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The tensile mechanical properties of silver nanowires produced by the polyol process and containing the characteristic pentatwinned microstructure are compared with single crystal nanowires prepared by template electrodeposition over a range of diameters, d, from 80 to 300 nm. The plastic flow strengths of both sets of nanowires show a significant size effect, ranging from about 400 MPa at d ? 300 nm to in excess of 1 GPa with d < 100 nm. The size effect is shown to follow the same empirical scaling law seen with other fcc structured metals. Transmission electron microscopy investigation of the deformed specimens found similar deformation structures in both classes of nanowire studied with relatively low dislocation densities found even after significant plastic strain. The deformed pentatwinned nanowires showed no evidence for any characteristic deformation structures associated with the twin boundaries running parallel to the nanowire axis. © 2021 Elsevier B.V. Henry Royce Institute: EP/P025021/1, EP/P025498/1, EP/R00661X/1, EP/S019367/1; Engineering and Physical Sciences Research Council, EPSRC: EP/J021229/1, EP/S009493/1; Royal Society; University of Manchester; China Scholarship Council, CSC The authors would like to acknowledge the support of the Engineering and Physical Sciences Research Council (EPSRC) through grants EP/J021229/1 and EP/S009493/1 . This work was also supported by the Henry Royce Institute for Advanced Materials , funded through EPSRC grants EP/R00661X/1 , EP/S019367/1 , EP/P025021/1 and EP/P025498/1 . HZ would like to thank the China Scholarship Council and the University of Manchester for financial support through a scholarship. ASE acknowledges financial support from the Royal Society.

The mechanical behavior of nanolaminates is dominated by interfaces that act as sources, barriers, and preferred sites for storage and dynamic recovery of glide dislocations. In this article, the deformation mechanisms of a variety of metal-based nanolaminates are reviewed with emphasis on unusual mechanical properties such as ultra-high flow strength without loss of plastic deformability.

Crack growth rate (CGR) testing in BWR normal water chemistry was performed on compact tension (CT) specimens of two different sizes (B = 8 mm and B = 19 mm), machined from a Type 304 SS core shroud at a dose of ~1 dpa. The objectives were to study the effect of specimen size on the CGR, and to determine the K validity limit for a CT specimen dimension used in previous studies. The results show that for materials with significant strain hardening capacity remaining, there is no effect of specimen size on the CGR when testing is conducted at stress intensity factors valid according to ASTM E399 using the flow strength. For materials at higher dose in which the strain hardening capacity is lost or greatly reduced, a different K validity criterion might be applicable.

The effect of the strength ratio extracted from an Archard model for wear is used to describe the wear rates expected in hot forging dies. In the current study, the strength ratio is the strength of the hot forging die to the strength of the work piece. Three hot forging die steels are evaluated. The three die steels are FX, 2714, and WF. To determine the strength of the forging die, a continuous function has been developed that describes the yield strength of three die steels for temperatures from 600 to 700 °C and for times up to 20 h (i.e., tempering times of up to 20 h). The work piece material is assumed to be AISI 1045. Based on the analysis, the wear resistance of WF should be superior and FX should be slightly better than 2714. Decreasing the forging temperature increases the strength ratio, because the strength of the die surface increases faster than the flow strength of AISI 1045. The increase in the strength ratio indicates a decrease in the expected wear rate.

This paper proposes a computational mechanical model to evaluate the effect of the angle between loading axis and twin boundary (TB) on the deformation behaviors of nanotwinned materials. In this model, the shear deformation across the TBs and the shear deformation parallel to the TBs were considered. The model correctly predicted the experimentally observed tendency of the influence of twin density on flow strength. Besides, the mechanical behaviors of nanotwinned Cu with different angle were studied. However, as twin density increases, the effect of the angle on the stress–strain relations was weakening. This analysis can offer some useful information for optimizing of strength and ductility.

The toughness of conventional injection-molded isotactic polypropylene bars has been investigated with respect to the notch location and β-nucleating agent. Superior toughness is achieved in the β-nucleated bars with notches near the gate, but is absent in the near-gate bars without β-nucleating agent or in the β-nucleated ones far from the gate. With detailed structural analysis across the sample thickness, it is indicated that in these tough bars, extensive flow close to the surface suppresses the formation of β-form to a large extent but favors the generation of oriented α-form, whereas toward inner region, an opposite tendency is presented with the decay of flow strength and the activation of β-nucleating agent. Allowing that this peculiar hierarchical structure is absent in other two kinds of bars, it is deduced that the cooperative effect of molecular orientation of α-form in the skin layer and rich β-form in the inner region is responsible for the significant toughness enhancement in the β-nucleated bars near the gate. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Strain hardening in metallic multilayers is shown experimentally to be greater in trilayer films of Cu–Ni–Nb than bilayer films of Cu–Ni or Cu–Nb using both direct measurements of flow strength at different effective strains and an analysis of the out-of-plane deformation around nanoindentation impressions. The mechanism that accounts for increased strain hardening in the trilayer is a proposed super-threader dislocation and cross-slip mechanism, modeled using three-dimensional dislocation dynamics simulations.

In the present work, the mechanical behaviour of base metal, friction stir welded (FSW) sheet and only weld zone of FSW sheet has investigated and evaluated the properties namely flow strength, elongation and hardness. The experimental data was compared with simulation results for individual tensile behaviour of all the three sheets. Micro-hardness showed a decreasing trend, from the base material to the centre of the nugget zone, except near the transition zone. The FSW sheets showed a decreased flow stress and improved elongation when compared to base material.

The present work uses focused ion beam methods to prepare samples for transmission electron microscopy in order to quantitatively characterize changes in the dislocation substructures obtained from undeformed and deformed pure Ni microcrystals having sample diameters that range from 1 to 20 μm. Following deformation, the dislocation density measured in the microcrystals is on average in excess of their expected initial density, with an apparent trend that the average density increases with decreasing microcrystal size. These dislocation density data are used to assess the contributions of forest hardening to the flow strength of the microcrystals. The combined effects of lattice friction, source-truncation hardening and forest hardening are found to be insufficient to fully account for the large flow strengths in smaller microcrystals.

When assessing the resistance of a steel structure to failure under load, fracture toughness is a key input variable. Since it is usually not possible to establish a priori if the anticipated service temperature (or temperatures) is in the fracture mode transition or on the upper shelf, it is useful to know the temperature dependence of fracture toughness in both the transition and on the upper shelf. In the transition, the master curve proposed by Wallin defines both the variation of the median value of fracture toughness with temperature and the scatter of fracture toughness about this median value. However, Wallin's master curve does not quantify fracture toughness on the upper shelf. In this paper we assemble a database of upper shelf fracture toughness data ( J Ic ) for ferritic steels. These data demonstrate that the temperature dependence of upper J Ic is consistent for all ferritic steels contained in the database and has the same form as the temperature dependence of the flow strength anticipated from dislocation mechanics considerations. This similarity between the temperature dependence of flow strength and the temperature dependence of J Ic is physically expected because both directly depend upon the energy required for dislocation mobility in the ferrite matrix. Both the empirically derived model and the physical basis for the model are described.

Finite element analyses were carried out to study the stress distribution in particulate Al 2 O 3 -reinforced Al metal–matrix composites subjected to external compressive and tensile load as a function of the interfacial bonding strength. Unit cells containing hard particles with either weak or rigid interfaces in the multi-linear kinematic hardening matrix were used to determine the corresponding flow strength. The effect of the interfacial strength on the flow response in tension and compression was also examined. The predictions of the cracking mode and hardening behavior based on FEM analyses were found to be in reasonable agreement with observations in 5083Al–10vol.% Al 2 O 3 and Al–5Mg–10vol.% Al 2 O 3 composites.

This paper deals with an analysis of the size effect on the flow strength of metal-matrix composites due to the presence of geometrically necessary dislocations. The work is based upon a cell model of uniaxial deformation. The deformation field is analyzed based on a requirement of the deformation compatibility along the interface between the particle and the matrix, which in turn is completed through introducing an array of geometrically necessary dislocations. The results of modelling show that the overall stress-strain relationship is dependent not only on the particle volume fraction but also on the particle size. It has been found that the material length scale in the strain gradient plasticity is dependent on the particle volume fraction, or in other words, on the relative ratio of the particle spacing to the particle size. The strain gradient is, besides the macro-strain and the particle volume fraction, inversely proportional to the particle size.

Revista de Metalurgia, vol. 34, Nº ext. 1998, La aleación MA956 es un material ferrítico fabricado por aleado mecánico que presenta la peculiaridad de generar mediante un proceso de oxidación térmica una delgada capa de alúmina a densa y bien adherida al substrato que protege al material contra los ambientes agresivos. En este trabajo se estudia la influencia del tratamiento de oxidación (1.100 °C/100 h) sobre el comportamiento mecánico de esta aleación a temperatura ambiente. En particular, se observa que en tracción y en compresión, la tensión de flujo plástico del material con capa es inferior a la del material sin capa. Dicha disminución de la tensión de flujo se puede atribuir aja formación, durante el proceso de oxidación, de dislocaciones en arista en una estrecha franja de substrato adyacente a la capa, The MA956 alloy is a ferritic oxide dispersión strengthened alloy processed by mechanical alloying which exhibits a good high temperature oxidation resistance due to the capability to develop a compact and tightly adherent a-Al203 scale by thermal oxidation. The present study deals with the effects of the oxidation treatment (1,100 °C/100 h) on its mechanical behavior at room temperature. It has been found that the oxide scale induces a decrease of the flow strength of the MA956/A1203 system with respect to that of scale-free specimens. This feature has been related to the formation during the preoxidation treatment of a high density of edge dislocations in a narrow zone of the substrate beneath the scale, Este trabajo ha sido financiado por la CICYT. Proyecto MAT95-0796

Following a test series consisting of sixty-seven experiments, the rails from a 90 mm diameter /spl times/10 m long launcher were removed for metallurgical characterization. The rails were machined from OFHC copper extrusions. The measured Brinell hardness values of the rails ranged from HB 60 to HB 86. The starting material had a hardness of HB 86. Observed values increased from the breech up to a distance of approximately 4 m and tended to decrease and level off beyond 4 m. These hardness values are normal for worked OFHC copper, falling between those for fully annealed (HB 34) and cold rolled (HB 91) conditions. The compressive flow strength of the as-received material was determined to be /spl sigma//sub f/=331 /spl epsi//sup 0.12/ MPa. Extensive cratering and hypervelocity gouging damage was observed except in the regions 1 m from the breech end and between 7.5 and 10 m. The microstructure of the as-received rail material was fully dense and equiaxed and the average grain size was 100 /spl mu/m. >

In order to evaluate the resistivity of flat parts in the outer car body skin to mechanical loads denting experiments are performed. During a denting experiment the aluminum sheet is continuously loaded normal to its surface up to a maximal force with a punch. The characteristic denting resistance and denting stiffness are calculated from the experimental data. In general an increase of the flow strength has positive effects on the resistance to denting. The mechanical resistivity of aluminum sheet metal against plastic deformations which is the flow strength is being improved by pre-stretching as the material strain hardens during stretch-forming. In this work two different 6xxx aluminum alloys are pre-stretched in uniaxial direction up to major strains of 0.02, 0.05, 0.08 and 0.1 with a device for segmented stretch-forming. Subsequently quasi-static denting tests have been performed. Characteristic values of the denting tests have been evaluated and compared with the mechanical properties of the respective pre-stretched sample.

The effect of interfacial properties on the strength of discontinuous reinforced metal-matrix composites is systematically studied by theoretical modelling. The calculations were carried out within the framework of continuum plasticity theory using cell models and the finite element method. A wide range of inclusion aspect ratios, volume fractions, and interfacial strengths were investigated for perfectly plastic and hardening matrices. Interfaces were modelled either as strongly bonded, or as shearable but strong normal to the inclusions, or as debonding at the reinforcement ends but strong on the sides. Additionally, the effects of reinforcement arrangement and extensive damage to continuous fibre composites were addressed. Debonding at the ends of the inclusions was found to have the most deleterious effect on the strength of the composite. When debonding does not occur but interface sliding takes place freely, an amount of strengthening is seen which is a function of the inclusion volume frac...

The effect of interfacial sliding strength on the strength of short fiber reinforced metal matrix composites is systematically investigated analytically with the finite element method. Additionally, the effect of interfacial sliding strength on the strength of a severely damaged continuous fiber composite is examined. In both cases no interfacial debonding is allowed to occur. A degree of strengthening is seen to occur, relative to the matrix material alone, when the interface is allowed to slide freely. This strengthening is primarily independent of inclusion aspect ratio. Increasing the interfacial sliding strength from the freely sliding case improves the composite flow strength greater for fiber shaped inclusions than for disk shaped inclusions. However, there is virtually no further strengthening for the case of particulate shaped inclusions. Hardening matrices are more severely affected by sliding interfaces. A nearly linear transition from the case of a sliding interface to a strong interface is seen for the case of a severely damaged continuous fiber composite.

Experimental studies conducted on particulate-reinforced A1 alloys are used to critically assess flow models. For this purpose, the influence of thermal expansion misfit and of reverse loading provide a particularly critical assessment. Comparison with models indicates that continuum cell calculations provide good predictions of trends, subject to an in situ matrix strength that may differ from that for the unreinforced alloy.

The flow properties of a ductile Al alloy reinforced with SiC particulates and randomly oriented platelets have been investigated to establish trends with such variables as reinforcement volume fraction, size and aspect ratio. The experimental results are compared with the trends predicted by recent continuum calculations. The general agreement found between experiments and the calculations has established the following characteristic features of the flow strength. This strength is strongly influenced by reinforcement volume fraction ƒ, especially when ƒ is large ( ƒ > 0.3 ). Particulates and non-aligned platelets having aspect ratio 10:1 exhibit about the same strengthening.

Grain size strongly influences the superplastic properties of a fine-grained, 20 wt.% Al2O3-reinforced, Y2O3-stabilized tetragonal ZrO2 (Al2O3/YTZ). The elongation to failure of the material decreases, and the flow strength increases, with increasing grain size. The flow stress at a constant true strain rate and at a given strain is proportional to the grain size raised to a 0.75 power. As a result, the superplastic deformation rate in Al2O3/YTZ is inversely proportional to the grain size raised to a 1.5 power.

This paper presents the results of a study of titanium Ti-10V-2Fe-3Al in two heat treatments for which we determined the static and dynamic flow and fracture properties. Complementary fractographic observations revealed the dominant microstructural failure mechanisms. We then used these results to guide preliminary finite element modeling of the two-phase microstructures aimed at rationalizing how the observed micromechanisms affect their global mechanical behavior.

Investigation of the flow properties of materials containing rigid reinforcements has been prompted by various technological challenges concerned with high specific strength composites. The materials of interest range from metallic materials such as Al alloys, to ceramic materials such as Si3N4 and also include the intermetallics: TiAl and MoSi2. The reinforcements are typically A12O3 and SiC. The strengths of interest may be the flow strength at ambient temperature or the creep strength. The present analysis constitutes an attempt to provide estimates of either the flow or creep strength for matrices that exhibit power law deformation.

The Bilby-Cottrell-Swinden model of a crack with a yielded region or plastic zone at its tip was adapted to the analysis of delamination wear. In contrast with linear-elastic models this analysis includes an explicit dependence on flow strength consistent with the well-known influence of hardness on wear rate. It also predicts step changes in wear rate at a critical load under certain conditions; this has occasionally been observed.

A re-evaluation of the factors affecting the flow strength of materials in the metal-cutting operation has been made by comparing experimental machining data with results from the dynamic shear testing and punching of metals. An analysis of the primary shear zone, made on the assumption that all the plastic work is done in a discrete, parallel-sided region, has been used to calculate the values of n and σl in the schematic stress-strain relationship σ=σl(e)n. Results are presented for commercially pure copper in the shear strain rate range 0·1–7 × 104S−1 and for low-carbon steel in the range 0·1–20 − 104S−1. It is also demonstrated that the flow strength of these materials in the secondary shear zone is considerably lower than the strength in primary shear and is comparable with the yield stress values. The physical significance of these results is qualitatively discussed in terms of the equivalent stress-strain relationships under warm-working conditions.

Single and multistage, uniaxial compression tests are conducted on Al-Mg-Si and 0.02% Nb HSLA steel alloys. Rate sensitivity, activation energy and the effect of interruption on the flow strength of the metals are determined.

Uniaxial tensile tests are performed on a polymethyl methacrylate (PMMA) grade over a range of temperatures near the glass transition and over two decades of strain rate. Deformation maps are constructed for Young's modulus, flow strength, and failure strain as a function of temperature for selected strain rates. The glassy, glass transition and rubbery regimes are identified, and constitutive relations are calibrated for the modulus and flow strength within each regime.