Tensile Impact Research Articles

Low-Temperature Fracture of Ultrafine-Grained Iron

Metals with a body-centered cubic structure such as iron exhibit a ductile-brittle transition which results in a brittleness below a particular temperature. This temperature depends on many factors such as strain rate, size and geometry of investigated samples or the purity of the material. Another important parameter influencing fracture mechanism is grain size. It is known that grain refinement can be an efficient way to change fracture mechanism.The goal of this study was to investigate fracture mechanisms of ultrafine-grained iron processed by hydrostatic extrusion (HE). Materials subjected to various total strain levels were tested. The average grain size of the HE-processed iron was below 350 nm. The mechanical tests were carried out at various temperatures, ranging from room temperature to liquid nitrogen temperature. It was found that the fracture mechanism depends on a density of dislocation and the loading direction. It was found that materials with the dislocation density above a certain critical value break in a ductile manner even at impact tensile test in liquid nitrogen. However, bending tests of miniature beams have shown that ductile fracture occurs only when the crack propagates along the radial direction of the extruded material, whereas, on the direction parallel to the axial direction, cleavage fracture was observed. A theoretical model explaining this phenomenon was proposed. This model is based on the Rice model and it considers the competition between two phenomena - dislocation slip in the stress field of the crack front and Griffith cleavage.

A Study in the field of Welding of Different Materials

Objectives: The investigation was done with the aim of studying the influence of basicity index on mechanical properties of the structural steel. Methods/Statistical Analysis: In this experiment, influence of Basicity index on the welding characteristics was analyzed in the submerged arc welding by keeping all other variables like current, voltage and welding speed constant. The effects of wire/flux (Basicity index) on ultimate tensile strength, Microstructure and impact strength of the weld metal was investigated. Weld deposits on structural steel plates were made at different flux composition. In these experiment plates of dimension 14x125x250 mm was used for welding. The specimens were cut out from the welded plate to carry out various tests after performing the saw operation. Five different types of fluxes were used to weld the plates. Findings: The impact toughness values at room temperature increases with increase in basicity index of flux and highest micro hardness values are formed at the Heat Affected Zone (HAZ) regions for welded specimens. Keywords: Dissimilar Metals, Steel, Welding

Effect of the Supplementary Aging Process on the Microstructure and Mechanical Properties of Mg–5Sn and Mg–5Sn–0.5Zn Alloys

This paper presents a novel aging process consisting of two stages: an aging at 250 °C for 12 h and a supplementary aging at 70 °C for 18 h. The ingots of Mg–5Sn and Mg–5Sn–0.5Zn alloys were solution heat-treated for 24 h at 480 °C and then quenched in water. Afterward, aging treatments were performed. To compare the effects of this process on age hardening response of both alloys, other aging treatments were performed at 200 °C for 60 h and at 280 °C for 12 h. The age hardening responses were measured by the Vickers hardness test. The structure of specimens was investigated by XRF, DSC, XRD, and FE-SEM. Also, mechanical properties were determined by tensile test and Charpy impact test. Although by using supplementary aging process, maximum hardness of these alloys is not very different in comparison with single- as well as double-aging processes, the necessary times of aging processes are significantly lower than those at around 90%, 85%, and 50%. After the aging process, the microstructure of Mg–5Sn and Mg–5Sn–0.5Zn alloys consists of α-Mg, nano-metric particles of Mg2Sn, and GP-zones. In Mg–5Sn alloy, after supplementary aging process, the yield strength, ultimate tensile strength, and elongation increase to 151.2 MPa, 221.2 MPa, and 8% sequentially. In Mg–5Sn–0.5Zn alloy, the YS, UTS, and elongation increase to 154 MPa, 224 MPa, and 7%, respectively. The impact energy in both alloys is 6.63 J and 7.05 J, respectively.

TEMPO-oxidized cellulose nanofiber-reinforced lignin based polyester films as a separator for electric double-layer capacitor

Recently we developed a self-standing and flexible lignin-based polyester film (LPF) as a separator for electric double-layer capacitor (EDLC). However, the film showed very low mechanical strength. In this study, reinforcement of LPF was attempted with TEMPO-oxidized cellulose nanofiber (TOCN). Modulus of elasticity was remarkably increased with an increase in TOCN content. By 1% addition of TOCN, tensile strength at failure was also significantly increased with its flexibility maintained, resulting in the highest strain energy density among tested samples. Zero-span tensile test revealed that the improved tensile strength was caused by the TOCN strength. In addition, dynamic mechanical analysis and differential scanning calorimetry demonstrated that TOCN suppressed thermal deformation of LPF at elevated temperature. However, TOCN did not affect the tensile impact strength of the LPF. Finally, EDLC was assembled with the TOCN-reinforced LPF as a separator, hand-made electrodes with commercial activated carbon and conductive carbon black, and triethylmethylammonium tetrafluoroborate/propylene carbonate as an organic electrolyte. Although this EDLC showed higher specific capacitance than EDLC with commercial cellulosic separator as a reference, intrinsic and charge transfer resistances of this EDLC were much higher than those of the reference EDLC. By conversion of the LPF to porous film, the resistances were dramatically improved, and the specific capacitance was further enhanced. Consequently, LPF reinforced with 1% TOCN is a promising separator for EDLC.

Synthesis and Characterization of Poly(ester amide)s Consisting of Poly(L-lactic acid) and Poly(butylene succinate) Segments with 2,2′-Bis(2-oxazoline) Chain Extending

An aliphatic polyester based poly(ester amide)s (PEA) consisting of poly (L-lactic acid) and poly(butylene succinate) was successfully prepared via chain extension reaction of poly(L-lactic acid)-dicarboxylic acid (PLLA-COOH) and poly(butylene succinate)-dicarboxylic acid (PBS-COOH) using 2,2′-bis(2-oxazoline) as a chain extender. PLLA-COOH was obtained by direct polycondensation of L-lactic acid in the presence of 1, 4-succinic acid. PBS-COOH was synthesized by condensation polymerization of 1,4-butylene glycol with excessive succinic acid. The structures of PLLA-COOH, PBS-COOH, and PEAs were characterized by fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (1H NMR). The molar masses were determined by gel permeation chromatography (GPC). The thermal properties of PLLA-COOH, PBS-COOH, and PEAs were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The lattice parameters of PLLA-COOH, PBS-COOH, and PEAs were investigated by X-ray diffraction (XRD). Furthermore, The mechanical properties were characterized by tensile testing and notch Izod impact testing. The FTIR and 1H NMR results demonstrated the formation of PLLA-COOH, PBS-COOH, and PEAs. The GPC measurements showed that the molar masses of copolymer PEAs decreased with increasing PBS-COOH content. The TGA analysis confirmed that the introduction of PBS improved the thermal properties. DSC data indicated that the melting temperatures of the PEAs were lower than that of the prepolymers. The results of XRD suggested that the PLLA crystal structures was destroyed by the PBS units, and the crystallization of the PEAs mainly attributed to the PBS chain segments.The introduction of PBS units into the polymer structure improved the toughness of PLLA, which was detected in mechanical properties.

Mechanical properties and microstructure of glass carbon hybrid composites

Abstract In recent years, automobile, naval and aircraft structures are manufactured using composite materials reinforced with glass fiber, carbon fiber, etc., because of their high specific strength, good corrosion resistance, strength to weight ratio and applicability in saline environments. In this study, glass fiber reinforced plastic (GFRP), carbon fiber reinforced plastic (CFRP) and glass-carbon fiber reinforced plastic (GCFRP) laminated composites were manufactured by means of the hand layup process. Subsequently, a hole was drilled into each specimen of the above composites by means of conventional drilling and fine blanking and finally, the specimens were prepared as per ASTM standards D256, D790, D3039 and D 5868. A detailed study of the mechanical properties and micro-structure analysis of the above specimens and lap jointed specimen was carried out. It turned out that the tensile strength, impact strength and flexural strength of glass carbon hybrid fiber reinforced plastic composite was significantly higher as compared to the glass fiber reinforced plastic composite due to lower fiber breakage and fiber pull out in the fine blanking of the GCFRP.

Mechanical Properties Study of High Impact Polystyrene Under Impact and Static Tests

This article deals with the study of high impact polystyrene (HIPS) mechanical properties. Injection moulded samples were subjected to the tensile impact test, tensile test, impact test – Charpy and three-point bending test at the ambient temperature. Tensile test was measured at two crosshead speeds 50 and 500 mm/min and bending test at 2 and 50 mm/min. The results show the great adaptability of HIPS which classify this material to the group of very well adaptable polymers to different loadings.

Effect of Electroslag Refining on Cleanness, Microstructure and Mechanical Properties of a Newly Developed CrNiMoWMnV Ultrahigh-Strength Steel

The cleanness, microstructure and mechanical properties of a newly developed CrNiMoWMnV ultrahigh-strength steel with and without electroslag refining (ESR) with 70% CaF2, 15% Al2O3 and 15% CaO have been studied. This steel was designed and melted in an air induction furnace followed by refining using ESR. Cast ingots with and without ESR were forged at temperatures in the range 1100 - 950 °C. Laser scanning confocal microscopy, field emission scanning electron microscopy electron back scattering diffraction, electron probe microanalysis and X-ray diffraction have been used to investigate the microstructure and non-metallic inclusions (NMIs) of forged ingots produced with and without ESR. Hardness, tensile and Charpy-V impact tests were performed. ESR reduced the total impurity level i.e. O%+ N%+ S% by 26 % and the area fractions and numbers of NMIs by 17% and 7% respectively. The NMIs are classified into four major classes: oxides, sulphides, nitrides and complex multiphase inclusions. The microstructure of the forged and air-cooled bars consisted of martensite with a small fraction of distributed retained austenite, a very small fraction of bainite and finely distributed precipitates. The reduction of impurity levels combined with the microstructural changes brought about by the changes in the chemical composition meant that ESR resulted in a significant improvement in some mechanical properties and a marginal improvement in others.

INFLUENCE OF ALBASIA WOOD ON MECHANICAL PROPERTIES AND MORPHOLOGY OF EPOXY COMPOSITES

This research aims to investigate the effects of albasia wood filler as alternative reinforcement for extravagant and non-renewable filler being used in epoxy composites. The filler size used was 30 mesh and various filler volume fractions were 10, 20, 30 and 40 percent. Composites were manufactured using hand lay-up method. Properties such as tensile strength, elongation, modulus elasticity and strain energy absorption were determined based on ASTM standard. The results show that filler volume content significantly affects the tensile properties and impact strength of albasia wood-epoxy composites. The optimum tensile properties are achieved when 10 percent filler is added into epoxy matrix. The impact test also shows the same results. Further addition of filler decreases the mechanical properties of composites due to the existence of weak interfacial interaction between the albasia wood filler and polymer matrix for higher filler volume concentration beyond 10 vol. %. The scanning electron micrograph reveals that there are voids and pull-out mechanism on tensile fracture surface which are the cause of the composites failure.

Effect of graphite nanoplatelets on fracture behavior of HDPE/PA66 microfibrillar composites

Effect of in situ formation of PA66 fibrils and modification with graphite nanoplatelets (GNP) on fracture behavior of the high‐density polyethylene (HDPE)‐matrix microfibrillar composites (MFC) has been evaluated using tensile impact strength (TIS) and J‐integral methods. According to J‐integral, the main mechanism of failure is unstable crack growth; dissimilar layout of both methods causes different contribution of reinforcement with GNP and PA66 fibrils to fracture process evaluated. More marked orientation and parallel loading lead to increase in impact energy by both GNP and fibrils in TIS; on the other hand, much lower contribution of fibres and even negative effect of GNP pre‐blended in HDPE was found for J‐integral as a consequence of load acting in perpendicular direction. The fact that lower addition of GNP pre‐blended in PA66 does not deteriorate impact behavior indicates that such modification of MFC is an efficient way to get materials with enhanced, well‐balanced parameters. POLYM. ENG. SCI., 59:382–388, 2019. © 2018 Society of Plastics Engineers

Studies of the Properties and Microstructure of Heat Treated 0.27% C and 0.84% Mn Steel

In the present work, different heat treatments like hardening with different cooling rates followed by tempering at different temperatures have been performed. The material used in this study is carbon steel of 0.27% C and 0.84% Mn. Samples of as-rolled steel were subjected to different heat treatment processes. The steel was heated to the austenitizing temperature of 870°C for 2hrs followed by water quenching, oil quenching, air and furnace cooling. Water and oil quenched samples were subjected to tempering for one hour at temperatures of 250°C, 350°C, 450°C and 550°C. Tensile and impact tests were carried out for as rolled and heat-treated steel. Results show that the heat treated steel revealed an excellent combination of tensile strength and impact strength, which is suitable for structural applications. Optical metallographic investigation was carried out for all samples compared with the as rolled steel. The heat treatment revealed remarkable changes in steel morphology and mechanical properties.

Improvement of surface quality of 1.6220 cast steel by calibrating process and effects on material behavior

There is a growing demand for thin walled steel casting structural parts especially in the automotive industry. Therefore an economic casting process is needed, that provides high surface quality. Requirements of spot weldability and corrosion protection need to be met, which is not possible with high surface roughness. Therefore a calibrating step is introduced aimed at reducing the surface roughness of the sand cast steel samples. Besides surface quality, also changes in geometrical dimensions and mechanical properties are investigated. Calibrating was carried out as planar forging on a forging device. This combined process of casting and forging did lead to a significant reduction of the roughness values, but this effect could only be observed in the edge area of the investigated sample plates. Furthermore a deformation of material in thickness direction and flow of material in width direction was noted. A relationship between deformation in thickness direction and straightening was detected. Another one between material flow and reduction of roughness values. Tensile tests and impact tests revealed a more brittle behavior of the material in calibrated state. Also the influence of wall thickness and heat treatment was investigated. Whereas wall thickness (as the local amount of material) mainly determines deformability and in consequence the straightening effect, heat treatment increases the ability of the material to flow, which contributes to the reduction of surface roughness. The inhomogeneity of the surface effect in combination with an extraordinary high required force remain as the main issue in trying to achieve a uniform surface quality improvement by calibrating process.

Dynamic Model and Mechanical Properties of the Two Parallel-Connected CRLD Bolts Verified with the Impact Tensile Test

Dynamic model was theoretically established for the two parallel-connected constant-resistance-large-deformation (CRLD) bolts, and the theoretical results were experimentally verified with impact tensile tests on the CRLD bolts samples. The dynamic responses of the double CRLD bolts were investigated under the impact loads with different intensities. The theoretical analyses showed that (1) under relatively small loading the CRLD bolts deform elastically and the deformation finally returns to zero and (2) under the high impact load, including the stable impact load and unstable impact load, the CRLD bolts export structural deformation after the initial elastic deformation. The deformation of the bolts eventually stabilizes at a certain amount of the elongation caused by the relative sliding of the sleeves and rebars. The essential difference between the stable impact load and unstable impact load is that, under the stable impact load, no structural deformation will occur after the impact load ends; under the unstable impact load, the structural deformation will still occur after the impact load ends. The obtained results are of theoretical implications for rock support design with CRLD bolts under the dynamical loading condition.

Developing High Strength-High Toughness Low Carbon Steel Using Combined V-Ti-Micro-Alloying and Different Thermo-Mechanical Treatments

This work aims at designing and developing low carbon steel alloys to meet the high tensile strength, high ductility and high impact toughness properties. The effect of solid solution mechanism, precipitation hardening, as well as grain refinement were developed with different Manganese content (0.78-2.36wt%) combined with Vanadium(0.008-0.1wt%) and Titanium (0.002-0.072wt%) microalloying additions. The controlled thermo-mechanical treatments and chemical compositions play a big role in developing the microstructure and the corresponding mechanical properties. Therefore, the studied chemical compositions were treated thermo-mechanically by two different ways of changing start and finish forging temperatures with subsequent air cooling. The first way by start forging from 1050 to 830oC and the second from 950 to730oC. The second way of forging process developed finer grain sizes and higher ultimate tensile strengths for all the studied steel alloys. In spite of finer grain sizes, the impact toughness value was lower in the second regime due to detrimental influence of precipitation strengthening in the ferrite. A combination of 544 MPa yield strength, 615 MPa ultimate tensile strength, 20% elongation and 138 Joule impact toughness has been attained.

The Electrical, Mechanical and Surface Properties of Thermoplastic Polyester Elastomer Modified by Electron Beta Radiation.

The main advantages of Thermoplastic Polyester Elastomers (TPE-E) are their elastomer properties as well as their ability to be processed in the same way as thermoplastic polymers (e.g., injection moulding, compression moulding and extrusion). However, TPE-Es’ properties, mainly their mechanical properties and thermal characteristics, are not as good as those of elastomers. Because of this TPE-Es are often modified with the aim of improving their properties and extending their range of application. Radiation cross-linking using accelerated electron beams is one of the most effective ways to change virgin polymers’ properties significantly. Their electrical (that is to say permittivity and resistivity measurements), mechanical (that is, tensile and impact tensile tests), as well as surface (that is, nano-indentation) properties were measured on modified/cross-linked TPE-E specimens with and/or without a cross-linking agent at irradiation doses of 0, 33, 66, 99, 132, 165 and 198 kGy. The data acquired from these procedures show significant changes in the measured properties. The results of this study allow the possibility of determining the proper processing parameters and irradiation doses for the production of TPE-E products which leads to the enlargement of their application in practice.

Improvement of heat resistance and mechanical properties of epoxy resin with nano-Cu-Ni supported RGO

ABSTRACTThis study reports the synthesis and characterization of epoxy resin/redox graphene/nano-copper-nickel (EP/RGO/Cu-Ni) composites. The RGO/Cu-Ni was characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Using dynamic thermodynamic analysis (DMA), the glass transition temperature (Tg) of the modified epoxy resin was increased by 21°C compared to EP. The addition of 1.3 wt% RGO/Cu-Ni to the epoxy matrix resulted in an increase of 79.6% and 161.3% respectively in the tensile strength and impact strength of the new material. Finally, the excellent mechanical properties of EP/RGO/Cu-Ni nanocomposites contribute to the research and development of new high-performance polymer materials.

Finite Element Analysis of Dynamic Fracture Behaviour of Drill Pipe Under Various Impact Loads

In this paper, finite element analysis is conducted to study dynamic responses of a defected drill pipe (DP) under impact loading encountered in working conditions. Longitudinal impact loading such as tensile, eccentric compressive and torsional impact loading and transverse collision loading are considered. A finite element model is firstly developed and validated, and then employed to evaluate the effects of various impact loading on dynamic responses of the defected DP. It is found that the inertial effect due to tensile impact is the most prominent among all the longitudinal impact loadings. In addition, the effect of the transverse collision between the DP and the borehole wall on the driving force of the crack is evaluated. It is concluded that the dynamic effects of the various impact loading frequently exerting on the DP should be taken into consideration for life prediction of DPs. DOI: http://dx.doi.org/10.5755/j01.mech.24.4.19503

Experimental and theoretical study on the strain rate dependence of the mechanical properties of Twaron fiber tows with different fiber fineness

In this study, the tensile impact property of Twaron fiber tows with different fiber fineness were characterized and compared. A self-designed split Hopkinson tension bar apparatus and MTS materials tester (MTS 810.23) were used to determine the tension behavior of Twaron fiber tows under different strain rates (quasi-static: 0.001 s–1, dynamic: 800–2400 s–1). The results showed that the mechanical properties of the Twaron fiber tows were sensitive to strain rate; the stiffness and failure stress of the fiber tows increased distinctly as the strain rate increased, whereas the failure strain decreased. The scanning electron microscope photographs showed that a fibrillated end of a Twaron single fiber failed at both quasi-static and high strain rates. The observations reaffirmed that the fiber fibrillation was more severe as the strain rate increases. In addition, the fiber of 220 dtex exhibited higher strength and stiffness than that of 1680 dtex. Combined with the aligned fiber bundle model and the statistical theory, a single Weibull distribution function is adapted to evaluate the strength distribution, and the Weibull plot for Twaron fiber tows under different strain rates provided a more accurate agreement with the experimental results.

Influence of strain parameters at rolling on the properties of wire-reinforced aluminium composites

The present experimental work is devoted to the analysis of strain parameters at rolling of aluminium composite with wire-reinforcement. The experiments on roll bonding of two strips of EN AW-5083 alloy with and without diagonal stainless steel net-reinforcement between them were carried out with different reductions. The rolling reduction was varied in a range from 25 to 55% and its influence on the straining of the wires and bonding mechanisms was analysed. The parameters describing the net behaviour in the composite established and used are the following: net cell elongation, wire elongation and wire ovalisation. The properties of the rolled composite are determined by means of longitudinal and transversal tensile testing, impact testing and microscopic analysis. The influence of the rolling reduction on the mechanisms of bonding formation in the composite, its properties and fracture behaviour are analysed. The optimum range of rolling reductions was established based on the conducted tests. The reinforcing net allowed reaching a tough bonding between the strip’s layers during rolling at lower plastic reduction, while the strips without reinforcement could not be bonded at rolling reduction below 45%. The wire-reinforced strips showed higher strength and ductility under the tensile loading in rolling direction and higher toughness during impact testing than the non-reinforced aluminium strips.

CHARACTERIZATION OF RECYCLED LINEAR DENSITY POLYETHYLENE/IMPERATA CYLINDRICA PARTICULATE COMPOSITES

Water-sachets made from low density polyethylene (LDPE) form a bulk of plastic wastes which creates environmental challenges, while certain species of plants like Imperata cylindrica constitute large portion of weeds on farm lands. As a technological approach to the reduction and utilization of these materials, composites of Imperata cylindrica (IC) particulate and synthetic polymer (from recycled waste water-sachets) were produced and evaluated for several mechanical and physical properties. The production of the composites and testing were done using the standard methods available in the literature. The results showed an increase in tensile modulus, hardness, impact strength, and water absorption of the composite in comparison with unreinforced polymer, as the IC particulate loading increased from 5 wt% to 30 wt%. However, there was a decrease in tensile strength, percentage elongation at break and density of the composite as the particulate loading increased from 5 wt% to 30 wt%. The combination of the recycled waste water-sachets and IC particulate is really promising for composites development. This creates opportunities to reduce LDPE wastes and add economic importance to an otherwise agricultural menace. It will mean creating an economic value from “wastes”.