Levels Of Tensile Loading Research Articles

Key trends in the response of suction bucket foundations to extreme axial cyclic loads

The offshore wind industry is currently expanding into emerging markets at a rapid pace. Some of these markets are located in areas characterized by frequent extreme events. From a geotechnical perspective, this results in new design challenges, as foundations must withstand severe loads repeatedly throughout their intended lifetimes. Jacket structures resting on suction buckets represent a new foundation concept that still requires research to become a potential optimal solution. The vertical cyclic response of bucket foundations constitutes the main topic of this article. The current study is based on observations of the behavior of a scaled model installed in dense sand. Both normal and extreme conditions were simulated by applying axial cyclic loads of varying amplitudes, means, and frequencies. High amplitude and low frequency cause significant stiffness degradation and permanent displacement. These scenarios occur due to build-up of excess pore pressure, with subsequent triggering of liquefaction. A criterion for liquefaction occurrence is identified and may be readily used for practical applications. Considerable levels of tensile loading lead to a high rate of heave, regardless of frequency. For one-way compressive forces, after an extreme loading sequence, stiffness returns to its initial level, as long as no liquefaction develops priorly. This bears essential implications in predicting the change of natural frequency of the system.

Influence of Selected Impregnation Materials on the Tensile Strength for Carbon Textile Reinforced Concrete at Elevated Temperatures

Carbon textile reinforced concrete (CTRC) has been investigated in terms of its elevated temperature and fire behavior in order to evaluate the influence of impregnation materials. Elevated temperature tests have already been carried out for material combinations of CTRC. For the tensile strength and the bond behavior between textile reinforcement and concrete, the impregnation of the textile reinforcement is the influencing factor. Impregnation materials such as epoxy-resin (EP) or styrene butadiene rubber (SBR) showed a deterioration of the elevated temperature behavior compared to unimpregnated materials. The aim of this paper is to close the research gap on the elevated temperature behavior of carbon textile reinforced specimens impregnated with silicic acid ester, epoxy-resin, and epoxy-resin additionally surface-modified with quartz sand. For this purpose, stationary and transient tensile tests at elevated temperatures up to 1000 °C were performed. Furthermore, thermal analysis of the impregnation materials was performed to analyze the tensile tests by correlating the chemical examination with the experimental test results, and the ignitability of the reinforcements was studied using single flame tests. For the investigated reinforcement materials, the failure temperature of the specimens increases with decreasing tensile strength load level for all test specimens. In comparison to the epoxy-resin impregnation material, the silicic acid ester impregnation resulted in higher failure temperatures for comparable load levels. The decomposition of the impregnation materials proved to be a decisive factor due to comparatively evaluated thermal analysis.

Influence of Temperature on the Mechanical Performance of Unidirectional Carbon Fiber Reinforced Polymer Straps.

The performance of pretensioned, laminated, unidirectional (UD), carbon fiber reinforced polymer (CFRP) straps, that can potentially be used for example as bridge deck suspender cables or prestressed shear reinforcements for reinforced concrete slabs and beams, was investigated at elevated temperatures. This paper aims to elucidate the effects of elevated temperature specifically on the tensile performance of pretensioned, pin-loaded straps. Two types of tests are presented: (1) steady state thermal and (2) transient state thermal. Eight steady-state target temperatures in the range of 24 °C to 600 °C were chosen, based on results from dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). Transient state thermal tests were performed at three sustained tensile load levels, namely 10, 15, and 20 kN, corresponding to 25%, 37%, and 50% of the ultimate tensile strength of the pin-loaded straps at ambient temperature. In general, the straps were able to retain about 50% of their ambient temperature ultimate tensile strength (UTS) at 365 °C.

Effect of shear and tensile-dominant cyclic loading on failure in SnAgCu solder

In the first part of this paper the differences between simulated SN-Curves under shearing and tensile cyclic loads are presented and compared with measurements published by A. Deshpande and A. Dasgupta [1, 2]. The measurements under the two load modes are simulated until a significant force reduction.The material model used in this work is based on visco-plasticity extended with an implicit damage formulation, enabling damage-driven cyclic softening of the structure. Additionally, multiaxiality of governing stress state is intrinsically included, with aim to account for different damage evolutions under shear and tensile load cases. The calculated damage paths are investigated and compared with cross-sections. Finally, numerically determined times to failure under different shear and tensile load levels are represented by means of SN-Woehler curves, showing a good agreement with experimental findings.Second part of the paper extends the investigation scope to lifetime prediction of a chip resistor soldered to free expanding PCB subjected to temperature cycling with variation of temperature amplitude, mean temperature and dwell time duration. The component is simulated under different temperature profiles until a specific lifetime reduction is observed. Also in this case, simulated lifetime is compared with measured data, and a good agreement with experimental results is achieved.

Theoretical prediction of the punching shear strength of concrete flat slabs under in-plane tensile forces

RC slabs can be subjected simultaneously to transverse loads and in-plane tensile forces, as it happens in top slabs of continuous box girder bridges decks, in the regions of negative moments, or in flat slabs subjected to horizontal loads, produced by wind or earth pressure. Tensile forces can reduce the shear punching capacity of slabs. However, few studies have been carried out to quantify this effect. With this purpose, a mechanical model has been developed to capture the influence of in-plane tensile forces on the punching shear strength and verified with punching tests under different in-plane tensile load levels. The model, presented in this paper, consists of an extension of the Punching shear Compression Chord Capacity Model to account for the effects of tensile forces on the resisting actions. A linear reduction of the punching shear strength as a function of the external load applied has been obtained for moderate tensile forces, whereas high level of tensile forces may produce premature yielding of the reinforcement and further reduction of the punching shear strength. The proposed model accurately captures the available test results, including the effects of the premature yielding of reinforcement when the tensile force produces concrete cracking. In addition, predictions of punching-shear-tensile tests available in the literature were made with different theoretical models included in design codes, which yielded in general conservative results and showed high scatter.

Analysis of the stress relaxation behaviour of sewing threads in the straight and loop form

Sewing threads as the main part of a seam, are exposed to various levels of tensile loading during sewing and garment use. Therefore, their tensile performance and time-dependent mechanical property such as stress relaxation may influence seam performance and appearance. The current study aims to evaluate and compare the stress relaxation of six common sewing threads in both straight and loop forms. Moreover, the influence of strain level and extension rate on stress relaxation were investigated. The obtained outcomes revealed that increase of extension rate would lead to the stress relaxation enhancement; however, strain level rise resulted in stress relaxation diminish. When sewing threads deform to the loop, higher values of stress relaxation were recorded. The obtained experimental outcomes were consistent with the two-component Maxwell’s model.

Numerical Investigation on the Influence of Tightening in Bolted Joints

In a bolted joint, the preload level resulting from the tightening torque represents a very important parameter governing the stresses distributions involving the joint under the real loading conditions. This paper deals with the development of a Finite Element (FE) model for the investigation of the effects of some selected preload levels on the stress-strain states affecting both bolt and plate in a single lap joint. The aim of this FE model is to support the design phase of strain gauges instrumented bolt to evaluate experimentally the rate of tensile load applied to the joint that the bolt absorbs with different preloads. The test article consists of two steel plates, a steel bolt and an aluminum nut. The results herein presented showed firstly that, without bolt preload, the tensile load applied to the joint is completely transferred to the bolt and that the load transferred to the bolt almost linearly decreases as the preload increases. Moreover, at a selected preload level, the transversal and longitudinal stresses (with respect to the load direction) increase as the tensile load increases, while the stress along the plate thickness direction decreases, reaching negative values. On the other hand, at a selected tensile load level, the transversal and longitudinal stresses as well as the stress along the thickness direction decrease as the preload level increases. Predicting the mechanical behaviour of the only bolted joint, if the same bolt model will be used to simulate the mechanical behaviour in a hybrid single-lap joint, possible imperfections of the model will have to certainly be linked to the modelling of the adhesive.

Effect of loading speed on the stress-induced magnetic behavior of ferromagnetic steel

The primary goal of this research is to investigate the effect of loading speed on the stress-induced magnetic behavior of a ferromagnetic steel. Uniaxial tension tests on Q235 steel were carried out with various stress levels under different loading speeds. The variation of the magnetic signals surrounding the tested specimen was detected by a fluxgate magnetometer. The results indicated that the magnetic signal variations depended not only on the tensile load level but on the loading speed during the test. The magnetic field amplitude seemed to decrease gradually with the increase in loading speed at the same tensile load level. Furthermore, the evolution of the magnetic reversals is also related to the loading speed. Accordingly, the loading speed should be considered as one of the influencing variables in the Jies-Atherton model theory of the magnetomechanical effect.

Foreign Object Damage in an Oxide/Oxide Ceramic Matrix Composite Under Prescribed Tensile Loading

Foreign object damage (FOD) behavior of an N720/alumina oxide/oxide ceramic matrix composite (CMC) was characterized at ambient temperature by using spherical projectiles impacted at velocities ranging from 100 to 350 m/s. The CMC targets were subject to ballistic impact at a normal incidence angle while being loaded under different levels of tensile loading in order to simulate conditions of rotating aeroengine airfoils. The impact damage of frontal and back surfaces was assessed with respect to impact velocity and load factor. Subsequent postimpact residual strength was also estimated to determine quantitatively the severity of impact damage. Impact force was predicted based on the principles of energy conservation.

Water permeability of concrete under uniaxial tension

AbstractConcrete structures can suffer from water permeating under stresses. This paper investigates the surface water permeability of reinforced concrete elements subjected to uniaxial tension. A testing system was developed to combine a conventional loading machine with a surface permeameter. To eliminate the effect of initial absorption of water, calibration tests were conducted on plain concrete samples with different surface saturated states. The experiment presented is designed to test the surface water permeability of a structural member under uniaxial tension. Specimens were reinforced centrally with different sizes of steel bar and fabricated with normal‐strength and high‐strength concrete. A uniaxial tensile load was applied from 0.10 to 0.80 of estimated ultimate cracking load in 0.10 increments. At the same time, water permeability was measured at each load step. Test results give the relationship between water permeability of concrete member and tensile load levels.

The Durability Failure of Pre-Damaged Concrete Induced by Mechanical Load

Chloride ion penetration and freezing and thawing damage are the two main factors that affect the durability of concrete structures. Through the chloride ion penetration test and freezing and thawing test of concrete specimens after tensile and compressive loading, the influence of load-induced damage on the long-term durability of concrete was studied. The results showed that the apparent chloride diffusion coefficient of concrete increased by 6.4% and 34%, and the surface chloride concentration increased 10% and 40%, respectively, both of which showed the "negative effect" when the uniaxial tensile load level reached the 65% and 75% of the ultimate capacity. However, with the increasing uniaxial compressive load level, the impact on the frost resistance of concrete experienced a transformation from the "positive effect" to the "negative effect".

Effects of temperature on the rupture strength and elastic stiffness of geogrids

ABSTRACT: An automated tensile loading system that can accurately control histories of both loading and temperature was developed. A series of unconventional tensile loading tests were performed on polypropylene (PP), high-density polyethylene (HDPE) and polyester (PET) geogrids using this system. The following was found. The temperature significantly affects the elasto-viscoplastic stress–strain properties of the tested polymer geogrids. The inviscid stress–viscoplastic strain relation changes with temperature. The tensile rupture strength decreases by 9.2%, 26.7% and 4.5% when the temperature rises from 30°C to 50°C with PP, HDPE and PET geogrids, respectively. The elastic stiffness of the geogrid was evaluated by applying small-strain-amplitude unload–reload cycles after a certain period of sustained loading during otherwise monotonic loading at a constant load rate. The value increases with an increase in the tensile load level at a fixed temperature, and decreases with an increase in the temperature at a fixed load level. A set of mathematical expressions are proposed to describe these trends of tensile rupture strength and elastic behaviour.

Conversion of Mechanical Force into TGF-β-Mediated Biochemical Signals

Mechanical forces influence homeostasis in virtually every tissue [1, 2]. Tendon, constantly exposed to variable mechanical force, is an excellent model in which to study the conversion of mechanical stimuli into a biochemical response [3-5]. Here we show in a mouse model of acute tendon injury and invitro that physical forces regulate the release of active transforming growth factor (TGF)-β from the extracellular matrix (ECM). The quantity of active TGF-β detected in tissue exposed to various levels of tensile loading correlates directly with the extent of physical forces. At physiological levels, mechanical forces maintain, through TGF-β/Smad2/3-mediated signaling, the expression of Scleraxis (Scx), a transcription factor specific for tenocytes and their progenitors. The gradual and temporary loss of tensile loading causes reversible loss of Scx expression, whereas sudden interruption, such as in transection tendon injury, destabilizes the structural organization of the ECM and leads to excessive release of active TGF-β and massive tenocyte death, which can be prevented by the TGF-β type I receptor inhibitor SD208. Our findings demonstrate a critical role for mechanical force in adult tendon homeostasis. Furthermore, this mechanism could translate physical force into biochemical signals in a much broader variety of tissues or systems in the body.

Viscoelastic properties of a silica-filled styrene-butadiene rubber under uniaxial tension

A model composite — a silica-filled styrene-butadiene rubber with a various filler volume content — was tested for creep and creep recovery at different tensile load levels to evaluate the effect of viscoelasticity on the deformational properties of filled rubbers. A constitutive equation describing the diagram of equilibrium deformation of the composite in quasi-static loading was obtained from an analysis of creep test results. The equation was common for the filled rubber at different filler content. The existence of such a curve has been confirmed by experimental unloading diagrams registered in cyclic loading-unloading tests. It is shown that the phenomenological equations obtained from an analysis of creep recovery test results can be used successfully for describing the hysteresis loops of second and subsequent cycles for cyclic tests with a constant maximum stretch ratio.

Ultrasonic detectability of potentially closed cracks from cold-worked holes under loaded conditions

Many non-destructive inspections for cracks rely on detecting ultrasound scattered or reflected from the crack. Recently, several methods for second-layer ultrasonic crack detection have been developed, sometimes using automated analysis methods to interpret the complex ultrasonic responses from multiple layers. In the validation of these techniques, the assumption is often made that fatigue cracks will reflect as much ultrasound as an artificially introduced EDM notch or saw cut. However, this is not always the case for 'closed' cracks, which can have a very low ultrasonic reflectivity. Of particular concern is the case of cold-worked holes, where a residual compressive stress field exists, extending to approximately one radius from the fastener hole. In addition, if a crack has grown under fatigue loads that include high peak stresses, there can be a closed region in the plastic zone at the crack tip. To complicate matters further, interference-fit fasteners apply an additional tensile stress, which may or may not counteract the cold-worked stress field near to the fastener, depending on the amount of interference. This problem was encountered whilst validating a two-layer ultrasonic inspection technique on real cracks in a real fatigue-test wing containing cold-worked holes. Inspections were performed at four different remote load levels by stress-jacking the wing. Whilst the ultrasonic indications from some of the cracks grew with increasing remote load, others did not. Some ultrasonic indications grew both towards the fastener and away from it, suggesting that both crack-tip closure and cold-worked crack-root closure were occurring. A possible reason for some cracks not growing is that they were already being held open by interference-fit fasteners. The aim of this project was to investigate and understand the effects of cold working, interference-fit fasteners and crack-tip closure on the ultrasonic detectability and sizing of cracks. In particular, information was required about the potential improvement in defect detectability by applying a remote tensile load to the structure to overcome the residual compressive stresses. Results will be reported of an experiment designed to grow fatigue cracks to a range of lengths at cold-worked holes in a single specimen, with interference-fit fasteners installed. These cracks could then be inspected ultrasonically at various remote tensile-load levels and the results compared with EDM notches in a similar specimen. Finally, the interference-fit fasteners could be removed and the ultrasonic inspections at the various loads repeated. Initial results have confirmed that ultrasonic indication size and amplitude both increase with remote tensile load but further results will be required to determine the dependence of defect detectability on remote load.

Diameter variations of irregular fibers under different tensions

The cross-section area of animal fibers varies along the fiber length, and this geometrical irregularity has a major impact on the mechanical properties of those fibers. In practice fibers are often subjected to tensile stresses during processing and application, which may change fiber cross-section area. It is thus necessary to examine geometrical irregularity of fibers under tension. In this study, scoured animal fibers were subjected to different tensile loading using a Single Fiber Analyzer (SIFAN) instrument. The 3D images of the fiber specimens were first constructed, and then along-fiber diameter irregularities of the specimens were analyzed for different levels of tensile loading. The changes in effective fineness of the fiber specimens were also discussed. The results indicate that for the wool fibers examined, there is considerable discrepancy in the fiber diameter results obtained from the commonly used single scan along fiber length and that from multiple scans at different rotational angles, and that the diameter variation along fiber length increases as fiber tension increases. The results also show that when diameter reduction treatments are applied to wool by stretching, the reduced average fiber diameter is associated with an increase in both within-fiber and between-fiber diameter variations. So in terms of effective fineness, the change is much smaller than the difference between the average diameters of the parent and treated wool. These results have significant implications for improving the accuracy of fiber diameter measurement and evaluation.

Comparison of residual stress in martensitic alloys by nondestructive techniques

Three martensitic materials, namely Alloys EP-823, HT-9 and 422 were subjected to tensile loading at ambient temperature. The cylindrical specimens tested at different levels of tensile loading were analyzed for characterization of residual stress resulting from plastic deformation corresponding to the applied loads between the yield strength and the ultimate tensile strength. The extent of residual stress developed at these applied stresses was analyzed by nondestructive positron annihilation spectroscopy, activation, and neutron diffraction techniques. The results indicate that the residual stresses characterized by all three techniques exhibited a consistent pattern showing a gradual enhancement in residual stress with increasing applied load.

Effect of cracked weld joint and yield strength dissimilarity on crack tip stress triaxiality

This paper is concerned with an elasto-plastic analysis of a weld joint containing a central crack in the weld material (WM) whose yield strength may differ from that of the base material (BM). Stress triaxiality along the path of expected crack extension is found to be influenced not only by the applied tensile load level and crack length relative to the specimen width but also by the degree of BM/WM mismatch in the yield strength. Three different cases are analyzed by application of a two-dimensional finite element analysis. They are referred to as under-match, even-match and over-match which correspond, respectively, to the WM yield strength being less than, equal to and greater than that of the BM. In general, the stress triaxiality along the crack front tends to increase for an under-matched weld and decrease for an over-matched weld using the even-matched case as a reference. As the crack length is reduced for a given specimen width, the stress triaxiality decreases accordingly and the BM/WM material dissimilarity becomes more obvious. Displayed graphically are also the crack front plastic zone size that increases with the applied tensile load level and suffers a discontinuity across the weld line.

An experimental study of toughening and degradation due to microcracking in a ceramic composite

An experimental investigation has been carried out to study the effects of controlled microcracking on the fracture resistance of brittle solids. The material chosen as a model system for the experimental study is an aluminum oxide reinforced with 33 vol.% SiC whiskers. The experimental program involves the determination of fracture toughness at room temperature on four-point flexure specimens containing sharp, through-thickness precracks where different amounts of microcrack damage are introduced a priori at different elevated temperatures and tensile load levels. The room temperature fracture initiation toughness of the pre-damaged material with a controlled amount of small-scale microcracking ahead of the stationary macrocrack is compared and contrasted with that of the undamaged material and the enhancement or reduction in fracture initiation toughness is estimated. Detailed transmission electron microscopy of the crack-tip damage zone has been conducted in an attempt to examine the mechanisms of permanent degradation and of microcrack formation. These observations reveal that the mechanism of microcracking by the coalescence of intergranular/interfacial cavities in the ceramic composite exposed to the high-temperature environment dominates over any other possible source of permanent deformation such as dislocation plasticity for the conditions of the experiments of this study. The fracture test results suggest that some toughness gains can be achieved, in certain cases, despite the creation of damage which primarily involves microcracking ahead of the crack-tip; however, significant increases in microcrack density, in fact, lead to a deterioration in the resistance of the material to fracture. The experiments of this study are discussed in the context of available theories of microcrack shielding, material degradation, and crack-microcrack interactions, as well as possible effects of dislocation plasticity and residual stresses.