Fracture Strain Decrease Research Articles

Tensile fracture of graphene nanoribbons encapsulated in single-walled carbon nanotubes

In this paper, we performed molecular dynamics simulations to study the fracture characteristics of a graphene nanoribbon encapsulated in a single-walled carbon nanotube (GNR@SWCNT) subjected to a uniaxial tensile loading. The effects of size and temperature on the fracture strength of nanocomposites under different strains were examined. The fracture strength and fracture strain of the nanocomposites increase with decreasing nanotube diameter. The maximum fracture strength and the corresponding fracture strain of GNR@SWCNT with a (10, 10) nanotube at 300 K were 126.3 GPa and 0.36, respectively. However, the fracture strength and fracture strain decrease with increasing temperature. The simulation results are useful in the design of nanodevices composed of carbon nanotubes and graphene nanoribbons.

Experimental investigation and modeling of ductile fracture behavior of TRIP780 steel in hot working conditions

In this research, the fracture and hardening behaviors of TRIP780 steel in hot working conditions are explored and studied via the uniaxial tensile test and using a newly proposed necking correction method. The hot working conditions used in the experiment include the forming temperature falling in 550–850°C and the strain rate range of 0.005–5s−1. It is revealed that the strain rate has a less effect on the formability of material at the testing temperature and the variation of hardening rate is less apparent at the higher working temperature. From the fracture point of view, the fracture strain is increased from 0.005 to 0.1s−1, due to the nucleation and growth of voids and the dynamic equilibrium between recovery and strain hardening. However, an apparent decrease of fracture strain at the strain rate of 0.1–5s−1 indicates that the decrease of ductility is caused by the dominating strain hardening mechanism, viz., dislocations pile-up. Furthermore, a set of damage-viscoplasticity constitutive model based on the nucleation growth of voids and dislocation density was proposed for in-depth understanding of the hardening and fracture behaviors of TRIP780 in hot working conditions.

Characterization and micromechanical modelling of microstructural heterogeneity effects on ductile fracture of 6xxx aluminium alloys

Ductile failure of three 6xxx serie aluminium alloys has been characterized and modelled for about thirty hardening conditions each. These alloys involve relatively similar composition and volume fraction of second phase particles. The tensile mechanical properties show the expected decrease of fracture strain with increasing strength but also major differences among the different alloys with a factor ten in terms of reduction of area at fracture between best and worst case. The origin of these differences is unraveled by detailed characterization of the void nucleation, growth and coalescence process involving in situ 3D microtomography. A cellular automaton model, involving a high number of particles with distributions of position, sizes and void nucleation stress is developed to predict the fracture strain. Excellent predictions are obtained based on the same unique nucleation stress distribution versus particle size for the three alloys. The key element setting the fracture strain is the effect of particle size distribution and spatial distribution on the void nucleation and coalescence processes. The dependence of ductility on strength is properly captured as well.

Study of effect of Zr addition on the microstructures and mechanical properties of (TiCx–TiB2)/Cu composites by combustion synthesis and hot press consolidation in the Cu–Ti–B4C–Zr system

The 50vol.% (TiCx–TiB2)/Cu composites were successfully fabricated by the method of combustion synthesis and hot press consolidation in a Cu–Ti–B4C–Zr system. The effect of the content of Zr on the microstructures, hardness, compression properties and abrasive wear behaviors of the composites was investigated. The final products consist of only Cu, TiCx and TiB2, and the ceramic particles distribute uniformly in the composites. The sizes of the ceramic particles decrease with Zr addition. With the increasing Zr content, the yield strength, ultimate compression strength and hardness increase, and the fracture strain decreases. The abrasive wear resistance of the composites increases with the increase in the Zr content.

Quasi-static and dynamic deformation behaviors of an in-situ Ti-based metallic glass matrix composite

Quasi-static and dynamic deformation behaviors of a dendrite reinforced metallic glass matrix composite: Ti58Zr16V10Cu4Be12 were investigated in this study. Upon quasi-static compression, the composite exhibits distinguished work-hardening capacity. The ultimate strength approaches 1970MPa, accompanied by the fracture strain of about 14.5%. The work-hardening of the ductile dendrites accounts for the macroscopic plasticity of the composite, and high strength of the glass matrix is responsible for the large ultimate strength of the composite. On the other hand, although the composites exhibit plasticity upon dynamic loading, the fracture strain decreases, due to the fact that there is not enough time for the initiation of multiple shear bands, leading to the decrease of the resistance to fracture. The ultimate strength and fracture strain of the present composites and some other in-situ and ex-situ composites upon dynamic loading reported by previous investigations are compared.

Effect of Cr Content on the Compression Properties and Abrasive Wear Behavior of the High-Volume Fraction (TiC–TiB2)/Cu Composites

The (TiC–TiB2)/Cu composites with 50 vol% TiC–TiB2 ceramic particles were successfully fabricated by the combustion synthesis and hot press consolidation in a Cu–Ti–B4C–Cr system. The effects of the Cr content on the microstructures, hardness, compression properties, and abrasive wear behaviors of the composites were investigated. The final products consist of only Cu, TiC, and TiB2 phases, and the ceramic particles are distributed uniformly in these composites. The size of the ceramic particles decreases with Cr addition. As the Cr content increases, the yield strength, ultimate compression strength, microhardness, and abrasive wear resistance of the composites increase, and the fracture strain decreases.

Mechanical properties and failure mechanisms of graphene under a central load.

By employing molecular dynamics simulations, the evolution of deformation of a monolayer graphene sheet under a central transverse loading are investigated. Dependence of mechanical responses on the symmetry (shape) of the loading domain, on the size of the graphene sheet, and on temperature, is determined. It is found that the symmetry of the loading domain plays a central role in fracture strength and strain. By increasing the size of the graphene sheet or increasing temperature, the tensile strength and fracture strain decrease. The results have demonstrated that the breaking force and breaking displacement are sensitive to both temperature and the symmetry of the loading domain. In addition, we find that the intrinsic strength of graphene under a central load is much smaller than that of graphene under a uniaxial load. By examining the deformation processes, two failure mechanisms are identified namely, brittle bond breaking and plastic relaxation. In the second mechanism, the Stone-Wales transformation occurs.

Sucrose release from agar gels: Effects of dissolution order and the network inhomogeneity

The effect of sucrose addition prior to or following the dissolution of agar on sucrose release from 1 wt% agar gels was studied. The order of addition was found to affect the fracture stress, fracture strain and sucrose release ratio. At sucrose concentrations below 30%, the rheology (fracture stress and strain) and structure of the gels did not depend on the order of addition of sucrose and agar. At sucrose concentrations >40%, however, the network structure of gels where sucrose was dissolved before agar addition was weaker than that of gels where sucrose was added after agar dissolution. The weaker network structure resulted in lower fracture stress and strain values. For gels prepared by adding agar to sucrose solutions, both fracture stress and strain decreased with increasing sucrose concentration in the range 40–55%. The decrease in fracture stress and strain led to an increase in the sucrose release ratio. The sucrose release ratio decreased monotonously with increasing concentration of sucrose when agar was dissolved prior to sucrose addition. The findings are discussed in relation to recent publications on gel inhomogeneity.

Effects of TiB2 content and alloy elements (Mg, Mo, V) on the compression properties of high-volume-fraction TiB2/Al composites

The compression yield strength and hardness of the TiB2/Al composites increase with the increase in the TiB2 content, while the fracture strain decreases, and the ultimate compression strength first increases and then decreases. The addition of Mg improves the ductility of the 50vol% TiB2/Al composite along with maintaining the ultimate compression strength. The fracture strain of the TiB2/Al–Mg composite increases from 8.18% to 10.68%. The addition of Mo significantly improves the compression yield strength and hardness of the composite while sacrificing the ductility. The compression yield strength and the hardness of the TiB2/Al–Mo composite are, respectively, 296MPa and 107.5Hv higher than that of the TiB2/Al composite, but the fracture strain decreases to 4.41%. With the addition of V, the TiB2/Al–V composite possesses the highest ultimate compression strength and relatively good ductility. The ultimate compression strength of the TiB2/Al–V composite is 218MPa higher than that of the TiB2/Al composite, and the fracture strain is 6.73%.

Effects of γ-irradiation and strain rate on the tensile and the electrical properties of Al-4043 alloy

Effects of γ-irradiation and strain rate on the tensile and the electrical properties of Al-4043 alloy were studied. Samples of Al-4043 alloy were exposed to γ-rays using 60Co radiation source with dose rate 74Gy/min at room temperature (RT), in air. The different doses are 0.5, 1, 1.5 and 2MGy, the samples were strained with strain rates (ε=5.4×10–5, 7.6×10−4 and 1.2×10−3s−1) at RT. It was found that; (i) the fracture stress (σF) increases as the dose and/or ε increases while the fracture strain (ɛF) decreases (ii) the strain rate sensitivity index (m) decreases as the dose increases and (iii) the electrical resistivity (ρ) increases as the dose and/or ε increases. Microstructure can be observed using X-ray diffraction technique (XRD) and Scanning Electron Microscope (SEM). It indicates the presence of Si-phase distributed within the Al-matrix. The interpretation of the results was offered on the ground that γ-rays interact with the alloy and create point and line defects that hinder the dislocation movement and finely distribute Si-phase leading to an increase in the alloy hardness.

Fracture analysis of single-layer graphene sheets with edge crack under tension

In this study, the fracture of single-layered graphene sheets (SLGSs) with edge crack under simple tension is investigated using molecular dynamics simulations, and the variations in fracture strength of SLGSs with crack length, strain rate and temperature are analysed. It is found that the existing edge crack weakens mechanical properties of SLGSs. Fracture strength and strain decrease with the increase in crack length and temperature, but increase with the increase in strain rate. It is also shown that shorter initial cracks propagate faster than longer initial cracks, but shorter initial cracks begin propagating at higher axial strain at a certain temperature and strain rate. And cracks are found to propagate faster in higher strain rates.

Effect of neutron irradiation on tensile properties of materials for pressure vessel internals of WWER type reactors

Tensile properties of austenitic stainless steels used for pressure vessel internals of WWER type reactors (18Cr–10Ni–Ti steel and its weld metal) in the initial and irradiated conditions were investigated. Based on the presented original investigations and generalization of the available experimental data the dependences of yield strength and ultimate strength on a neutron damage dose up to 108dpa, irradiation temperature range 320–450°С and test temperature range 20–450°С were obtained. The method of determination of the stress–strain curve parameters was proposed which does not require uniform elongation of a specimen as an input parameter. The dependences was proposed allowing one to calculate the stress–strain curve parameters for 18Cr–10Ni–Ti steel and its weld metal for different test temperatures, different irradiation temperatures and doses. The dependences were obtained to describe the fracture strain decrease under irradiation at a temperature range 320–340°С when irradiation swelling is absent.

Macroscopic Fracture Behaviour of CrN Hard Coatings Evaluated by X-Ray Diffraction Coupled with Four-Point Bending

Fracture behavior of hard nanocrystalline coatings decisively influences the lifetime and performance of coated tools. In this work, residual stresses in as-deposited and annealed CrN coatings deposited at 350 °C using bias voltages of −40 V and −120 V were evaluated using synchrotron X-ray diffraction coupled with four-point bending. The stress development during the bending experiments was used to analyse fracture properties of the coatings. The results indicate that an annealing at 550 °C does not deteriorate the fracture behavior of the coatings prepared using −40 V bias. In the case of −120 V bias coatings, the residual stress relaxation after the thermal treatment is accompanied by a fracture strain decrease and a fracture stress increase. The as-deposited and annealed CrN coatings deposited using −120 V bias exhibit significantly large fracture strains in comparison with −40 V samples. Finally the results document that the fracture stress may not be the only relevant parameter when comparing different coating systems. Also the strain at fracture can be considered as significant indicator of the coating fracture response. Methodologically, the results indicate that in-situ X-ray diffraction coupled with four point bending can be effectively used to evaluate macroscopic fracture behaviour of hard coatings.

The effect of degradation on κ-carrageenan/locust bean gum/konjac glucomannan gels at acidic pH

The feasibility of textural and rheological modification of gels containing κ-carrageenan (KC) and locust bean gum (LBG) by addition of konjac glucomannan (KGM) was investigated. Special attention was paid to the effect of polysaccharide degradation during heating at acidic pH. The general effect of polysaccharide degradation was to decrease the Young's modulus, while the fracture strain in extension was scarcely affected unless the degradation was very severe.Differential scanning calorimetry showed that the melting peak corresponding to dissociation of KC–KGM bonds decreased faster than the melting peak of KC-only bonds with increasing degree of polysaccharide degradation. The implication is that as degradation proceeds, fewer KGM molecules can interact with KC to form elastic bonds, and the excess of KGM which reinforces the existing elastic network and increases the fracture strain actually increases. For this reason, the fracture strain remains nearly unchanged with increasing degradation levels. A decrease in fracture strain is thus observed only at very severe degradations, where KC no longer forms a self-supporting gel by itself.

Experimental and numerical study of dynamic strain ageing and its relation to ductile fracture of a C–Mn steel

Abstract Ductile fracture of a C–Mn steel was characterized by tensile tests performed in a large temperature range (from 20 to 350 °C) on round notched and CT specimens. The experimental results revealed a sharp decrease in fracture strain and fracture toughness around 200 °C. These temperatures correspond to the domain of dynamic strain ageing (DSA). The Portevin-Le Chatelier (PLC) effect, which is the most classical manifestation of DSA, was simulated for round notched and CT specimens with a mechanical constitutive model which includes the strain ageing effect and the stiffness of the testing machine. It is shown that changes in stiffness can amplify the DSA effect. 3D-Modeling was used to correctly capture the complex space-time correlation of strain localization, particularly in side-grooved CT specimens. The results were compared to classical elastic–plastic simulations. The local approach to fracture was then applied to predict the ductile fracture of round notched specimens using the Rice and Tracey criterion. In the DSA domain, the approach used in this study predicts a decrease of the fracture strain which is less than observed experimentally.

Modifying the mechanical properties of lead-free solder by adding iron and indium and using a lap joint test

Eliminating lead in electronics is an environmental consciousness that is taken prior to manufacturing. Lead-free solder has recently been developed to advance that goal. One of the most common types of lead-free solder is Sn–Ag–Cu(SAC). Adding alloying elements can modify the properties of SAC. The present study is devoted to the research and development of SAC for microelectronic packaging applications. The effects of iron and indium addition to SAC were investigated. Four different samples were fabricated by casting: Sn–3.6Ag–0.9Cu, Sn–3.6Ag–0.9Cu–0.2Fe, Sn–3.6Ag–0.9Cu–0.6Fe, and SAC-InCe. Reliability tests were done on Cu and Ni–P substrate. The shear strength of the joint was improved by decreasing the intermetallic compound (IMC) thickness; so the IMCs thickness must be controlled, because the formation of IMC leads to joint embrittlement at the interface. In conclusion, the addition of In and Fe can improve mechanical properties, such as shear strength, but the addition of In appears to be more effective for increasing the fracture toughness. The addition of Fe lowers the wetting angle and it can effectively improve the solder reliability, this improvement in shear behavior for the samples, which were reflowed on Cu substrate, is enhanced compared with the Ni substrate, but 0.6% Fe addition for the Cu substrate illustrates an decrease in fracture strain, because of abnormal growth of Cu6Sn5Whiskers in this case.

Experimental studies on mechanical behavior and microstructural assessment of glass/epoxy composites at low temperatures

A series of flexure tests with varying crosshead speed were conducted to study the mechanical behavior of glass/epoxy composites at low temperature. The micromechanics of damage growth and failures underpin the understanding of the revealed fractography. The three-point flexure test of heat-treated and untreated samples was carried out, which were further exposed to low and ultra-low working temperatures of −20°C, −40°C, −60°C, −80°C. The interlaminar shear strength was found to be affected by these conditionings. The unbalanced and inhomogeneous stress concentration within entangled chain of matrix reduces conformational isomerism which in turn reduces the ILSS value considerably at low crosshead speed. At increased crosshead speed (strain rate), the matrix becomes brittle and fracture strain decreases, but at very high strain rate, the fracture strain increases. The reason is anticipated to be adiabatic heating. Temperature-modulated differential scanning calorimetry shows increase in glass transition temperature ( Tg). A change in crosshead speed may result in variation of failure modes, which is observed in scanning electron microscope.

Microstructural and Mechanical Properties of Polyester/Nanoclay Nanocomposites: Microstructure-Mixing Strategy Correlation

ABSTRACTDifferent nanoclay mixing strategies using a three-roll mill and ultrasonication is proposed to obtain the desired polyester/nanoclay dispersion, intercalation, and exfoliation. The dispersion states of the modified nanoclay in polymer with 2, 4 and 6 wt% loading were characterized with X-ray diffraction, scanning electron microscopy (SEM), and low and high magnification transmission electron microscopy (TEM). The mechanical properties of the clay-reinforced polyester nanocomposites were a function of the nature and the content of the clay in the matrix. The nanocomposite containing 4 wt% modified Cloisite® 15A exhibits excellent improvement in modulus (by ~51%) and tensile strength (by ~12%) with a decrease in fracture strain (by ~26%) and fracture energy (by ~17%). These mechanical characteristic changes can be attributed to the dispersion, intercalation, and exfoliation of the nanoclays inside the polyester matrix.

GS20 マイグレーションを考慮した諸燃糸複合材料の力学特性(GS-4 一般セッション4,一般セッション)

This paper describes an effect of twist contraction ratio (TCR) on tensile properties of ramie twisted yam for green composites. Twisted yams were made from single yams using an automatic or hand-operated twisting machine, in which the number of single yams and twist per inch (TPI) were changed. Then, TPI and TCR of twisted yarns using the automatic twisting machine were measured, and compared with those obtained from the hand-operated twisting machine. As a result, the former tends to have a variation in TCR. Tensile test was carried out for the two types of twisted yams. The results show that, as TCR increase, both type of twisted yarns increase in fracture load and decrease in fracture strain, but hand-operated twisting machine can give higher tensile properties. The correlations between TCR and fracture load, and fracture strain were strong, and it is expected that TCR can be a parameter related with tensile properties of twisted yams, rather than TPI. Further more, the twisted yarn was used as a reinforcement of poly-vinyl alcohol (PVA) resin, and its mechanical properties were measured.

High room-temperature plastic and work-hardening effect of the NiAl-matrix composites reinforced by particulates

The microstructures, interfaces, compression properties and work-hardening effect of the NiAl-matrix composites reinforced by 5–20 wt.% ceramic particulates (Nb 2C, NbC and NbB 2) fabricated by combustion synthesis and hot pressing (CSHP) have been investigated. The ultimate compression strength and yield strength increase with the increasing content of the ceramic particulates, while the fracture strain and work-hardening capacity ( H c) decrease. The NiAl-matrix composite with 5 wt.% ceramic particulates has a high true ultimate strength of 1497 MPa, a fracture strain of 18.3%, and work-hardening capacity H c = 1.29. The good interface bonding between ceramic particulate and matrix, the high density dislocation in the NiAl matrix, the seriously distorted lattices and the intense interactions between dislocations and other crystal defects contribute to its prominent mechanical properties.