High Strain Conditions Research Articles

The low-grade Canal de las Montañas Shear Zone and its role in the tectonic emplacement of the Sarmiento Ophiolitic Complex and Late Cretaceous Patagonian Andes orogeny, Chile

The Canal de las Montañas Shear Zone (CMSZ), southern Patagonian Andes (51–52°S), is a low-grade mylonite belt generated from felsic ignimbritic, pelitic and basaltic protoliths of the Late Jurassic–Early Cretaceous Rocas Verdes basin. The different types of rock fabrics across the CMSZ are thought to be associated with relatively intermediate and high strain conditions, characterized by the development of a narrow western belt of S–C´-type mylonites and phyllonites interpreted as the metamorphic sole thrust of the Sarmiento Ophiolitic Complex. Highly strained rocks of the CMSZ display a reverse, continent-ward tectonic transport, with a minor dextral component of shearing. Transitional pumpellyite–actinolite and upper greenschist facies metamorphic conditions at ca. 5–6kbar and 230–260°C indicate that the primary shearing event occurred in a subduction zone setting. In-situ 40Ar/39Ar laserprobe chronology yielded ages of ca. 85Ma on syntectonic phengite which are interpreted as representing cooling synchronous with mica crystallization during the main compressive deformational event. The 78–81Ma U–Pb zircon crystallization ages of cross-cutting plutonic and hypabyssal rocks and 40Ar/39Ar amphibole age of ca.79Ma from lamprophyric dikes within the fold-thrust belt constrain an upper age limit of the ophiolite tectonic emplacement deformation.

Single particle impact tests using gas gun and analysis of high strain-rate impact events in ductile materials

Abstract Removal of material by the action of impinging particles is known as erosion. Based on the understanding of the material removal mechanisms in ductile materials, in normal impact, material removal occurs predominantly by deformation whereas in oblique impacts, material is removed through a combination of cutting and deformation. Although material can be removed in cutting by a single impact, material removal through deformation requires multiple impacts. Erosion of surfaces occurs over a wide spectrum of particles sizes and velocities. In general, erosion models rely on quasi-static material properties such as; hardness, yield strength, ultimate tensile strength and strain. However, material properties change dramatically under high strain and strain-rate conditions typical of erosive environments. This can lead to serious deficiencies in the developed erosion models. Adequate understanding of the strain-rate dependent material response can help in developing predictive models for wear. Single particle impact tests were performed using a high pressure gas gun at the University of Newcastle. Using specialized attachments, particles were impacted on polished ductile samples at velocities up to 200 m s−1. Both angular and spherical particles have been used to demonstrate the material behaviour under high strain-rate conditions. Impact craters were analysed using scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM). SEM analysis was performed to observe the surface phenomena at high strain-rate as well as micro-mechanics of the material removal process. The mechanisms observed are then discussed in light of the theories of elastic and plastic deformation, temperature variation at high strain-rates as well as the response of the flow stress at high strain-rate. Impact craters were analysed quantitatively using the LSCM. Using specialized software, crater depth and deformation volumes were calculated for individual impact craters and different impact velocity and impact angles. Based on the particle impact energy and the material removed, the unit energy for cutting and deformation are determined and compared with the values obtained in standard erosion tests. The difference between the energy factors is discussed with respect to the effects of high strain-rate and temperature increase.

Study of woven fabric shear behaviour

The paper presents the shear frame test with a new method of gripping the fabric sample to describe the shear behaviour of fabrics used in the garment industry under high shear strain conditions (maximum shear angles of 20°). This shear frame test was also used to compare between hysteresis curves given by the Kawabata evaluation system (KES) test, the bias extension test and the shear frame test for 10 woven fabrics. The linear viscoelastic theory was used to analyse the shear relaxation behaviour of the woven fabrics. In addition, in this study, the kernel function of the generalised Maxwell model has been used to describe the viscoelastic properties of the fabrics.

The effect of strain rate on fracture toughness of human cortical bone: A finite element study

Evaluating the mechanical response of bone under high loading rates is crucial to understanding fractures in traumatic accidents or falls. In the current study, a computational approach based on cohesive finite element modeling was employed to evaluate the effect of strain rate on fracture toughness of human cortical bone. Two-dimensional compact tension specimen models were simulated to evaluate the change in initiation and propagation fracture toughness with increasing strain rate (range: 0.08–18 s −1). In addition, the effect of porosity in combination with strain rate was assessed using three-dimensional models of micro-computed tomography-based compact tension specimens. The simulation results showed that bone’s resistance against the propagation of a crack decreased sharply with increase in strain rates up to 1 s −1 and attained an almost constant value for strain rates larger than 1 s −1. On the other hand, initiation fracture toughness exhibited a more gradual decrease throughout the strain rates. There was a significant positive correlation between the experimentally measured number of microcracks and the fracture toughness found in the simulations. Furthermore, the simulation results showed that the amount of porosity did not affect the way initiation fracture toughness decreased with increasing strain rates, whereas it exacerbated the same strain rate effect when propagation fracture toughness was considered. These results suggest that strain rates associated with falls lead to a dramatic reduction in bone’s resistance against crack propagation. The compromised fracture resistance of bone at loads exceeding normal activities indicates a sharp reduction and/or absence of toughening mechanisms in bone during high strain conditions associated with traumatic fracture.

EXPERIMENTAL STUDY ON BRITTLE FRACTURE OF BUCKLING-RESTRAINED BRACES

The authors conceived a buckling-restrained brace providing stable hysteretic characteristic even under high-strain conditions. In the past paper, conducting cyclically static loading tests, the performance evaluation formula of the buckling-restrained brace was presented. The many buckling-restrained braces in practical uses have weldings in the energy absorption area of the core plate. Brittle fracture might be caused, when the welding exists. In this case, the performance of the buckling-restrained brace decreases. In this paper, the specimens with different welding specifications and steel kinds are fabricated. Tensile loading tests are conducted as parameter of temperature. The tensile performance of the specimens with local welding and without welding is almost the same. The other hand, the performance of the specimens with continuous welding reduces.

EXPERIMENTAL STUDY ON BRITTLE FRACTURE OF BUCKLING-RESTRAINED BRACES

The authors conceived a buckling-restrained brace providing stable hysteretic characteristic even under high-strain conditions. Based on the cyclic static loading tests, the performance evaluation formula of the buckling-restrained brace is presented. The buckling-restrained braces in practical uses have welding on the energy absorption area of the core plate. Brittle fracture might be caused at the welding or welding effected zone. In this case, the performance of the buckling-restrained brace would be decreased. In this paper, four kinds of specimens with different welding specifications on the core plates are fabricated. And, cyclic static loading tests are conducted as parameter at temperatures. The performance of the specimens with local welding of well preheating & fishing and without welding is the almost same. The other hand, the performance of the specimens with continuous welding has reduced. Irregularities of weld beads cause brittle fracture in an early stage.

Annealing induced interfacial layers in niobium-clad stainless steel developed as a bipolar plate material for polymer electrolyte membrane fuel cell stacks

Roll-bonded niobium (Nb)-clad 304 L stainless steel (SS) is currently being developed as a metallic bipolar plate material for polymer electrolyte membrane fuel cell stacks. Prior work has shown that post-roll annealing significantly softens the constituent core and cladding materials, enhancing the ductility and formability of each. However under the vacuum annealing condition employed in the previous study (900 s, 982 °C (1800 F)), an interfacial layer was observed to form between the two bonded materials. Subsequent bending and flattening tests indicated brittle failure of this interfacial region under high strain conditions. The present study employs transmission electron microscopy to examine the composition, structure, and thickness of phases generated at the Nb/SS interface as functions of annealing temperature and time. Corresponding selected electron diffraction patterns indicate that above a threshold annealing temperature of ∼950 °C, the formation of (Fe 1− x Cr x ) 2Nb appears to control the failure behavior of the Nb/304 L SS material. Annealing treatments conducted below this temperature generally avoid the formation of this intermetallic layer.

Structural–geological setting of the Elura-Zn–Pb–Ag massive sulphide deposit, Australia

The Elura deposit is located in the Cobar Basin, one of several intracratonic basins developed during Silurian–Devonian time in the central province of the Lachlan Orogen, eastern Australia. The deposit contained a total pre-mining resource of 45 Mt at 8.5% Zn, 5.3% Pb and 69 g/t Ag. The deposit is hosted by an Early Devonian sedimentary sequence, which transits from a shallow-water shelf facies into a deep-water turbidite facies. The host rocks comprise open platform reef limestone, back-reef calcareous mudstone, open platform clastic sediments and distal turbiditic mudstone and siltstone, interbedded with fine-grained sandstone (CSA siltstone). The structural setting of the deposit is at the north–northeastern margin of the half-inverted Cobar Basin, adjacent to the north–northwest trending Elura growth-fault and north–northeast transform–transfer Buckwaroon Fault. These major structures controlled lithofacies distribution during basin formation, flow and focus of metal-bearing fluids during mineralisation, as well as strain distribution during basin inversion. The deposit comprises two mineralised systems: massive sulphide mineralisation hosted in fine-grained turbidites and semi-massive sulphides hosted in limestone. The dominant mineral assemblage in the turbidite-hosted mineralisation is pyrite–sphalerite–pyrrhotite–galena with minor chalcopyrite, whilst mineralisation in the limestone comprises pyrite–sphalerite and minor galena and pyrrhotite. The Elura deposit is interpreted as a syn-diagenetic, replacement massive sulphide deposit formed by mixing of metamorphic fluids derived from basement and basinal brines discharged along the growth-fault. In comparison with other base metal deposits, the Elura deposit is similar to the Irish-type base metals deposits. During basin inversion, the deposit underwent high strain and greenschist metamorphic conditions which caused modification and distortion.

Boundary Mixing Associated with Tidal and Near-Inertial Internal Waves

Abstract Moorings deployed on the south (August–November 2002) and north (November 2002–June 2003) flanks of the Kaena Ridge, Hawaii, are used to document the flow variability associated with mixing within 200 m from the boundary, deep along the ridge, as part of the Hawaii Ocean Mixing Experiment (HOME). At both sites, strong temperature inversions are detected with vertical scales of ∼100 m. A Thorpe-scale analysis of the overturns yields a time-averaged dissipation near the bottom at the south site (1.2 × 10−8 W kg−1) that is 10 times higher than the north site (1.9 × 10−9 W kg−1), with both higher than the dissipation at similar depths 30 km from the ridge. On the south flank, observed horizontal currents and vertical displacements are dominated by the semidiurnal internal tide. On the north flank, the semidiurnal tide is less energetic than on the south, with a different vertical structure as tidal amplitudes decrease toward the boundary. These differences are attributed to greater separation from the bottom of downward-propagating internal tides at the north site compared to the south site, resulting in higher mixing at the south site. Near the boundary, near-inertial to diurnal oscillations are more energetic at the north than the south site. This asymmetry is attributed to near-inertial internal waves that are generated north of the ridge by winter storms; the ridge shadows the equatorward-propagating near-inertial internal waves leading to negligible amplitudes on the southern lee side. The near-inertial waves combine with internal tidal motions to create high strain conditions that lead to mixing at the north site.

Improvement of the Fatigue Characteristic of AZ31 Magnesium Alloy by Microstructures Control

High-strain conditions as a means of microstructure control have recently been investigated to improve the ductility and enhance the strength of magnesium alloys. The level of superplastic deformation and the fatigue properties of the wrought materials have also been studied. In comparison, only a small number of such reports are available on cast materials. As a part of the search for applications of magnesium alloys, comparisons of structural changes and mechanical properties should be made between wrought and cast materials. In the present study, the grain refinement of cast and extruded materials made from commercially available AZ31 magnesium alloy was conducted using a multi-axial alternative forging method. The relationships between the structural changes and working processes and the relationships between changes in the mechanical properties as well as grain sizes and fatigue properties are discussed. Both the cast and the extruded materials tended to exhibit uniform crystalline structures with an increasing number of working cycles. Dynamic recrystallization was observed during both working and static recrystallization during both reheating and holding. When an equivalent strain of 0.6 was applied, the localized formation of ultra-fine grains of 0.5 μm was observed. The tensile strength and yield stress had maximum values in the initial stage of the multi-axial alternative forging. Although ductility improved with higher numbers of working cycles, the strength decreased. This can be explained by the dynamic and static recrystallization processes and work softening.

Finite Element Simulation of High-Speed Cutting Alloy Cast Iron

A finite element model (FEM) of high-speed cutting was built to study the mechanism of high-speed machining of alloy cast iron used widely in auto panel dies. The mechanics properties of workpiece material were obtained in the conditions of high strain-rate, high temperature and high strain through high-speed impact compress experiments. Several key technologies are studied such as friction and chip-tool heat conduction. The cutting temperature, stress distribution, and the chip formation process in the process of high-speed cutting alloy cast iron were analyzed based on the finite element model, which was validated through cutting force experiments. It shows that the FEM can simulate the high-speed cutting process of alloy cast iron materials.

Assessment of Fragment Micromotion in Distal Femur Fracture Fixation with RSA

To assess fragment micromotion in three fracture fixation constructs 18 composite femur models were sectioned to create AO-C3 fractures and fixed using the Less Invasive Stabilization System (LISS), Dynamic Condylar Screw (DCS), or the Condylar Buttress Plate (CBP). Tantalum beads were attached to each fracture fragment. The constructs were tested for permanent deformation after cyclical loading (amplitude = 242.2N) and elastic deformation during static loading with 490.5N. Radiographs were taken before loading and then after unloading to determine permanent deformation or during loading to determine elastic deformation. We used RSA to quantify the six degrees of freedom interfragmentary maximum total motion, strain, and stress. For maximum total motion the CBP had more permanent deformation and two failures, whereas the LISS underwent the greatest elastic deformation. LISS and CBP had the highest strain conditions in the fracture gap and LISS had the greatest stress movements between fragments, all of which exceeded the upper limits for bone healing. LISS and CBP may not be indicated for comminuted fractures due to the high degree of flexibility of the LISS, resulting in high stress and strain conditions and susceptibility to catastrophic failure and high strain conditions with the CBP.

Modeling Misfit Dislocation Arrays for the Growth of Low-Defect Density AlSb on Si

ABSTRACTWe present analytical models and experimental results to describe low-defect density growth (∼ 6 × 105/cm2) of highly mismatched antimonides on Si and GaAs substrates, with strain relief achieved at the growth interface through periodic, 90° interfacial misfit dislocations (IMF). We use molecular mechanics (MM) based modeling techniques to understand, at the atomic level, the spontaneous formation and energetics of these IMF. We have modeled, grown and characterized two systems extensively, these are - AlSb on Si with ∼ 13% mismatch and GaSb on GaAs with 7.83% lattice mismatch. Growth of these materials by molecular beam epitaxy (MBE) and subsequent High-Resolution Transmission Electron Microscopy (HR-TEM) has indicated that there is no tetragonal distortion in these two systems despite the high lattice mismatch. Instead, the mismatched epi-layers spontaneously form periodic IMF arrays that run along both [110] and [1-10] directions and relieve almost 100% of the strain in a few monolayers of deposition. To model this form of strain relief, we use existing theories of strain relief adapted for very high strain conditions and we also use bond energetics to model the strain-relieving interface. The IMFs in these systems are periodic and so is the deviation in bond lengths and bond angles, which restricts our calculation space to a finite number of elements. We shall also demonstrate extensive growth and characterization results of the materials grown with a particular emphasis on the strain-relieving interface to show excellent agreement of the experimental data with the proposed models. The high quality and low-defect density in AlSb grown on Si, has helped us demonstrate optically pumped IR VCSELs and edge emitters monolithically on Si (001) and this data will also be presented.

Effect of an overheating temperature on cyclic isothermal stress-induced transformations in single crystal Cu–13.3Al–4.0Ni (wt.%) shape memory alloys

Motivated by eventual applications as high temperature actuators, cyclic isothermal stress-induced transformations of Cu–13.3Al–4.0Ni (wt.%) single crystal wires with stress-free transformation temperatures: M f = 80 °C, M s = 100.5 °C, A s = 104.5 °C and A f = 117 °C were studied under the two adverse conditions of high overall strain (9%) and an overheating temperature (175 °C for 30 min). Wires were subjected to isothermal stress cycling at 25 °C using an Instron testing machine with environmental chamber until fairly repetitive stress–strain response was obtained. These tests were repeated on the same specimen at progressively higher temperatures of 40, 60, 80 and 100 °C. It is seen that the initial cyclic response is primarily shape memory whereas the subsequent cyclic response is primarily pseudoelastic, attended by some residual inelastic deformation. Tests on a different virgin specimen at 100, 120, 140 and 160 °C showed a similar trend. This points to the possibility of a downward shift in the stress-free transformation temperatures. Possible reasons are generation of dislocations as well as the domination of α-martensites over β-martensites due to the overheating temperature and stress cycling. The effect of stress cycles on overall strain on full loading, after unloading and after heating in between stress cycles has been discussed.

The First Observation of a Shear‐Induced bcc→fcc Transformation in Nanocrystalline Ferrite

Ferrite has been transformed to austenite at room temperature in an initially pearlitic steel. This occurs under high shear strain conditions once the alloy has been grain‐refined down to a nanoscale dimensions by high‐pressure torsion deformation. This transformation must have occurred by a martensitic mechanism and plays the role of an additional deformation mechanism for the nanostructured material.

FLOW STRESS DATA FOR FINITE ELEMENT SIMULATION IN METAL CUTTING: A PROGRESS REPORT ON MADAMS

ABSTRACT To obtain reliable results from Finite Element (FE) simulation of machining processes, it is necessary to have as input the properties of the workpiece and tool materials as well as the characteristics of the tool/chip interface. These input parameters include physical and thermal data, friction and heat transfer, and most importantly the flow stress of the workpiece material under high strain, strain rate and temperature conditions that exist during the process. This paper presents a brief review of FE simulation of machining processes, a review of the approaches used to determine the flow stress at high deformation rate, and the examples of different constitutive equations used to represent such flow stress data. A material property database (MADAMS) has been developed and provides useful information to conduct simulations of machining processes. The main objectives of the material database are to assist researchers in areas of machining analysis and material modeling and to promote collaboration between various international research groups.

Compositional variations of syntectonic white-mica in low-grade ignimbritic mylonite

The Silla del Gobernador Shear Zone (SGSZ), Coastal Range of central Chile (32°S), is a low-grade mylonite generated from a Triassic acidic ignimbritic protolith. Different microstructures (e.g. quarter mats and pressure shadow structures) associated with pressure solution and solution transfer processes and well-preserved porphyroclasts can be observed. White-mica generation appears to be favoured by reaction-softening from dissolved quartz and feldspar porphyroclasts. According to the mylonite fabrics three different types of white-mica can be established (A, B and C) representing mylonites with evidences of relatively low, intermediate and high strain conditions. Deformation mechanisms suggest low-grade (350–400 °C) conditions for mylonitic deformation in the presence of fluids, consistent with the temperature estimations based on chlorite chemistry. The geological setting of the SGSZ also suggests low-pressure (<3 kbar) conditions. No major element mobility with respect to protolith composition was observed in low-strained mylonites, whereas for the highly strained mylonites, a marked K 2O secondary input and higher fO 2 conditions during deformation are suggested. The chemical composition of the neoformed white-mica correlates with strain intensity: the high-strained mylonites contain phengitic–celadonitic micas, whereas low-strained mylonites have paragonitic and muscovitic micas. White-mica geobarometry in highly deformed rocks yields pressure values with no geological significance, because the metasomatic K-input favour their high K content, independent of the confining pressure. Thus, the white-mica composition in the mylonites of the SGSZ is controlled by the whole-rock geochemistry and is related to strain conditions.

Fast-start muscle dynamics in the rainbow troutOncorhynchus mykiss: phase relationship of white muscle shortening and body curvature

Muscle length changes of the lateral myotomal fast fibers of rainbow trout (Oncorhynchus mykiss) were measured using sonomicrometry during induced fast-starts. Simultaneous high-speed videography allowed for the analysis of midline kinematics to estimate the degree of muscle strain that occurs during body deformation. Comparison of these data was used to examine the phase relationship between local muscle shortening and local body bending during unsteady, large amplitude maneuvers. Our analysis finds that muscle shortening is temporally decoupled from body bending, probably due to the influence of hydrodynamic forces. The phase shift was such that midline curvature lagged behind muscle shortening at both the anterior (0.4 L, where L is fork length) and posterior (0.7 L) axial positions. Stronger escape responses were correlated with high peak strains and rapid strain-wave velocities, but not faster curvature-wave velocities. Under these conditions of high strain, the phase shift at the posterior position is significantly increased, whereas the anterior position fails to be affected. Curvature lag was still observed at both axial locations under conditions of low strain, suggesting that hydrodynamic forces are still significant during weaker escape responses. These data support a previous model that suggests fast-start body bending is determined by the interaction between muscle torque and hydrodynamic resistance along the body.

Continuity Plate Detailing for Steel Moment-Resisting Connections

The 1994 Northridge, California earthquake resulted in the fracture of complete-joint-penetration groove (CJP) welds connecting girder flanges to column flanges in steel moment-resisting connections in a number of steel frame structures ranging from one to 26 stories in height (FEMA, 2000a). These welds fractured due to a combination of reasons, including the weld material having low fracture toughness; the pre-Northridge connection geometry making the CJP welds more susceptible to high strain and stress conditions; and welding practices that resulted in inconsistent weld properties (FEMA, 2000a). As a result of these fractures, in the subsequent years there has been a tendency to be more conservative than necessary in the design and detailing of steel moment-resisting connections both in seismic and non-seismic zones within the United States. In particular, continuity plates and web doubler plates have often been specified when they are unnecessary and, when they are necessary, thicker plates have been specified than would be required according to the applicable specifications. In addition, the welds of the continuity plates to the column flanges have often been specified as being complete-joint-penetration groove welds, even though the use of more economical fillet welds may have sufficed. This paper has given the background of the local web yielding and local flange bending limit states and the conclusions of previous researchers regarding the behavior of continuity plates and the welds attaching them to columns. It has also summarized the results of nine pull-plate tests and corresponding finite-element analyses studying column-stiffening details. The preliminary conclusions from these tests are focused on monotonic loading applications and will be synthesized with future cyclic loading experiments, with implications for seismic design, in Lee and others (2002) and other ongoing research.

An electron microscopy study of deformation microstructures in granitic mylonites from southwestern Sweden, with special emphasis on the micas

The lithology, age, geological setting, structural and metamorphic history of the granitic mylonites from the Mylonite Zone (MZ) in southwestern Sweden have been studied extensively. The deformation history, growth of microstructures, intensity of deformation, changes in mineral compositions, and pressure-temperature conditions of deformation have, however, not been addressed. In this study, powder X-ray diffraction, optical microscopy, electron microprobe analysis and transmission electron microscopy of micas, chlorite, and plagioclase are combined to understand the physical and textural changes experienced by the rocks during mylonitization. It is shown that the occurrence of foliated micas in shear bands, recrystallization of quartz and biotite, and undulatory extinction in quartz grains were not uniform throughout the samples studied. Occurrence of dislocations and low-angle grain boundaries confirm that deformation occurred largely by glide dislocations. The low-angle grain boundaries observed are formed by the re-arrangement of these dislocations during grain size reduction processes. The micas show a high degree of spatial stacking order, but spatial stacking disorder in micas and chlorites has also been found. Ordered stacking faults are formed during low strain while disordered stacking faults are formed under high strain conditions. Occurrence of both ordered and disordered stacking faults indicates that the intensity of deformation was not uniform through the entire MZ. Moreover, the chemical composition of plagioclase shows that the exsolution lamellae observed with optical and electron microscopy are due to Ca-subsolidus reactions during low temperature deformation. Several substitution reactions occurring in the micas indicate that deformation took place between 0.3 and 0.4 GPa, at a temperature higher than 500degreesC. (Less)