Simultaneous Straining Research Articles

On the tensile embrittlement of lamellar Ti–5Al–5V–5Mo–3Cr alloy

In this paper, we investigated the tensile embrittlement of lamellar Ti-5553 alloy by analyzing its deformation mechanism, damage behavior and tensile fractography. The lamellar alloys were prepared by solution at 900 °C and ageing at 500 °C, 600 °C, 700 °C and 800 °C respectively. Although the lamellar alloys are different in the dimension and volume fraction of Alpha precipitation, they exhibit the same deformation, damage and fracture feature. The deformation of the alloy is dominated by the shearing of the Alpha precipitation and the simultaneous straining of the Beta matrix inside the lamellar unit, and the strain localization of lamellar unit may lead to the formation of the deformation band. The damage of the alloy initiates at the intrinsic ruptured Alpha precipitation. As the strain increases, the micro-crack may propagate inside the deformation band by the coalescence of the micro-void inside the lamellar unit. Once the crack reaches the critical length, the trans-granular shearing fracture takes place, leading to the final failure. In summary, the tensile embrittlement of lamellar Ti-5553 alloy is mainly caused by the strain localization of lamellar unit and the trans-granular shearing fracture.

Fracture prediction under the simultaneous bending and straining of a wide bar at an elevated temperature

In processes of metal formation at an elevated temperature, the fracture criterion should depend at least on the parameter of a triaxial stressed state, the equivalent strain rate, and the temperature. This significantly complicates the investigation in comparison with the case of cold processing. However, in the case of fracture initiation at the free surface under plane-strain conditions, a computational scheme is found that is similar to the one used in processes of cold working under pressure, although in another space. This scheme is used for the prediction of the beginning of the fracture in the process of the simultaneous bending and straining of a wide bar.

Simultaneous mechanical and electrical straining of conventional thick-film resistors

In this paper results from the study of simultaneous mechanical and electrical straining effects on performances of conventional thick-film resistors based on three different resistor compositions with sheet resistances of 1 kΩ/sq, 10 kΩ/sq and 100 kΩ/sq are presented. For experimental purposes thick-film test resistors of different dimensions were realized. Resistors were simultaneously subjected to mechanical straining with maximal substrate deflection of 300 μm and multiple high-voltage pulses. Obtained experimental results are analyzed from micro- and macrostructural, charge transport and low-frequency noise aspects. Correlations between resistance, gauge factor and low-frequency noise changes with resistor degradation due to simultaneous mechanical and electrical straining are observed.

The role of the T 1 phase in the pre-exposure and hydrogen embrittlement of AlLiCu alloys

A series of slow strain rate tests were conducted on longitudinal specimens of two AlLi binary and two AlLiCu alloys, to determine the possibility of embrittlement by hydrogen and to investigate the role of the T 1 phase in the embrittlement process. The binary AlLi alloys were not embrittled. The copper-containing alloys were susceptible to hydrogen embrittlement that can be induced by pre-exposing in NaCl solution or simultaneous cathodic charging and straining. It was shown that the T 1 phase facilities hydrogen entry into the copper-containing alloys and is responsible for their susceptibility. The hydrogen embrittlement susceptibility of the different microstructures of the two AlLiCu alloys was found to correlate very well with the amount of T 1 present and the slip behavior. The fracture mode was mainly transgranular. Some secondary intergranular cracking was also present and its extent related to the amount and distribution of hydrogen present.

Microstructure property relationships and hydrogen effects in a particulate-reinforced aluminum composite

The relationship between the composite microstructure and tensile behavior of a 2124-SiCP powder-formed composite was the subject of the present investigation. In particular, emphasis was placed on the role of the composite microstructure in determining the operative fracture processes. The susceptibility of the composite to hydrogen embrittlement was examined using straining electrode tests which involved simultaneous specimen straining and cathodic hydrogen charging. The behavior of the composite was compared to that reported for an unreinforced 2124 alloy.

Microstructural effects on hydrogen embrittlement in a high purity 7075 aluminum alloy

A high-purity 7075 alloy was heat treated to produce a variety of precipitate sizes and populations in grain interiors and at grain boundaries. Specimens were then evaluated for slip character and hydrogen embrittlement susceptibility following cathodic precharging or by simultaneous cathodic charging and straining. Embrittlement susceptibility was found to correlate very well with the size and type of matrix precipitates, consistent with the rationale that slip character controls the extent of dislocation transport of hydrogen and thereby may control and dominate the distribution of hydrogen in the material and the degree of hydrogen embrittlement. The results also indicate that a smaller role is played by grain boundary precipitates in controlling hydrogen embrittlement susceptibility.

Volume change and the nonlinearly thermo‐viscoelastic constitution of polymers

AbstractThe time‐dependent behavior of linearly viscoelastic materials is known to be very sensitive to changes in temperature and in solvent (water) concentration. Following an investigation by the authors of this sensitivity in terms of the associated small volume changes, a nonlinearly viscoelastic model of constitutive behavior was formulated earlier in terms of the free volume concept and evaluated in terms of experiments on poly(vinyl acetate). Following a brief presentation of the earlier results these concepts are expanded and refined in the present paper to deal with transient deformation histories under pressure. In this connection, model computations explore the effect of simultaneous pressurization and straining. In addition the effect of “ageing” the polymer under pressures of various magnitudes and for different lengths of time are investigated. It becomes clear that the yield phenomenon depends sensitively on pressure and on the ageing time. In addition, the volume change under transient thermal histories in the glass transition range is explored, largely in terms of Kovacs' experimental data and attendant computations. These considerations are presented from a unified point of view of nonlinear thermoviscoelastic constitutive behavior, principally with phenomenological material description in mind. These computations provide guidance to the design of experiments for the proper determination of the relevant material functions and seem to indicate a need for the reevaluation of certain experimental procedures in the time histories of thermal material characterization.

Strain Effects on Sensitization Development in 304 Stainless Steel as Measured by EPR and Stem/Eds Methods

AbstractThe effect of uniaxial straining during isothermal heat treatment of a Type 304 stainless alloy has been examined using scanning transmission electron microscopy/energy dispersive x-ray spectroscopy (STEM/EDS) and electrochemical potentiokinetic reactivation (EPR) methods. Solution-annealed, flat tensile specimens were deformed at 600°C at various strain rates up to 6%/h. EPR and STEM/EDS results show an acceleration in sensitization development with increasing deformation. STEM/EDS measurement suggest that simultaneous straining affects both the kinetics of sensitization and the chromium concentrations established at grain boundaries.

The interaction of simultaneous cyclic straining and aqueous corrosive attack in the behavior of persistent slip bands

We have studied the corrosion of copper single crystals as a function of applied anodic potential when the metal was cycled in deaerated 0.1 M HClO 4, i.e. an aqueous environment which prevented the formation of oxide films. The behavior has been studied both in the presence and absence of cycling. The dominant corrosion fatigue mechanism under these conditions is preferential dissolution of PSB's. Some temporary preferential dissolution also occurs during rapid hardening, but if saturation is obtained below the region of the plateau in the cyclic stress-strain curve, then the corrosion becomes uniform. Crystals containing PSB's, but not simultaneously cycled, show preferential dissolution only over a very narrow range of anodic potential. Cycling acts to widen that range and to intensify the preferential dissolution. We believe that the main cause of preferential dissolution is the heightened activity of fresh surfaces created in the active bands.

The effect of copper content and microstructure on the hydrogen embrittlement of AI-6Zn-2Mg alloys

Two commercially-processed Al-6Zn-2Mg alloys, 7050 and a “low copper” 7050, were tested for susceptibility to embrittlement by precharged hydrogen and by simultaneous cathodic charging and straining (SET procedure). Specimens were heat treated to underaged, peak-strength aged, and overaged conditions. In 7050, the peak strength and overaged conditions were not embrittled by hydrogen, though underaged material showed marked embrittlement. All microstructures tested for the low-copper alloy were embrittled. The results agree with the microstructural rationale established through earlier work on 7075 and 2124 aluminum alloys, particularly with respect to the susceptibility of underaged material to hydrogen. As in earlier work, the extent of dislocation transport of hydrogen, and local hydrogen accumulation at grain boundaries, evidently controlled the extent and degree of brittle fracture. These three important alloys can now be ranked in the order 7050, 2124, 7075 of increasing relative susceptibility to theonset of stress corrosion cracking.

Hydrogen Embrittlement in a 2000-Series Aluminum Alloy

Tensile tests were performed on an Al-Cu-Mg alloy, 2124, in plate form, after aging to seven different tempers. Cathodic charging with hydrogen caused no significant loss of ductility for any temper, in contrast, for example, to 7075. Simultaneous straining and cathodic charging did, however, result in reduction in area losses up to 25 pct. The fracture mode was not altered by hydrogen. In general, the results conformed to the framework established through investigation of 7075 alloys, in that the underaged microstructures were the most susceptible to hydrogen embrittlement; this susceptibility can be explained in terms of microstructure and slip behavior.

Dynamic strain age hardening of Cu-Be alloys

AbstractThe effect of plastic strain on the ageing kinetics of Cu-Be alloys has been studied by means of yield-stress measurements and transmission electron microscopy. The results show that plastic strain introduced before ageing retards the ageing kinetics at lower temperatures but has little effect at higher temperatures, while simultaneous straining accelerates the ageing kinetics over the entire temperature range tested (90–350°C). The retarding and stimulating effect of prior and simultaneous strain is associated with elimination and generation of excess vacancies during nonconservative motion of dislocations.

Electron microscope specimen holder for simultaneous straining, tilting and rotating of thin foils

A straining device which has been built to be inserted in the normal tilting and straining attachment of a JEM-6A microscope is described. This permits the simultaneous tilting, rotating and straining of thin foil specimens that is necessary in order to observe dislocations during straining.

Strength Tests of Fiber Arrays

Basic differences between tensile tests of single fibers versus similar fibers in arrays such as yarn, skeins, tow, and staple comhings keep the strength of arrays from exceed ing that of single fibers. The reverse holds true for strain. Moreover, experimental difficulties of achieving simultaneous straining among the fibers in an array further reduce the apparent strength and increase apparent strain, by amounts that depend on the extent of departure from simultaneity, i.e. the strain distribution in the array. Close equivalence of group tests of strength and maximum strain to single fiber measurements can be obtained even for the wide range of slackness observed in some tow, by recourse to a parameter that is not affected by departure from simultaneity of straining, namely, -the energy absorbed in rupture. Strength, maximum strain, and associated measures of variability can be calculated from energy via the tenacity-strain function for the fiber type. Good agreement with single fiber measurements has been obtained for acrylic fibers in the form of tow.