Cone Fracture Research Articles

Use of the quasi-static Johnson-Cook model in the failure assessment of tensile specimens with metallurgical constraints

Direct quenching has recently been used to develop cost-effective novel high and ultra-high strength steels. In weldments made of these steels, a distinct soft zone, which can lower the ultimate strength and deformation capacity of the welded joint, can form in the heat affected zone of the joint. In order to accurately estimate the static strength and deformation capacity of a welded steel structure fabricated from these steels, the effect of this softening must be taken into account. In this study, the effect of the softened zone is explored based on round tensile test specimens with metallurgical constraints using experiments and numerical calculations. The applicability of the quasi-static part of the Johnson-Cook material model and failure model for fracture assessment under given conditions was hereby examined. Firstly, the material parameters were determined for direct-quenched armor steel and cold-formed structural steel using notched tensile test specimens and FE models combined with an optimization routine. A good agreement was achieved between the tests and the results from the FE models for the notched specimens. Specimens with metallurgical constraints were manufactured from the materials using rotational friction welding, and the corresponding FE models were created using the material parameters obtained from optimization. Two different fracture mechanisms were observed in the tensile tests conducted for the specimens with metallurgical constraints, namely cup and cone fractures at the center of the specimen and fractures near the weld interface. In the corresponding FE models, the fracture initiations were observed in the same areas. A good agreement between the FE models and experimental tensile tests was thus achieved in the case of the cup and cone fractures. However, the generated FE models underestimated the fracture displacement in the specimens where the fracture occurred near the weld interface.

Effect of bead characteristics on the fatigue life of shot peened Al 7475-T7351 specimens

The present work aims to analyse the effect of shot peening processing parameters, material and size of beads on the fatigue behaviour of aluminium alloy AA7475-T7351. A systematic study was carried out on the roughness, surface hardening, residual stress profiles and fatigue life. Fatigue tests were carried out under both three points bending (3 PB) and tensile loadings. For 3 PB tests it was concluded that shot peening does not introduce significant improvement on fatigue life and that the use of low size glass beads is potentially beneficial, with roughness being as or more important than residual stresses. All tensile treated specimens presented an improvement of fatigue life in comparison to the untreated specimens, particularly when the crack initiated internally. Internal crack propagation generates a conical fracture surface until transition to mode I propagation.

Quasi-static and dynamic response, and texture evolution of two overaged Al 7056 alloy plates in T761 and T721 tempers: Experiments and modeling

The thermo-mechanical behavior and texture evolution of two overaged Al 7056 alloy plates, in T761 and T721 tempers, are measured over a wide range of strain rates (10−4 – 3 × 103 s−1) and temperatures (22–300 °C) under uniaxial tension and compression along the thickness direction, i.e. normal to the plate surface. A detailed study of the initial microstructure reveals an increase in precipitate size and decrease in density of precipitates, as the alloy is aged from the T761 to T721 temper; which in turn affects the flow stress and strain hardening behavior. Differences in flow strength and strain hardening rate, as well as tension-compression asymmetry in the two tempers, are apparent at the lower temperatures (22 °C & 100 °C) and decrease significantly at the higher temperatures (200 °C & 300 °C). Furthermore, initial texture measurements show a strong texture gradient along the normal direction (ND) of the plate. This texture gradient affects the ultimate stress insignificantly. However, it does have a considerable effect on the failure strains of specimens taken from different locations through the thickness. A transition from shear fracture at and below 200 °C to cup and cone fracture mode above 200 °C is observed in tension. Both tempers exhibit a positive strain rate sensitivity (SRS) that is dependent on temperature and strain rate. A sharp decrease in flow stress is found at 300 °C. The Khan-Liu (KL) model is modified to correlate with the measured thermo-mechanical responses of the two tempers over the studied, wide range of strain rates and temperatures. There is a close correlation between simulated and observed results.

Mechanical control on patterns of overburden deformation induced by dyke-fed sandstone intrusions: Insights from numerical experiments

Conical sandstone intrusions, as a distinct type of hydrocarbon reservoir, remain poorly understood regarding their emplacement mechanics. Here, we report a numerical modelling study of conical sandstone intrusions using the two-dimensional discrete element method. We built numerical models that contain bonded elastic particles with predefined mechanical properties in an open box as the overburden. A thin tube filled with unbonded particles, and connected to the upper box, was used to model the feeder dyke. The dynamic behavior of the assembly was enabled by the displacement of a driving wall that defines the lower boundary of the feeder dyke. The results show that the model composed of soft materials produced a pair of conical, opening-mode fractures in the host sediments as the result of tensile stress concentrations in the fracture tip zones. The overburden deformation was largely localised within the sediments adjacent to the sandbody, and without the formation of a forced fold and significant uplift of the surface. In contrast, the model composed of stiffer materials produced conical fractures that have closed lower segments and opening upper segments with a reverse sense of shear. The intrusion also caused a forced fold in the overburden, with a vertical opening-mode fracture generated in the fold hinge. The modelling results demonstrate that dyke-fed sand intrusions can significantly distort the local stress field and the overburden can be subjected to fracturing and/or folding due to differential compaction during gradual inflation of the intrusive sandbody. Importantly, deformation patterns of the overburden in response to sandstone intrusion largely depend on mechanical properties of the host sediments.

The Formation of Forced Folds and Wing‐Like Sand Intrusions Driven by Pore Fluid Overpressure: Implications From 2‐D Experimental Modeling

AbstractSand injections form by intrusion of overpressured, fluidized sand into surrounding low‐permeable, fine‐grained rocks. Modern 3‐D seismic data revealed their abundant occurrence in many sedimentary basins and that their intrusion is typically associated with forced folding and tensile fractures of the sealing cover layer. In order to investigate the kinematic evolution of forced folds in relation to the associated propagation of fractures originating from an overpressured source layer, we performed idealized, quasi‐2‐D analog experiments. The models consist of noncohesive and cohesive granulates to mimic a sand reservoir and its overburden layer and injected air to produce fluid overpressure in the layered materials. Our results show that forced folding first induces tensile bending fractures at the base of the fold limbs at a certain critical fluid pressure. Due to further increase of the fluid pressure, the apex of these bending fractures serves as origin for branching, conical fractures characterized by shear and tensile failure. Fracture breakthrough is accompanied by a rapid uplift of the breached fold limb and a pressure drop in the reservoir layer followed by a continuous subsidence of the central forced fold. The morphology of the fracture pattern and the forced fold provides helpful implications for understanding formation processes of natural sand injections observed in seismic data and in outcrops.

Mechanical Properties and Microstructure Characterization of AISI “D2” and “O1” Cold Work Tool Steels

This research analyzes the mechanical properties and fracture behavior of two cold work tool steels: AISI “D2” and “O1”. Tool steels are an economical and efficient solution for manufacturers due to their superior mechanical properties. Demand for tool steels is increasing yearly due to the growth in transportation production around the world. Nevertheless, AISI “D2” and “O1” (locally made) tool steels behave differently due to the varying content of their alloying elements. There is also a lack of information regarding their mechanical properties and behavior. Therefore, this study aimed to investigate the plasticity and ductile fracture behavior of “D2” and “O1” via several experimental tests. The tool steels’ behavior under monotonic quasi-static tensile and compression tests was analyzed. The results of the experimental work showed different plasticity behavior and ductile fracture among the two tool steels. Before fracture, clear necking appeared on “O1” tool steel, whereas no signs of necking occurred on “D2” tool steel. In addition, the fracture surface of “O1” tool steel showed cup–cone fracture mode, and “D2” tool steel showed a flat surface fracture mode. The dimple-like structures in scanning electron microscope (SEM) images revealed that both tool steels had a ductile fracture mode.

Forced folding and fracturing induced by differential compaction during post-depositional inflation of sandbodies: Insights from numerical modelling

Abstract Three series of numerical models based on the discrete element method were constructed to simulate forced folding and fracturing triggered by postdepositional inflation of fluidised sandbody. The models consist of numerous particles that have relatively low to high interparticle bonds to represent overburden sediments with a relatively low to high cohesion, and cohesionless, frictionless particles to represent fluidised sands. The modelling results show that normal faults were produced due to the upward inflation of sand domes and the resulting flexed overburden, when the cohesion of the host sediments is low. Opening voids were created as a result of strata collapse, when the intrusion-related normal faults terminated within the host sediments as blind faults. Conical fractures that are aligned along sandbody margins were produced, which consist of closed, lower segments with a reverse displacement, and opening, middle-upper segments with a minor to zero shear component. Forced folds were generated in most models with a moderate to high cohesion, resulting in differential compaction in the overlying sediments that can account for the formation of fold-related fractures, which are either shear, hybrid or pure tensile, depending on their structural positions. The amplitude of forced folds is closely associated with both cohesion and thickness of sediments in the overburden, whilst fold wavelength is mainly controlled by sediment cohesion. Based on the modelling results, three types of preferential sites for the storage of injected sands were suggested, which are believed to be instructive for subsurface sandbody detection and prediction. This study demonstrates that differential compaction induced by sand inflation can play an important role in overburden folding and fracturing.

Closed system fluid-mineral-mediated trace element behaviour in peralkaline rare metal pegmatites: Evidence from Strange Lake

Large peralkaline complexes are ‘factories’ that have produced a variety of ‘exotic’ minerals including high field strength element minerals. In most cases, these minerals are secondary and crystallise in a hydrothermal paragenesis that is extremely difficult to decipher due to the complexity of the textural relationships. The Strange Lake pluton is one of these complexes, and contains 37 exotic minerals, most of which are secondary. Adding to the difficulty in establishing a comprehensive paragenesis for these minerals and an alteration/precipitation path for the pluton is the fact that there were several stages of crystallisation of the same exotic and common secondary minerals, e.g., bastnäsite, fluocerite, gadolinite, aegirine, fluorite, and zircon.In this paper, we present a model, which describes a detailed path for the alteration and precipitation of minerals in the closed hydrothermal system of a peralkaline granitic pegmatite, based on direct measurements of the evolving composition of the aqueous fluid that exsolved from the late-stage magma crystallising rare-metal pegmatites in the Strange Lake pluton. The driving force for this evolution was cooling-induced oxidation that ultimately transformed the CH4-H2 gas in this fluid to CO2. This led to a large drop in the pH, which was a major control on the composition of the fluid and the crystallisation of secondary minerals.Although large numbers of minerals formed and were replaced during the different stages of fluid evolution, the changing chemistry of the fluid was largely a response to the alteration of four minerals, namely arfvedsonite, elpidite, narsarsukite and fluorite. The earliest stage of alteration, which took place at ~360 °C, was marked by the replacement of arfvedsonite by aegirine. This alteration decreased salinity and released K, Li, and Rb to the fluid, causing K-metasomatism. At ~300 °C, CH4 and higher hydrocarbons reacted to produce CO2. This caused a massive drop in pH from a value > 10 to a value of ~3 and intense alteration, which included the dissolution of fluorite, the breakdown of elpidite to zircon and quartz and the replacement of narsarsukite by titanite. With ongoing dissolution of fluorite, Ca activity reached a level sufficient to promote the alteration of elpidite to armstrongite or gittinsite. This was accompanied by alteration of arfvedsonite to ferroceladonite and microcline to Al-phyllosilicates, enriching the fluid in Na, Fe and F. Soon after, there was a near total loss of CO2 (at ~230 °C). This loss was catastrophic and was focused along conical fractures (these developed as a result of the collapse of the roof of the pluton), with resultant fragmentation of the rocks along the fluid path. Alteration to phyllosilicates continued after the loss of CO2, as the system cooled to ~190 °C. This marked the beginning of the final stage of alteration, which involved the replacement of arfvedsonite by aegirine and hematite. It also coincided with large scale hematisation within the pluton. Finally, it led to the cementation of the fragments along the fluid path to form the fluorite-hematite ring breccia that is now evident at the margins of the pluton.The model of fluid evolution presented here is potentially applicable to many other peralkaline complexes. The only requirements are that the system was closed until a relatively late stage and that the exsolved fluid was saline and contained a reduced carbonic component. This is a feature of many peralkaline complexes, most notably, the Khibiny and Lovozero complexes in Russia, and Ilímaussaq in Greenland.

Study on Diffusion Bonding Characteristics of Austenitic Stainless Steels

This study was conducted by using type 304 austenitic stainless steel as experimental material to clarify the diffusion characteristics of diffusion bonding and diffusion brazing. The bonding variables such as the bonding pressure, bonding time and surface roughness affecting the tensile behavior of joints. The main results obtained were as follows: The tensile strength of diffusion bonded joint was almost equivalent to that of the base metal, and the joint efficiency of almost 100%. Although the surface roughness did not have significant influence on the tensile strength of diffusion bonded joints, it shows notable difference in terms of the fracture appearance. The fracture occurred in the interface of bonded joints when the surface roughness was not so smooth. However, all of the tensile specimen fractured at base metal and showed typical a cup and cone fracture, when the surface was smooth. The pressure was an extremely critical factor when conducting diffusion brazing. It was observed that as the pressure became higher, the better interface was produced, showing high quality interface with the tensile strength of the joints amounting to nearly 500MPa. The homogenization heat treatment after diffusion brazing had some influence on the strength of joints. Key words: Diffusion bonding, Diffusion brazing, Homogenization, Surface roughness, Tensile strength

Theoretical Study on Flat Tooth Cone Fracture Type Rock Breaking based on Plane Indentation

Theoretical Study on Flat Tooth Cone Fracture Type Rock Breaking based on Plane Indentation

Distinct Fracture Patterns in Construction Steels for Reinforced Concrete under Quasistatic Loading— A Review

Steel is one of the most widely used materials in construction. Nucleation growth and coalescence theory is usually employed to explain the fracture process in ductile materials, such as many metals. The typical cup–cone fracture pattern has been extensively studied in the past, giving rise to numerical models able to reproduce this pattern. Nevertheless, some steels, such as the eutectoid steel used for manufacturing prestressing wires, does not show this specific shape but a flat surface with a dark region in the centre of the fracture area. Recent studies have deepened the knowledge on these distinct fracture patterns, shedding light on some aspects that help to understand how damage begins and propagates in each case. The numerical modelling of both fracture patterns have also been discussed and reproduced with different approaches. This work reviews the main recent advances in the knowledge on this subject, particularly focusing on the experimental work carried out by the authors.

Model test to investigate failure mechanism and loading characteristics of shallow-bias tunnels with small clear distance

Based on the similarity theory, a tunnel excavation simulation testing system under typical unsymmetrical loading conditions was established. Using this system, the failure mechanism of surrounding rock of shallow-bias tunnels with small clear distance was analyzed along with the load characteristics. The results show that: 1) The failure process of surrounding rock of shallow-bias tunnels with small clear distance consists of structural and stratum deformation induced by tunnel excavation; Micro-fracture surfaces are formed in the tunnel surrounding rock and extend deep into the rock mass in a larger density; Tensile cracking occurs in shallow position on the deep-buried side, with shear slip in deep rock mass. In the meantime, rapid deformation and slip take place on the shallow-buried side until the surrounding rocks totally collapse. The production and development of micro-fracture surfaces in the tunnel surrounding rock and tensile cracking in the shallow position on the deep-buried side represent the key stages of failure. 2) The final failure mode is featured by an inverted conical fracture with tunnel arch as its top and the slope at tunnel entrance slope as its bottom. The range of failure on the deep-buried side is significantly larger than that on the shallow-buried side. Such difference becomes more prominent with the increasing bias angle. What distinguishes it from the "linear fracture surface" model is that the model proposed has a larger fracture angle on the two sides. Moreover, the bottom of the fracture is located at the springing line of tunnel arch. 3) The total vertical load increases with bias angle. Compared with the existing methods, the unsymmetrical loading effect in measurement is more prominent. At last, countermeasures are proposed according to the analysis results: during engineering process, 1) The surrounding rock mass on the deep-buried side should be reinforced apart from the tunnel surrounding rock for shallow-buried tunnels with small clear distance; moreover, the scope of consolidation should go beyond the midline of tunnel (along the direction of the top of slope) by 4 excavation spans of single tunnel. 2) It is necessary to modify the load value of shallow-bias tunnels with small clear distance.

Low Short-Stem Revision Rates: 1-11 Year Results From 1888 Total Hip Arthroplasties

BackgroundIn total hip arthroplasty, short stems were developed as a bone-conserving alternative to traditional cementless stems. So far, there have been very few recorded medium to long-term results of these comparatively new implants. The aim of our retrospective study was to report on the survival of calcar-loading short stems. MethodsAll Metha stem implantations from 2004 to 2014 were recorded from the operation protocols (n = 1888). Due to the chronological development of the stem, 3 different versions were implanted: modular titanium stems with neck adapters from titanium or cobalt-chrome and monoblock stems. Patients were questioned by post about revision, dislocation, and satisfaction. ResultsData were complete for 93% of the procedures (1090 monoblock stems, 314 modular stems with titanium neck, and 230 modular stems with cobalt chrome neck). Mean follow-up was 6 years (1-11 years). Fifteen modular titanium implants were affected by cone fractures (4%). Therefore, monoblock, modular cobalt chrome, and modular titanium implants were analyzed separately. The 7-year revision rate for monoblock stems was 1.5%; for modular cobalt-chrome stems it was 1.8%, and for modular titanium stems it was 5.3%. ConclusionOur data show the midterm survival of the monoblock and modular cobalt-chrome implants equivalent to the traditional cementless stems. These might, therefore, be considered as a bone-conserving alternative for young and active patients.

Special zone in multi-layer and multi-pass welded metal and its role in the creep behavior of 9Cr[sbnd]1Mo welded joint

The creep properties of 9Cr1Mo welded joint are determined by special zone (SZ) in equiaxed grain zone of welded metal (WM) suffered from multiple thermal cycles during multi-layer and multi-pass welding process. The SZ in WM was characterized in detail and its role in creep behavior was discussed in this paper. The creep test of 9Cr1Mo welded joint was carried out in 566°C under 270MPa and 250MPa, and great difference of fracture morphology was observed as “cup and cone” and “wave” shapes, respectively. The cup and cone fracture consists of many deep and cone-shaped dimples. For wave-shaped fracture, some honeycomb-like structure is observed at bottom and top of wave, which is shallow and inclined to coalesce. Banded structure along prior austenite grain boundaries inside SZ is responsible for wave fracture. Some small grains with size of about 2μm are observed in banded structure, which increases the real length of the grain boundary and might deteriorate the creep performance. For long-term creep behavior, creep voids and cracks firstly form along boundaries of small grains in banded structure of SZ, and then creep crack propagates along the fusion line direction of weld beads. Grain boundary failure induced by banded structure is considered as the main rupture mechanism in this condition.

Formation Mechanism of Inclusion Defects in Large Forged Pieces

Nonmetallic inclusions mixed into large forged metal objects destroy the continuity in the metal and affect the quality of the forged product. Research on how inclusions affect the plastic deformation of a matrix shows the significance of the formation mechanism of inclusion defects. For upset forging, the nonlinear finite element model was shown to be appropriate for the ingot hot-forging process by comparing the results with experiments involving plastic and hard inclusions inserted into the forged piece. The high-temperature stress-strain curves of MnS plastic inclusions were obtained experimentally. The results show how, during upsetting, the morphology of MnS plastic inclusions varies from spherical to ellipsoidal, until finally becoming flat in shape. The larger the inclusion is, the larger the degree of deformation of the inclusion is, and large inclusions enhance the risk of the final product failing to pass inspection for inclusion flaws. Strain significantly concentrates in the matrix near a hard inclusion. When the hard inclusion reaches a certain size, conical fractures form on both sides of the inclusion. To pass inclusion-flaw inspection and close hole defects to the extent possible, the flat-anvil upsetting is recommended. Finally, the inclusion-deformation state obtained by finite element simulation is verified experimentally.

Effect of rolling temperature on the microstructure and mechanical properties of interstitial free steel

In the present research, to improve the mechanical of interstitial free steel, the hot rolling process has performed for 50% reduction in area at three different phase regions (below the lower critical point, above the upper critical point and intermediate region) of interstitial free steel. Samples were cooled down to room temperature by normal air cooling in the room temperature. The microstructure and mechanical properties of control rolled steel have been investigated by an optical microscope, Vickers hardness tester and tensile test. It has found that yield strength and ultimate tensile strength of sample rolled at a lower critical temperature (600°C) improved significantly without much significant change in ductility, due to ferrite grain refinement and an increase of dislocation density. Scanning electron microscope fractography analysis shows cup and cone fracture. Finally, it is suggested that a controlled rolling process of interstitial free steel in pure ferritic region conferred optimum properties.

Resistance to impact of porcelain stoneware tiles

The impact resistance of ceramic tiles is an important technical requirement, especially for large size and/or low thickness slabs. The standard test for ceramic tiles (ISO 10545-5) is non-destructive: it determines the coefficient of restitution of a small sample (75×75mm2) assembled on a concrete substrate under a weak impact energy (0.27J). This method does not provide neither an impact strength nor information on the way a ceramic tile is broken by impact. In order to fill this gap, an investigation was undertaken to describe, by a phenomenological approach, how ceramic tiles break under different conditions of impact. For this purpose, unglazed porcelain stoneware tiles with different size (12×12, 25×25 and 60×60cm2) and thickness (3.5, 5 and 8mm) were assembled on a concrete basement and tested for the coefficient of restitution (ISO 10545-5) and Roesler index. Their physical and mechanical properties were determined by measuring: water absorption, porosity, bulk density (ISO 10545-3), flexural strength (EN 843-1), elastic moduli (EN 843-2), fracture toughness (SENB). The impact strength was measured by falling steel balls (50, 80, 200 and 500g) with increasing energy (from 0.2 to 6J) and with different speed at the moment of impact (from 1.9 to 5.5m/s). The effects caused by impact were visually inspected, revealing for increasing energy the formation of an impact ring, radial cracks, one or two concentric Hertzian cone fractures, a highly fractured inner zone. Such damages were quantified by measuring the impact ring diameter as well as number, length and estimated surface of radial and conical cracks. A nearly linear dependence on the impact energy was found for crack length and surface, while the ring diameter and crack number seem to follow a quadratic law. The impact strength depends on the tile thickness, but also the sample size may somehow affect the mechanical behavior under impact. A map of seven levels of damage was drawn by contrasting increasing impact energy with tile thickness: it can help to predict the tile behavior in operation and to address the correct tile type in different applications.

Finite element failure analysis of wires for civil engineering applications with various crack-like laminations

This paper presents the finite element (FE) failure predictions and analyses of a typical wire for civil engineering applications with various crack-like lamination types (Single and double), geometries (straight-end and inclined-end) and orientations (longitudinal, lateral and transverse). FE prediction and analysis of the failure of notched pre-cracked wires with a surface across-the-thickness crack-like lamination validated with experimental results are also presented. The FE predicted fracture shape for the notched pre-cracked wires that consists of a cup and cone fracture shape below the bottom tip of the surface across-the-thickness crack-like lamination agrees with the experimental fracture shape. Wires with the double straight-end and double inclined-end crack-like/line-type laminations exhibit a “slant-middle W” and a “zigzag” fractures respectively. Above and below the lateral mid-width across-the-thickness lamination, the wires with the lateral mid-width across-the-thickness lamination exhibit a combination of a transverse mid-thickness flat fracture that is perpendicular to the lateral mid-width across-the-thickness lamination and negatively inclined slant fractures on each side of the mid-thickness flat fracture at the remaining outer edges of the wire's thickness. On both the front and back sides of the transverse mid-thickness across-the-width lamination, the wires with the transverse mid-thickness across-the-width lamination exhibit a combination of transverse flat fractures parallel to the transverse mid-thickness across-the-width lamination and positively inclined slant fractures at the outer edges of the wire's thickness. FE failure analysis reveals that fracture initiations do not always begin at the termini of every longitudinal crack-like/line-type lamination as reported in a published fractographic failure analysis report of wires with longitudinal crack-like laminations. Fracture initiation only begins at the termini/tip of longitudinal inclined-end crack-like laminations and at the termini/tip of transverse and lateral laminations. FE failure analysis also reveals that wires with single straight-end, double straight-end and double inclined-end longitudinal crack-like/line-type laminations do not exhibit cup and cone fractures as reported. This work further demonstrates the need to employ FE failure analysis as a complimentary or alternative failure analysis approach where the destruction/alteration of the fracture markings by corrosion could affect the accuracy of fractographic failure analysis.

Failure processes governing high-rate impact resistance of epoxy resins filled with core–shell rubber nanoparticles

Epoxy resins are classically toughened by rubber additives, but the effectiveness of rubber toughening tends to diminish with increasing strain rate, decreasing temperature, and decreasing matrix ductility. In this study, we demonstrate that low loadings of 100–200-nm core–shell rubber (CSR) particulate additives can improve high strain rate (104–105 s−1) impact resistance by nearly 200 % for epoxy resins with glass transition temperatures T g in a range between 60 and 110 °C, without large reductions in T g or stiffness. In addition, CSR additives improve low-temperature impact resistance of the epoxies down to 0 °C. Size and surface chemistry of the CSR particles influence the ballistic response, with 200-nm diameter, weakly bound, and poorly dispersed CSR particles providing the greatest toughening performance at low filler loadings and high rates. Impact resistance for a systematic series of CSR-modified epoxies covers a transition from brittle to tough behavior, where the failure mechanism changes with effective fracture resistance. For brittle resins, failure is dominated by initiation of Hertzian cone fracture which depends strongly on fracture toughness K IC, while for tough resins, failure is dominated by plastic yield at the impact site and is independent of fracture toughness above a minimum K IC value of approximately 1.2–1.5 MPa m1/2. Interestingly, quasistatic mechanical properties are reasonably effective qualitative predictors of high-rate impact resistance, suggesting that the toughening mechanisms of CSR particles are similar over the rates studied here. The insights gained from this study are valuable for design of next generation adhesives, polymers, and polymer composite matrices for lightweight protective applications.

Flint knapping and determination of human handedness. Methodological proposal with quantifiable results

The products of technological activity of our ancestors, and particularly the artefacts made by hand, are a potential source of information for a diachronic study of the handedness process in different human species. In the flint flakes, around the point of percussion, a system of fractures is developed in connection with the cone of percussion and the conical fracture of the flint. On this paper we prove that the direction of percussion can be deduced from these fractures, and the knapper's handedness can be determined if the direction of percussion is known.