Undeformed Specimens Research Articles

Virtual reconstruction of the Canis arnensis type (Canidae, Mammalia) from the Upper Valdarno Basin (Italy, Early Pleistocene)

Taphonomic deformation, whether it be brittle or plastic, is possibly the most influential process hindering the correct understanding of fossil species morphology. This is especially true if the deformation affects type specimens or applies to or obscures taxonomically diagnostic or functionally significant traits. Target Deformation, a recently developed virtual manipulation protocol, was implemented to address this issue by applying landmark-guided restoration of the original, deformed fossils, using undeformed specimens (or parts thereof) of the same species as a reference. The enigmatic Early Pleistocene canid Canis arnensis provides a typical example of a fossil species in dire need of virtual restoration. Its lectotype specimen is heavily deformed and none of the few known skulls are well preserved, obscuring the recognition of its systematic and phylogenetic position. Our results indicate that the algorithm effectively countered the lectotype skull’s laterolateral compression and its concomitant rostrocaudal elongation. Morphometrically, comparison of the retrodeformed cranium (IGF 867_W) with other specimens of the same species, and to other fossil and extant canid material, confirms IGF 867_W consistently clusters within C. arnensis variability. Overall, the evidence presented here confirms that Target Deformation provides a powerful tool to better characterize complex taxa like C. arnensis, whose knowledge is severely affected by the state of preservation of its fossil material.

Effect of high temperature deformation on the behavior of FeO eutectoid transformation

Eutectoid transformation behavior of FeO at different temperatures after high temperature deformation was investigated through simulation experiments and compared with undeformed specimens. The results show that the deformation behavior caused a significant effect on both the morphology and the formation process of the oxide scale. After deformation, the outer side of the deformed FeO, which produces a large number of micropores, provides the nucleation plasmas for the proeutectoid, which directly affects the concentration of Fe in the FeO. Fe supersaturation in FeO boundary which caused by “Fe-vacancy” makes the eutectoid transformation occurs rapidly, and Fe-cluster formed in FeO grain boundary.

Effect of torsional deformation on crystallographic evolution of carbide-free nano-bainitic steels prepared at two different austempering temperatures

The current study investigates the nature and extent of crystallographic change after torsional deformation in nano-structured bainite. This is extremely useful as nano-structured bainite is not stable under mechanical deformation and the evolved structure under torsion is finally going to determine other mechanical responses like fracture and fatigue. Two blocks of nano-bainitic steels were prepared after austenitization at 950°C and austempering at 250°C (NB250) and 350°C (NB350) respectively. It was found that there was a decrease in the bainitic ferrite (BF) and retained austenite (RA) length scale with a reduction in austempering temperature along with reduction in the RA content. Specimens from the undeformed two blocks (NB250-UD and NB350-UD) were subjected to torsional deformation till failure (NB250-T and NB350-T) and the crystallographic characteristics of the torsion-tested and undeformed specimens were obtained using electron back-scattered diffraction (EBSD). The orientation relationship (OR) between BF and RA for NB250-UD and NB350-UD was close to Kurdjumov-Sachs (K-S) which changed to predominantly Nishiyama Wassermann (NW) after torsion deformation (NB250-T and NB350-T). Significant refinement in packet and block was observed as a result of torsional deformation. Variant selection was stricter for NB350-UD than NB250-UD but torsional deformation led to weakening of variant selection. The extent of lowest misorientation V1-V4 variant pairing was higher for NB350-UD but it did not change much with torsion in case of NB250-T whereas NB350-T displayed a reduction. Fractography revealed that the dimple size corresponded to block size range between the undeformed and torsion-tested sample for the respective austempering condition.

Influence of Sheet Metal Pre-forming on Edge Crack Sensitivity using an AHSS Steel Grade

Especially in the automotive sector, high-strength sheet materials are processed in the manufacturing industry. These steels often show a pronounced sensitivity to edge cracks. Because of this, many edge crack testing methods for a wide variety of stress conditions have been developed to describe the edge crack sensitivity of a material. Only the hole expansion test according to ISO 16630 has been standardized. However, the standardization has some gaps in the process description, which has resulted in test modifications. Another disadvantage is the dependence of the results on the machine operator. In the past, the influence of the shear cutting parameters die clearance, cutting edge geometry, and type of cutting line on the edge crack sensitivity was only calculated for undeformed sheet materials. Not only are shear cutting operations carried out on undeformed sheet blanks in the context of the manufacturing of sheet metal components, but more and more pre-formed sheets are mechanically separated and subsequently further formed. Therefore, it is essential to consider the influence of the type and amount of pre-forming introduced on the sensitivity of a material to edge cracks. The discrete types of pre-forming, uniaxial tension, plane strain, and equi-biaxial stretch forming were introduced to sheet metal blanks using dual-phase steel. The Edge-Fracture-Tensile-Test was used to identify the residual formability of the undeformed and pre-formed specimens. The Edge-Crack-Sensitivity-Factor{K}_{mathrm{ec}}, which can be used to predict edge cracks in a finite element forming simulation, was determined from the recorded major strains for selected parameter configurations.

Investigation into structural and mechanical aspects of localization of plastic deformation and fracture under dynamic loading

An experimental testing technique was developed to conduct experimental study of plastic strain localization in specimens made of AMg6, D16 and Steel 3 alloys subject to dynamic torsion tests in the split Hopkinson pressure bar device fitted with infrared camera. The temperature values determined in-situ during dynamic torsion tests of the specimens made from AMg6, D16, Steel 3 alloys do not exceed 50° C, which indicates that temperature softening contributes insignificantly to the process of plastic strain localization. A method was developed and applied for determining the strain fields in the zone of plastic shear localization in the specimens made of AMg6, D16, and Steel 3 alloys, which were specially designed to study plastic strain localization during static deformation and dynamic loading on the split Hopkinson pressure bar using for this purpose the StrainMaster system. A comparison of the experimentally obtained strain fields with the results of numerical simulation, which was made using the kinetic equations for the evolution of defects of the mesoscale, yields rather good agreement to within 20%. This study examined post-test specimens specially designed for studying plastic deformation localization. The application of an optical interferometer-profilometer New View - 5010 allowed structural analysis of these specimens, processing of 3D data on the deformation relief and subsequent computation of the scale invariant (Hurst index) and the spatial scale of the zone where the correlated behavior of microshears is observed. The comparison of the scale invariant characteristics of the D16 alloy specimens obtained during static deformation and dynamic loading revealed a significant increase in the Hurst exponent (H~0,74) over a wide range of spatial scales (0,6-110,8 μm ) compared to the undeformed specimens (H~0,42 in the range of spatial scales 1,9-29,2 μm ). More meaningful results can be associated with the changes in both lower and upper scales, which indicates pronounced features of the localization of deformation. The structure of specimens made of AMg6 alloy, specially designed for studying the plastic strain localization after dynamic tests in the split Hopkinson pressure bar, was examined using the scanning electron microscope. The obtained data testify to significant evolutionary processes occurring in the defective subsystems undergoing dynamic deformations.

Microstructure, mechanical properties and wear resistance of an Al–Mg–Si alloy produced by equal channel angular pressing

Microstructure, mechanical properties and wear resistance in an ultrafine-grained Al–Mg–Si alloy fabricated utilizing a combination of equal channel angular pressing (ECAP) and dynamic aging were investigated in this paper. The results indicated that the grain size of the ECAP alloy was significantly refined, i.e., to ~239 nm after three ECAP passes. Meanwhile, the yield and tensile strength of the ECAPed material reached 340 MPa and 445 MPa, respectively, while maintaining a significant uniform elongation of 14%. Wear resistance results demonstrated that the wear rate, wear depth and width of the ECAPed material decreased in comparison with the solution-treated (SST) and peak-aged (T6) conditions under a load range of 5–25 N. The adhesive wear that occurs in the undeformed specimens at 10 N does not appear in the ECAPed specimen at the same load, indicating that the ECAPed specimen delay the appearance of more serious wear mechanisms under certain loads. The cooperative interaction of high density nano-scale β" precipitates and dislocations resulted in a combination of super-high strength and good work hardening ability which suppressed the extension of cracks between the friction layer and the plastic deformation zone. As a consequence, the combination of ECAP and dynamic aging brings a significant improvement for antifriction performance of the 6061 aluminum alloy.

On the interaction between γ′′ precipitates and dislocation microstructures in Nb containing single crystal nickel-base alloys

The precipitation of the metastable γ′′ phase has been studied in a Nb containing nickel-based alloy in single crystalline state, with a composition close to the commercially available superalloy IN718. Solution heat treatment and isothermal aging treatment are applied to undeformed single crystalline samples.We focus on the investigation of heterogeneous γ′′ precipitation on dislocation sites, without the interference of grain boundaries or co-precipitation with other phases. The γ′′ precipitation microstructure after aging is found to be strongly related to the dislocation microstructure before aging. The dislocations found in the undeformed specimens have been generated during the dendritic solidification or the water quenching after solution heat treatment.Two specific patterns dominate the precipitation microstructure after aging. First, some γ′′ particles precipitate along curved lines formed initially by the dislocations during solution heat treatment along the dendritic boundary. Second, γ′′ particles are found to be arranged along the dislocation in slip planes, which can be seen as largely extended straight lines parallel to the 〈011〉 directions within the (001) plane, similar to a basket weave structure. Such an aligned arrangement of γ′′ particles has been previously observed in polycrystalline IN718 within individual grains (Choi and Choi, 1972). In contrast, the bands of numerous γ′′ particles can span the whole sample of millimeter size in single crystals, cutting several hundred dendrite cores. All γ′′ particles are in the shape of an oblate spheroid, where the normals of the plates are pointing in 〈001〉 directions.

In situ identification of Action 4, SECA and QD-PEP bullets from special police ammunitions by computed tomography.

Special deformation bullets were developed for police forces to achieve a defined penetration depth (avoiding over-penetration) and a controlled energy transfer (avoiding collateral damage). This article focuses on Action 4, SECA and QD-PEP bullets. These 9 mm bullets were specially designed for controlled deformation. The characteristic slight mushrooming with a front cross-section of approximately 11.5 mm after entering a ballistic simulant was verified in ballistic tests. To achieve such slight mushrooming, the projectile's core is hollowed. The purpose of this study was to investigate the feasibility of visualising the hollowed cores of Action 4, SECA and QD-PEP bullets using a standard clinical computed tomography (CT) scanner for non-invasive identification of these special bullets from police ammunitions. First, undeformed specimens were scanned to reveal the shape of the hollowed core of each type of special bullet. Second, Action 4, SECA and QD-PEP bullets were fired towards animal cadaver models to visualise their hollow core after deformation inside biological tissue. Third, two reviewers were tasked with identifying special bullets from police ammunition (Action 4 bullets: n = 3) among 10 CT examinations of humans with lodged projectiles who were selected by the supervisor of the study. The CT scans of the undeformed specimens revealed the special design of the bullets' metal core. All special bullets from police ammunitions that were fired towards an animal cadaver model demonstrated the characteristic slight mushrooming. In accordance with the CT scans of the undeformed bullets, visualisation of the individual internal cavities of the special bullets allowed the Action 4, SECA and QD-PEP bullets to be clearly distinguished. With regard to the real forensic cases, both reviewers clearly identified each of the three Action 4 bullets among all other lodged projectiles. This study demonstrates the feasibility of identifying Action 4, SECA and QD-PEP bullets from special police ammunitions by CT. The individual shapes of the cavity inside the bullets were clearly visible on CT. In situ identification of these bullets can aid in the assessment of injuries, and since these bullets are fabricated from non-ferromagnetic metals, their clear identification allows for magnetic resonance imaging (MRI) without the risk of bullet movement inside the body due to the magnetic pull of the MRI unit. Furthermore, this approach could be of great interest to forensic investigators if patients who received gunshot wounds underwent non-operative treatments and the projectile remains in the body. Since the use of CT is also increasing for medico-legal post-mortem examinations, the identification of lodged projectiles is of interest for a virtual autopsy or 'Virtopsy'.

Effects of lamellar structure on tensile properties and resistance to hydrogen embrittlement of pearlitic steel

The hydrogen embrittlement (HE) and H trapping sites of pearlitic steel specimens with various lamellar spacings (λ) were evaluated through slow strain rate tensile testing and thermal desorption analysis. When λ decreases, both tensile strength and resistance to HE were unusually improved. This is because tearing, which is the initiation of H cracking, was delayed in the specimen with fine λ and short cementite (θ) platelets. Undeformed H-charged specimens showed a peak (peak 1), which is separable into two sub-peaks (peak 1-1 and peak 1–2) in their H desorption rate curves, regardless of λ. Peak 1-1 and peak 1–2 were generated by H atoms detrapped from FP/θ interfaces and from dislocations inside FP, respectively. The Ea values of H desorption for peak 1-1 and peak 1–2 were 23.2 kJ/mol, and 26.1 kJ/mol, respectively. Meanwhile, deformed H-charged specimens exhibited the second peak (peak 2) with peak temperature (TP) of ∼600 K, as well as peak 1 with TP of ∼375 K. When tensile strain increased, peak 2 increased at the expense of peak 1. Primary H trapping sites for peak 2 are strained FP/θ interfaces with interfacial dislocations.

Optimizing physical aging in poly(ethylene terephthalate)-glycol (PETG)

Amorphous glassy polymers are widely used as structural materials. However, their mechanical properties continuously evolve with physical aging, which significantly influences their applications. In this work, we investigate the effects of aging on stress response of poly(ethylene terephthalate)-glycol (PETG). The PETG specimens are either quenched or annealed around or below the glass transition temperature (Tg) for a period of time. The uniaxial compression tests are then performed at Tg-40 °C and strain rate 0.001/s. The quenched polymers exhibit the smallest yield strength and strain softening, indicating that negligible structural relaxation occurs for the quenched condition. For annealed polymers, the yield strength increases with aging time. The results also show that there exists an optimal temperature to achieve the highest structural relaxation rate, which is around Tg-20 °C. Compared with annealing at a single temperature, annealing at multiple temperatures in discrete steps is a more efficient method for structural relaxation. The same experiments are also performed on specimens with 30% predeformation. The optimal aging temperature does not change with predeformation. However, at the same annealing condition the yield strength of specimens with 30% predeformation is around 5 MPa less than that of undeformed specimens.

EFFECT OF AGING TREATMENT PARAMETERS ON MICROSTRUCTURE AND PROPERTIES OF Cu-Ni-Si ALLOY

In this paper, effect of cold pre-deformation and sequent aging time and temperature on microstructure and properties of Cu-2.8Ni-1.0Si alloy are reported. The results shown that, hardness and electrical conductivity of alloy increase with increasing cold deformation degree after quenching and subsequent aging. With undeformed specimens after quenching, hardness and electrical conductivity of alloy reach maximum values with subsequent aging at 425 and 475 oC, respectively. Alloy attains maximum hardness of 255 HV5 with aging at 425 oC for 4.5 hours, while maximum electrical conductivity of 38.5 %IACS with aging at 475 oC for 8 hours. In the case of deformed specimens after quenching and subsequent aging, this rule is still preserved. Especially, at 70 % cold pre-deformation degree, alloy attains the maximum hardness of 274.3 HV5 with aging at 425 oC for 3.5 h, while maximum electrical conductivity reaches 42.4 % IACS with aging at 475 oC for 6 h.

Reversibility of the Mullins effect for extending the life of rubber components

ABSTRACTThis paper investigates the recovery of the Mullins effect by heat-treatment of predeformed (300% tensile strain) carbon-black filled ethylene-propylene-diene rubber (EPDM) in an air-circulating oven. The tensile response was measured, and the secant modulus at 100% strain, energy to deform to 300% strain, ultimate tensile strength, strain to failure and permanent deformation were compared to undeformed specimens subjected to the same heat-treatments, 3–24 h at temperatures of 60–80°C. Recovery of properties is dependent on time and temperature of treatment, increasing with longer times and higher temperatures. Recovery of secant modulus follows time-temperature superposition (TTS) with an activation enthalpy of 111 kJ mol−1; TTS is shown to be applicable to the other measures, probably because of additional cure in the rubber resulting from the heat-treatment. Treatments under vacuum led to similar effects as in an air-circulating oven.

Influence of pre-deformation on the precipitation of Cu-rich clusters in RPV model steel

The effect of pre-deformation on the precipitation process of Cu-rich clusters in reactor pressure vessels (RPV) model steel is studied. In this research, Fe-1.16wt%Cu binary alloy is selected as RPV model steel to simulate the precipitation process of Cu-rich clusters. The solid-solution Fe-Cu alloys were cold rolled with pre-deformation of 0, 10%, 25%, 40%, 60%, followed by aging at 450°C for a series time. The dislocation density, Vickers hardness and microstructure evolution of Fe-Cu alloys after aging were determined. It is revealed that the Vickers hardness of un-deformed specimens reaches to peak hardness after aging at 450°C for 100 h, while the specimens with larger dislocation density reach to peak hardness faster from the Vickers hardness test result. The result of transmission electron microscopy (TEM) indicates that pre-deformation promotes the process of precipitation of Cu-rich clusters and inhibits the growth of the Cu-rich clusters.

Effect of high temperature deformation on the microstructure, mechanical properties and hydrogen embrittlement of 2.25Cr–1Mo-0.25 V steel

In this paper, the effects of high temperature deformation on the microstructure, mechanical properties and hydrogen embrittlement (HE) of the 2.25Cr–1Mo-0.25 V steel was investigated by a scanning electron microscope (SEM), a transmission electron microscope (TEM) and tensile tests. The SEM and TEM images demonstrated that high temperature plastic deformation (HTPD) led to the coarsening of carbides and the dislocation density increase. The tensile tests displayed that the HTPD resulted in the cracking susceptibility increase, as indicated by the increased numbers and sizes of cracks at the fractured surface. This was attributed to the coarsening of carbides during high temperature deformation. In contrast, the HTPD highly decreased the loss of ductility compared to the un-deformed specimens, although the amount of ductility losses (elongation or reduction of area) did not change significantly as the HTPD increased. The correlations among carbides, hydrogen and cracks were discussed.

Strain-induced precipitation in Nb + Ti dual stabilisation ferritic stainless steel

ABSTRACTStrain-induced precipitation was observed in Nb + Ti dual stabilisation 17%Cr ferritic stainless steels. Nb-containing precipitates were observed in the case of 0.4%Nb but not in the case of 0.2%Nb addition. The precipitation induced by strain is identified (Nb,Ti)C, which is a NbC-rich structure and different from the precipitation in undeformed specimens. The (Nb,Ti)CNbC-rich particles occupied Nb atoms and prevented Fe2Nb from precipitating. The precipitation transformation in 17Cr-0.4Nb-0.2Ti steel is shown as below:The pinning effect induced by (Nb,Ti)C makes stainless steels difficult to hot roll, which is in agreement with actual production.

Effects of hot compression on carbide precipitation behavior of Ni—20Cr—18W—1Mo superalloy

The effect of hot compression on the grain boundary segregation and precipitation behavior of M6C carbide in the Ni–20Cr–18W–1Mo superalloy was investigated by thermomechanical simulator, scanning electronic microscope (SEM) and X-ray diffraction (XRD). Results indicate that the amount of M6C carbides obviously increases in the experimental alloy after hot compression. Composition analyses reveal that secondary M6C carbides at grain boundaries are highly enriched in tungsten. Meanwhile, the secondary carbide size of compressive samples is 3–5 μm in 10% deformation degree, while the carbide size of undeformed specimens is less than 1 μm under aging treatment at 900 and 1000 °C. According to the thermodynamic calculation results, the Gibbs free energy of γ-matrix and carbides decreases with increase of the compression temperature, and the W-rich M6C carbide is more stable than Cr-rich M23C6. Compared with the experimental results, it is found that compressive stress accelerates the W segregation rate in grain boundary region, and further rises the rapid growth of W-rich M6C as compared with the undeformed one.

Nonlandmark classification in paleobiology: computational geometry as a tool for species discrimination

AbstractOne important and sometimes contentious challenge in paleobiology is discriminating between species, which is increasingly accomplished by comparing specimen shape. While lengths and proportions are needed to achieve this task, finer geometric information, such as concavity, convexity, and curvature, plays a crucial role in the undertaking. Nonetheless, standard morphometric methodologies such as landmark analysis are not able to capture in a quantitative way these features and other important fine-scale geometric notions.Here we develop and implement state-of-the-art techniques from the emerging field of computational geometry to tackle this problem with the Mississippian blastoid Pentremites. We adapt a previously known computational framework to produce a measure of dissimilarity between shapes. More precisely, we compute “distances” between pairs of 3D surface scans of specimens by comparing a mix of global and fine-scale geometric measurements. This process uses the 3D scan of a specimen as a whole piece of data incorporating complete geometric information about the shape; as a result, scans used must accurately reflect the geometry of whole, undamaged, undeformed specimens. Using this information we are able to represent these data in clusters and ultimately reproduce and refine results obtained in previous work on species discrimination. Our methodology is landmark free, and therefore faster and less prone to human error than previous landmark-based methodologies.

Surface softening in metal-ceramic sliding contacts: an experimental and numerical investigation.

This study investigates the tribolayer properties at the interface of ceramic/metal (i.e., WC/W) sliding contacts using various experimental approaches and classical atomistic simulations. Experimentally, nanoindentation and micropillar compression tests, as well as adhesion mapping by means of atomic force microscopy, are used to evaluate the strength of tungsten-carbon tribolayers. To capture the influence of environmental conditions, a detailed chemical and structural analysis is performed on the worn surfaces by means of XPS mapping and depth profiling along with transmission electron microscopy of the debris particles. Experimentally, the results indicate a decrease in hardness and modulus of the worn surface compared to the unworn one. Atomistic simulations of nanoindentation on deformed and undeformed specimens are used to probe the strength of the WC tribolayer and despite the fact that the simulations do not include oxygen, the simulations correlate well with the experiments on deformed and undeformed surfaces, where the difference in behavior is attributed to the bonding and structural differences of amorphous and crystalline W-C. Adhesion mapping indicates a decrease in surface adhesion, which based on chemical analysis is attributed to surface passivation.

Effect of austenite deformation in non-recrystallization region on microstructure development in low-silicon content TRIP-assisted steels

Abstract The influence of austenite deformation in non-recrystallization region on microstructural development in low-silicon content TRIP-assisted steels was investigated. Laboratory simulation of a typical thermomechanical control processing was carried out in an automated hot-compression testing machine. Specimens subjected to a typical multi-stage isothermal deformation/cooling program were deformed to true strains of 0, −0.15, −0.25 and −0.35 at various temperatures in austenite non-recrystallization region. Mossbauer spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and a novel tint-etching method were used to investigate the microstructure of deformed specimens. The results indicated that the maximum volume fraction ( V RA ) and carbon content ( C RA % ) of retained austenite can be obtained by deforming samples to some intermediate strains ( e =−0.15 for V RA and e =−0.25 for C RA % ). However, further straining of samples to e =−0.35 resulted in a drastic reduction of both parameters due to formation of pearlite. It was found that a decrease in deformation temperature resulted in increasing V RA and C RA % . Moreover, deformation of austenite was associated with morphology changes in retained austenite particles from interlath film-like type in undeformed specimens to blocky and encapsulated types in the deformed specimens.

The effects of detwinning on the mechanical properties of AZ31B magnesium alloy with different strain rates at 423 K

In order to investigate the effects of detwinning on the mechanical property of AZ31 extruded magnesium alloy at different strain rates, tensile tests were conducted on samples which had been subjected to pre-compression to 3% along the extrusion direction, with strain rates ranging from 10−1s−1 to 10−4s−1 at 423K. The results show that the strength decreases by decreasing the strain rate both on the as-received and on the pre-compressed specimens. Yield strength of pre-compressed alloy decreased comparing with as-received specimens in the whole strain rate range. Fracture elongation of undeformed specimens increased as the strain rate decreased. However, in pre-compressed materials it decreased when the strain rate ranged from 10−2s−1 to 10−4s−1. Changes in mechanical properties were mainly related to the softening orientation induced by the twins. Detwinning occurred during the inverse tensile deformation in the pre-compressed AZ31 alloy. Due to detwinning, DXR was delayed.