Monotonic Tensile Behavior Research Articles

Viscoelastic Behavior of HDPE Polymer using Tensile and Compressive Loading

Large containers for liquids, exposed to different static loadings, are mainly made of high-density polyethylene (HDPE). The viscoelastic response of HDPE under long-term tensile and compressive creep is investigated. Monotonic experiments under tension are performed over a wide range of strain rates. In these experiments, the transition in the damage mechanisms (development and propagation of contraction in the HDPE specimen) is analyzed. The monotonic tensile behavior of the HDPE is found to be nonlinear and depends on the strain rates. It is observed that both elastic modulus and plastic flow stress present an increase with displacement speed due to the viscoelastic behavior of HDPE. A similar observation can be made for monotonic compressive tests by developing a new experimental device that ensures accurate measurement of the strain. Such a device makes use of an extensometer of compressive displacement of the specimen. In addition, the long-term behavior of HDPE is evidenced through creep and relaxation tests at an imposed range respectively of lower stresses and strains. It is shown that the normalized curves, associated with these tests, can be represented by a single curve characterizing the compressive creep compliance or relaxation stresses versus time. The linearity of the viscoelastic behavior is confirmed within the linear domain of the monotonic compressive and tensile tests.

Effect of loading rate and temperature on monotonic tensile behavior in an enhanced SiC/SiC composite

Tensile behavior in an enhanced SiC/SiC composite has been studied in air at 1200–1400 °C with different loading rates. Tensile strength and failure strain increase with increasing temperature from room temperature to 1200 °C. The glassy phase in the matrix is effective to protect the composite from oxidation.

Fatigue behavior of Nextel™ 312/Blackglas™ ceramic matrix composite with tensile and zero mean load

This study characterized a woven fabric reinforced ceramic matrix composite, Nextel™ 312/Blackglas™, under monotonic and fatigue loading conditions at room and elevated (760°C) temperatures in order: (1) to investigate monotonic tensile and compressive loading behavior at room and elevated temperatures, (2) to establish the fatigue life diagrams (S - N curves) with tensile and zero mean load under low frequency (0.1 Hz) cycling condition at room and elevated temperatures, and (3) to investigate damage mechanisms and failure modes under monotonic and fatigue loading conditions. Fatigue lives under tension-compression cycling were much longer than those under tension-tension cycling at a given stress range for both room and elevated temperatures. However, fatigue lives under tension-compression cycling were much shorter than those under tension-tension cycling for a given maximum stress level at room temperature, but lives were about equal under these two loading conditions for a given maximum stress level at elevated temperatures. Further, fatigue lives were much shorter at elevated temperature than their counterparts at room temperature for a given stress range or for a given maximum stress level under the both tension-tension and tension-compression cycling conditions.

Monotonic and fatigue loading behavior of quasi-isotropic graphite/epoxy laminate embedded with piezoelectric sensor

This study investigated the effects of embedding piezoelectric lead zirconate-titanate (PZT) sensors on the tensile strength and fatigue behavior of a quasi-isotropic graphite/epoxy laminate as well as the embedded sensor's voltage degradation under these loading conditions. For this, AS4/3501-6 laminates were fabricated with a lay-up where PZT was inserted into a cut-out area in the two middle plies. Monotonic tensile tests showed that both the average ultimate strength and Young's modulus of the tested laminate with or without PZT were within 4% of each other. The fatigue lives with and without PZT were very close to each other as well. Overall, the sequence of damage in this study agreed with previous investigations of the damage mechanisms for quasi-isotropic laminates. The ranges of modulus reduction in both cases, with and without PZT, were within 5 to 15% of each other during fatigue loading. Delamination growths in both cases during most of the fatigue life were also very comparable to each other. Further, this study showed that the embedded PZT would maintain a steady voltage output indefinitely when mechanically cycled within its operational strain limit. It thus appears that the embedment of PZTs in a cut-out area of plies of quasi-isotropic graphite/epoxy laminates would not affect their monotonic tensile and fatigue behavior.

Effects of sequential cyclic and monotonic loadings on damage accumulation in nickel 270

Specimens of polycrystalline nickel 270 were tested by subjecting them to loading paths of either (1) monotonic prestrain followed by strain controlled cyclic loading to failure or (2) strain controlled precycling followed by monotonic loading to failure. The effects of initial condition as produced by cold working or annealing, cyclic strain range, frequency and degree of monotonic prestrain on subsequent fatigue behavior were investigated. The effects of precycling on the subsequent monotonic tensile behavior of the test material were also studied. The heat dissipated from the specimens under fatigue loading was measured. It was found that 76.6% of the irreversible work was dissipated as heat; the remaining portion caused material damage. The relative effects of monotonic prestrain on subsequent cyclic behavior were more harmful than the effects of precycling on subsequent monotonic behavior. The results showed that the energy absorbed by the material, which corresponds to damage, is a function of various loading parameters and is therefore path dependent under these conditions.

Exponential model for the tensile true stress-strain behavior of as-irradiated and oxidatively degraded ultra high molecular weight polyethylene.

Following sterilization by gamma radiation, ultra high molecular weight polyethylene components for total joint replacement undergo oxidative degradation upon exposure to air and the in vivo environment. Oxidative degradation is accompanied by an increase in density. The primary objective of this study was to develop a mathematical model to predict the monotonic tensile mechanical behavior of these sterilized components as a function of changes in density arising from oxidative degradation. Tensile specimens of ultra high molecular weight polyethylene were sterilized with gamma radiation and then oxidatively degraded in an air furnace. The average density of each specimen was measured using a density gradient column. Differential scanning calorimetry and Fourier transform infrared spectroscopy were conducted on selected specimens to characterize the physical and chemical changes due to accelerated aging as opposed to ambient shelf aging. Mechanical testing was conducted in monotonic uniaxial tension. An exponential model was fitted to the true stress-strain data (up to a true strain of 0.12). The observed fitted stress had a correlation coefficient of 0.996. The model permits a quantitative prediction of the association between the true stress-strain curve and density for the ultra high molecular weight polyethylene components. The proposed exponential model effectively describes changes in the large-strain monotonic tensile behavior of as-irradiated and oxidatively degraded ultra high molecular weight polyethylene components.

Effect of Loading Rate on the Monotonic Tensile Behavior of a Continuous‐Fiber‐Reinforced Glass‐Ceramic Matrix Composite

The stress‐strain behavior of a continuous‐fiber‐reinforced ceramic matrix composite has been measured over a wide range of loading rates (0.01 to 500 MPa/s). It was found that the loading rate has a strong effect on almost every feature of the stress‐strain curve: The proportionality stress, the composite strength and failure strain increase with increasing loading rate. The microstructural damage varies also with the loading rate; with increasing loading rate, the average matrix crack spacing increases and the average fiber pullout length decreases. Using simple models, it is suggested that these phenomena are caused partly by time‐dependent matrix cracking (due to stress corrosion) and partly by an increasing interfacial shear stress with loading rate.

Deformation and Fatigue Behavior of Vanadium-Based Microalloyed Forging Steel in the As-Forged and Q&T Conditions

Abstract The use of microalloyed (MA) forging steels in the asforged condition can result in the elimination of the costly post-forging quenching and tempering (Q&T) processes. MA steels can therefore serve as economical alternatives to the traditional Q&T steels if equivalent mechanical properties can be obtained. In this study, monotonic and cyclic behaviors of a vanadium-based MA forging steel, one of the most commonly produced MA steels, were investigated under both the as-forged and Q&T conditions. The mechanical properties evaluated and compared include monotonic tensile behavior, cyclic deformation response, and low and high cycle fatigue resistance. Experimental results are presented and the differences in the behaviors under the two processing conditions are discussed.

Low-Cycle Fatigue Behavior of Polycrystalline NiAl at Room Temperature

The room temperature cyclic deformation of a cast and extruded NiAl alloy has been investigated. Low-cycle fatigue tests were performed under plastic strain control at strain ranges from 0.0002 to 0.0016. Cyclic hardening behavior has been analyzed and compared to the monotonic tensile and compressive behavior of the same material. Electroless nickel films applied to NiAl samples have little effect on monotonic deformation behavior, but do have a significant effect on cyclic deformation behavior, particularly cyclic stress asymmetry. Fractographic analysis has suggested that cycling at low plastic strain ranges may promote stable microcracking, while step testing indicates that cycling at lower plastic strain ranges can improve the cyclic life and/or stress levels achieved at the higher plastic strain ranges. Low plastic strain range cyclic prestrain can also significantly increase the monotonic tensile yield and ultimate strength of the material while most of the tensile ductility is retained.