A series of multiphase microstructures with different contents of bainite, martensite and retained austenite are obtained by the austempering treatment of 18Mn3Si2CrNiMo steel at different temperatures below Ms. And the low cycle fatigue (LCF) behaviour of the test steel at different cycle times, such as the first cycle, the maximum peak cyclic stress cycle and the half-life cycle, is also investigated. The results show that the reduction in mobile dislocation density is the main cause of very high strain hardening observed under the first cycle of cyclic tensile load. Through the analysis of fatigue life, it is found that the transformation of large block retained austenite to martensite in the sample after austempered at 315 °C accelerates the fatigue failure behaviour. The test steel with a microstructure of 69.5% VM + 23.5% VB + 7.0% Vγ at the lower total strain amplitude and with 49.9% VM + 40.6% VB + 9.5% Vγ at the higher total strain amplitude has an optimal LCF life.