Autowave Criteria of Fracture and Plastic Strain Localization of Zirconium Alloys

Plastic deformation and fracture of Zr–1% Nb alloys exposed to quasi-static tensile testing have been studied via a joint analysis of stress-strain curves, ultrasound velocity and double-exposure speckle photographs. The possibilities of ductility evaluation through the εxx strain distribution in thin-walled parts of zirconium alloys are shown in this paper. The stress-strain state of zirconium alloys in a cold rolling site is investigated considering the development of localized deformation bands and changes in ultrasound velocity. It is established that the transition from the upsetting to the reduction region is accompanied by the significant exhaustion of the plasticity margin of the material; therefore, the latter is more prone to fracture in this zone exactly. It is shown that traditional methods estimating the plasticity margin from the mechanical properties cannot reveal this region, requiring a comprehensive study of macroscopically localized plastic strain in combination with acoustic measurements. In particular, the multi-pass cold rolling of Zr alloys includes various localized deformation processes that can result in the formation of localized plasticity autowaves. Recommendations for strain distribution division over the deformation zone length in the alloy in the pilger roll grooves are provided as well.

PEEK based cranial reconstruction using thermal assisted incremental sheet forming

Compared to conventional sheet forming operations, incremental sheet forming (ISF) is a flexible forming technique that can achieve higher formability in terms of localized deformation. Due to excellent mechanical properties and X-ray penetration, polyether-ether-ketone (PEEK) is an ideal alternative to titanium alloy and stainless steel in orthopedic applications. In this study, a 3-axis desktop manufacturing system has been fabricated to investigate the temperature-dependent formability of PEEK in terms of manufacturing the cranial plate by using the ISF technique. Meanwhile, the forming force, temperature distribution, geometrical accuracy, and thermal properties were obtained and analyzed. The findings indicate that the ISF technique provides technological and economic advantages in cranial reconstruction by using PEEK.

Patterns of incision and deformation on the southern flank of the Yellowstone hotspot from terraces and topography

Understanding the dynamics of the greater Yellowstone region requires constraints on deformation spanning million year to decadal timescales, but intermediate-scale (Quaternary) records of erosion and deformation are lacking. The Upper Snake River drainage crosses from the uplifting region that encompasses the Yellowstone Plateau into the subsiding Snake River Plain and provides an opportunity to investigate a transect across the trailing margin of the hotspot. Here, we present a new chronostratigraphy of fluvial terraces along the lower Hoback and Upper Snake Rivers and measure drainage characteristics through Alpine Canyon interpreted in the context of bedrock erodibility. We attempt to evaluate whether incision is driven by uplift of the Yellowstone system, subsidence of the Snake River Plain, or individual faults along the river’s path. The Upper Snake River in our study area is incising at roughly 0.3 m/k.y. (300 m/m.y.), which is similar to estimates from drainages at the leading eastern margin of the Yellowstone system. The pattern of terrace incision, however, is not consistent with widely hypothesized headwater uplift from the hotspot but instead is consistent with downstream baselevel fall as well as localized deformation along normal faults. Both the Astoria and Hoback faults are documented as active in the late Quaternary, and an offset terrace indicates a slip rate of 0.25−0.5 m/k.y. (250−500 m/m.y.) for the Hoback fault. Although tributary channel steepness corresponds with bedrock strength, patterns of χ across divides support baselevel fall to the west. Subsidence of the Snake River Plain may be a source of this baselevel fall, but we suggest that the closer Grand Valley fault system could be more active than previously thought.

An effective parameterization of texture-induced viscous anisotropy in orthotropic materials with application for modeling geodynamical flows

In this article, we describe the mathematical formulation and the numerical implementation of an effective parametrization of the viscous anisotropy of orthorhombic materials produced by crystallographic preferred orientations (CPO or texture), which can be integrated into 3D geodynamic and materials science codes. Here, the approach is applied to characterize the texture-induced viscous anisotropy of olivine polycrystals, the main constituent of the Earth's upper mantle. The parameterization is based on the Hill (1948) orthotropic yield criterion. The coefficients of the Hill yield surface are calibrated based on numerical tests performed using the second order Viscoplastic Self-consistent (SO-VPSC) model. The parametrization was implemented in a 3D thermo-mechanical finite-element code developed to model large-scale geodynamical flows, in the form of a Maxwell rheology combining isotropic elastic and anisotropic non-linear viscous behaviors. The implementation was validated by comparison with results of the analytical solution and of the SO-VPSC model for simple shear and axial compression of a homogeneous anisotropic material. An application designed to examine the effect of texture-induced viscous anisotropy on the reactivation of mantle shear zones in continental plates highlights unexpected couplings between localized deformation controlled by variations in the orientation and intensity of the olivine texture in the mantle and the mechanical behavior of the elasto-viscoplastic overlying crust. Importantly, the computational time only increases by a factor 2-3 with respect to the classic isotropic Maxwell viscoelastic rheology. Comment: 32 pag.; 5 figures; 4 tables

Analysis of fracture deformation field and energy evolution of granite after high confining pressure cyclic load pre-damage

Considering the recent developments of deep mining, investigating the rock properties under high ground stress periodic load is highly demanded. Studies show that these characteristics are important factors affecting the long-term steadiness of rock. However, the mechanical properties of rock mass without macro failure after cyclic load should be studied. In the present study, granite in a mine is considered as the research object. A rock pre-damage experiment is conducted with the same cycles under different confining pressures and constant cycle upper and lower limit loads. The pre-damaged rock sample is subjected to a uniaxial compression test, and a high-speed charge couple device camera is used to record the speckle field image of the sample surface during the whole loading process. The digital speckle techniques are used to analyse the image of the pre-damaged sample, the deformation field of the specimen surface, the displacement dislocation value of the localized deformation area and the deformation energy value of the specimen surface. The results show that for the same cycle times, the confining pressure is less than 80 MPa, which has a weakening effect on the rock's axial strength. As the confining pressure approaches 120 MPa, the pre-damaged rock uniaxial peak strength increases. The characteristics of displacement dislocation energy evolution of the localized deformation bound are divided into three stages (pre-peak stage, peak point and post-peak stage). After pre-damage under the same cycle times and different confining pressure conditions, the deformation field evolution of rock is relatively consistent.