Tensile Strength Of Specimens Research Articles

Microstructure evolution and mechanical properties of intermetallic Ni–xSi (x = 5, 10, 15, 20) alloys

In this study, the microstructure and mechanical properties of conventionally solidified Ni–xSi (x=5, 10, 15, 20) alloys were investigated. The microstructures of the Ni–Si alloys were characterized by SEM and the phase composition was identified by XRD analysis. The phase transition during the solidification process was studied by DTA under an Ar atmosphere. The results show that the microstructure and solidification behavior are closely related to the composition of Ni–Si alloys. The hardness and tensile strength of specimens at room temperature were examined. The tensile properties of the Ni–Si alloys were also improved and the alloy containing 20wt.% Si exhibited the highest tensile strength. Experimental results showed that the mechanical properties of Ni–Si alloys were enhanced, which can be attributed to significant changes in the microstructure. Vickers micro-indentation tests were performed on the samples with different peak loads at room temperature. It was found that the hardness and effective elastic modulus values increased with Si-addition and these values showed peak load dependence.

Mechanical Characteristics of PVA/STMP Hydrogel in Tensile and Unconfined Compression

Hydrogels based on Poly(vinyl alcohol) (PVA) were synthesized using the combining method of chemical agent and freezing-thawing cycle. Sodium Trimetaphosphate (STMP) is a kind of crosslinking agent in this reaction. The resulting hydrogels were characterized in terms of tensile properties and compression stress-strain testing. The influences of STMP and water content on mechanical properties of hydrogels were investigated. It is suggested that PVA hydrogel has excellent tensile strength, higher elongation at break and viscoelastic materials’ stress-strain curve. Tensile strength of specimens without STMP increases from 4 to 6.8 MPa, as well as elongation increase from 300% to 458%, respectively. When the strain changes from 10% to 50%, tangent compressive modulus dramatically increases from 0.58 to 9.9 MPa for hydrogels with 80wt % water and 0.41 to 5.4 MPa for 85wt % water. Meanwhile, the addition of STMP can further improve the mechanical properties of PVA hydrogel.

Intrinsic variability of the mechanical properties of Maha Sarakham salt

Abstract Laboratory mechanical tests were carried out to study the intrinsic variability of rock salt specimens obtained from the Middle and Lower members of the Maha Sarakham formation in the Khorat basin. Prior to the mechanical tests, the types and amount of inclusions were identified by visual examination and after testing by X-ray diffraction and dissolution methods. The uniaxial compressive strength of the specimens linearly increases from 27 MPa to about 40 MPa as the anhydrite content (by weight) increases from 0% (pure halite) to 100% (pure anhydrite). The combined stiffness of the salt and the anhydrite causes an increase of specimen elasticity from 22 GPa (pure salt) to as high as 36 GPa (pure anhydrite). Tensile strengths increase with increasing anhydrite content, particularly when the content is above 60% by weight. Below this limit the anhydrite has an insignificant impact on the specimen tensile strength. The tensile strength of salt crystals can be as high as 2 MPa, whereas that of the inter-crystalline boundaries is 1 MPa. The visco-plasticity increases exponentially with crystal size, as dislocation glide mechanisms become predominant for the specimens comprising large crystals. Salt specimens with fine crystals deform by dislocation climb mechanisms, and hence reduce the specimen9s visco-plasticity. The true understanding of the impact of the inclusions on the mechanical properties of the salt is important for the design and stability analysis of underground mines and storage caverns.

기공닫힘부 폐쇄정도 결정을 위한 평가방법 연구

This paper presents methods for analyzing the extent of cylindrical-shaped void closure. In addition, a quantitative relationship between change in void fraction and height reduction ratio of a compressed specimen is proposed. The height reduction ratio, number of deformation steps and billet rotation were chosen as key process parameters influencing the void closing behavior, namely, the changes in void shape and size during hot open die forging of a large ingot. The extent of void closure was analyzed from microscopic observations and estimated from tensile test results. The tensile strengths of specimens with closed voids and those without were compared for various reduction ratios in height. The results confirmed that void closure occurs at reduction ratios greater than 30 %. The void closing behavior could be expressed as a hyperbolic tangent function of reduction ratio in height, number of paths, and billet rotation. The knowledge presented in this paper could be helpful for optimizing deformation paths in open die forging processes.

Influence of cover thickness on the mechanical properties of steel bar in mortar exposed to high temperatures

AbstractConcrete protects the steel inside against several effects of the external environment. One of the most important of these effects is high temperature. Cover plays a critical role in concrete's protection on reinforcement against high temperature. In this study, the changes after high temperatures in mechanical properties of the reinforcement steels placed between 3 and 5 cm covers inside the mortar specimen prepared with CEM I 42.5 R and CEM II/B‐M (P‐L) 32.5 R cements were investigated. In order to ensure 3 and 5 cm covers 76 × 76 × 310 and 116 × 116 × 350 mm sized reinforced mortar specimen were prepared. These reinforced mortar specimens were exposed to 20, 100, 200, 300, 500 and 800°C temperatures and after that on the steels taken out of these mortar specimen tensile strength, tests were applied in order to determine the mechanical properties. With the tensile strength tests performed stress–strain curves of the steel bars exposed to several temperatures were drawn. Besides, the yield and ultimate strengths of the steel bars were determined. The results of the study have shown that the larger the covers, the better the steel bars are protected against high temperatures. Copyright © 2010 John Wiley & Sons, Ltd.

応力集中部を有する各種鋼材熱影響部の引張強さに及ぼすひずみ速度の影響

It is well known that the strain rate affects tensile behavior; for example, it affects the tensile strength and fracture elongation of metals. When examining the tensile behavior of steel, it is important to pay attention to the heat-affected zone (HAZ) as well as the base metal. The effects of the strain rate on the tensile strength were investigated by using specimens with stress concentrations; in particular, the tensile strength of SM400, SM490, and HT780 were obtained from HAZs by performing tensile tests at strain rates of 0.085%/s, 85%/s, and 1000%/s. The HAZs were simulated by using a thermal/mechanical simulator.The main results are summarized as follows: 1) Regardless of the grade of steel, the tensile strength of specimens that underwent ductile fracture increase at high strain rates, whereas the tensile strength of specimens that underwent brittle fracture did not increase. 2) Regardless of the grade of steel and regardless of whether welding heat was supplied or not, the rate of increase in the tensile strength as a result of the high strain rate can be predicted from the tensile strength, which can be determined by static testing.

Effects of part geometry and injection molding conditions on the tensile properties of ultra-high molecular weight polyethylene polymer

In this study, the influences of process parameters and different cross-sectional dimensions on the tensile strength of specimens with and without a weld line are investigated. In addition, the weld line characteristics of structures with different cross-sections are explored as well. With the Taguchi method and confirmation test, it can be concluded that Taguchi method is suitable to improve the mechanical properties occurring in the injection molded UHMWPE parts. The single-factor experimental results indicate that the process parametric influence is relatively smaller than the cross-sectional dimensions on the tensile strength of specimens without weld line. The experimental observations present that the frictional heating can be enhanced the molecular bonding and self-diffusion in the frozen layer of two sides on the weld line region. The SEM images showed that the micro-voids, cracks and incomplete molecular bonding are the major surface defects on the weld line region.

Effect of heavy metals and water content on the strength of magnesium phosphate cements

In this paper the mechanical properties of magnesium potassium phosphate cements used for the Stabilization/Solidification (S/S) of galvanic wastes were investigated. Surrogate wastes (metal nitrate dissolutions) were employed containing Cd, Cr(III), Cu, Ni, Pb or Zn at a concentration of 25 g dm −3 and different water-to-solid (W/S) ratios (0.3, 0.4, 0.5 and 0.6 dm 3 kg −1) have been employed. Cements were prepared by mixing hard burned magnesia of about 70% purity with potassium dihydrogen phosphate. Compressive strength and tensile strength of specimens were determined. In addition the volume of permeable voids was measured. It was found that when comparing pastes that the volume of permeable voids increases and mechanical strength decreases with the increase of water-to-solid ratio (W/S). Nevertheless pastes with the same material proportions containing different metals show different mechanical strength values. The hydration products were analyzed by XRD. With the increase of water content not previously reported hydration compound was detected: bobierrite.

DISCUSSION ON RELATIONSHIP BETWEEN STRENGTH AND DUCTILITY OF INTERFACE BETWEEN NEW AND OLD CONCRETE EMPLOYING TENSION-SOFTENING-DIAGRAM AND PULL-OUT DOWEL MODEL

This study discusses the relationship between strength and ductility of vertical placing joints of concrete specimens, each of which has one of 5 differently treated surfaces. The main feature of this study is that the authors employed both tension softening diagram (TSD) and pull-out dowel model for discussion. The conclusions are as follows.1. Relationship between tensile strengths of specimens with joint and no-joint is a linear one reflecting the fractured area on the surface of the joint. These strengths would be considered the sum of those by matrix and dowels in dowel model.2. The strong interface would be modeled to have longer dowels that cause the longer critical crack width in TSD, which leads to larger fracture energy, and vice versa.3. The dowel model proposed in this study can describe some important aspects in achieved TSDs of specimens with joint.

Effect of Low Temperature on Mechanical Properties of Bidirectional Glass Fiber Composites

In this article, low temperature and its degradative influence on the material together with hygro-thermal effect are highlighted. Hygrothermal factor is a major environmental factor experienced by the composites. An attempt has been made to study the mechanical properties of bidirectional glass cloth specimens exposed to low temperature and humid condition. Tensile strength records its highest value after 10 days exposure at -55°C, compressive strength at 0°C exposure increases but after 10 days exposure at -55°C decreases, shear strength of exposed specimen at 0°C increases, flexural strength of exposed specimen at -55°C increases and records its highest value of 10 days exposed specimen. Further, it has been observed that the strength of the composite is in the following order: Compressive strength of specimen<shear strength of specimen<tensile strength of specimen<flexural strength of specimen. In this article an attempt has been made to study effect of low temperature on mechanical properties of bidirectional glass fiber composites.

Effects of high shear rate shearing on material structure and mechanical property of iPP/PC blends

Polycarbonate (PC) and crystalline polymer, isotatic polypropylene (iPP), are extruded using a mechanical blending extruder and a reciprocated mechanism for shearing is designed to perform long term shearing at a high shear rate in the packing stage. The present work investigates the effects of high shear rate shearing on the orientation of the phase morphologies and mechanical properties. The experiment utilises the technologies of specimen preparation and observation to examine the change in phase morphology. Additionally, the mechanical properties of injection moulded specimens under different processing conditions are measured. Experimental results show that adding a little PC into the iPP matrix, less than around 20%, increases the tensile strength of specimens. The orientation of the phase is improved and most of the tensile strength of the blends is increased after shearing. The tensile strength of the shearing specimens with a PC content of <25% exceeds that of the normal specimens of pure iPP. A higher iPP content corresponds to a higher tensile strength after shearing. This investigation also considers the possibility of using iPP/PC blends in industrial applications, indicating that shearing is valuable in industrial applications when the PC content in iPP/PC blends is <25%.

An investigation into reutilizing of waste materials using friction welding and upset manufacturing methods

PurposeThe present study seeks to examine the possibilities of combined usage of friction welding and plastic forming in recycling of bar‐shaped waste materials.Design/methodology/approachIf the waste materials can be reproduced using various manufacturing methods without melting, their economic values could be increased economically. For this reason, using a combination of friction welding and plastic forming was chosen as an alternative recycling method. Upsetting was chosen as the plastic forming method due to its ease of application.FindingsIn the present study, dimensional changes, hardness variations in heat affected zone (HAZ), variations of torsion and tensile strengths with upsetting ratio of specimens were examined. Hardness values of test material are raised to higher levels within the HAZ by the local hardening. The maximum shear stress in torsion and the tensile strengths of specimens are closely harmonious with hardness values of test material.Research limitations/implicationsAlthough it was observed in general that the increasing upsetting ratio increased the torsion and tensile strengths, experimental study must be improved and extended in order to obtain more precise results.Practical implicationsIt can be concluded that combined usage of just welded and additional cold deformation can be considered as an alternative recycling method owing to obtained positive results.Originality/valueThis paper helps individuals reutilize waste materials because of the small lengths of the bars. Furthermore, it can be observed that the combination of friction welding and plastic forming produces savings in the material and the cost in this study.

The fabrication and property of SiC fiber reinforced copper matrix composites

SiC fiber reinforced copper matrix composites were prepared by foil-fiber-foil method (FFF) and, fiber-coating method (MCF) with and without a Ti6Al4V interlayer, respectively. The copper coating was prepared by different electroplating processes and the Ti6Al4V interlayer by magnetron sputtering. The results show that the tensile strengths of specimens without Ti6Al4V interlayer are nearly identical and poor, between 250 and 290 MPa, while the ones of specimen with Ti6Al4V interlayer can be greatly improved, over 500 MPa. This great increase attributes to the improvement of the SiC/Cu interfacial bonding strength because the interfacial reactions occur at Cu/Ti6Al4V interface and Ti6Al4V/SiC interface. Additionally, there are generally many micropores produced by hydrogen and oxygen in the electroplated coating, which would influence the density of the matrix. Therefore, the densification of the matrix was worth investigating since it would influence the thermal and electrical conductivity of the composite, though it has only a little contribution to the tensile strength. Experiments indicate that proper heat-treatment before hot pressing could improve the densification of the matrix.

Microstructural characterization of a fine-grained ultra low carbon steel

Fine-grained ultra low carbon steel was prepared by equal-channel angular extrusion. The evolution of the microstructure and the deformation behavior were investigated as a function of the route. At room temperature the tensile strength of specimens prepared by route A is higher than that of the route C samples. The differences in microstructure between these two types of samples are discussed in terms of misorientation between the subgrains. The latter is correlated to the cumulated crystal rotations.

Durability of GFRP composite exposed to various environmental conditions

This paper presents a short-term durability test program for E-glass/vinylester composite exposed to various environmental conditions. The main objective of this study is to investigate the degradation of GFRP composite and its influence on the tensi le strength. A total of 530 strand-type E-glass/vinylester specimens were fabricated and exposed to six different environmental conditions for up to 150 days. To examine the degradation of conditioned specimens, the weight gain was measured and scanning electronic microscope images were taken at fractured section. Also, the tensile strength of the specimens was tested. From the test results, it is clear that the tensile strength of the conditioned specimens was significantly reduced due to the degradation of GFRP under the environmental conditions considered.

Comparison of fracture models to assess the notched strength of composite/solid propellant tensile specimens

Modifications are made in the well-known inherent flaw model as well as in the stress fracture models for accurate prediction of notched tensile strength of composite laminates containing holes or slits. To examine the adequacy of these modifications, fracture data on different composite materials reported in the literature are considered. The notched strength estimates from the present fracture models are found to be close to the existing test results. An attempt is made to correlate the fracture data of center crack tension specimens made of nitramine and HTPB-based propellant materials. The present analysis results from the above simple models are found to be in good agreement with test results. This study confirms the applicability of the above three fracture models to solid propellant materials having relatively low stiffness and strength. Since the notched strength estimates of composite/solid propellant tensile specimens are close to the test results, any one of them can be utilized while evaluating the notched tensile strength of specimens.

Numerical Simulation on Failure Patterns of Rock Discs and Rings Subject to Diametral Line Loads

Brazilian test is a standardized test for measuring indirect tensile strength of rock and concrete disc (or cylinder). Similar test called indirect tensile test has also been used for other geomaterials. Although splitting of the disc into two halves is the expected failure mode, other rupture modes had also been observed. More importantly, the splitting tensile strength of rock can vary significantly with the specimen geometry and loading condition. In this study, a numerical code called RFPA2D (abbreviated from Rock Failure Process Analysis) is used to simulate the failure process of disc and ring specimens subject to Brazilian test. The failure patterns and splitting tensile strengths of specimens with different size and loading-strip-width are simulated and compared with existing experimental results. In addition, two distinct failure patterns observed in ring tests have been simulated using RFPA2D and thus this verifies the applicability of RFPA2D in simulating rock failure process under static loads.

Microstructures and tensile properties of Ti–45.5Al–2Nb–2Cr rolled sheets

Tension tests were carried out at 20, 704, 760, and 815°C on sheet specimens machined from pack rolled and heat-treated sheets of a multi-phase gamma titanium aluminide alloy, Ti–45.5Al–2Nb–2Cr. The microstructures of the heat-treated sheets ranged from equiaxed, (recrystallized) primary gamma structure obtained by annealing at 1200°C to the fine-grained, fully lamellar structure obtained by a short-term solution treatment at 1320°C followed by air cooling to 900°C. The yield strength and the tensile strength of specimens containing the equiaxed, primary gamma microstructure were consistently low at all test temperatures, while the strength properties of duplex and fully lamellar structures were comparatively quite high. The tensile ductility values showed a complex dependence on the microstructure and the test temperature. Fully lamellar structures exhibited poor ductility at all temperatures up to 815°C. Fractography and metallography of the tensile test specimens revealed evidence of a mixture of failure mechanisms: cleavage cracking, ductile failure by microvoid coalescence, and intergranular fracture by cavitation and wedge cracking. The relative contributions of these mechanisms varied with the initial microstructure and the test temperature. Both the lamellar grains and the gamma grains became significantly elongated near the fracture zone, particularly in specimens deformed at 760 and 815°C. The yield and tensile strength of Ti–45.5Al–2Nb–2Cr alloy sheets in all microstructural conditions were significantly higher than those reported for a majority of alloys containing 47–49% aluminum. However, the ductile-to-brittle transition temperatures of the Ti–45.5Al–2Nb–2Cr alloy were somewhat higher than those obtained for the majority of gamma titanium aluminides.

Investigating tensile strength and fragmentation of anisotropic rocks in 3D using the Brazilian test

Abstract This paper presents laboratory work where rock strength anisotropy and fines fraction of a gneiss has been determined by means of the Brazilian test of core samples. Samples of a diameter of 42 mm were taken in 3D from rock blocks, cut into 21 mm specimens and subjected to the Brazilian test. Samples of each direction were loaded at two perpendicular directions. The results have been expressed as two factors (a) tensile strength- and (b) fines fraction-anisotropy. The tensile strength anisotropy is defined as Ku = [sgrave]iv/[sgrave]tv where [sgrave]tv and [sgrave]tp are the tensile strength of specimens loaded perpendicular and parallel to foliation respectively. This factor had different values for specimens of different directions and varied between 1.2 to 1.5. The fines fraction anisotropy is defined as the percentage of rock particles smaller than 2 mm in thickness generated due to failure of the specimen. This factor is defined as Kfa = f v/f P where f v , and f p are the fines fraction of ...

An experimental study of the interaction of internal cracks in PMMA

Internal cracks in polymethyl methacrylate (PMMA) specimens were generated by pulsed laser light. The interactions of coplanar cracks, parallel cracks, and cracks in T and H configurations were investigated. The tensile strength of specimens with a single internal crack decreased with increasing crack size, and the strength correlated well with the initial crack and unstable crack size in the Griffith relationship. For specimens with coplanar and parallel cracks, the strength increased and decreased with the crack distance, respectively. For the T and H crack configurations, the presence of delamination cracks decreased the strength, and the reduction in strength became more significant when the crack distance was small. All fracture surfaces showed similar fracture morphology in the sequence of laser-generated crack, smooth fracture mirror, mist with hyperbolic markings, and rough hackle region with rib markings. Examination of the fracture surfaces revealed crack arrest by the delamination cracks in both T and H configurations, and crack bowing between delamination cracks in the H configuration. The propagating crack was eventually able to circumvent the delamination cracks. The experimental results are compared with the available theoretical analyses, and the relevance of the present study to the toughening of brittle materials is discussed.