Tearing energy of AZ31 magnesium alloy sheets determined by the multiple tensile testing method

Tearing energy of the AZ31 magnesium alloy sheets in the annealed (O-tempered) and half-hard (H24) conditions was studied in both rolling and transverse directions by the multiple tensile testing method. The results showed that while plastic deformation energy was primarily controlled by the strain hardening exponent, tearing energy was directly related to the neck breadth parameter N, which depends on the strain hardening, strain rate hardening, and plastic anisotropy of the tested sheets. It was also found that the tearing energies obtained for the annealed AZ31 sheets were comparable to those of AA5010 aluminium sheets, while the plastic deformation energies were much higher than those of aluminium sheets. This may imply that AZ31 magnesium sheets can be potential candidates for dissipating the impact energy in the vehicles structures which are prone to collision.     

Deformation energy of NiTi shape memory wires

Deformation energy of NiTi wires with B2 and R phases was studied by the multiple tensile testing (MTT) method. In traditional materials, the total energy required to tear specimens is assumed to be the sum of elastic, uniform plastic, and post-uniform or tearing energy components. For the shape memory alloys, however, this classification is not valid due to their unusual superelastic/shape memory characteristics. Using a modified MTT method, different energy components were calculated by plotting different combination of deformation energies divided by the specimen cross-sectional area against the gage length of the specimens. The slope of the obtained straight line demonstrates the summation of the elastic, superelastic/shape memory, second elastic, and plastic energy per unit volume and its intercept gives the value of tearing energy. It was found that the uniform plastic energy per unit volume for the R-phase wires was considerably higher than that for the B2-phase wires. This caused a marked enhancement in the total deformation energy of the R-phase wire, as compared to the B2-phase wire. The effect of strain rate on the tensile behaviour and deformation energies of these materials was also investigated. Except the plateau stress of the tensile curve which was raised for both wires, the B2-phase wires were almost strain-rate-independent, whereas the R-phase wires were significantly influenced by the variation in strain rate.     

Numerical analysis of panels’ dent resistance considering the Bauschinger effect

The Bauschinger effect should be considered in the analysis of panels’ dent resistance, because sheet metal experiences a complex loading history from stamping to denting. This paper studies the modeling and simulation of panels’ static dent resistance, taking the Bauschinger effect into consideration. Our work covers two parts: simulation and experiment. Procedures of drawing, springback I, indenting and springback II are simulated in a multiple step analysis. Different hardening models, including the isotropic hardening model, the linear kinematic hardening model and the nonlinear combined hardening model are used, respectively, in simulation. Comparing the simulation results with the experiment results, we find that the Bauschinger effect has a great influence on panels’ dent resistance. When panels are made of high strength steel or stamped with a high Blank Holder Force (BHF), the Bauschinger effect on panels’ dent resistance is more severe. Considering the effect in numerical analysis would improve the simulation accuracy effectively. The work of this paper is beneficial to material selection and processing optimization for automobile exterior panels.     

Drawing,flanging and hemming of metallic thin sheets: A multi-step process

This study deals with the multi-step classical hemming process on samples with complex geometries and a pre-strain state linked to the forming of curved surface. The influence of taking the anisotropy and the Bauschinger effect into account on the roll-in and loads is studied. The design of a specific device was realised so as to compare the numerical results and the experimental values. The simulations show a certain relevance in the use of shell elements compared to solid elements despite their use restriction, and good correlation between the calculations and the tests. The roll-in differences and the level of stress reached are low at the end of pre-hemming and hemming, although a significant rotation of sections which are initially perpendicular to the mean fiber is observed during flanging.     

A parametric study on residual stresses and loads in drawing process with idle rolls

A comprehensive study of drawing process with flat idle rolls of round wires is presented through 3D mechanical finite element simulations. An elastic–plastic model is used for the wire material and contact behavior is simulated by a sliding–sticking friction model. The results of numerical simulations are compared with measurements on wires produced with a laboratory equipment. The comparison of drawing load and some geometrical characteristics of experimental samples with numerical model predictions allowed to establish a good correspondence of model with experimental findings, thus validating the numerical model. Residual stress of flat roll drawn wires, pressure distribution on the forming rolls and drawing load are studied. The effects of main process parameters such as initial workpiece diameter, forming rolls diameter and percentage of deformation are investigated. The results present a helpful insight into the process parameters effect in wire drawing with flat idle rolls thus furnishing the basic guidelines for process design and optimization.     

Effect of extrusion ratio on mechanical and corrosion properties of AZ31B alloys prepared by a solid recycling process

Some AZ31B magnesium alloy bars were prepared by a solid recycling process with different extrusion ratios. A reference specimen was processed by extruding an as-received AZ31 ingot. The microstructures, mechanical and corrosion properties of AZ31B magnesium recycled specimens were investigated. With increasing extrusion ratio, the yield strength, tensile strength and yield ratio increases. The reliability of the recycled alloy is poorer than the reference specimen. The corrosion rates of recycled AZ31B magnesium specimens increase immersed in both alkaline and neutral 4% NaCl solution with a decrease extrusion ratio. The corrosion resistance of recycled AZ31B magnesium specimens is improved with increasing pH of immersed solution. The recycled specimens show superior corrosion resistance than reference specimen.     

Optimization of magnetic arc oscillation process parameters on mechanical properties of AA 5456 Aluminum alloy weldments

The present work pertains to the improvement of mechanical properties of AA 5456 Aluminum alloy welds through magnetic arc oscillation process. Taguchi method was employed to optimize the magnetic arc oscillation welding process parameters of non-heat treatable AA 5456 Aluminum alloy welds for increasing the mechanical properties. The same optimum condition was observed in all the properties. Regression models were developed. The effect of welding current, welding speed, amplitude and frequency on mechanical properties was also studied. Analysis of variance was employed to check the adequacy of the developed models. Microstructures of all the welds were studied and correlated with the mechanical properties.     

Two-step method to evaluate equibiaxial residual stress of metal surface based on micro-indentation tests

The present study proposed a method to evaluate the equibiaxial compressive residual stress of a metal surface by means of a depth-sensing indentation method using a spherical indenter. Inverse analysis using the elastic–plastic finite-element model for an indentation test was established to evaluate residual stress from the indentation load–depth curve. The proposed inverse analysis utilizes two indentation test results for a reference specimen whose residual stress is already known and for a target specimen whose residual stress is unknown, in order to exclude the effect of other unknown mechanical properties, such as Young’s modulus and yield stress. Residual stress estimated by using the indentation method is almost identical to that measured by X-ray diffraction for indentation loads of 0.49–0.98 N. Therefore, it can be concluded that the proposed method can effectively evaluate residual stress on metal surface.     

Evaluation the effect of aspect ratio for Young’s modulus of nanobelt using finite element method

The traditional nanoindentation method provides experimental data for the calibrating mechanical parameters of nanobelt through semi-empirical formulae. In this paper, a technique to identify Young’s modulus of nanobelts with different aspect ratios is introduced combining finite element method (FEM) and nanoindentation test. For the nanobelt on the substrate, the power function relationship is used to describe the loading curve of the nanobelt indentation behavior. The loading curve exponent of the power function which is the fitting parameter can reflect the influence of aspect ratio of nanobelt on Young’s modulus of nanobelts as well as the maximum indentation load. In the forward analysis, considering the substrate effect and the size effect, the numerical loading responses are simulated at the appropriate penetration depth, and then the dimensionless equations between the parameters characterizing the indentation loading curve and the properties of nanobelt/substrate system can be established via extensive FEM simulation. In the reverse analysis, the nanoindentation tests were performed on ZnO and ZnS nanobelts, and the experimental indentation loading curves can be fitted as power function. The maximum indentation loads and the loading curve exponents are extracted from two experimental loading curves, and then they are substituted into the dimensionless equations to solve the Young’s moduli of ZnO and ZnS nanobelts. The results show the Young’s moduli solved are close to previous values, indicating that the Young’s moduli are reasonable. This developed method is effective to identify the Young’s modulus of nanobelt and it can be applied to identify the Young’s modulus of other nanobelts in practice.     

Enhancement and prediction of modulus of elasticity of palm kernel shell concrete

This paper presents results of an investigation conducted to enhance and predict the modulus of elasticity (MOE) of palm kernel shell concrete (PKSC). Scanning electron microscopic (SEM) analysis on palm kernel shell (PKS) was conducted. Further, the effect of varying sand and PKS contents and mineral admixtures (silica fume and fly ash) on compressive strength and MOE was investigated. The variables include water-to-binder (w/b) and sand-to-cement (s/c) ratios. Nine concrete mixes were prepared, and tests on static and dynamic moduli of elasticity and compressive strength were conducted.     

Nanoindentation study of magnetron-sputtered CrN and CrSiN coatings

CrN and CrSiN coatings were deposited on stainless steel substrate by reactive magnetron sputtering. The coatings were characterized for phases, chemical composition, microstructure, and mechanical properties by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM)/energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), and nanoindentation technique, respectively. The cubic phase was the only phase observed in both the coatings as observed in XRD results. A dense morphology was observed in these coatings deposited with high nitrogen and Si contents, 50:50 and 18.65 at.%, respectively. Nanoindentation measurement of CrN coatings, with Ar + N₂ proportions of 60:40, showed maximum hardness (H) and modulus (E) of 21 ± 0.85 GPa and 276 ± 13 GPa, respectively. The CrN coatings deposited in pure N₂ atmosphere showed H and E values of 27 ± 1.62 and 241 ± 10 GPa, respectively. The measured H and E values of CrSiN coatings were found to be 28 ± 1.40 GPa and 246 ± 10 GPa, respectively. The improved hardness in both the coatings was attributed mainly to a reduction in crystallite size, decrease in surface roughness, and dense morphology. The incorporation of Si into the CrN coatings has improved both hardness and Young’s modulus.     

Effects of applied pressure on microstructure and mechanical properties of squeeze cast ductile iron

In this study, the effects of applied pressure during solidification on the microstructure and mechanical properties of cylindrical shaped ductile iron castings were investigated. Magnesium treated cast iron melts were solidified under atmospheric pressure as well as 25, 50 and 75 MPa external pressures. Microstructure features of the castings were characterized using image analysis, optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. Tensile properties, toughness and hardness of the castings were also measured. The results showed that average graphite nodule size, free graphite content and ferrite content of the castings decreased and pearlite and eutectic cementite contents increased as the applied pressure was raised from 0 to 75 Mpa. Graphite nodule count was first increased by raising the applied pressure up to 50 MPa and then decreased. The highest graphite nodule count was obtained at 50 MPa applied pressure. The microstructural changes were associated with the improved cooling rate and the expected changes in the corresponding phase diagram of the alloy under pressure. The ultimate tensile strength (UTS), yield point strength (0.2% offset) and fracture toughness of the castings were improved when the applied pressure was raised from 0 to 50 MPa. Further increase of the applied pressure resulted in slight decrease of these properties due to the formation of more cementite phase in structures as well as reduced graphite nodule count. Hardness of the castings continuously increased with increasing the applied pressure.     

Study of microstructural evolution and mechanical properties exhibited by non alloyed ductile iron during conventional and stepped austempering heat treatment

It was evaluated the microstructural and mechanical response that a non alloyed ductile iron (DI) presented when was subjected to Conventional Austempering (CA) and Stepped Austempering (SA) heat treatments. X-ray Diffraction (XRD) quantification techniques demonstrated to be the more reliable method for monitoring phase transformations taking place during both CA and SA. When CA was applied some intercellular areas remain untransformed even for long time, however when samples were subjected to SA those untransformed areas disappeared and instead finer ausferrite was found. Additionally mechanical properties values obtained from tensile and impact tests confirmed that for all times used, SA was superior to the CA.     

Microstructural evolution and mechanical properties of oil jet peened aluminium alloy,AA6063-T6

Grain size refinement by severe surface plastic deformation is one way of improving the surface properties. This paper describes the microstructural evolution due to severe surface plastic deformation by oil jet peening in aluminium alloy, AA6063-T6. Detail characterization of the treated surfaces using X-ray diffraction analysis and transmission electron microscopy revealed the formation of submicron size grains at and near the surface. The nozzle-traveling velocity decides the peening intensity and coverage and affects the surface properties. The specimen peened at low nozzle-traveling velocity exhibited an ultrafine grain size (∼210 nm) with high surface hardness (∼0.88 GPa), compressive residual stress (−102 ± 7 MPa) and dislocation density. The hardness is high at the surface and the depth of hardened layer is ∼400 μm. Formation of high-density dislocations and associated grain refinement resulted in increased surface hardness. Presence of surface modified layer will be beneficial in improving the fatigue and tribo behavior.     

Influence of microstructures on fatigue damage mechanisms in Ti-15-3 alloy

In this study, the fatigue behavior of Ti-15-3 alloy thin plate specimens with two different microstructures was determined. Two kinds of specimens were prepared with different heat treatments: solution treatment (S) and solution treatment followed by aging (S+A). The effects of the microstructures on the fatigue properties and fatigue crack growth behavior were significant in both specimens. The fatigue crack in both specimens propagated in transgranular mode. In the specimen S+A, crack propagation has occurred on non-crystallographic and was closely connected with the configuration of the α-phase platelet, which was caused by the heat treatment. The damage was characterized by dislocation debris clustering ahead of the crack tip.     

Analysis of mixed-mode interlaminar fracture and damage behavior of GFRP woven laminates at cryogenic temperatures

The objective of this work is to investigate the interlaminar fracture and damage behavior of glass fiber reinforced polymer (GFRP) woven laminates loaded in a mixed-mode bending (MMB) apparatus at cryogenic temperatures. The finite element analysis (FEA) is used to determine the mixed-mode interlaminar fracture toughness of MMB specimen at room temperature (RT), liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). A FEA coupled with damage is also employed to study the damage distributions within the MMB specimen and to examine the effect of damage on the mixed-mode energy release rate. The technique presented can be efficiently used for characterization of mixed-mode interlaminar fracture and damage behavior of woven laminate specimens at cryogenic temperatures.     

Design and fabrication of porous ZrO2/(ZrO2 + Ni) sandwich ceramics with low thermal conductivity and high strength

3Y–ZrO₂/(3Y–ZrO₂ + Ni) sandwich ceramics were fabricated through cold isostatic pressing and pressureless sintering. Porous 3Y–ZrO₂ ceramics with large connecting open pores and permeability were used as interlayers for insulation, whereas outer metal–ceramic layers were used as bearing loads. Microstructures and properties of the porous ZrO₂ and ZrO₂/(ZrO₂ + Ni) sandwich ceramics were investigated in detail. The ZrO₂/(ZrO₂ + Ni) sandwich ceramics exhibited better mechanical properties than the monolithic porous ZrO₂ ceramics at the same low thermal conductivity (approximately 0.85 W/m K). The mechanical properties of the sandwich ceramics were influenced by metal toughening and sintering-induced residual thermal stress.     

Strength development versus process data in ultrasonic welding of thermoplastic composites with flat energy directors and its application to the definition of optimum processing parameters

Ultrasonic welding of thermoplastic composites is a very interesting joining technique as a result of good quality joints, very short welding times and the fact that no foreign material, e.g. a metal mesh, is required at the welding interface in any case. This paper describes one further advantage, the ability to relate weld strength to the welding process data, namely dissipated power and displacement of the sonotrode, in ultrasonic welding of thermoplastic composite parts with flat energy directors. This relationship, combined with displacement-controlled welding, allows for fast definition of optimum welding parameters which consistently result in high-strength welded joints.     

Investigation on the effect of lubrication and forming parameters to the green compact generated from iron powder through warm forming route

In order to generate green compacts of iron ASC 100.29 powder at above ambient temperature and below its recrystallization temperature, a warm compaction rig is designed and fabricated which can be operated at various temperature and load. The aim of this paper is to present the outcomes of an investigation on the effect of lubrication and forming parameters, i.e., load and temperature to the green compacts generated through warm compaction route. The feedstock was prepared by mechanically mixing the main powder constituent, i.e., iron ASC 100.29 powder with different weight percent of zinc stearate at different mixing time. Compaction load was varied from 105 kN to 125 kN using simultaneous compaction mechanism. The microstructures of the green compacts were analyzed by Scanning Electron Microscopy (SEM), and the mechanical properties are measured through density measurement, hardness test and electrical conductivity test. The study found that increase in compaction load as well as forming temperature give improved microstructure and mechanical properties. It is also found that effects of lubrication to the mechanical properties of green compacts are strongly dependant on the lubricant content as well as mixing time of iron powder with the lubricant.     

Development,characterization and analysis of auxetic structures from braided composites and study the influence of material and structural parameters

Auxetic materials are gaining special interest in technical sectors due to their attractive mechanical behaviour. This paper reports a systematic investigation on missing rib design based auxetic structures produced from braided composites for civil engineering applications. The influence of various structural and material parameters on auxetic and mechanical properties was thoroughly investigated. The basic structures were also modified with straight longitudinal rods to enhance their strengthening potential in structural elements. Additionally, a new analytical model was proposed to predict Poisson’s ratio through a semi empirical approach. Auxetic and tensile behaviours were also predicted using finite element analysis. The auxetic and tensile behaviours were observed to be more strongly dependent on their structural parameters than the material parameters. The developed analytical models could well predict the auxetic behaviour of these structures except at very low or high strains. Good agreement was also observed between the experimental results and numerical analysis.