Monotonic Tension Tests Research Articles

TRANSVERSE STRAIN RESPONSE OF HI-NICALON FIBRE REINFORCED SILICON NITRIDE MATRIX COMPOSITES

The relation between the longitudinal stress {sigma} and the transverse strain {var_epsilon}{sub tr} during monotonic tension testing of unidirectional fiber toughened ceramic matrix composites (UD-CMCs) has been studied experimentally and theoretically by several authors. Matrix cracking and interface debonding generally causes {var_epsilon}{sub tr} to increase or to become positive. Recently, this has been theoretically explained by a model taking into account the Poisson contraction of fiber and matrix, the redistribution of mechanical stress and the relief of residual thermal strain upon damage development, and the built-up of compressive radical stresses at the interface caused by the radial interfacial mismatch after interface debonding and sliding. In this paper, the {var_epsilon}{sub tr} response of a series of Hi-Nicalon (SiC) fiber reinforced silicon nitride matrix composites is reported and described by a previously developed model. This paper focuses on the extension of the model to composites with a radial gap {delta} after interface debonding, which was necessary to model the present CMC materials.

フラクトグラフィ ロータ鋼の各種破壊挙動に及ぼす組織異方性の影響

In order to clarify the anisotropy of fractography at fracture initiation site, monotonic tension, bending fatigue and tensile creep fracture tests were carried out at room and elevated temperatures, using three oriented specimens extracted from a Cr-Mo-V steel turbine rotor. In the case of monotonic tension, although the effects of temperature on tensile properties and fractography was prominent, the effects of specimen orientation on those were quite small at room and 839K temperatures. The fatigue limit of L-R oriented specimen was about 380MPa, and 25% higher than those of C-R and C-L oriented specimens. The scattering of fatigue life of C-R oriented specimen at the near fatigue limit stress condition was clearly larger than those of the other oriented specimens. Under bending fatigue, markedly different fractographic patterns were observed at the crack initiation site for all the three oriented specimens. It was found that the orientation of two kinds of inclusions, MnS and Al2O3 particles at the fatigue crack initiation site, influences the fractographic mode strongly. The creep result of L oriented specimen showed the longest life, as compared with those of the other oriented specimens, under nearly the same stress condition. The effect of specimen orientation on the fractographic patterns of creep was quite small.

High strain-rate impact studies of predamaged rocket propellants. I. Characterization of damage using a cumulative damage failure criterion

The effect of predamage on the high strain-rate behavior, ignition sensitivity, and impact ignition mechanism of a HTPB/AP rocket propellant was assessed using a modified Hopkinson Bar. Damage was induced by constant stress and monotonic tension tests prior to testing on the modified Hopkinson Bar. Predamage was characterized using a failure criterion based on a linear Cumulative Damage model. Creep and recovery experiments were conducted to determine the amount of recovery (due to relaxation or viscoclastic effects) and rehealing of damage (nonrecoverable strain), and the effect of recovery time on the induced mechanical damage. The effect of residual void volume on the impact ignition sensitivity and mechanism for freshly damaged, rehealed, and undamaged propellant samples was also investigated.

A RE‐EVALUATION OF THE LIFE TO RUPTURE OF DUCTILE METALS BY CYCLIC PLASTIC STRAIN

Abstract— Experiments have been performed on specimens subjected to strain cycles similar to those experienced by sub‐surface elements of material in rolling/sliding contact. It has been observed that if the strain cycle is closed then failure takes place by low cycle fatigue and the Coffin‐Manson relationship may be used to predict the number of cycles to failure. If however, the strain cycle is open, so that the material accumulates unidirectional plastic strain (the situation known as “ratchetting”) a different type of failure, which is termed ratchetting failure may occur. It occurs when the total accumulated plastic strain reaches a critical value which is comparable with the strain to failure in a monotonic tension test. The number of cycles to failure under these circumstances may be estimated by dividing this critical strain by the ratchetting strain per cycle. It is suggested that low cycle fatigue and ratchetting are independent and competitive mechanisms so that failure occurs by whichever of them corresponds to a shorter life. The results of both uniaxial and biaxial tests reported in the literature have been re‐evaluated and these, together with new data on biaxial tests on copper, found to be consistent with this hypothesis.

On simulating steel-concrete interaction in reinforced concrete part II: Validation studies

The simulation capability of the mixture model developed in a companion paper (Murakami and Hegemier, 1986), has been examined for the special case of ‘steel-concrete bond action’. Validation studies were conducted for monotonic pull-out and tension tests and cyclic tests of full-scale reinforced concrete panels. It has been observed that using the elementary mixture relations together with simplified bond-slip and crack opening, closing and reopening algorithms, one can achieve excellent agreement with experimental data.

鋼構造溶接接合部の低サイクル疲労強度に関する実験的研究 : その 2 理想化された柱はり溶接接合部の疲労強度

In order to clarify the mechanical properties and the low-cycle fatigue strength of the idealized beam-to-column welded joints, this experimental investigation was carried out. Specimens, consisted of JIS SS 41 mild steel plates, were welded by means of CO_2-Gas butt welding or Non-Gas butt welding and fabricated to flat plate shapes which were named A-Type, or crossed shapes named B or C-Type. Three types of specimens were loaded at constant amplitudes from ±0.5% to ±1.5% as the deformations between the gauge length in a manner of quasi-static state. Only the C-Type specimens were subjected to constant bi-axial forces which simulated cyclic bending moments and column axial forces, using a special loading apparatus. The following phenomena were clearly observed from the results of the monotonic tension tests; anisotropy of the mild steel plates in the thickness direction existed and the sensitivity on Lamellar Tearing was quite high. The low-cycle fatigue strength of the A and B-Type specimens is well expressed by the well known Manson-Coffin formulae in terms of the non-dimensional elastic and plastic strain amplitudes and the equivalent fatigue lives. No deteriorations can be remarkable observed from the biaxial fatigue tests using the C-Type specimens in the nondimensional form of fatigue strength, which employed the plastic anisotropy proposed by Hill's yield criteria.

Low-cycle fatigue studies on nuclear reactor Zircaloy-2 fuel tubes at room temperature, 300 and 350°C

Constant amplitude strain controlled fatigue tests were conducted on the Zircaloy-2 fuel tubes at room temperature, 300 and 350°C on the modified Moore type, four-point-loaded, deflection-controlled, rotating bending fatigue testing machine. The relationship between the plastic strain range, Δϵ p and the number of cyles to failure, N f was found to be of a simple power law of the form N β f · Δϵ p = constant, at all the test temperatures. Strain-hardening coefficients were determined from monotonic tension tests at these temperatures and it was concluded that the material is more or less in a cyclically stable condition.