Wire Stress Research Articles

Semi-active vibration control device based on superelastic NiTi wires

SUMMARY The present paper presents a physical prototype that simulates the response of a single degree of freedom dynamic system, equipped with a novel semi-active vibration control device. This device comprises two superelastic NiTi elements working in phase opposition and aims to prevent deck unseating in simply supported bridges, during a seismic excitation. The special design of this device allows to avoid problems related to stress–relaxation phenomena and material degradation because of cyclic loading that have been observed in similar passive dissipation devices. The proposed design uses a strategy that permits the continuous adapting of the accumulated stress in the NiTi wires, on the basis of the response of the device to external excitations. Although unloaded, the NiTi elements remain strain/stress free, preventing stress–relaxation phenomena. With the occurrence of a dynamic excitation, a cumulative strain/stress process in the superelastic wires is initiated, enabling higher martensite transformation ratios and therefore increasing the damping capacities of the system while keeping the stresses in the wires inside a narrower superelastic window. The strain/stress accumulation in the superelastic wires is a direct result of the motion of the structure itself, with no need for external energy input. Copyright © 2012 John Wiley & Sons, Ltd.

Mechanical Properties of Si Nanowires as Revealed by in Situ Transmission Electron Microscopy and Molecular Dynamics Simulations

Deformation and fracture mechanisms of ultrathin Si nanowires (NWs), with diameters of down to ~9 nm, under uniaxial tension and bending were investigated by using in situ transmission electron microscopy and molecular dynamics simulations. It was revealed that the mechanical behavior of Si NWs had been closely related to the wire diameter, loading conditions, and stress states. Under tension, Si NWs deformed elastically until abrupt brittle fracture. The tensile strength showed a clear size dependence, and the greatest strength was up to 11.3 GPa. In contrast, under bending, the Si NWs demonstrated considerable plasticity. Under a bending strain of <14%, they could repeatedly be bent without cracking along with a crystalline-to-amorphous phase transition. Under a larger strain of >20%, the cracks nucleated on the tensed side and propagated from the wire surface, whereas on the compressed side a plastic deformation took place because of dislocation activities and an amorphous transition.

Elastic wave simulation in ground anchors for the estimation of pre-stress

Application of pre-stress on strand wires inside a structure is a way to reinforce the low tensile strength of concrete and soil materials. After years in service, the strands may lose the pre-stress due to corrosion or other reasons endangering the whole structure. Since there is no accessibility to the strands inside the structure, any inspection should be conducted on the anchor head. In this study, elastic waves on the anchor head are numerically simulated. Parameters like the wave amplitude and propagation time are influenced by the stress of the strand wires which affects the contact between the threaded steel rod, and the surrounding anchor head influencing the acoustic impedance mis-match on the interfaces. The change of contact pressure between the strands and anchor head is simulated by modifying the rigidity of a model interphase material. Results are compared with experimental under different levels of pre-stress. Therefore, an easy and fast procedure for non-destructive inspection of the pre-stress load on the strands is discussed.

Seismic protection of lap-spliced RC columns using SMA wire jackets

This study used two forms of shape memory alloy (SMA) wires, nickel–titanium–niobium (NiTiNb) and nickle–titatanium (NiTi), to retrofit reinforced concrete (RC) columns with lap splices. NiTiNb shape memory alloys are considered to show a wider temperature window compared with NiTi shape memory alloys and thus may be beneficial for applications in the area of civil structures. The goals of this study are to assess the mechanical behaviour of the two shape memory alloy wires and investigate the seismic performance of the shape memory alloy wire jackets for reinforced concrete columns with lap splices. First, the study investigates the recovery and the residual stress of NiTiNb and NiTi shape memory alloy wires. This study also evaluates the behaviour of the NiTiNb shape memory alloy wire under residual stresses. The results indicate that the shape memory alloy wire jackets show good performance for reinforced concrete columns with lap splices. The shape memory alloy wire jackets increase the ductile behaviour of the lap-spliced columns without strength degradation. The results show that their performance is superior to that of the RC column with continuous reinforcements. The study shows that the NiTiNb shape memory alloy wire jackets are more adaptive for retrofit of RC columns than the NiTi shape memory alloy wire jackets since the NiTiNb shape memory alloy shows more appropriate temperature windows for the applications of shape memory alloys in civil structures.

Hysteretic behavior of NiTi and NiTiNb SMA wires under recovery or pre-stressing stress

Abstract Shape memory effect of shape memory alloy (SMA) wires generates recovery stress and provides external confining pressure on concrete. Previous studies showed the effectiveness of SMA wire jackets to increase peak strength and failure strain of concrete through experimental tests. However, the behavior of SMA wires under recovery stress was not investigated seriously. Thus, this study plans a series of tensile tests for NiTi and NiTiNb martensitic SMA wires under recovery stress with varying pre-strain. This study also assesses the behavior of SMA wires under pre-stressing. Remaining residual stress is reduced with increasing additional loading and unloading strain subsequently. In general, initial and effective stiffness of the hysteretic curves are stable with increasing strain, however, unloading stiffness decreases with increasing strain. Damping ratio also decrease generally with increasing strain. When the SMA wires are heated up to the transformation temperature under pre-stress, the stress of the wires increases due to transformation of the state. Also, the stress decreases with decreasing temperature of the wires down to room temperature. The stress of the NiTiNb wires with heating is higher than the pre-stress though that of the NiTi SMA wires is less than the pre-stress. Thus, the developed stress under pre-stress seems to depend on the composition and temperature windows of SMAs.

Thermomechanical Characterization of NiTiNb Shape Memory Alloy for Concrete Active Confinement Applications

Despite growing interest in the use of shape memory alloys (SMAs) in civil structures, much is still to be understood about their behavior in real loading environments. This experimental work focuses on characterizing the thermomechanical behavior of a thermally prestressed NiTiNb SMA under thermal and loading conditions pertinent to civil structural applications. The work aims at exploring the feasibility of using this type of alloy in developing seismic retrofitting spirals that could be used to actively confine vulnerable reinforced concrete columns to improve their flexural ductility and shear strength under earthquake loading. Differential scanning calorimetry tests are conducted to determine the transformation temperatures of the used alloy. A testing program is carried out on 2-mm-diameter NiTiNb wires to examine the recovery stress of prestrained wires and the monotonic and cyclic behaviors of thermally prestressed wires under various testing durations and ambient temperatures. A thermal chamber is used to induce a realistic range of ambient temperature (−10°C to 55°C) during testing. The results show that the recovery stress is quite stable within the studied range of temperature. The prestressed NiTiNb alloy exhibits nonlinear behavior with a modulus that is highly dependent on ambient temperature.

Behavior of NiTiNb SMA wires under recovery stress or prestressing

The recovery stress of martensitic shape-memory alloy [SMA] wires can be used to confine concrete, and the confining effectiveness of the SMA wires was previously proved through experimental tests. However, the behavior of SMA wires under recovery stress has not been seriously investigated. Thus, this study conducted a series of tests of NiTiNb martensitic SMA wires under recovery stress with varying degrees of prestrain on the wires and compared the behavior under recovery stress with that under prestressing of the wires. The remaining stress was reduced by the procedure of additional strain loading and unloading. More additional strains reduced more remaining stresses. When the SMA wires were heated up to the transformation temperature under prestress, the stress on the wires increased due to the state transformation. Furthermore, the stress decreased with a decreasing temperature of the wires down to room temperature. The stress of the NiTiNb wires was higher than the prestress, and the developed stress seemed to depend on the composition of the SMAs. When an additional strain was subsequently loaded and unloaded on the prestressed SMA wires, the remaining stress decreased. Finally, the remaining stress becomes zero when loading and unloading a specific large strain.

Experimental Study on the Recovery Stress of Shape Memory Alloy Strands and Wire

Considering the advantages of steel strands in mechanical properties, a new form of shape memory alloy (SMA) wire, SMA strands, is designed in this study. To compare the recovery properties of martensitic SMA strands and SMA wire, the recovery stress of which with different prestrains were tested by using a material testing machine with a temperature-controlled cabinet. In this experiment, the SMA strands and the SMA wire have the same composition and the same cross-sectional area. The experimental results show that the maximum recovery stresses of the SMA strands with different prestrain are almost the same, which illustrates that the prestrain has no much effect on the maximum recovery stress of the SMA strands. Moreover, the recovery stress curve in heating stage does not coincide with that in cooling stage. Furthermore, the residual recovery stress of the SMA strands in cooling stage is also smaller than that of the SMA wire. This demonstrates the SMA strands can recovery initial state better.

Experimental Study on the Recovery Stress of Shape Memory Alloy Strands and Wire

Experimental Study on the Recovery Stress of Shape Memory Alloy Strands and Wire

The deployment of deep-earth sensor probes for landslide detection

In this paper, we present a state-of-the-art wireless sensor network (WSN) of deep-earth probes (DEPs) that has been deployed to monitor an active landslide in the Western Ghats mountain range of South India. While India has one of the highest incidences of landslides and landslide-induced fatalities—primarily in the Himalayas of North India and in the Western Ghats of Central and South India—our study is perhaps the first comprehensive attempt to instrumentally detect landslides in the Western Ghats. Wireless networks have enabled us, since June 2009, to continuously monitor the deployment site in real time and from anywhere around the globe. There have been a few earlier landslide monitoring WSNs using accelerometers in Emilia Romagna Apennines, Italy; global navigation satellite system (GNSS) sensors to monitor the Hornbergl landslide, Austria; and vibrating wire stress sensors to monitor a slope in China. We improved upon these WSN systems by incorporating a variety of sensors—piezometers, dielectric moisture sensors, strain gauges, tiltmeters, a geophone, and a weather station—and installing some of these sensors as deep as 20 m below the ground surface. We present the salient aspects of the field deployment of DEPs: the selection of sensors and their incorporation in DEPs, the methodology we used in embedding these DEPs into the soil, and a few of the key aspects of the wireless sensor network. We also present a description of the deployment site and some of the results of geotechnical investigations carried out on borehole corings. Finally, we present the more interesting field data collected from the monitoring system during a rainy season in July and August 2009.

Research on stress distribution between wires of single thigh steel strand

A three-dimensional contact model of 1×7 steel strand was established. Contact point was searched by Splitting-pinball algorithm, and Augmented-Lagrangian algorithm was applied for analysis of contact loads. The exerted tensile loads to the model were analyzed using finite element method. After analyzing calculation results, the laws of steel wire stress distribution in axis direction and in its cross-section were found. Friction coefficients were set as 0.10, 0.11, and 0.12, respectively, to obtain the influence law of friction coefficient to steel wire stresses. Research result shows that friction coefficient has significant influence on the shear stress of steel wire. Analyzed the calculation results of steel strand with five different lay pitch multiples and got the influence law of lay pitch multiple to the stresses of steel wire in steel strand. The Von Misses stress of steel wire increases following with the increasing of lay pitches multiples, but the increment value is not very prominent. The shear stress of steel wire decreases following the increase of lay pitch multiple, and the changing amplitude is large when lay pitch multiple is small. Finally, carried out a steel strand tensile deformation test and the consistency of test results with the calculation results shows that the selected model is reasonable.

Inducing recovery stress of NiTiNb SMA wires using heat of hydration for confining concrete

This study suggests the utilization of heat of hydration of concrete to activate the shape memory effect (SME) of shape memory alloy (SMA) wires embedded in concrete and produce recovery and residual stress on the wires. This method is more convenient than the previous electronic resistance heating. For the purpose, this study prepares NiTiNb SMA wires that show appropriate temperature window for the use of heat of hydration. Axial compressive tests of concrete cylinders confined by the NiTiNb SMA wire jackets are used to prove that the utilization of heat of hydration is valid to generate recovery and residual stress in the SMA wires. The confined cylinders show increased peak strengths and much larger failure strains than those of the plain concrete. The general behavior of the SMA wire-confined specimens in this study is similar to that of specimens heated by electronic heating jacket. Also, this study explains two examples for the utilization of heat of hydration for the SME in reinforced concrete beams and columns.

Shape memory alloy CuAlBe strands subjected to cyclic axial loads

Structural cables are composed of wires helically wound into strands, which, in turn, are wound around a core. They have high redundancy and can be used to carry large tensile forces in many civil engineering structures. Better dissipation and/or recentering capacity can be expected if the cable is composed of shape memory alloy (SMA) wires in the austenite phase. Tensile tests were performed on strands made of CuAlBe SMA wires to characterize their behavior and demonstrate their potential utility as adaptive or resilient tension elements. In particular, equivalent viscous damping and forward-transformation and maximum stresses were determined for different strain amplitudes. Nearly ideal superelastic properties were obtained up to 3% axial strain. The equivalent damping increased with strain, reaching a value of 4% for a strain amplitude of 5%. Strand experimental results were used to validate a two-dimensional numerical model developed to estimate the strand response to axisymmetric loads within the superelastic deformation range. The model relies on the linearization of the wire geometry and on a multilinear CuAlBe wire stress–strain relationship. The proposed model adequately predicts the maximum strand stress and the residual strains for different strain amplitudes.

Modelling of contact regimes in wire sawing with dissipative particle dynamics

Optimization of the wire sawing process of silicon ingots requires a profound understanding of the dynamic interaction of wire, slurry and silicon material. In this paper, the influence of wire velocity and applied wire stress on the process is investigated using dissipative particle dynamics and discrete element simulations for modelling the fluid and the grains in the abrasive suspension. In our simulations, different contact regimes occur depending on grain shape and a stress balance within the system. We observed semi-contact for high wire stress and low wire velocity and non-contact for low stress and high velocities in agreement with predictions from elasto-hydrodynamic modelling. Our simulations suggest the usage of sharp grains, since in this case, stress localization on the base of the sawing groove occurs even in the non-contact regime. These insights are likely to provide a scientific base for the optimization of sawing rates and reduction of kerf loss.

Recovery stresses in SMA wires for civil engineering applications: experimental analysis and thermomechanical modelling

AbstractThe present study deals with the creation of so‐called “recovery stresses” in SMA wires. Two approaches are developed. First, experiments are performed on nickel‐titanium wires with suitable transformation temperatures. The wires are stretched in the martensite state at ambient temperature. A thermal cycle at constant strain is applied to transform the martensite to austenite, in order to activate the shape memory effect. During the thermal loading, both the phase transformation and the thermal expansion lead to stresses in the wires. Second, a thermomechanical model is used to analyze the experimental results. The model accounts for the phase transformations caused by combinations of stress and temperature loadings. The results are then discussed in the framework of application to concrete component reinforcement.

A numerical approach on the inclusion effects in ultrafine gold wire drawing process

This study examined the effects of inclusions on the gold wire drawing stress using the Finite Element Method (FEM). Al 2O 3 and SUS304 are used as the model inclusion materials, which are frequently found on the fracture surfaces of drawn wire. The wire drawing stress showed a strong correlation with the size and yield stress of the inclusions. In the case of Al 2O 3, a larger diameter induced more drawing stress in the wire, whereas in case of SUS304, a larger diameter induced less drawing stress in wire. The difference was estimated quantitatively by comparing the amount of equivalent plastic strain (PEEQ) in the wire, which is the result of an interaction between the wire and inclusion. This result shows that the reason of difference in drawing stress variation is due to the yield stress of the inclusion.

Effect of Annealing on Strain-Temperature Response under Constant Tensile Stress in Cold-Worked NiTi Thin Wire

The present paper aims to understand the influence of annealing on the strain-temperature response of a cold-worked NiTi wire under constant tensile stress. It was found that transformation behavior, stress-strain relationship, and strain-temperature response of the cold-worked NiTi wire are strongly affected by the annealing temperature. Large martensitic strains can be reached even though the applied stress is below the plateau stress of the martensite phase. At all stress levels transformation strain increases with increasing annealing temperature in the range of 350∘–450∘C and decreases with increasing annealing temperature in the range of 450∘–650∘C. The martensitic strain at lower stress levels exhibits the same tendency. At higher stress levels the martensitic strain increases with increasing annealing temperature.

Fabrication and characterization of microstrip array antennas integrated in the three dimensional orthogonal woven composite

A 3D Integrated Microstrip Antenna (3DIMA) is a new concept for the smart skin structure. In this design concept, a microstrip antenna was woven into the 3D orthogonal woven composite for superior integration and impact resistance to the traditional conformal load-bearing antenna structure. This paper gives the design and fabrication of a three dimensionally integrated microstrip array antenna. The antenna was designed to work in the L band range. For comparison, a single-element patch microstrip antenna integrated into three dimensional composite was also fabricated. The results showed that the simulated and measured return losses were in good agreement for each antenna. By using array configuration, the array antenna showed more concentrating main beam in the radiation pattern and higher gain than the single-element antenna. In the mechanical test comparison, 3DIMA had a significantly lower tensile and bending strengths and somewhat lower tensile and bending moduli than those of the baseline composite due to the lower yield stress and lower tensile modulus of the copper wire. The peel strength of 3DIMA showed as high as 4.016 N/mm, which was much higher than that of the conventional glass fiber/PTFE laminates adhered with copper foil.

Development of Reciprocating Heat Engine Using Shape Memory Alloy

This research aims at developing the heat engine system using Shape Memory Alloy (SMA) wires, which work by alternating supply of hot/cold water through the newly developed automatic valves. The SMA wire is connected to the chain and sprocket system having the ratchet type bearing and the spindle with the flywheel. The valves for supplying hot/cold water to the SMA wires are driven by the flywheel, so no outside power is necessary. Output power of the developed heat engine with two φ 0.3 mm SMA wires is 0.1W at 30∼40 rpm. The SMA wire used in the developed heat engine was produced by the Furukawa Electric Co., Ltd.. The wire shows the fatigue life of more than 105 cycles under conditions of 150 MPa in loading and heating/cooling cycle rate of 0.5 Hz in the cyclic transformation fatigue tests. The heat engine system works without any adjusting process of a length of SMA wire and water supplying timing. The stress of the SMA wire is kept to be rather higher during working because that the engine has no crank system. So, the developed heat engine system is hopeful to use in recovering energy from waste hot water.

Influence of pre-strain on recovery stress of annealed NiTi thin wire during isothermal holding

The present research aims to understand the recovery stress of NiTi wires generated during heating and isothermal holding under constrained condition. Both pre-strain and isothermal holding temperature have significant effects on the evolution of recovery stress during heating and isothermal holding. In general, increasing isothermal holding temperature and/or pre-strain causes an increase of recovery stress reduction or relaxation. This effect can be attributed to different dislocation densities and mobility of dislocations generated in those conditions.