Tensile Fracture Strength Research Articles

Tensile properties of polypropylene flame-retardant composites

The polypropylene (PP) flame-retardant composites filled with aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), zinc borate (ZB), nanometer calcium carbonate (nano-CaCO3), and polyolefin elastomer (POE) were prepared using a twin-screw extruder, and the tensile properties were measured at room temperature by means of an electronic universal test machine (Model CMT4104) in this paper, to identify the influence of the flame-retardant content on the tensile properties. The results showed that the tensile strength decreased roughly nonlinearly while the tensile elongation at break decreased nonlinearly with increasing the flame-retardant weight fraction. The Young’s modulus and the tensile fracture strength increased nonlinearly with an addition of the flame-retardant weight fraction. The tensile ductility of PP/Al(OH)3/Mg(OH)2/ZB/Nano-CaCO3/POE composite was the best in the three kinds of the composite systems. Moreover, good agreement was showed between the predictions and the measurements of the tensile strength.

Improvement of high-temperature oxidation resistance and strength in alumina-forming austenitic stainless steels

A new alumina-forming austenitic stainless steel with greatly improved high-temperature oxidation resistance and strength was developed via alloying 3.0 wt.% Al in the Fe-25Ni-18Cr based alloy. Continuous, stable and exclusive alumina scale was formed in either dry air or air with 10% water vapor mixed environment at 800 °C. The long-term high-temperature oxidation performance is appreciably enhanced which is associated with the high density of the B2-NiAl precipitation phase maintaining the Al 2O 3 surface layer. Moreover, when tested at 750 °C in dry air environment, the new steel showed high yield and fracture tensile strength of 310–335 and 480–500 MPa, respectively.

Advanced hollow epoxy particle-filled composites

The micro-spherical hollow epoxy particles (HEPs) were prepared using water-based emulsion method in this study. It is determined that spherical HEP with desirable size, shape, and structure can be produced using the homogenizing time of 9 min under the homogenizing speed of 15,000 rpm. The HEPs produced were then incorporated into the diglycidyl ether of bisphenol-A epoxy matrix to strengthen and toughen the epoxy matrix. The HEP-reinforced composites were prepared using simple casting technique. The fracture toughness, tensile strength, tensile modulus, and flexural strength of HEP-reinforced epoxy composites increase with increasing the HEP loading up to 3 wt% after which there is a drop. The strengthening and toughening of epoxy composites involves the interlocking of epoxy matrix into the pore region on the HEP. The interlocking mechanism was further supported by the fracture morphology of the epoxy composites observed under scanning electron microscope.

Theoretical considerations of the influence of polymer film coatings on the mechanical strength of tablets.

A theoretical analysis of the influence of polymer film coatings on the mechanical strength of tablets has been undertaken. Making some basic assumptions, the theory predicts that neither the thickness of the substrate nor that of the coating has any influence on which fractures first, this being solely determined by the ratio of the tensile fracture strength to the Young's modulus for the two materials. Such a finding suggests that in practice for film-coated tablets the substrate will usually fracture before the coating. Simple measurements of maximum failure loads are of little value in assessing the influence of film coating on the mechanical strength of tablets.

Characterization of tensile strength and fracture toughness of nuclear graphite NBG-18 using subsize specimens

The mechanical properties of NBG-18 nuclear grade graphite were characterized using small specimen test techniques and statistical treatment on the test results. New fracture strength and toughness test techniques were developed to use subsize cylindrical specimens with glued heads and to reuse their broken halves. Three sets of subsize cylindrical specimens of different sizes were tested to obtain tensile fracture strength and fracture toughness. The mean fracture strength decreased as the specimen size increased. The fracture strength data indicate that in the given diameter range the size effect is not significant and much smaller than that predicted by the Weibull moduli estimated for individual specimen groups of the Weibull distribution. Further, no noticeable size effect existed in the fracture toughness data. The mean values of the fracture toughness datasets were in a narrow range of 1.21–1.26 MPa√m.

The mechanical behaviour of an ultrafine grained Ti–47Al–2Cr (at%) alloy in tension and compression and at different temperatures

A bulk ultrafine grained (UFG) Ti–47Al–2Cr (at%) alloy has been produced using a powder metallurgy process that combines high energy mechanical milling (HEMM) of a mixture of Ti, Al and Cr powders to produce a Ti/Al/Cr composite powder and hot isostatic pressing (HIP) of the composite powder compact. The purpose of the present study is to determine the mechanical behaviour of the alloy in tension and compression at room temperature (RT) and elevated temperatures, and also to compare the compression behaviour of the material with its tensile behaviour. It has been found that due to the residual pores, lack of full level interparticle bonding and high oxygen content (0.87 wt%) in the consolidated samples, the UFG TiAl based alloy has a very low room temperature tensile fracture strength of ∼100 MPa and shows no tensile ductility. However these microstructural defects and high oxygen content have much less significant effect on the room temperature compressive mechanical properties, and the alloy shows a high compressive yield strength of ∼1410 MPa, and some ductility (plastic strain to fracture ∼4%). At elevated temperatures of 800 °C and above, the alloy shows high tensile and compressive ductility as demonstrated by 75% tensile elongation to fracture and no cracking in upset forging with a height reduction of 50% at 900 °C. The yield strength of the alloy at 900 °C is 55 MPa in tension and ∼33 MPa in compression, both of which are lower than those of coarse grained TiAl based alloys with similar compositions at 900 °C. This is due to a higher creep rate of the UFG alloy caused by the small grains. The good formability of the UFG TiAl based alloy as reflected by the lower critical temperature above which the alloy becomes highly formable indicates that the material can be used as a suitable precursor for secondary thermomechanical processing and super-plastic forming.

Tension-Softening Properties for Concrete-Concrete Interfaces

The tension-softening parameters for different concrete-concrete interfaces are determined using the bimaterial cracked hinge model. Beams of different sizes having a jointed interface between two different strengths of concrete are tested under three-point bending (TPB). The load versus crack mouth opening displacement (CMOD) results are used to obtain the stress-crack opening relation through an inverse analysis. In addition, the fracture energy, tensile strength, and modulus of elasticity are also computed from the inverse analysis. The fracture properties are used in the nonlinear fracture mechanics analysis of a concrete patch-repaired beam to determine its load-carrying capacity when repaired with concrete of different strengths.

Influence of ZrC content on the elevated temperature tensile properties of ZrCp/W composites

The influence of ZrC content on the tensile deformation behavior and fracture strength of ZrCp/W composites in a temperature range of 800–1400°C was investigated. Both of the non-linear feature of the stress–strain curve and the rupture strain of the composites decreased with increasing ZrC content from 20 to 50vol% in all the tested temperatures. The maximum ultimate tensile strength of each ZrCp/W composite was found in the temperature range of 1000–1200°C. With increasing ZrC content from 20 to 50vol%, the maximum ultimate tensile strength of the ZrCp/W composite was decreased due to the porosity increase and the plasticity decrease of the composite although ZrC enhanced the tungsten matrix via load transferring and blocking dislocation movement in tungsten matrix.

Residual strength of laminated composites after impact

This article deals with the residual strength assessment on completely as well as partially penetrated laminated composites due to impact loads by idealizing the damage locations as holes and cracks. Modifications are made in the inherent flaw model (IFM) of Waddoups, Eisenman, and Kaminski (known as the WEK model) to correlate the fracture data of laminated composites. For velocities above complete penetration, the residual strength is identical to the static strength of the laminated composite with a hole having the same diameter as the impacting particle. For this case, the inherent flaw length ahead of the notch is correlated with notched and un-notched strengths through fracture parameters. For the case where the impact velocities are less than the penetration velocity, an empirical relation is proposed following the IFM for the residual strength in terms of kinetic energy of the impact. The adequacy of the modified IFM is demonstrated through comparison of fracture analysis results with tensile, compressive, and impact fracture strength of laminated composites containing holes and cracks.

Hydrogen Embrittlement in Metallic Amorphous Alloys: An Overview

Abstract In hydrogen-related energy technologies, the selection of materials is critical since hydrogen can modify the initial microstructure and induce damage that could result in the reduction of mechanical properties and embrittlement. In this context, metallic amorphous alloys are viable candidates due to their high hydrogen solubility. Earlier studies demonstrated the positive interaction of hydrogen with amorphous alloys. However, similar to crystalline metals, embrittlement by hydrogen was also reported. In order to clarify the role of hydrogen in this class of alloys, we present an overview on the hydrogen interaction and embrittlement, encompassing results from published studies and from our own investigations on several Zr-, Ni-, and Ti-based amorphous alloy systems. The importance of the constituent elements and composition in determining the structure, hydrogenation kinetics, and hydrogen absorption capacity were brought out. The resistance to embrittlement varies upon the alloy system, constituent elements, and atomic packing of the amorphous alloy. In metalloid-free amorphous alloys, the bending ductility and tensile fracture strength of thin ribbons could be preserved up to a critical concentration beyond which hydrogen degradation occurs. The value of this critical concentration was found to vary from a few percent to about 45 at. % H. The mechanism of embrittlement induced by hydrogen was identified from the correlation of the observed changes in structural, thermal, and mechanical properties. It was found that hydrogen plays a prime role in altering the local atomic structure by reordering the nearest neighbor atomic configuration. The structural dilatation so produced was found to be the source of hydrogen-induced failure in these amorphous alloys. Also a “hydrogen concentration versus dilatation” map has been proposed, which would serve as a tool to predict the hydrogen-induced ductile-to-brittle transition in these alloys.

Effects of drawing on the tensile fracture strength and its reliability of small-sized metallic glasses

The effects of drawing on the structure and mechanical properties of a Co-based metallic glass under tension were thoroughly investigated. Surface changes induced by drawing, including removal of surface flaws, surface chemical homogenization and generation of compressive residual stress tend to increase the fracture strength, whilst open volumes created during drawing, particularly nano-voids, are likely to soften the wires. Initially, the surface changes are decisive factors, but as drawing proceeds, the open volumes gradually become dominant, yielding a maximum fracture strength in the wires with an area reduction ratio of 22%. Moreover, it was found that the fracture strength reliability was enhanced by the drawing, which is due not only to the surface perfection but also to the increase of plastic deformation capability, manifested by the decrease in the activation energy of individual shear transformation zones. Our results imply that the drawing technique could be a promising approach to continuously producing small-sized glassy wires with improved overall properties.

Mechanical characterization of post-buckled micro-bridge beams by micro-tensile testing

A micro-tensile testing system has been developed to measure the mechanical properties of post-buckled silicon dioxide micro-bridge beams. A kind of vernier-groove carrier is presented to improve alignment precision and repeatability of the measurement, and the stiffness coefficient of the tensile system is calibrated in situ in order to obtain the deformation of the tensile beams. Through analyzing a series of stress states in the beam over film preparation, post-buckling and unfolding of the beam, the initial residual stress in the film is obtained from the original load–displacement curves. The residual stress of 354 MPa is consistent with that calculated from the theory of finite deflection of buckled beams. Young’s modulus and tensile fracture strength are also obtained from the load–displacement curves. The measured modulus and strength are 64.6 ± 3 GPa and 332–489 MPa respectively. The measured properties of the thermal silicon dioxide film are reasonably coherent with other reports.

Effects of Nano-CaCO3 Content and Surface Treatment on Tensile Properties of PPS/GF Ternary Composites

Nanometer calcium carbonate (nano-CaCO3) filled polyphenylene sulfide (PPS/GF) ternary composites reinforced with glass fiber were fabricated in this paper, and the Young's modulus, tensile strength and tensile elongation at break were measured at room temperature, to identify the influence of the content and surface treatment of the nano-CaCO3 particles on the tensile mechanical properties of these ternary composites. It was found that the Young's modulus, tensile strength and tensile fracture strength of the composites increased slightly with an addition of the weight fraction (φ f ) of the nano-CaCO3 particles, and the maximum increase of them was more than 7.5% at φ f = 2%. When φ f was less than 4%, the tensile elongation at break of the composites increased obviously and then increased gently with an increase of φ f , and the maximum increase of it was more than 21% at φ f = 4%. Relatively, the tensile properties of the PPS/GF/nano-CaCO3 composite systems for the particle surface treated with titanate coupler were somewhat better than those of the systems for the particle surface treated with stearic acid at the same nano-CaCO3 content.

A composite kidney stone phantom with mechanical properties controllable over the range of human kidney stones

A novel composite kidney stone phantom has been developed. This stone phantom is producible with mechanical properties mimicking the range of tensile fracture strength and acoustic properties of human kidney stones and is an inorganic/organic composite material, as are natural kidney stones. Diametral compression testing was used to measure tensile fracture strength, which determines the acoustic comminution behavior of kidney stones. Ultrasound transmission tests were made to characterize the acoustic properties of these stone phantoms. Both the tensile fracture strength (controllable from 1 to ∼5 MPa) and acoustic properties ( C L = 2700–4400 m/s and C T = 1600 – 2300 m/s ) of these composite phantom stones match those of a wide variety of human kidney stones. These artificial stone phantoms should have wide utility in lithotripsy research.

Formation and bioactivation of Zr-Al-Co bulk metallic glasses

A Cu- and Ni-free Zr-based metallic glass with high glass-forming ability was found in the Zr-Al-Co ternary system. The eutectic Zr56Al16Co28 alloy could be cast into glassy cylindrical rods with diameters up to 18 mm. The glassy alloy exhibited high tensile fracture strength of 1830 MPa and low Young's modulus of 83 GPa in conjunction with better corrosion resistance compared with the glassy Zr57Nb5Al10Ni12.6Cu15.4 in a simulated body fluid. Hydrothermal-electrochemical treatment in the aqueous 5M-NaOH solution resulted in the formation of amorphous sodium cobaltate layer on the surface of glassy Zr56Al16Co28 alloy. Hydroxyapatite was spontaneously formed on the surface of the alloy, indicating bioactivity after surface modification. The discovery of a Cu- and Ni-free Zr-based metallic glass with a critical diameter larger than 1 cm in conjunction with excellent mechanical properties, superior corrosion resistance, and good bioactivity may open up the application field as biomaterials.

The Damage Tolerance of a Sandwich Panel Containing a Cracked Honeycomb Core

Abstract The tensile fracture strength of a sandwich panel, with a center-cracked core made from an elastic-brittle diamond-celled honeycomb, is explored by analytical models and finite element simulations. The crack is on the midplane of the core and loading is normal to the faces of the sandwich panel. Both the analytical models and finite element simulations indicate that linear elastic fracture mechanics applies when a K-field exists on a scale larger than the cell size. However, there is a regime of geometries for which no K-field exists; in this regime, the stress concentration at the crack tip is negligible and the net strength of the cracked specimen is comparable to the unnotched strength. A fracture map is developed for the sandwich panel with axes given by the sandwich geometry. The effect of a statistical variation in the cell-wall strength is explored using Weibull theory, and the consequences of a stochastic strength upon the fracture map are outlined.

Synthesis and characteristics of 80 vol.% tungsten (W) fibre/Zr based metallic glass composite

Based on full understanding of wettability between Zr based bulk metallic glass (BMG) matrix and tungsten (W) fibre, and liquid/solid interfacial atomic interaction, the high density and high strength 80 vol.% W fibre/Zr based BMG composite, with optimum interfacial layer, was successfully developed by strictly controlling the infiltration and solidification process. Its density was 17 g/cm 3. The average value of tensile fracture strength was 1685 MPa. Fracture mode represented instant rupture which was vertical to the axial direction. The average value of compressive fracture strength and strain were 2550 MPa and 23% respectively. Its fracture mode was complex splitting along loading direction. The initiation of shear bands occurred when the compressive specimen reached plastic strength. Shear bands' continuous expanding, branching, propagation and build up responded the improvement of plasticity under the continuous loading. Shear bands distributed on the fracture surface in two ways. One was consistent with the maximum shear force direction and at 45° angle with the loading direction. The other was nearly horizontal and vertical to the loading direction. The characteristics of plastic deformation and fracture were also investigated and discussed in detail.

Processing of Fe-6.5wt.%Si alloy foils by cold rolling

Thin foils of 50 μm in thickness of Fe-6.5wt.%Si alloy were obtained by conventional hot-cold rolling method. The rolling texture and basic mechanical properties of the foils were examined. The foils were heavily work-hardened and exhibited high tensile fracture strength with some extent of plastic elongations. Their bending ductility was more remarkable.

APPLICATION OF ANN BACK-PROPAGATION FOR FRACTURE TOUGHNESS IN MICROALLOY STEEL

Artificial neural network (ANN) back-propagation model was developed to predict the behavior of fracture toughness and tensile strength as a function of microstructure. Both fracture toughness and tensile strength were found to increase with the increase in martensite content in a dual phase microstructure of microalloy steel. The primary objective of the ANN Back-propagation (BP) prediction model was to validate and extend the application of microalloy steels for various engineering applications. The ANN training model has been used to predict the optimum toughness properties in terms of intercritical annealing temperature and martensite content. This can be used as a practical tool for predicting the fracture toughness in other series of steels comprising dual-phase microstructures and also to optimize strength and ductility properties. The ANN model exhibited excellent comparison with the experimental results. It is concluded that predicted fracture toughness by the trained neural network model seem more reasonable compared to approximate methods. It is possible to claim that, ANN is fairly promising prediction technique if properly used. Training ANN model was introduced at first. And then the neural network architecture is designed. The performance of system is summarized at last. In order to facilitate the comparisons of predicted values, the error evaluation and mean relative error are obtained. The result show that the training model has good performance, and the experimental data and predicted data from ANN are in good coherence.

Formation and thermal stability of new Zr–Cu-based bulk glassy alloys with unusual glass-forming ability

The simultaneous addition of Al and Ag to Zr–Cu binary alloys increased in the stabilization of supercooled liquid, the reduced glass transition temperature and γ value, leading to greatly enhance the glass-forming ability (GFA). The Zr–Cu–Ag–Al glassy alloy samples with diameters above 15 mm were obtained in the wide composition range of 42–50 at% Zr, 32–42 at% Cu, 5–10 at% Ag, and 5–12 at% Al. The best GFA was obtained for Zr 48Cu 36Ag 8Al 8 alloy, and the glassy samples with diameters up to 25 mm were fabricated by an injection copper mold casting. The Zr 48Cu 36Ag 8Al 8 glassy alloy exhibited high tensile and compressive fracture strength of over 1800 MPa.