Search

Copyright of Iron Steel Vanadium Titanium is the property of Iron Steel Vanadium Titanium Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Laminated glass is extensively used in automotive windshields, making it crucial to have a comprehensive understanding of its fracture mechanism to ensure driver and pedestrian safety in various windshield impact scenarios. Current research on the cohesive zone model of glass impact failure has encountered challenges related to accuracy and computational efficiency. This paper addresses these issues by utilizing the finite element software LS-DYNA, which integrates a cohesive zone model and thick shell (Tshell) elements to simulate and analyze the impact failure process of laminated glass. The combination of Tshell and cohesive elements was validated using a DCB example. Subsequently, the proposed method was applied to simulate the impact damage on an automobile's front windshield, providing valuable insights from the obtained results. Finally, the influence of curvature, the number of layers, and the thickness ratio of each layer were investigated, leading to some valuable conclusions. Firstly, an increase in the thickness of the upper glass layer correlates with a decrease in the peak acceleration of the dummy-head model due to the ductility of PVB material. Secondly, when a curvature exists, the arched configuration of the windshield promotes higher resistance against impact, consequently leading to increased peak acceleration. [ABSTRACT FROM AUTHOR]

The effects of retained austenite on the crack propagation behavior of a submicron-structured bainitic steel under impact fracture were studied. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron back-scattering diffraction (EBSD) were employed to characterize the size, distribution, and quantity of the matrix structure, and the microstructure of the impact fracture samples under conditions of two different bainitic processes. The retained austenite content at 280 °C was higher than that at 320 °C, and the microstructure appeared more uniform and refined, resulting in better impact toughness. The martensite + retained austenite constituents took part in the initiation of the fracture process and the crack ended at film of retained austenite. During fracture, a mixture of brittle, hard block martensite + retained austenite was easy to induced a crack opening. The effect of the transformation-induced plasticity of the retained austenite with a small block and film can effectively cause passivity and even inhibit crack growth.

The load-bearing capacity of a CC(T) specimen (Center-Cracked Tension) in the ductile fracture regime is usually controlled by plastic collapse. If the material’s tearing resistance is sufficiently low, the load-bearing capacity can drop below the plastic collapse value. Here, a recently developed simple fracture mechanics-based Charpy-V impact energy criterion for plastic collapse was used to provide a best estimate assessment of the CC(T) specimen load-bearing capacity.

The integrity of concrete structures under strong earthquakes and the stability of concrete structures with cracks are concerns of national security strategies.These two issues are closely related to the time-dependent fracture behavior of concrete.The time-domain dependent fracture behavior of concrete can be generalized into two aspects: short-term impact fracture under dynamic impact load and long-term steady-state creep fracture failure.Although they both are related to time, there is a huge difference in the loading time, which leads to the different internal mechanism of dynamic failure in concrete.Herein, the development history and main achievements of time-dependent fracture model of concrete are reviewed, including macroscopic fracture mechanics model and method, mesoscopic fracture mechanics model and method, dynamic fracture, and creep fracture behavior of concrete.

The goal of the performed experiments was to assess the effect of ion bombardment on the mechanical properties of α-quartz. The 40 keV Ar+-ions were implanted with fluences of 1014 and 1016 ion/cm2 were used. The accumulation of broken interatomic bonds in the sample surface layer was traced with the reflectance IR spectroscopy. The sample surface was subjected to the localized impact damaging by a pointed striker prior to and after the Ar+ implantation. The fractoluminescence (FL) excited in damaged samples was recorded with a 20 ns resolution during 1 ms. The statistical analysis of the energy distributions in impact-induced FL time series detected in unirradiated samples showed a random accumulation of newly formed point defects. The FL energy distributions in the ion-implanted samples followed a power law typical for the fracture of heterogeneous solids such as rocks, ceramics, etc. [ABSTRACT FROM AUTHOR]

The percentage of shear fracture largely determines the service performance of 9Ni steel used in low-temperature pressure vessels. Through elemental analysis, microstructural characterization, and mechanical property tests, this study investigates why the percentage of shear fractures is low in 9Ni steel and clarifies the mechanism by which the microstructural characteristics influence the low-temperature impact behavior of 9Ni steel. It was found that cleavage fracture zones, formed when segregation bands appear in the microstructure, decrease the percentage of shear fractures at the impact fracture surface. Specifically, as the segregation area increases from 0.9% to 7.1%, the shear-fracture percentage in 9Ni steel sharply decreases from 100% to 65%, accompanied by a deterioration in low-temperature toughness. The segregation zone is enriched in austenite-forming elements (Ni, C, Mn), leading to a tempered martensite microstructure with a lath shape. The small number of high-angle grain boundaries and low interface bonding strength cannot effectively prevent crack initiation and propagation, resulting in brittle cleavage fracture. In contrast, the non-segregated zone is tempered sorbite with a uniform structure, several high-angle grain boundaries, and a high interface bonding strength. These features hinder crack initiation and propagation. Furthermore, the shear-fracture zone generated in the non-segregated zone exhibits ductile fracture characteristics.

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The study of palaeopathology provides valuable information about injury and behaviour in extinct organisms. Appendicular pathologies are interesting as they directly affect mobility and therefore the ability of an animal to survive. Here, the injuries recorded in the left pes of the neornithischian Othnielosaurus consors are described. The implications of these injuries in its behaviour are also discussed. Othnielosaurus shows pathological features in all its pes digits, with three types of pathologies have been identified: calcium pyrophosphate deposition disease (CPPD), and pilon and impact fractures. Calcium pyrophosphate deposition disease is visible on the articular surface of phalange II-3 as a small osseous plaque. A pilon fracture is evidenced by the growth of callus tissue on the shaft of the phalange I-1 and demonstrates healing before death. The impact fractures are identified as a focal subsidence on the articular surfaces of phalanges III-1 and IV-4, which are partially healed. Perhaps the suite of palaeopathologies encountered would generate pain and discomfort when walking, which probably resulted in a limp that would have impacted on its lifestyle. Finally, the fact that the fractures are in different stages of healing would suggest that impact fractures could have contributed to the death of the individual. [ABSTRACT FROM AUTHOR]

Accumulation of microcracks in response to point impact damage in MgAl2O4 ceramics doped with Cr3+ ions has been studied using acoustic emission measurements. The results demonstrate that the maximum crack length at a higher chromium concentration in the ceramics is smaller than that at lower doping levels. By contrast, doping with LiF (in addition to Cr3+) reduces the decrease in microcrack length caused by chromium oxide. [ABSTRACT FROM AUTHOR]

The peridynamic theory is advantageous for problems involving damage since the peridynamic equation of motion is valid everywhere, regardless of existing discontinuities, and an external criterion is not necessary for predicting damage initiation and propagation. However, the current peridynamic modeling methods utilize regular or quasi-regular lattice structures, which poses difficulties in modeling laminated structures with alternating thin interlayers and thick ply layers. This study proposes an extended version of a nonlocal ghost interlayer model for simulating laminated structures with multi-body interactions. Using numerical studies, the proposed numerical schemes are verified. It is further confirmed that the proposed schemes are valid for simulating the high-velocity impact fracturing behavior of laminated glass. [ABSTRACT FROM AUTHOR]

• An ECC-concrete composite beam with a fully-discrete model, taking into account the cementitious matrix and concrete softening characteristics, has been established. • An energy-based interface model using the peridynamic method has been established. • The effects of factors such as fiber volume fraction, ratio of ECC layer thickness, impact velocity, and fiber length on the performance of an ECC-concrete composite beam considering the strain rate effect under impact loading have been analyzed. Engineering cement-based composite materials (ECC) are widely used for strengthening concrete structures and resisting impact loads. However, the impact failure process of materials involves the material discontinuity. To address this issue, this paper constructs a fully discrete model of ECC concrete composite beams under impact loads based on peridynamics (PD). In this model, the cement matrix is described using an exponential model, while the fibers are modeled using PD rods. The interaction between the fibers and the matrix is described based on the classical exponential friction attenuation model, while considering failure criteria based on strain rate effects. Finally, by employing the established model, the effects of impact velocity, fiber volume fraction, ECC layer thickness ratio, and fiber length on the impact performance of ECC concrete composite beams were investigated. Results showed that impact velocity affects the damage evolution and crack propagation mode of the composite beams by affecting the dynamic critical elongation of PD bonds. The fiber volume fraction, ECC layer thickness ratio, and fiber length all have important effects on the ductility and energy absorption capacity of composite beams. [ABSTRACT FROM AUTHOR]

A computational method in the impact fracture behavior simulation for laminated safety glass is presented using the discrete element (DE)/finite element (FE) surface-center coupling method and cohesive model. Automotive laminated glass is an important component of vehicle safety system, it consists of two glass sheets bonded with a polyvinyl butyral film. It is directly related to the safety of passengers and pedestrians. In-depth research and analysis of the failure mechanism of this glass is of great engineering significance. Drop hammer tests wire conducted to evaluate the simulation results. The DE/FE surface-center coupling method and cohesive model are shown to be capable of simulating the impact failure characteristics of laminated glass. The results would be instrumental for simulation and analysis of automotive collision safety and pedestrian protection as regard to the damage of automotive windshield. [ABSTRACT FROM AUTHOR]

In this work, the impact fracture of coarse grain heat-affected zone (CGHAZ) of an X80 steel weld with various heat inputs was investigated in the absence and presence of hydrogen (H)-charging by metallographic characterization, microhardness and impact testing, electrochemical H permeation measurements. The results show that, as the heat input (HI) during welding decreases, the microstructure of the CGHAZ changes from granular bainite (GB) to lath bainite (LB). When the LB content exceeds 70%, the microhardness of the material increases remarkably. For H-free specimens, the fracture surface transforms from ductile to brittle fracture at the HI of 29.2 kJ/cm. Upon H-charging, the fracture surfaces show brittle transgranular cleavage fracture when the HI is 18.1 kJ/cm. The H atoms decrease the threshold HI where a brittle fracture occurs. Compared with the GB microphase, the LB-containing microstructure requires a higher H concentration to cause transgranular impact brittle fracture. [ABSTRACT FROM AUTHOR]

In this study, in order to investigate the influence of Cr element on the impact fracture process of ductile Ni-resistant alloyed iron at low temperature, different contents of Cr element were added to ductile Ni-resistant (DNR) austenitic alloyed iron. The experimental results show that Cr addition can increase the hardness of the DNR alloyed iron, but it has an destructive effect on low-temperature impact properties. Through the analysis of the dynamic load and absorbed energy of samples with different Cr contents in the impact fracture process, and the comparison of the impact fracture process at room and low temperatures, it reveals that Cr addition into the DNR alloyed iron can facilitate the formation of the carbide mixture in Mn23C6 and Cr23C6 with homogeneous and discontinuous distribution. Meanwhile, Cr addition also can improve the the maximum dynamic load and crack initiation energy at low temperature, but has no obvious effect on the yield behavior of the DNR alloyed iron in the impact fracture process. Compared with the impact crack propagation process at room temperature, the metastable propagation energy at low temperature declines significantly with an increase in Cr content. This is because the micro-cracks that caused by the carbides weaken the matrix, resulting in the decline of impact crack propagation resistance. The fracture analysis results also show that the impact fracture mechanism gradually transforms from ductile to brittle with an increase in Cr content at low temperature. It explains that too much Cr addition can lead to brittle fracture even though the austenitic matrix has a good toughness at low temperature.

Laboratory testing data concerning the full sized laminated glass panel with different glass make-ups under impact is limited. An experimental investigation on the impact resistance of LG panels under hard body impact is reported in this paper. A test approach namely, mean minimum breakage velocity approach, is adopted to capture the minimum impact energy that triggers each glass breakage. The crack morphology of glass panels is firstly investigated. Results indicate that the intersection angle of the radial crack edges increases when the strengthening level of glass decreases. The impact resistance is then revealed by investigating the effects caused by three design variables, i.e., the glass types, interlayer thickness and interlayer types. It reveals that the configuration with inner HS glass and outer FT glass panel can provide better impact resistance, and performs better in keeping initial stiffness under repeated impacts with higher impact velocity. In the contrast, placing HS glass in the both side may weaken the impact resistance. A 1.52 mm PVB interlayer can provide better impact resistance and higher initial stiffness when compared to a thicker interlayer, it is more likely to produce stiffness degradation between consecutive breakages as well. The difference of SGP LG and PVB LG in MMBV is found to be negligible, however, SGP LG exhibits evidently higher initial pre breakage stiffness and remains greater post breakage strength.

In this research, failure mechanisms of carbon fiber reinforced polymer (CFRP) wrapped protective arches under static and blast loadings were investigated through experiments. Adopting bonding and partially-wrapping scheme, the plain concrete (PLC) arch is strengthened and its load carrying ability achieves the level of steel bar reinforced concrete (RC) arch in the static loading experiment. Adopting bonding and fully-wrapping scheme, it’s akin to apply hollow CFRP tubular arch to reinforce plain PLC arches. Load carrying capacity of the CFRP composite arch achieves twice as much as that of the RC arch and the composite arch fails in a shear mode. Subjected to explosive loading, anti-blast ability of the CFRP tubular concrete arch is much better than the PLC arch. Critical scaled distance to prevent the arch from dynamic broken is considerably reduced. According to the research, it is confirmed that using the composite technique an efficient composite protective arch structure can be constructed and steel reinforcements can be entirely replaced by CFRP in some cases, such as coastal engineering and anti-blast structures. [ABSTRACT FROM AUTHOR]

This study focuses on an investigation of the fracture behavior of zeolite-HDPE composites after annealing treatment under atmospheric pressure. Annealing processes were carried out at various holding time (12, 24, 36, and 48 hours). The fracture toughness of composites was investigated based on the essentia! work of fracture (EWF) concept, and the surface morphology of composite was evaluated using scanning electron microscope (SEM). The results show that the essential work of the fracture increases with the increase of the holding time of annealing process up to 36 hours. However, all tested materials exhibit negative values in term of non-essential fracture work. The outer plastic deformation zone cannot be observed around the ligaments of the fracture propagation pathway on the surface of the broken sample. Thus, all the fracture energy was used to create a new fracture surface in the inner fracture process zone. [ABSTRACT FROM AUTHOR]

As an important component of a vehicle, the automotive windshield glazing normally consists of two glass sheets bonded with one polyvinyl butyral (PVB) film. In the context of pedestrian-vehicle accidents, the impact cracking mechanism of the windshield is conductive to pedestrian safety protection and traffic accident reconstruction. The purpose of this paper is to validate the capacity of the intrinsic cohesive zone model (CZM) in impact fracture simulations of a windshield. A windshield finite element (FE) model is established, where cohesive elements are inserted into all the common faces between glass hexahedral finite elements. The fracture behavior of a windshield impacted by a standard adult headform impactor is simulated with the commercial explicit finite element code LS-DYNA. Numerical simulation results are validated by comparison with the corresponding experimental outcomes. For comparison, additional simulations have been performed by the widely used element deletion method (EDM) with a plasticity strain failure criterion. Simulation results show that the intrinsic CZM is more suitable to capture the impact failure characteristics of windshield. Finally, the effects of the glass cohesive strength, mechanical properties of PVB and interfacial adhesion on the impact fracture behavior of the windshield are investigated. [ABSTRACT FROM AUTHOR]

Although the Charpy impact test has been routine for decades to assess the ductile or brittle nature of materials, the impact toughness, which is strongly sample-thickness dependent, is not an intrinsic property. By re-examining the energy absorption during fracturing of relatively high strength alloys, here we find a remarkably good linear relation between the impact energies and the fracture surface areas of samples with different thickness, and the slope essentially renders the intrinsic impact toughness. The new findings, which also provide a scaling law to well predict the thickness effect on the traditional impact toughness, may have broad applications for precisely determining the ductile-to-brittle transition temperature of small-dimensional devices, selecting materials according to their toughness at the thickness in usage, and evaluating the intrinsic toughness of emerging high strength materials with limited achievable size. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study on the available numerical approaches for modelling the fracturing of brittle materials. These modelling techniques encompass the finite element method (FEM), extended finite element method (XFEM), discrete element method (DEM) and combined finite-discrete element method (FEM/DEM). This study investigates their inherent weaknesses and strengths for modelling the fracture and fragmentation process. A comparative review is first carried out to illustrate their fundamental principles as well as the advantages for the modelling of cracks, followed by the state-of-the-art trial application in the example cases. An example of a glass beam subjected to low velocity hard body impact is examined as a plane stress problem. By evaluating the applicability of different models, the most desirable model for the entire dynamic fracture response is identified, and this is found to be the FEM/DEM. The FEM/DEM model is further examined by comparing results with the experimental data from high velocity and oblique impact tests. The study reveals that the FEM/DEM yields the most satisfactory results when modelling the dynamic fracture process of brittle materials such as glass. [ABSTRACT FROM AUTHOR]

This study takes an experimental and comparative approach in order to evaluate the circumstances driving the deployment of microlithic tool technologies by food-producing mobile herders during the Mid-to-Late Holocene in southern Kenya. The predominately obsidian microliths used by contemporaneous, but culturally distinct, herding communities were replicated and used as arrow tips in archery experiments and within composite knives used in animal processing. This allowed for patterns of damage associated with production, different forms of projectile use, and butchery to be identified on microlithic specimens and evaluated against each other to assess the criteria for diagnostic macrofracture and wear patterns reflective of each activity. Experimentally generated criteria were used to identify the most likely functions for microlithic tools in three archaeological assemblages belonging to early Kenyan pastoralists. The analyses showed that while the same microlithic form is shared by culturally distinct groups across a wide time range, these tools were being used to vary different functions that do not clearly correlate with subsistence economy, culturally affiliation, or time period. Environmental variability and instability throughout the Late Holocene likely contributed to the persistence of highly adaptable microlithic toolkits. These data contribute to ongoing dialogues on the emergence and evolution of microlithic toolkits. [ABSTRACT FROM AUTHOR]

This paper studies the impact fracture behavior of the 14%Cr Oxide Dispersion Strengthened (ODS) steel (ODM401) after high temperature exposures in helium and air in comparison to the as-received state. A steel bar was produced by mechanical alloying and hot-extrusion at 1150 °C. Further, it was cut into small specimens, which were consequently exposed to air or 99.9% helium in a furnace at 720 °C for 500 h. Impact energy transition curves are shifted towards higher temperatures after the gas exposures. The transition temperatures of the exposed states significantly increase in comparison to the as-received steel by about 40 °C in He and 60 °C in the air. Differences are discussed in terms of microstructure, surface and subsurface Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) observations. The embrittlement was explained as temperature and environmental effects resulting in a decrease of dislocation level, slight change of the particle composition and interface/grain boundary segregations, which consequently affected the nucleation of voids leading to the ductile fracture. [ABSTRACT FROM AUTHOR]

A set of heterogeneous and homogeneous materials differing in their brittle and ductile characteristics (granite, marble, silica ceramics, silicon carbide, organic glass) were subjected to impact damaging by a falling weight. Multiple chemical bond ruptures produced by elastic waves propagating from a damaged zone were accompanied by the photon emission generated throughout the sample (tribo- or fractoluminescence, FL). The statistical analysis of the FL time series detected with high resolution (10 ns) showed that the energy release distributions in brittle solids follow the power law typical for the correlated nucleation of primary defects. At the same time, the formation of damaged sites in ductile materials (marble and organic glass) was found to be fully random.

Automotive laminated glass is generally composed of two pieces of outer glass layers and one piece of polyvinyl butyral (PVB) interlayer. Its impact fracture behavior is very important to the safety of drivers, passengers and pedestrians. The objective of this work is to numerically investigate the impact fracture behavior of laminated glass via an intrinsic cohesive model (CM). To achieve this end, we propose a laminated glass model by inserting cohesive elements on all common surfaces of solid finite elements (FEs) in glass layers prior to simulations and describing the nonlinear characteristic of PVB by using the generalized Mooney-Rivlin (MR) model. Besides, the difference between this MR model and another one commonly used MR model is investigated. Then, the impact fracture process of a laminated glass plate is simulated, and the proposed approach is verified by comparing the numerical results with the corresponding experimental observations. Afterwards, parametric studies are performed to investigate the influence of the cohesive penalty stiffness and the strength of glass. Finally, the effects of the stiffness of the PVB film, the support conditions and the thicknesses of glass layers on the impact force history, the cracking and the kinetic energy loss of the impactor are investigated. [ABSTRACT FROM AUTHOR]

This work describes the fracture behaviour of the 14Cr ODS steel produced by mechanical alloying process, after high temperature exposures. Small specimens were exposed to helium gas in a furnace at 720 °C for 500 h. Another set of specimens was exposed to flowing liquid lead in the COLONRI II loop at 650 °C for 1000 h. All specimens were tested for the impact and tensile behaviour. The impact test results are compared to other sets of specimens in the as received state and after isothermal annealing at 650 °C for 1000 h. The impact curves of the exposed materials showed positive shifts on the transition temperature. While the upper shelf value did not change in the Pb exposed ODS steel, it significantly increased in the He exposed one. The differences are discussed in terms of surface and subsurface microscopy observation. The embrittlement can be explained as the effect of a slight change in the grain boundary and size distribution combined with the depletion of sub-surface region from alloying elements forming oxide scale on the surface. [ABSTRACT FROM AUTHOR]

This study presents both experimental testing and phenomenological mesomodeling for composite laminates under high-velocity impact. First, we conducted high-velocity impact tests on CFRP laminates and investigated the penetration and damage behaviors. Three kinds of internal damage were observed: fiber breakage, matrix cracking, and delamination. The observed matrix cracks were classified into two categories: multiple (diffuse) cracks around the impact point and large (dominant) cracks on the bottom ply. A phenomenological mesomodel was then developed based on these experiment observations. In the presented model, both continuous and discrete damage models were implemented for modeling two crack configurations. For comparison, we presented two conventional models (one using only the discrete damage model, and the other using only the continuous damage model). To validate the presented model, high-velocity impact simulations were performed, and the predicted results were compared with experiment and conventional models in terms of the damage area and distribution. [ABSTRACT FROM AUTHOR]

Radiography remains pivotal to the workup of instability lesions of the shoulder, both in the acute as well as the chronic settings. The goal of radiography is to detect osseous abnormalities and locate them in order to determine the direction of instability. In antero-inferior instability, Hill-Sachs lesions are often visible at radiography and should not be confused with various differential diagnoses, which are usually more laterally located. Bankart lesions are more difficult to detect on conventional radiography, but there are less false positives than for Hill-Sachs lesions. The Garth view represents an excellent radiographic view to detect antero-inferior instability impaction fractures at both the humeral and glenoid sides. Accurate quantification of bony abnormalities and detection of lesions to the soft-tissue stabilizers of the shoulder however require advanced cross-sectional imaging techniques.

This paper studies the impact fracture behavior of the 14%Cr Oxide Dispersion Strengthened (ODS) steel (ODM401) after high temperature exposures in helium and air in comparison to the as-received state. A steel bar was produced by mechanical alloying and hot-extrusion at 1150 °C. Further, it was cut into small specimens, which were consequently exposed to air or 99.9% helium in a furnace at 720 °C for 500 h. Impact energy transition curves are shifted towards higher temperatures after the gas exposures. The transition temperatures of the exposed states significantly increase in comparison to the as-received steel by about 40 °C in He and 60 °C in the air. Differences are discussed in terms of microstructure, surface and subsurface Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) observations. The embrittlement was explained as temperature and environmental effects resulting in a decrease of dislocation level, slight change of the particle composition and interface/grain boundary segregations, which consequently affected the nucleation of voids leading to the ductile fracture.

• Experiments were conducted to investigate the NiTi dynamic fracture behaviors. • The micro features of the fracture surface under an impact loading were revealed by the electron microscope. • A novel constitutive model based on the Boyd and Lagoudas formulation was proposed. • The dynamic fracture behaviors of NiTi can be well predicted by using the constitutive model and cohesive elements. • The effects of grain size on intergranular fracture toughness were characterized. The mechanical behaviors of NiTi shape memory alloy under the impact loading raised many interests in the fields of engineering and science, whereas its fracture process has not been well understood so far. In this work, multi-scale experiments and numerical simulations were conducted to comprehensively study the dynamic fracture performances of NiTi alloy. The impact crack experiments were carried out with the utilization of split Hopkinson compression bar, which showed the variation of crack propagation rate versus impact velocity. The Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) were employed to observe the fracture surfaces. The micro images revealed that the fracture behaviors were manifested as quasi-brittle fracture features. By taking the plastic evolution into consideration, a novel constitutive model based on Boyd and Lagoudas phase transition formulation was proposed, which overcomes the limitation of simultaneously describing super-elastic and plastic behaviors of NiTi. With the novel constitutive model, the crack propagation process was accurately reproduced with numerical results in good agreements with our experimental observations. Furthermore, the representative volume element (RVE) with Voronoi tessellation was employed to numerically study the grain size effect on intergranular fracture toughness. It was demonstrated that the reduction of grain size promoted the hinderance effect of intergranular fracture, which led to an evident improvement of intergranular fracture toughness in model with a smaller grain size. [Display omitted] [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) from laboratory samples of coarse-grained granite hit by a dropped weight at temperatures from 20 to 500 °C is recorded within a frequency range of 80 kHz-4 MHz. The time series of AE signals bear information on the size of primary defects, since the AE frequency is proportional to the growth rate of microcracks and inversely proportional to their lengths. According to AE data obtained in this study, impact fracture of granite produces cracks at grain boundaries at temperatures below 400 °C and additional defects inside grains at 400 °C and higher. The reason is that overheated water-vapor inclusions increase pressure in the grain interior, which affects the mechanic behavior of granite. [ABSTRACT FROM AUTHOR]

Two unusual sets of artefacts, the base of a pointed-bottom pot and a cluster of impact-fractured armatures, from the upper deposits of excavations at Rhino Cave and Corner Cave, Tsodilo Hills, will be presented and a range of interpretations explored. These artefacts are directly associated with rock carvings or cupules. Previously unpublished local oral accounts relating to cave and open-air localities at Tsodilo Hills will also be presented. Recurrent components of ritual behaviours provide a perspective from which to interpret these archaeological finds. It will be argued that the sets of artefacts represent ritual offerings made at these sites during the hunter-gatherer/early pastoralist period (also commonly referred to as the Later Stone Age/Early Iron Age). [ABSTRACT FROM AUTHOR]