Tensile Stages Research Articles

Impact of Local Texture on Recrystallization and Grain Growth via In Situ EBSD

While electron backscatter diffraction (EBSD) has become an established technique within materials characterization labs around the world, the technique is still relatively young and new applications are continuing to emerge. Automated EBSD or Orientation Imaging Microscopy (OIM) systems are being used in combination with other equipment within the scanning electron microscope (SEM) to perform in-situ measurements. This includes tensile stages for observing changes in local orientation during deformation and heating stages for studying orientation changes arising during recrystallization and grain growth as well as phase transformations. In addition to these temporally three-dimensional studies, spatially three-dimensional studies can be performed by in-situ serial sectioning in microscopes equipped with both electron and focused ion beams. These in-situ techniques are briefly reviewed. The review is followed by a detailed analysis of in-situ heating experiments on copper. The movement of grain boundaries during recrystallization and subsequent grain growth are tracked. The effect of orientation relationships on grain boundary mobility and nucleation are explored. No special relationship with grain boundary mobility was observed. However, twins appear to play a significant role in the nucleation process.

Double yielding behaviors of polyamide 6 and glass bead filled polyamide 6 composites

Double yield points before necking were observed in injection molded specimens of polyamide 6 (PA6) and PA6/glass bead (GB) composites under tensile loading. The results indicated that the unusual phenomenon was in correlation with the tensile velocity, the composition of the composites and the crystallinity of the matrix at different stages in the course of the tensile test. With higher tensile velocity, addition of glass beads and bead content increasing, the phenomenon of double yielding was depressed. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) studies indicated that the double yielding was only present in samples with less than 50% crystallinity and the crystalline structure and the size of crystallite of the samples in different tensile stages were also changed.

Deformation behavior of bismuth–tin alloy wires with eutectic morphology produced by the Ohno continuous casting process

The Ohno continuous casting (OCC) process has been used to generate 62% Bi–Sn alloy wires approximately 2 mm in diameter with eutectic morphology at speeds between 30 and 387 mm/min. The microstructure was examined and tensile tests performed for wires cast at various speeds. The deformation behavior was investigated by observing the surface structure of wires at various tensile deformation stages. It was found that the eutectic morphology was of a quasi complex-regular structure for wires cast at higher speeds, whereas at lower speeds it contained a remnant of Chinese script type structure. It was found that bismuth fracture begins before inter-phase cracking in the initial stages and proceeds concurrently with inter-phase cracks in the latter part of the deformation process, allowing the accommodation of large strain. For wires cast at higher speeds, the inter-phase cracks play a leading role in wire fracture, whereas for wires cast at lower speeds, the bismuth fracture exerts a leading role in crack propagation and fracture. This difference was manifested in the fracture surface and elongation value.

Failure of Lightly Reinforced Concrete Members under Fire. I: Analytical Modeling

This paper is concerned with the failure of lightly reinforced concrete members under fire conditions, with particular emphasis given to the catenary action arising from axial restraint at the supports and the ensuing rupture of the reinforcement. The relevance of this work stems from the need to make a fundamental step toward understanding the conditions that influence the failure of a steel-decked composite floor slab, which is shown to become effectively lightly reinforced at elevated temperature. A new analytical model is proposed for lightly reinforced members subject to axial restraint, which accounts for the compressive arch and tensile catenary stages, bond-slip, yielding, and rupture of the steel reinforcement as well as the effect of elevated temperature. The versatility of the proposed model and the conditions which govern its validity are illustrated in this paper through comparisons with detailed computations based on nonlinear finite element analysis. The companion paper utilizes the proposed analytical model to perform a parametric investigation into the factors influencing the failure of lightly reinforced members, and to highlight key implications for structural fire resistance design.

Change of modulus and yielding properties of syndiotactic polypropylene with the glass transition

AbstractSemi-crystalline polymers like syndiotactic polypropylene pass during tensile deformation different stages with cross-overs at four critical points. Temperature variation above ambient changes the stresses at the critical points, but leaves the strains constant. Cooling down to the glass transition leads to the following changes: Fracture occurs before the onset of strain hardening. Yield point strain shifts to lower values. Young’s modulus increases by a factor on the order of the inverse of the crystallinity, as can be expected when the amorphous regions also contribute to the transmission of forces.

Tensile damage stages in cast A356-T6 aluminium alloy

This paper reports an investigation of the damage stages during straining of A356-T6 alloy by means of quantitative metallography, tensile tests, in situ tensile tests, and in situ micro-extensometry experiments with a SEM. Quantitative analysis of the microstructure and the damage mechanisms have identified the eutectic spatial arrangement as the crucial feature in fracture; interdendrite fine eutectics (eutectic channels) and extended eutectic zones (eutectic clusters) play different roles, so that the Si particle breaking rate varies from one region to another. The current models of Si particle breaking were then checked and their predictions compared with the local cracking rates. None of them were consistent with the experimental results. Next, cavity growth was investigated and the experimental results compared with data reported in literature and with predictions obtained by the Rice and Tracey law. It was shown that the initial porosity generated by Si particle breaking was very low and that void growth calculations completely underestimate void growth rate; once more, the specific role of Si particles spatial arrangement was decisive. Lastly, the analysis of the fracture stage revealed that cracks mostly propagate along the interdendritic channels, and this indicates the localisation of the damage, thus invalidating the ductility predictions of current fracture models.

Creep behaviour of single crystal nickel base superalloy

The creep activation energy and structure constant at the different creep stages have been calculated, and the microstructures have been observed by SEM and TEM. The results showed that the internal stress σo decreased with an increase in temperature. Over the stress and temperature range, there are different activation energies, time exponents, and structure constants at different creep stages. The change in microstructure has an influence on creep resistance in this superalloy (Ni-6.0AI-7.0Ta-8.5Mo, wt-%). It is shown that the dislocation climb is the major deformation mechanism during tensile creep stages I and II, but during the tertiary stage, the creep resistance decreased as a result of dislocations shearing into the γ′ rafts. Creep fracture occurs mainly by the cavities and microcracks produced at the γ′/γ phase interface due to the interaction of multislips.

Optimized tensile conditions for thein situX-ray topographic observation of glide dislocations in single crystals

Abstract In order to observe in situ, by X-ray topography, the dislocation mechanisms responsible for the microplastic deformation of crystals, several tensile methods have been used in the past. In a review of the different types of tensile stages it appears that, for most of them, the crystal was subjected to bending stresses, 80 that a quantitative interpretation of the observed phenomena could hardly be given. The magnitude of bending effects and their consequences on dislocation configurations are analysed in this paper. It is shown, by experiments on a new type of tensile stage and a finite-element computation, that a set-up with the two ends of the crystal cemented firmly onto guided holders is preferable to an imperfect freedom at the grips. The proposed method, applied to the microdeformation of cadmium and zinc crystals, produces dislocation configurations which are characteristic of a uniform tensile stress. The theoretical computation shows that the technique cannot get rid of a local enhancem...

Principles of the Design of Straining Stages

AbstractThe paper describes the elastic properties of tensile stages for the HVEM. The quality of the force control depends on the accuracy of the drives related to the maximum elongation as well as on the elastic compliance of the stage. The best accuracy of the load is obtained in soft stages. The fundamental operation of a soft and a hard stage is reviewed. These stages use a special thermal drive.

Design and Application of a Tensile Testing Stage for the SEM

Dynamic SEM studies of plastic flow in a uni-axial tensile test requires that the loading stage possess more than an ability to apply large loads to the test specimen. In such a test, observations of the details of the fracture processes are feasible only if the transfer of stored energy from the test system to the test specimen is minimal. This requires careful choice of test system compliance. This paper discusses system-specimen interactions and identifies the key criteria to be met for the design of satisfactory SEM tensile stages. The design and use of such a new stage is described. Preliminary results from a 0.08 percent carbon steel sheet tensile specimen are presented to demonstrate the utility of rigid tensile stages. The relevance of such tests, particularly for the characterization of the fracture resistance of test materials, is indicated.