Cyclic Tensile Loading Research Articles

Energy Storage and Dissipation in Consecutive Tensile Load-Unload Cycles of Gum Metal.

Multifunctional β-titanium alloy Gum Metal, characterized by a relatively low elastic modulus, superelastic-like behavior and high strength, was subjected to cyclic tensile loadings. The characteristics of macroscopic scale energy storage and dissipation in the consecutive loading-unloading cycles were studied. Various kinds of energy components related to the alloy deformation process were determined experimentally and analyzed using thermodynamic relations. The values of the entire work needed to deform the alloy Wext, the work used for recoverable deformation Wrec consisting of the elastic deformation energy Wel , the superelastic-like energy Wpt , and the energy of thermoelastic effect Eth , were derived from the Gum Metal stress and temperature vs. strain curves. The irrecoverable mechanical energy Wir expended on plastic deformation, the dissipation energy Q, and finally the stored energy Es were estimated. The stored energy represents a change in the internal energy of the deformed material and is an essential measure of cold-worked state. The Es value turned out to be not large for the Gum Metal, which confirms the alloy low hardening property. The energy components determined for each of the 24 loading cycles enabled us to analyze various stages of the Gum Metal deformation process, including necking and damage.

Electric arc furnace slag as aggregates in semi-dense asphalt

Electric Arc Furnace Slag (EAFS) is one of the primary by-products of the steel recycling industry, which comes out initially as large pieces, that can be further crushed and be used as aggregates in infrastructure materials. While being a waste product, the relatively high strength of the aggregates means that EAFS can provide favorable properties when used correctly. One possible destination for EAFS of higher value is semi-dense asphalt (SDA), a surface course used as low-noise pavement. Due to the relatively high percentage of air voids in SDA (10–18%), the mixture mechanical properties depend on strong interlocking of the aggregates. This study looks at the incorporation of EAFS fractions (2/4 and 0.125/2 mm) into SDA 4 mixtures at replacement of 13% by volume of the aggregates. These mixtures are compared to the control mixture with sandstone aggregates in terms of volumetrics, water sensitivity, stiffness modulus and fatigue by cyclic indirect tensile loading, along with permanent deformation by the cyclic compression test. The water sensitivity, rheological properties and fatigue resistance of the EAFS mixtures did not vary significantly from the control. The life cycles assessment (LCA) shows that compared to the reference SDA, the EAFS-modified SDA reduces the greenhouse gas emissions and ecological scarcity eco-points by 40% and 90%, respectively due to the avoidance of EAFS landfilling. However, the non-renewable cumulative energy demand is not improved by using EAFS in SDA, due to the additional consumption of bitumen.

Investigation of the leak tightness of structural adhesive joints for use in battery housings considering mechanical and corrosive loads

ABSTRACT Due to increasing legal requirements to reduce emissions from vehicle fleets, vehicle manufacturers are focusing on the electrification of the powertrain. In entirely electrically driven vehicles, the energy is stored in traction batteries integrated below the passenger cell between the axles and thus located in the vehicle’s wet area. Therefore, high requirements apply to the protection of the sensitive cells against mechanical stress as well as against moisture penetration. In addition, one of the main requirements for the connections of the battery housing is to ensure gas tightness over the entire service life. Adhesive bonding technology as a planar joining process offers the potential to produce functionally tight connections. However, there is a lack of reliable test methods for validating the long-term tightness of structural adhesive joints under mechanical and corrosive loads. For this reason, the paper deals with developing a test concept with laboratory-scale test specimens for leak testing under mechanical loading. Various leakage test methods investigate the leakage rate of structurally bonded joints. An analysis of the leakage rate under superimposed cyclic mechanical shear tensile loading follows this. The test method is validated on a specially developed sample battery housing on a laboratory scale.

Constitutive model of duplex stainless steel S22053 and its weld under cyclic large plastic strain loading

This study investigated the mechanical properties and constitutive models of duplex stainless steel S22053 under cyclic large plastic strain loading. To this end, smooth round bar specimens of the base metal, deposited metal, and heat-affected mixing zone material were tested under monotonic tensile loading and cyclic loading. Furthermore, the failure modes and stress–strain curves of the specimens were analysed. Based on the test results of the smooth round bar specimens under cyclic symmetric constant amplitude and monotonic tensile loading, the N3L1 and S10 parameters of the Chaboche model for duplex stainless steel S22053 were calibrated, respectively. Then, the accuracy of the calibrated Chaboche model was verified against the test results of the smooth round bar and circular notched bar specimens. The results showed that the base metal and heat-affected mixing zone material have higher ductility, and the strength of the deposited metal is the highest. Furthermore, the N3L1 parameters can accurately simulate the behavior of smooth round bar specimens under cyclic medium plastic strain loading, while the S10 parameters are more suitable for simulating the mechanical response of circular notched bar specimens under cyclic large plastic strain loading. The accuracy of the Chaboche model depends on the matching of the loading strain range of the test data for calibrating the model with that of the simulation cases. The results of this study provide fundamental data for analysing the seismic and ductile fracture performance of duplex stainless steel and its welded structures.

Fatigue fracture investigation of a tube-to-tubesheet welded joint

A novel fatigue test specimen was developed to investigate the fatigue fracture behaviors of a shell and tube heat exchanger. It consists of a single tube and a tubesheet joined by welding and produces a tube-to-tubesheet welded joint. A fatigue test was conducted under tensile cyclic load. Defects were generated from the root of the joint and propagated with complicated crack front trajectories. Crack propagation (CP) simulation is performed to review the CP behavior using the extended finite element method (X-FEM). The experimental and numerical studies are succeeded to interpret the fundamental fracture characteristics of the welded joint.

Effect of stress level on creep-fatigue interaction of woven angle ply GFRP laminates

In this study, effect of stress level on creep-fatigue interaction of woven angle ply glass fiber reinforced polymer (GFRP) has been studied. The rectangular test specimens were manufactured using bidirectional woven ply (45˚/-45˚) E-glass fiber of eight layers with 300 GSM and layer thickness to be 0.25 mm used as fibre reinforcement and LY556 epoxy Araldite based on Bisphenol A and HY951 hardener mixed as matrix material in the ratio of 10:1. Rectangular specimens were made from the prepared laminates and tested under tensile cyclic loading of constant amplitude at stress ratio 0.1 for three stress levels 80%, 70% and 60% of ultimate tensile strength (UTS) as per ASTM standard D3479. The results showed that cyclic creep strain depends on the stress level and rapid increase in strain happens after 75% of lifecycle at all stress level.

The C1 wedge connection in towers for wind turbine structures, tensile behaviour of a segment test

This paper shows a part of the analysis of the development of the second generation of the C1 wedge connections for use in offshore wind turbine supporting towers. The novelty of this connection is that bolt failure is avoided under static and fatigue loads. This study aims to investigate the tensile behaviour of the connection by combining the findings of experiments and finite element (FE) analysis. Two specimens subjected to uniaxial and cyclic tensile loading tested until failure are used for illustration. Advanced quasi-static FE analysis results, considering the most detailed geometry and using an explicit dynamic solver, are compared to the experimental results. The FE analysis results agree well with the experimental results. Based on the FE model, a parametric study is carried out to analyse the influence of the bolt grade, friction coefficient between contact surfaces, and preloading force level on mechanical behaviour. Failure modes, bolt force development, and the evolution of gap opening between contacted segments are analysed. Results demonstrate that the tensile fracture of the C1 wedge connection mainly appears in the lower segment. All the investigated parameters have a negligible effect on the connection's ultimate resistance and failure mode. However, the friction coefficient between contact surfaces and bolt preload level significantly affects the connection's local deformation capacity and the response of the bolt stress range. The FE simulation provides practical guidance for designing this connection without bolt failure.

Repair of tendons treated with peracetic acid-ethanol and gamma irradiation by EDC combined with NHS: a morphological, biochemical and biomechanical study in vitro.

The purpose of this study was to investigate whether 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) combined with n-hydroxysuccinimide (NHS) can repair tendon damage caused by peracetic acid-ethanol and gamma irradiation sterilization. The semitendinosus tendons of 15 New Zealand white rabbits were selected as experimental materials, and the tendons were sterilized in a solution containing 1% (v/w) peracetic acid and 24% (v/w) ethanol. After 15kGy gamma irradiation sterilization, the tendons were randomly divided into three groups (n = 10). The tendons were repaired with EDCs of 0, 2.5 and 5mM combined with 5mM NHS for 6h, the tendons were temporarily stored at - 80 ± °C. The arrangement and spatial structure of collagen fibers were observed by light microscopy and scanning electron microscopy, the collagen type and collagen crimp period were observed under a polarizing microscope, and the collagen fibril diameter and its distribution were measured by transmission electron microscopy, from which the collagen fibril index and mass average diameter were calculated. The resistance of collagen to enzymolysis was detected by the free hydroxyproline test, and tensile fracture and cyclic loading tests of each group of tendons were carried out, from which the elastic modulus, maximum stress, maximum strain, strain energy density and cyclic creep strain were calculated. The obtained results showed that the gap between loose collagen fibers in the 0mM control group was wider, the parallel arrangement of tendons in the 2.5 and 5mM groups was more uniform and regular and the fiber space decreased, the crimp period in the 5mM group was lower than that in the 0mM group (P < 0.05), and the concentration of hydroxyproline in the 5mM group (711.64 ± 77.95μg/g) was better than that in the control group (1150.57 ± 158.75μg/g). The elastic modulus of the 5mM group (424.73 ± 150.96MPa) was better than that of the 0mM group (179.09 ± 37.14MPa). Our results show that EDC combined with NHS can repair damaged tendons after peracetic acid-ethanol and gamma radiation treatment, and 5mM EDC has better morphological performance, anti-enzymolysis ability and biomechanical properties than 2.5mM EDC.

Adipose and Bone Marrow Derived-Mesenchymal Stromal Cells Express Similar Tenogenic Expression Levels when Subjected to Mechanical Uniaxial Stretching In Vitro.

The present study was conducted to determine whether adipose derived mesenchymal stromal cells (AD-MSCs) or bone marrow derived-MSCs (BM-MSCs) would provide superior tenogenic expressions when subjected to cyclical tensile loading. The results for this would indicate the best choice of MSCs source to be used for cell-based tendon repair strategies. Both AD-MSCs and BM-MSCs were obtained from ten adult donors (N = 10) and cultured in vitro. At passaged-2, cells from both groups were subjected to cyclical stretching at 1 Hz and 8% of strain. Cellular morphology, orientation, proliferation rate, protein, and gene expression levels were compared at 0, 24, and 48 hours of stretching. In both groups, mechanical stretching results in similar morphological changes, and the redirection of cell alignment is perpendicular to the direction of stretching. Loading at 8% strain did not significantly increase proliferation rates but caused an increase in total collagen expression and tenogenic gene expression levels. In both groups, these levels demonstrated no significant differences suggesting that in a similar loading environment, both cell types possess similar tenogenic potential. In conclusion, AD-MSCs and BM-MSCs both demonstrate similar tenogenic phenotypic and gene expression levels when subjected to cyclic tensile loading at 1 Hz and 8% strain, thus, suggesting that the use of either cell source may be suitable for tendon repair.

Characterization of glass fiber reinforced polymer via digital volume correlation: Quantification of strain activity and damage growth

Strain and damage distributions within a dogbone specimen containing a rectangular notch were assessed in-situ via X-ray computed tomography coupled with digital volume correlation. The specimen cut from a continuous glass fiber mat reinforced polyester resin composite plate was subjected to cyclic tensile loading. The strain–damage interplay was evaluated by analyzing major eigen strain and correlation residual fields. The horizontal strained band emanating from the notch root was present from the beginning of loading. The final failure proceeded along this strained band. The first cracks did not initiate in the notched region, despite high strain gradients. Strain activity and damage growth were quantified by analyzing the cumulative probabilities of major eigen strains. The comparison was made between the notched region and the remaining part of the inspected specimen. It is shown that, although the mean levels were higher in the notched region, the standard deviations of the major eigen strain distributions were higher in the remaining part of the specimen.

Impact of Initial Cyclic Loading on Mechanical Properties and Performance of Nafion.

Nafion possesses many interesting properties such as a high ion-conductivity, hydrophilicity, and thermal and chemical stability that make this material highly suitable for many applications including fuel cells and various (bio-)chemical and physical sensors. However, the mechanical properties of a Nafion membrane that are known to be affected by the viscoplastic characteristics of the material itself have a strong impact on the performance of Nafion-based sensors. In this study, the mechanical properties of Nafion under the cyclic loading have been investigated in detail. After cyclic tensile loading (i.e., maximum elongation about 25% at a room temperature and relative humidity about 40%) a time-dependent recovery comes into play. This recovery process is also shown being strain-rate dependent. Our results reveal that the recovery behavior weakens after performing several stress-strain cycles. Present findings can be of a great importance in future design of various chemical and biological microsensors and nanosensors such as hydrogen or glucose ones.

Fatigue properties evaluation of fillet weld joints in full-scale steel marine structures

This study investigated the fatigue behavior of fillet weld steel joints (including cruciform and T-welded joints) in marine structures based on experimental tests and finite element analysis (FEA). In cyclic tensile loading, fatigue failure of full-scale specimens consistent with in-plane failure mode of marine structures was validated with ultrasonic phased array testing (UPAT). The effect of incomplete penetration and weld profile on fatigue performance were analyzed based on traction structural stress method. The results showed that the failure mode of load-carrying cruciform joints would change when the incomplete penetration ratio p’/tr reached 0.91. And the concave weld profile is better choice for welded structures anti-fatigue design. In view of the complexity of fatigue performance evaluation of fillet weld joints in IIW and BS7608 standards, a unified master S–N curve covering different plate thicknesses, materials, and weld profiles was proposed.

Evaluation and optimization of meshless methods to estimation of the 3D-stress intensity factors in mode I–III for fatigue life prediction cracked shaft under uni and multi-axial cyclic loading

In this research, in order to estimate 3D-Stress Intensity Factors in mode I–III, fatigue crack growth and fatigue life prediction of a cracked shaft under various cyclic loading, meshless methods are evaluated and the most appropriate method is selected. For better results, the Base Functions (BFs) are first identified and their performance and efficiency are compared with each other. In addition, while enriching the BFs in all methods and study the effect of increasing the number of sentences of Polynomial-BFs (m = 4, 7,10) and their Linearity or Quadraticity in the accuracy of calculations, two sets of Extend-Enriched-RBFs including the Multi-Quadrics and Gaussian RBFs are used in MQ-RPIM and EXP-RPIM methods. To optimize the shape parameters in the RPIM method and determine the Penalty Factor in the MLPG method, Uni and Multi-objective PSO algorithm was used. Then, a shaft with an initial semi-elliptic surface crack as a 3D-meshless domain for discretizing the weak differential equations was selected and modeled under a fixed latitude tensile, bending, and torsional cyclic loads. Changing the standard values of the shape parameters and estimating their optimal values by the PSO algorithm and comparison of findings with the results of Experimental, MLPG, PIM, FEM, and XFEM methods, has led to the best answer from the applied methods for calculation of; displacement, strain and stress fields, and the SIFs in Mode I–III. Finally, based on the results of uniaxial cyclic load analysis and selection of the MQ-RPIM method, the Multi-axial Cyclic load analysis has been performed on 3D-domain. During this analysis, the Paris Parametric equation along with the Elliptic equation and Liu’s Virtual Strain Energy (VSE) model was used to estimate the fatigue crack growth and fatigue life prediction of a submersible cracked shaft of a pump used in water pumping stations.

EFFECT OF TENSILE FATIGUE CYCLIC LOADING ONPERFORMANCE OF TEXTILE-BASED STRAIN SENSORS

Textile-based strain sensors are a potential platform used in wearable devices for sensing and. 8 sensors containing monitoring the human body. These sensors not only have all the conventional sensors benefits but also, they are low-cost, flexible, light-weight, and easily adopted with three-dimensional shape of the body. Moreover, recent research has shown they are the best candidates for monitoring human’s body motion. In this study, the effect of tensile fatigue cyclic loads on performance and sensitivity of textilebased strain sensors was investigated polyester/stainless steel staple fiber blend yarn as a conductive part with different structures were produced. The sensors varied in weft and warp density, percentage of stainless steel in conductive yarn, the number of conductive yarns, and weave pattern. The sensors were subjected to 500 cyclic loads operations and their tensile properties and sensitivity were investigated and compared before and after applying tensile fatigue cyclic loads. The results showed the textile-based strain sensors containing less percentage of stainless-steel fiber, lower number of conductive yarns, twill weave pattern and lower density in warp and weft direction have shown better performance after tensile fatigue cyclic loads.

Mechanical properties and damage behavior of tapered unidirectional CFRP laminates

An understanding of damage mechanisms induced by drop-off plies in tapered composite laminates is crucial. This study investigated the mechanical properties and damage behaviors of asymmetric tapered unidirectional carbon fiber-reinforced plastic laminates. Damage observations of laminates with simultaneous tapered and staggered tapered structures under monotonic and cyclic tensile loads were done by an optical microscope and X-ray radiography. Based on the results, matrix cracks in the resin pocket and delamination occurred earliest in the simultaneous tapered specimen due to a greater stress concentration in a single large resin pocket in the structure. Intralaminar damages in the staggered tapered specimen with a shorter step spacing occurred mainly in the lower dropped ply as there was a more significant interaction between the neighboring steps in the specimen. The drastic decrease in the stress concentration after the occurrence of damages in the neighboring step(s) then suppressed the occurrence of intralaminar damages in the upper dropped ply. This is in contrast to the specimen with a longer step spacing where the intralaminar damages occurred in both dropped plies due to the distributed stress distribution. Delamination propagated between the dropped plies and continuous (belt and core) plies for both staggered laminates regardless of the length of the step spacing at higher applied stress levels. The results showed that internal ply-drop configuration and step spacing in staggered tapered structures contribute to significant differences in the mechanical properties and damage behavior in the laminates.

Highly stable and strain-insensitive metal film conductors via manipulating strain distribution.

Metal film-based stretchable conductors are essential elements of flexible electronics for wearable, biomedical, and robotic applications, which require strain-insensitive high conductivity over a wide strain range and excellent cyclic stability. However, they suffer from serious electrical failure under monotonic and cyclic tensile loading at a small strain due to the uncontrolled film cracking behavior. Here, we propose a novel in-plane crack control strategy of engineering hierarchical microstructures to achieve outstanding electromechanical performance via harnessing the strain distribution in metal films. The wrinkles delay the crack initiation at undercuts which should be the most vulnerable sites during the stretching process. The surface protrusions/grooves/undercuts inhibit the crack propagation because of the effective strain redistribution. In addition, hierarchical microstructures significantly improve cyclic stability due to the strong interfacial adhesion and stable crack patterns. The metal film-based conductors exhibit ultrahigh strain-insensitive conductivity (1.7 × 107 S m-1), negligible resistance change (ΔR/R0 = 0.007) over an ultra-wide strain range (>200%), and excellent cyclic strain durability (>15 000 cycles at 100% strain). A range of metal films was explored to establish the universality of this strategy, including ductile copper and silver, as well as brittle molybdenum and high entropy alloy. We demonstrate the strain-insensitive electrical functionality of a metal film-based conductor in a flexible light-emitting diode circuit.

Behavior of 3D Printed Stretchable Structured Sensors

Piezoresistive structures inspired by serpentines, auxetic, and kirigami arrangements have demonstrated good flexibility and sensitivity under tension. Piezoresistive structures display optimal performance when the characteristics entail reliable stretchability and repeatability. These structures can be implemented as wearable sensors by compressing and elongating the conductive nanocomposites to vary the flow of electrons and to provide resistance change. To guarantee the reliability of these structures for strain sensing, it is important that the resistance change in these structures remains constant under repeated loads. In this study, the performance of different piezoresistive structures under cyclic tensile load is investigated and compared. Based on the performance of different types of structures, novel hybrid structures have been also proposed to design for both high stretchability and sensitivity of piezoresistive sensors. All the structures were tested with position limits rather than a fixed force to avoid permanent deformation. First, small position limits were used to determine Young’s Modulus, then a 10-cycle tensile test with larger position limits was used to further study the electromechanical behavior of different piezoresistive structures under larger deformation and repetition. Finally, the gage factor was derived for all the studied structures, and they were re-categorized based on properties’ similarities.

Comparison of Bond Strength Evaluation Methods Between Pavement Layers

Tack coats are generally used to facilitate a bonding between pavement layers in construction of hot-mix asphalt pavements and overlays. The goal of applying a tack coat material is to ensure the new or consecutive pavement layers respond monolithically under loading and avoid premature failure caused by debonding, mat slippage, or fatigue cracking. Multiple different in-situ and laboratory tests have been developed to evaluate bond strength of tack coat materials under tension, shear, and mixed-mode loading mechanisms. However, there is no universally accepted bond strength test method or performance criteria for tack coats within the United States. While some specifying agencies have gained familiarity and comfort with a particular bond strength test, a gap exists for many states that have not adopted a testing procedure. The objective of this paper is to compare current and newly developed tack coat bond strength tests to help determine which is most indicative in predicting field performance. Field cores from four different pavement sections with varying traffic loading conditions and early bond strength performance were sampled and tested in the laboratory using four different bond strength evaluation methods. Statistical analysis of bond strength testing results shows a strong linear correlation between pull-off and shear strength testing. Meanwhile, a novel approach to tack coat bond testing under cyclic tensile loading was explored and showed appreciable discrimination between sample locations and agreement with early field performance.

Experimental and theoretical investigation of FRP-steel composite plate under cyclic tensile loading

As the basic element of fiber-reinforced polymer (FRP) strengthened steel structures, FRP-steel composite plate (FSP) is a type of superior composite plate that combines the advantages of steel and FRP. This study combines different types of FRP and steel plates to develop an FSP element. Cyclic tensile tests are conducted to investigate the hysteretic behavior of the FSP, and the yield strength, peak strength, initial stiffness, post-yield stiffness, and residual deformation are analyzed. The experimental results indicate that the stress–strain curves of the FSP are bilinear prior to the fracture of the FRP, and the FSP exhibits a more stable post-yield stiffness and smaller residual deformation than a steel plate, which endows structures with better repairability after an earthquake. A finite element model (FEM) is established to investigate the mechanical behavior and failure process and is validated using experimental results. In addition, a theoretical model based on the composite material superposition theory is proposed and verified to simulate the stress–strain restoring force curves of FSP under cyclic tensile loading. The FEM and theoretical models can guide the practical design of FRP strengthened steel structures.

The heterogeneous nature of mechanically accelerated grain growth

AbstractWhile grain growth is traditionally viewed as a purely thermally driven process, nanocrystalline metals can undergo grain growth under mechanical loads, even at room temperature. We performed a detailed atomistic study of the heterogeneous nature of mechanically accelerated grain growth in a polycrystalline Pt nanowire. Using molecular dynamics simulations, we compared the grain-growth behavior of individual grains during tensile and shear cyclic loading, for three different equivalent strain levels, and at two temperatures. Pure thermal grain growth with no mechanical loading provided a baseline reference case. On average, grains that were already susceptible to thermal grain growth were stimulated to grow faster with mechanical loading, as expected. However, when analyzed on a grain-by-grain basis, the results were far more complex: grains that grew fastest under one stimuli were less accelerated under other stimuli. Even when the magnitude of loading changed, the relative growth of individual grains was distorted. We interpret this complexity from the perspective of superimposed growth mechanisms.