Investigation of Properties of the Zr,Hf-(Zr,Hf)N-(Zr,Hf,Me,Al)N Coatings, Where Me Means Cr, Ti, or Mo

The article describes the results of the investigation focused on the properties of the Zr,Hf-(Zr,Hf)N-(Zr,Hf,Me,Al)N coatings, where Me means chromium (Cr), titanium (Ti), or molybdenum (Mo). These coatings have three-layer architecture, including adhesion, transition, and wear-resistant layers, while the latter, in turn, has a nanolayer structure. Despite the fact that the coatings under study have close values of hardness and critical fracture load LC2, there are noticeable differences in wear resistance during the turning of steel. The tools with the coatings under study demonstrated better wear resistance compared to an uncoated tool and the tool with the commercial ZrN coating. The best wear resistance was detected for a tool with the Zr,Hf-(Zr,Hf)N-(Zr,Hf,Ti,Al)N coating. The study of the pattern of cracking in the structure of the coatings has found that, during the cutting process, active cracking occurs in the coating with Cr, which leads to the fracture of the coating, while the process of cracking is noticeably less active in the coatings with Ti or Mo.

Establishment of Thermal Ductile Fracture Criterion for As-Cast 42CrMo Steel and Its Application in Hot Ring Rolling Process

The casting-rolling compound forming process of ring parts is an advanced plastic forming technology that has been developed due to the merits of high efficiency and energy and material saving. However, cracks often occur during the hot ring rolling process, especially at the edges of the ring parts, which severely affects the forming quality. To predict and try to avoid the occurrence of cracks in the casting-rolling compound forming process of ring parts, the high-temperature fracture behaviors of as-cast 42CrMo steel were investigated by thermodynamic experiment method. The high-temperature tensile tests were carried out using the Gleeble-3500D thermomechanical simulator at various temperatures and strain rates. Stress-strain curves and fracture morphology were examined, through which the sensitivity of stress to temperature and strain rate and the effect of dynamic recrystallization and cavity evolution on fracture were found. The law of critical fracture strains was analyzed, and the model of critical fracture strain as a function of temperature and strain rate was established. Based on Oyane criterion, the thermal ductile fracture criterion was established in conjunction with the model of critical fracture strain. By embedding this thermal damage model into the finite element (FE) model for hot ring rolling of an as-cast 42CrMo ring, the damage prediction for this process was realized, and the thermal ductile fracture criterion was proved to be reliable. From the FE results for hot ring rolling, mechanism of damage and fracture in the hot ring rolling process was analyzed. The damage threshold C f is small, and the damage ratio D is large at the top and bottom edges of the inner surface area of the ring, which have the greatest propensity to cracking in the course of hot ring rolling. This is of great significance in terms of improving the forming quality of ring parts in the casting-rolling compound forming process.

Effect of Hole Arrangement on Failure Mechanism of Multiple-Hole Fiber Metal Laminate under On-Axis and Off-Axis Loading

Mechanical joints are commonly required in structures made of fiber metal laminate (FML), which pose a threat due to multi-site stress concentrations at rivet or bolt holes. Thus, for a reasonably designed FML joint, it is essential to characterize the failure mechanism of multiple-hole FML; however, little information about this has been found in open literature. In the present work, influences of hole arrangement and loading strategy (on-axis or off-axis) on the failure mechanism of multiple-hole FML were investigated, by performing finite element analyses and energy dissipation analyses with elastoplastic progressive damage models that took curing stress into account. Six types of specimens with holes arranged in parallel and staggered forms were designed, whose geometrical parameters were in strict accordance with those specified for composites joints. It indicated that the stress distribution, gross/net notched strength, critical fracture path, and damage evaluation process were only slightly influenced by the hole number and hole arrangement. On the other hand, they were strongly influenced by the loading strategy, due to the transition of failure domination. Results presented here can provide evidence for introducing design regulations of composite joints into the more hybrid FML, and for reasonably determining its multiple-hole strength merely based on the sing-hole specimen.

Shear Damage Suppression Model of Magnesium Alloy Plates

By shearing Q235 steel, aluminum, and AZ31 magnesium alloy at room temperature, the shear area of Q235 steel and aluminum is found to be relatively flat whereas that of AZ31 magnesium alloy exhibits many defects, such as potholes and cracks. The influence of temperature and strain rate on the critical fracture strain of AZ31 magnesium alloy was obtained using isothermal compression experiment. Results show that high temperature and larger strain lead to large and small critical fracture strains. Therefore, based on the isothermal compression experiment and the effects of temperature and strain rate on the critical fracture strain of AZ31 magnesium alloy, the magnesium alloy plate is heated to 100, 200, 300, and 400 °C, and shearing was conducted after 30 min of heat preservation. Based on the cross-sectional shape and the degree of damage, the optimum shear temperature ranges from 160 °C to 260 °C. At this temperature, the sheared magnesium alloy plate not only obtains an improved cross-sectional shape but also has a small shear corner area. Simultaneously, the shearing basic process model of Q235 steel plate is also obtained based on the industrial test. Furthermore, the shearing basic process model of AZ31 magnesium alloy was acquired based on the elongation ratio of magnesium alloy and Q235 steel under the same process conditions.

Thermal influences on macroscale rock damage

<p>Fracture processes in rock have widespread implications in the geohazard, geomorphologic, and civil and mining engineering communities.  Propagation of fractures reduces overall rock mass strength, can lead to large-scale gravitational instabilities, and can cause significant hazard and damage to infrastructure.  The potential for critical fracture in the form of rock falls and rock bursts are often the primary driver for scientific investigations, civil work project planning, and mining investment outlays.  However, slower subcritical fracture from long-term monotonic and/or cyclic stress perturbations often control the eventual more rapid (and more catastrophic) response of rock.  These slower damage mechanisms may result from existing or perturbed tectonic stresses, stress relief from exhumation or excavation, or long-term environmental stressors such as thermal cycling and frost cracking.</p><p>Here we investigate the role of thermal cycling in generating subcritical stresses to which virtually all rock cliffs worldwide are exposed.  Our hypothesis – that diurnal and seasonal cycles of temperature can lead to substantial subcritical fracture propagation and eventual critical fracture – has led us to design several field and laboratory experiments to measure both the deformations and the stresses associated with environmental thermal forcing in rock.  Our studies focus on granitic exfoliation environments, common in many mountainous regions of the world, where relatively thin (centimeters to decimeters) exfoliation sheets are able to undergo a full thickness thermal response, and where exfoliation-related rock falls are common and in some places, well-documented.</p><p>In cliff environments located in Yosemite National Park (California, USA), our field studies using in-situ measurements (i.e., crackmeters and temperature sensors) have shown that diurnal and seasonal thermal cycles lead to cyclic stresses in the subcritical range, with resultant cumulative and seemingly permanent rock deformation outwards from the main cliff surface.  Additional field studies using thermal IRT (InfraRed Thermography) imaging identify the locations of rock bridges that likely serve as focal points for these thermally-induced stress concentrations.  Although we did not measure the critical fracture conditions that would result in a rock fall, we did, fortuitously, capture the deformation signals leading up to explosive fracture of a nearby granitic 100-m-diameter exfoliation dome during peak temperatures at the site (located ~60 km northwest from Yosemite), thereby proving the efficacy of thermal stresses in driving both long term – and catastrophic – rock damage.  These field studies are substantiated by analytical fracture mechanics solutions which show how rock may eventually fail under these conditions.  These studies therefore serve as proxies for understanding how some rock falls eventually occur under subcritical thermally-induced cyclic stress conditions, but also more generally for how thermal-stress conditions may affect rock damage in a multitude of environments.</p>

Examination of Consistent Application of Interfacial Fracture Energy Versus Mode-Mixity Curve for Delamination Prediction

Experimentally characterized critical interfacial fracture energy is often written as an explicit trigonometric function of mode-mixity and is used to determine whether an interfacial crack will propagate or not under given loading conditions for an application. A different approach to assess whether an interfacial crack will propagate is to employ a failure locus consisting of the critical fracture energies corresponding to different fracture modes, represented by an implicit formulation. Such a failure locus can be linear, elliptical, among other shapes. As it is nearly impossible to obtain isolated GIc or GIIc values through experimentation, extrapolations are used to determine these two extreme values based on intermediate experimental data. However, the magnitude of these extreme values as well as the shape of the two forms of failure curves are at risk of being inconsistent should proper care not be taken. An example of such an inconsistency would be to use a trigonometric formulation to obtain the extreme values through extrapolation and then employ those values in simulation through an elliptical failure. In this work, we have employed a series of commonly used interfacial fracture energy measurement techniques over a range of mode-mixities for a metal/polymer interface to demonstrate the potential discrepancy in the two approaches and to underscore the need for a consistent approach in evaluating interfacial crack propagation.

EFFICIENCY EVALUATION OF WATERFLOODING OF LOW-PERMEABILITY RESERVOIRS BY HORIZONTAL WELLS WITH WATER-INJECTION INDUCED FRACTURES

In this paper, semi-analytical model of waterflooding by parallel horizontal wells with transverse water-injection induced fractures has been reviewed for low-permeability reservoirs. The numerical experiments can be divided in following stages: equilibrium pressure of stable water-injection induced fracture existence estimation; evaluation of the critical equilibrium pressure of the injection-induced fractures and estimation of the conditions for the stable fracture growth; evaluation of the critical injection fluid rate for the stable fracture growth; prognosis of the fracture growth dynamics. The main idea of the proposed work is to obtain the conditions of the stable fracture existence. This situation is possible in the late stages of field development, when oil production is compensated by fluid injection, and the pressure distribution does not depend on time. Numerical modeling shows the existence of the critical fracture half-length and pressure, after which the equilibrium of injection-induced fractures becomes unstable. Before this critical fracture length is exceeded, the fracture growth can be controlled by bottomhole pressure and flow rate, since each subcritical length of the equilibrium existence of a fracture corresponds to its equilibrium pressure and flow rate. It is possible to control fracture growth before its unstable state, knowing this pressure and flow rate. The early fracture growth can be estimated by the analytical formula for the fracture half-length in the so-called Carter regime. These results were obtained for specific parameters of the development system, but can be scaled to another homothetic system. The developed model will help to understand the fundamentals of water-injection induced fracture initiation and poroelasticity, as well as develop methods that allow to control and regulate the growth of water-injection induced fractures.

Elucidation of Shearing Mechanism of Finish-type FB and Extrusion-type FB for Thin Foil of JIS SUS304 by Numerical and EBSD Analyses

A numerical analysis using FE (finite element) analysis was performed to clarify the shearing mechanism in the process of extrusion-type fine blanking (FB) for a thin foil of JIS SUS304 in this study. Extrusion-type FB, in which a negative clearance between the punch and the die has been developed and investigated experimentally to improve the quality of the sheared surface in the blanking of thin foils. The resultant sheared surface for extrusion-type FB indicated an almost completely sheared surface, and the fracture portion on the sheared surface was much smaller than that in conventional FB, the so-called finish-type FB. The material flow and fracture criteria in extrusion-type FB were analyzed in comparison with those in finish-type FB. The differences in material flow and so-called critical fracture value were verified for the two processes. The principal stress near the shearing surface has mostly compressive components in extrusion-type FB due to its negative clearance, and the critical fracture value was also less than that in finish-type FB, in which the principal stress near the shearing surface has mostly tensile components. Furthermore, SEM observation with EBSD (electron back-scatter diffraction) analysis of the shearing surface was performed to verify the phenomena. Reductions in deformation-induced crystal orientation rotation and martensite transformation in extrusion-type FB were confirmed in comparison with those in finish-type FB from the analysis results.