Instrumented Tensile Tests Research Articles

Damage tolerance of the prestressing steel in a bridge stay-cable after thirty years of service in a graded, extremely adverse environment

The paper assesses the damage tolerance of the presstressing steel composing a 30 m-long bridge stay-cable subjected for decades to the singular environmental conditions originated at a hidden fault, which behaved as a latent defect and produced the sudden failure of the stay cable 30 years after construction. The structural design of the bridge was redundant, meaning that the failure did not entail consequences other than those derived from taking it out of service for inspection and subsequent repair to restore its structural and functional integrity. Removal of the failed stay-cable provided a hardly repeatable opportunity of analyzing and correlating the tensile behavior, deterioration condition and damage mechanisms of the component strand-wires. The latent defect created a graded-adverse environment for the prestressing steel, which produced a damage gradient high enough to supply a wide-ranging series of samples for the exhaustive assessment of its damage tolerance. The instrumented tensile testing and scanning electron microscopy (SEM) analysis of these samples allowed assessment on a comparative basis, comprising tensile behavior and damage mechanisms, and providing highly encouraging results as to the contribution of prestressing steel to the structural integrity of the stay-cables.

Tensile behavior of EUROFER ODS steel after neutron irradiation up to 16.3 dpa between 250 and 450 °C

During the development of structural material for future fusion reactors, a 50kg heat of reduced-activation ferritic-martensitic 9%CrWVTa steel with nanoscaled Y2O3-particles, EUROFER97 ODS HIP, was produced using powder metallurgy fabrication technology. This first batch of EUROFER97 ODS HIP and, for comparison, the steel EUROFER97 were prepared for a post-irradiation tensile test program. During neutron irradiation in the HFR (High Flux Reactor, The Netherlands), an accumulated dose of up to 16.3dpa was reached for 771 days at full power, with the irradiation temperature ranging between 250 and 450°C. During the post-examinations, all specimens showed the highest tensile strength at lower irradiation temperatures between 250 and 350°C. However, ODS-alloy and steel were found to clearly differ in the mechanical behavior, which could be documented by fully instrumented tensile tests. In the un-irradiated state, tensile strength of the ODS-alloy already was increased considerably by about 60% compared to the steel. Strengthening was further increased by another 20% after neutron irradiation, but with a much better ductility than observed in the steel. The typical irradiation-induced strain localization of EUROFER97 or RAFM steels could not be observed in the EUROFER97 ODS HIP alloy.

Experimental investigation on influence of Kevlar fiber hybridization on tensile and damping response of Kevlar/glass/epoxy resin composite laminates

This study investigates the tensile and damping behavior of Kevlar/glass/epoxy hybrid laminates. Hybrid Kevlar/glass with epoxy resin composites is fabricated considering different fiber volume fractions in combinations to show the influence of hybridization. Mechanical properties were inspected by an instrumented tensile test machine. A series of vibration tests were conducted to determine dynamic characteristics of the samples. Damping properties are calculated from logarithmic decrement method by using vibration response envelope curve. In addition, effects of fiber angle on natural frequencies were examined using ANSYS. The results show that the hybridization of relatively brittle material S-glass fibers with tough and high performance Kevlar fibers has showed to be highly effective in improving damping capacity of S-glass fiber composite laminates.

Simulation of Thermo-Mechanical Controlled Rolling and Continuous Cooling of Wire Rods

In this study the effect of thermo-mechanical controlled rolling and continuous cooling of different grades of steel wire rod (e.g. high-carbon for cold drawing applications, medium-carbon micro-alloyed for cold forming) has been analysed through the application of a set of integrated mathematical models simulating hot rolling and continuous cooling, and a laboratory work involving hot rolling simulation on a pilot plant and heat treatments on a laboratory scale. The samples have been characterised by means of instrumented tensile tests, metallographic analyses including determination of pearlite interlamellar spacing, and controlled compression tests. The results show that: - The mechanical strength of high-carbon steel is essentially related to interlamellar pearlite spacing, and can be enhanced through the control of continuous cooling. Improvements in cold drawability can be obtained by means of prior austenitic grain size (PAGS) reduction, through the application of thermo-mechanically controlled hot deformation processes. - In the case of medium-carbon micro-alloyed steels for cold forming, the reduced PAGS achieved by means of thermo-mechanically controlled process reflects on a closer control of as-rolled mechanical properties, avoiding hardness hot spots asking for annealing treatments before cold forming. Moreover, the finer ferrite grain size could affect the forces needed during forming at the same deformation level.

Micro- and nanoscale tensile testing of materials

This article reviews concepts and techniques for performing instrumented tensile testing of materials at small dimensions. State-of-the-art methods to probe tensile behavior of micro- and nanoscaled materials span many orders of magnitudes of force and displacement, often requiring a custom solution for each new material discovery. We discuss the experimental opportunities, challenges, and pitfalls in concert with the scientific insights revealed from tensile investigations at length scales where conventional wisdom is challenged on how materials deform.

Post irradiation plastic properties of F82H derived from the instrumented tensile tests

F82H (Fe–8Cr–2W) and its variant doped with 2%Ni were irradiated up to 20dpa at 300°C in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Post irradiation tensile testing was performed at room temperature. During testing, the images of the specimens including the necked region were continuously recorded. Tests on cold worked material were also carried out for comparison. From the load–displacement curves and the strain distributions obtains from the images, flow stress levels and strain hardening behavior was evaluated. A preliminary constitutive equation for the plastic deformation of irradiated F82H is presented. The results suggest that the irradiation mainly causes defect-induced hardening while it did not strongly affect strain hardening at the same flow stress level for F82H irradiated at 300°C. The strain hardening of Ni doped specimens was, however, strongly affected by irradiation. Results provide basics to determine allowable stress levels at temperatures below 400°C.

Tensile dilatometric studies of deformation in polymeric materials and their composites

The theory for volume changes in deformation for polymeric materials is presented, together with a brief literature review of the general area of tensile dilatometry. The theory has been used to enable the prediction of the volumetric response of a material to a deformation, which allows for the detection of the onset of cavitation (volume increasing)-type mechanisms in materials displaying such responses. A series of experiments has been performed using an instrumented tensile dilatometry technique on PMMA and on talc-filled reinforced polypropylene at 23 and 60 °C. The engineering constants, tensile modulus and lateral contraction ratio were measured and found to be viscoelastic. The determination of strain in three mutually perpendicular directions during the instrumented tensile test resulted in the measurement and prediction of the volumetric strain response with applied load. A significant cavitation-type mechanism was recorded in the case of the talc-filled reinforced polypropylene, whereas PMMA showed a deviatoric type mechanism. The volume strain has been found to be directly related to the bulk modulus for these materials. Finally, a new method of presenting volumetric strain versus applied stress data is shown and its relevance explained.

Wire tensions and bending moments in axially loaded seven wire strand

Carefully instrumented tensile tests were performed on a straight single steel strand of seven‐wire construction having core and helical wire diameters of 3–66 mm and 3–33 mm, respectively, and a lay angle of 14‐6d̀. Strain gauges in groups of three with their grid axes parallel and having a common backing were attached to all six helical wires at the mid‐strand position. For loading within the linear range of the load‐extension response (all tests) and load‐rotation response (in tests with free and partial torsional restraint of the ends) the outputs from these strain gauges were used to compute wire tensions and bending moments. Strand extension, rotation and torque generated under axial load (fixed‐end and partial torsional restraint) were also recorded.Test results showed that the share of the total strand load taken by the helical wires decreased as the torsional restraint on the strand was reduced. The mean tension in the helical wires was found to be 27‐5% smaller in the free‐end tests than in fixed‐end tests for a given strand load. Theoretical predictions underestimate this reduction in tension by up to 80%. Bending moments in the wires were found to be about 8% less than predicted in the fixed‐end condition and over 20% smaller in the free‐end condition.As expected, the slope of the linear regions of the load‐extension and load‐rotation plots decreased as the torsional restraint was reduced. However, the rate of decrease in the case of load‐extension plots was found to be less than predicted theoretically and the rotation measured was generally less than predicted theoretically. This is consistent with the helical wire tensions being smaller than the predicted values since the tangential components of these reduced tensions would have less effect in their unwrapping action on the strand under increasing axial load.