Mechanical Properties In Tension Research Articles

FE-Modelling of the Rubber Mould Behaviour during Press Forming of Thermoplastic Composites

Rubber is a hyperelastic material with a non linear behaviour which is very different in tension and compression. The behaviour in tension shows an initially increasing stiffness, followed by a decreasing stiffness at higher strains, while in compression the stiffness is increasing at higher loads. In the present paper, the rubber mechanical properties in tension and compression are implemented in ABAQUS via a hyperelastic material model present in the FE package, which perfectly represent the tested material behaviour. The material model uses a strain energy potential polynomial of second degree to model the stress-strain curve of the material. The validation of the material model is shown and compared with the material tests. A sensitivity analysis for other properties such as the Poisson’s ratio and the friction coefficient between the two moulds is given. FE-simulations of the press forming process for the production of a U-beam are presented and compared with test results, showing good agreement.

Photo-Cross-Linked PDMSstar-PEG Hydrogels: Synthesis, Characterization, and Potential Application for Tissue Engineering Scaffolds

Inorganic-organic hydrogels with tunable chemical and physical properties were prepared from methacrylated star polydimethylsiloxane (PDMS(star)-MA) and diacrylated poly(ethylene glycol) (PEG-DA) for use as tissue engineering scaffolds. A total of 18 compositionally unique hydrogels were prepared by photo-cross-linking, varying weight ratios of PEG-DA and PDMS(star)-MA of different molecular weights (M(n)): PEG-DA (M(n) = 3.4k and 6k g/mol) and PDMS(star)-MA (M(n) = 1.8k, 5k, and 7k g/mol). Introduction of PDMS(star)-MA caused formation of discrete PDMS-enriched microparticles dispersed within the PEG matrix. The swelling ratio, mechanical properties in tension and compression, nonspecific protein adhesion, controlled introduction of bioactivity, and cytotoxicity of hydrogels were studied. This library of inorganic-organic hydrogels with tunable properties provides a useful platform to study the effect of scaffold properties on cell behavior.

Effect of Decorin and Dermatan Sulfate on the Mechanical Properties of a Neocartilage

Decorin is known to influence the size of collagen fibrils in ligaments and tendons and it has been hypothesized to provide a structural link between collagen fibrils in connective tissues, including cartilage. Coincidently, mechanical properties of skin, ligament, and tendons are altered in decorin knockout mice, suggesting it may influence the structural properties of tissue or tissue matrix organization. To further examine the role of decorin in the extracellular matrix development and subsequent material properties of cartilage, tissue (neocartilage) was grown in a 3D culture model using a pure population of genetically modified chondrocytes stably overexpressing decorin (DCN) or decorin lacking dermatan sulfate (MDCN). An empty vector (CON) served as a virus control. Following generation of the cartilage-like tissues, mechanical properties in tension and compression, collagen fibril diameter, matrix organization, and biochemistry of the tissue were determined. There were no differences between CON and DCN tissues in any parameter measured. In contrast, tissue generated in MDCN cultures was thinner, had higher collagen density, and higher elastic moduli as compared to both CON and DCN tissues. Considering there was no difference in stiffness between CON and DCN tissues, the notion that decorin contributes to the mechanical properties via load transfer was refuted in this model. However, contrasts in the mechanical properties of the MDCN tissue suggest that the dermatan sulfate chains on decorin influences the organization/maturation and resultant mechanical properties of the matrix by as an yet-unidentified regulatory mechanism.

Structural Characterization and Mechanical Behaviour of LDPE Structural Foams. A Comparison with Conventional Foams

Structural foams are composed of two solid layers enclosing a foamed core. The application of sandwich structural foams has rapidly increased in the last decade. Injection moulding is currently used to produce these foams, being not common to produce conventional foams of similar densities and chemical compositions in a similar process. In this paper an alternative route to produce structural foams has been used. This method allows fabricating conventional foams with the same chemical composition and density than the structural foams, so comparisons between properties of both kinds of materials can be made in a proper way, i.e. avoiding effects of different chemical compositions and/or different densities. The structural and mechanical properties in tension, compression and bending have been characterized both for structural and conventional foams based on a low density polyethylene. The results have showed that the sandwich structure of structural foams improves a 50% the mechanical behaviour in bending, however no improvements in compression or tension have been found.

The Optimization of the Isothermal Transformation Dwell of the ADI Obtained at Transformation Temperature of 380 °C

The structure of austempered ductile iron (ADI) matrix and consequently its mechanical properties are influenced by the heat treatment conditions, above all by the temperature and dwell length of isothermal transformation. The paper is focused on deeper understanding the interrelation between matrix mixture composition and static mechanical properties of ADI in dependence on the isothermal transformation dwell. Practical aim of the paper is to find the optimal isothermal transformation dwell range for ADI isothermally transformed at the temperature of 380 °C with emphasis on the level of static mechanical properties in tension. Microstructure and mechanical properties changes that proceed during isothermal transformation are observed and evaluated for the transformation dwells of 2, 5, 10, 25, 60, 120, 270, and 540 minutes.

Abnormal manifestation of the high-temperature degradation of the weld metal of a low-alloy steel welded joint

We have shown that hardness, impact toughness, mechanical properties in tension, and the local parameters of fracture mechanics (static and cyclic crack resistance) are sensitive to the operating degradation of weld metal of steam pipelines of thermal power plants made of 15Kh1M1F steel. The simultaneous decrease in the resistance to brittle and plastic fracture (hardness, strength, and impact toughness) represents a phenomenon of the operating degradation of weld metal. We have established a specific correlation between the characteristics of plasticity and other mechanical parameters of operated metal: the increase in °5 of operated weld metal is in good agreement with the decrease in its strength, whereas the reduction of Ψ correlates with the lowering of resistance to brittle fracture. Electrolytic hydrogenation decreases the characteristics of strength and plasticity of operated weld metal much stronger than in the initial state. The absence of ferritic edgings on the boundaries of primary austenitic grains makes for a low resistance to brittle fracture, and the change in acicular ferrite deteriorates the mechanical properties. The ductile fracture of nonoperated metal is replaced by brittle intercrystalline failure in operated metal.

Functional Properties of Nanostructured Ti-50.0 at % Ni Alloys

Abstract Ti-50 at % Ni alloy wire is subjected to cold-rolling (true strain e=0.3-1.9) and post-deformation annealing (200–700°C range). For all levels of cold work, the maxima of recovery strain and stress are obtained after annealing in the 350–400°C range. For the moderately-to-high cold-worked material (e=0.3-0.88), this annealing leads to polygonization, while for the severely cold-worked one (e=1.9), to the material nanocrystallization (grains of 50–80 nm in size). Nanocrystallized alloy generates 30 % higher recovery stresses (up to 1450 MPa) and 10% higher completely recoverable strains (more than 8 %) as compared to the polygonized alloy, while having comparable mechanical properties in tension.

Cartilage degeneration in post-collapse cases of osteonecrosis of the human femoral head: Altered mechanical properties in tension, compression, and shear

Osteonecrosis, or avascular necrosis, is a painful and debilitating condition characterized by progressive joint degeneration subsequent to collapse of necrotic regions of trabecular bone. A clear understanding of the mechanism of cartilage degeneration in osteonecrosis is critical to the development of treatment strategies aimed at sparing the femoral head. An analysis of 13 post-collapse osteonecrotic (ON) human femoral heads was performed relative to 24 non-ON controls to determine quantitatively the biomechanical and histological properties of post-collapse osteonecrotic cartilage. Cartilage mechanical properties were measured in tension, compression, and shear at different sites on the femoral head and correlated to histologic measures of cartilage degeneration using a semi-quantitative grading scale. Decreasing cartilage tensile strength correlated with histologic evidence of degeneration in the ON group; however, less correlation was noted with shear and compressive properties. After statistical correction for the more severe histologic degeneration in the ON group, the non-ON samples were found to exhibit significantly smaller loss angles during shear testing, while samples from the ON group were found to have greater tensile strength. Similarly, the ON group was found to exhibit significantly greater proteoglycan loss while the non-ON group showed significantly increased surface fibrillation. This study provides evidence that the changes occurring in post-collapse cases of osteonecrosis may involve mechanisms other than those typically attributed to osteoarthritic degeneration. One potential explanation is that decreased loading of cartilage overlying collapsed ON lesions leads to proteoglycan loss similar to that occurring with cartilage disuse. Unlike degenerative changes, some articular cartilage changes caused by disuse may be reversible. The presence of reversible changes would likely increase the chances of success of head sparing treatment strategies that rely on the viability and mechanical integrity of the articular cartilage.

Measurement of the mechanical properties of structural adhesives in tension and shear over a wide range of temperatures

The aim of this study was to select suitable adhesives for use in a mixed adhesive joint and to measure their mechanical properties over a wide range of temperatures. Three adhesives were selected: a bismaleimide adhesive (Redux 326) for high temperatures and two paste-form epoxies (Hysol EA 9359.3 and Supreme 10HT) for low temperatures. The mechanical properties in tension (dogbone specimens) and in shear (thick adherend shear test) are presented from −55 to 200°C for all three adhesives. Dynamic tests were also carried out to confirm the static modulus results. The correlations between the tensile and the shear properties are reasonable in terms of stiffness and strength but are poor in terms of ductility. In a single-lap joint, Redux 326 is stronger at high temperatures as it becomes more ductile. However, it is very stiff and brittle until 100°C. Supreme 10HT has very good performance up to 100°C. The combination of Redux 326 and Supreme 10HT formed a joint that had a good load carrying capacity from −55 to 200°C.

Effect of porosity on the tensile properties of low ductility aluminum alloys

The literature contains reports of several studies correlating the porosity and mechanical properties of aluminum alloys. Most of these studies determine this correlation based on the parameter of global volumetric porosity. These reports, however, fail to separate the effects of microstructural features and porosity on alloys, though recognizing the influence of the latter on their mechanical properties. Thus, when the decrease in tensile strength due to the porosity effect is taken into account, the findings are highly contradictory. An analysis was made of the correlation between mechanical properties and global volumetric porosity and volumetric porosity in the fracture, as well as of the beta-Al5FeSi phase present in 380 aluminum alloy. Our findings indicate that mechanical properties in tension relating to global volumetric porosity lead to overestimations of the porosity effect in detriment to the mechanical properties. Moreover, the proposed models that take into account the effects of particles, both Si and beta-Al5FeSi, are unapplicable to low ductility alloys.

Mechanical Properties of Polyethylene and Poly(Ethylene Terephthalate) Blends

The results of experimental investigation of mechanical properties in tension of polyethylene (PE) and poly(ethylene terephthalate) (PET) blends are reported. Seven types of specimens with PE/PET weight ratios of 100/0, 90/10, 70/30, 50/50, 30/70, 10/90, and 0/100 were examined. The data on the influence of blend composition on the yield stress, breaking stress, yield strain, and ultimate elongation are obtained. The features of the effect of PE/PET ratio on the elastic properties of the blends are discussed.

Relación entre porosidad y propiedades mecánicas en tracción de aleaciones de aluminio de moldeo. Estado del conocimiento

This article reviews several works for different cast aluminium alloys and analyzes own preliminary experimental results obtained with the aim to establish the state of knowledge of the porosity effect on the mechanical properties in tension. It is concluded that the operative conditions employed, mainly the change of solidification rate, modify the microstructural characteristics which affect the mechanical properties not allowing the determination of the porosity contribution. The publications of Surappa and Caceres, that propose a model to relate properties with porosity, open a promissory field in this subject.

The effect of physical and chemical treatment on the mechanical properties of the cell wall of the alga Chara corallina.

Single large internode cells of the charophyte (giant alga) Chara corallina were dissected to give sheets of cell wall, which were then notched and their mechanical properties in tension determined. The cells were subjected to a thermal treatment in excess water (cf. cooking), which had little effect on strength but increased the stiffness, contrasting with the behaviour of higher-plant tissues. Extraction in CDTA (cyclohexane-trans-1,2-diamine-N,N,N',N'-tetraacetate) or 4 M KOH reduced the strength from 17 MPa to 10 MPa, although sequential extraction in CDTA and 4 M KOH reduced the strength further to 4 MPa. The stiffness decreased from 500 MPa to 300 MPa on extraction in CDTA or 4 M KOH, while falling to 70 MPa after extraction in CDTA followed by 4 M KOH. Conventional sequential extraction in CDTA, Na2CO3 at 1 degrees C and 20 degrees C, and KOH at 0.5 M, 1 M, 2 M and 4 M caused a gradual decrease in stiffness and strength after the CDTA treatment to the same lower values. This result is in keeping with mechanical properties for plant tissues, but in contrast to the removal of pectic polysaccharides from model cell wall systems, which does not reduce the stiffness.

Testing the deformation behaviour of polymer foams

Some of the numerous parameters which influence the mechanical properties in tension and compression of polymeric foams have been studied. The density of the foam is the dominating parameter. Foams with open cells are less stiff and strong than those with closed cells. In foams with closed cells the stretching of the lamellae in tension is more effective in stress bearing than the folding in compression. The deformation pattern beyond the yield point in compression is inhomogeneous. In anisotropic foams strength and stiffness in the direction of elongated cells are higher than perpendicular to it. The air included in closed cells starts to be squeezed out of the foam near its compression strength. The cells are destroyed heterogeneously. In foams expanded from pellets the crack can propagate along internal weak interfaces. The temperature dependence is mainly determined by the matrix.

Effect of the chemical structure of the polymer matrix on the properties of foam polyurethanes at low temperatures

The dependence of physical and mechanical properties of oligoether-based foam polyurethanes on the molecular mass (Mc) of polymer chains between the nodes of the polymer network and on the content of rigid segments in the polymer is investigated at 293 and 98K. The values of Mc at which the foam plastics have the best mechanical properties at low temperatures are determined. The content of rigid segments in the polymer at which foam polyurethanes have the best combination of the linear thermal expansion coefficient and mechanical properties in tension at a temperature of 98K is found.

Effect of solution treatments on the FCC/HCP isothermal martensitic transformation in Co-27Cr-5Mo-0.05C aged at 800°C

Laser powder bed fusion (L-PBF) of Co–28Cr–6Mo alloy is a powerful tool for many engineering applications but one has to be familiar with its microstructural instability in the as-produced state. In our previous study [Roudnicka et al., Additive Manuf. 44 (2021) 102025], we depicted the phenomenon of this instability when exposing the material to temperatures above 673 K. Microstructural changes bringing about hardening of the material were studied thoroughly. In the present study, we follow up by revealing the effect of this hardening on mechanical properties in tension and show the beneficial effect of heat treatment on removing the observed instability. Hardening associated with increasing the proportion of HCP ε-phase and with the precipitation of σ-phase has a detrimental effect on material plasticity and can be negatively affect the fatigue too. We thus applied a two-stage heat treatment comprising solution annealing at 1473 K/2 h and aging at 1173 K/5 h. Not only it induced material stability but also increased the material strength with not such a detrimental decrease in material plasticity as was brought by direct aging at 1173 K/5 h.

Mechanical properties in tension of mechanically attrited nanocrystalline iron by the use of the miniaturized disk bend test

The mechanical properties of warm compacted nanocrystalline (nc) iron powder compacts of near theoretical density in the grain size range between 8 and 33 nm were investigated. The elastic and plastic behavior were characterized by miniaturized disk bend tests and hardness measurements. Light and scanning electron microscopy (SEM) were used to document the deformation and fracture morphologies. The Young's modulus of the nc Fe was essentially the same as that of coarse grained Fe. All samples failed in a macroscopically brittle manner. Local plasticity in shear bands was observed in the samples with the larger grain sizes (>20 nm). An increasing failure stress with increasing grain size is probably due to a processing effect on the flaw controlled failure of the samples. The results are discussed in the context of the deformation and fracture behavior of micrometer grain size metals and alloys.

Synthesis and characterization of leather impregnated with bismaleimide (BMI)-Jeffamine� resins

Leather/polymer composites were prepared by impregnating chrome-tanned cattlehide with a solution containing 1,1′-(methylenedi-4,1-phenylene)bismaleimide and Jeffamine® D-230. The mechanical properties in tension, glass transition temperatures, dynamic storage moduli, and moisture absorption of the composites were measured. Impregnated samples showed significant changes in tensile properties, such as the Young's modulus and strain at break, when compared with chrome-tanned cattlehide. In addition, impact energy increased significantly upon formation of the leather/polymer composite over that of the bismaleimide–Jeffamine® resin itself. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1019–1027, 1998

Ecopetrol's integrity evaluation programme: A case study of a refinery furnace evaluation

This paper presents the relation between internal carburization of tubes fabricated in a ferritic 9Cr-1Mo steel and their mechanical properties in tension and impact, before and after operation for operating times of 14 400, 50 400, 64 800 and 72 000 h in the radiation zone of the visbreaking furnace of the Cartagena Refinery. The skin temperature of the tubes was 566 degrees C, on average, and the fluid temperature (heavy hydrocarbons) was 485degrees C. The carburized layer was observed to have a depth of 1.6 mm and a maximum concentration of 0.775% C on the internal surface of the tube with 72 000 h of continuous operation.

Some characteristics of the binder phase in cemented carbides

This paper examines the properties of binder alloys and mixtures that relate to possible composition of the binder phase in cemented carbide alloys with some emphasis on the sub-stoichiometric state in metal carbides. The investigation looks for a better understanding of the role of carbon deficiency in the performance of alloys in industrial applications. Cobalt was the primary metal chosen for the study with a small companion study of nickel. Low concentrations of carbon; tungsten; a simple mixture of tungsten and carbon; tungsten carbides of both high and low carbon content; di-tungsten carbide; and a solid solution of 50/50 tungsten-titanium carbide were pressed, sintered and heat treated. Sintered materials were tested for mechanical properties in tension and for magnetic properties in strained and unstrained conditions. With the exception of carbon all the alloy additions exhibited some degree of solution strengthening. Tungstentitanium carbide was found to be the most effective additive followed closely by di-tungsten carbide and metallic tungsten. Some relationship was found between mechanical and magnetic properties. Results support a model where WC acts as the primary solution strengthening agent. Tungsten in solution caused by the presence of sub-stoichiometric tungsten carbide further increases the solution strengthening.