An experimental study of uniaxial creep,cyclic creep and relaxation of aisi type 304 stainless steel at room temperature

Following previous work (Krempl, 1979), a servocontrolled testing machine and strain measurement at the gage length were used to study the uniaxial rate(time)-dependent behavior of AISI Type 304 stainless steel at room temperature. The test results show that the creep strain accumulated in a given period of time depends strongly on the stress-rate preceding the creep test. In constant stress-rate zero-to-tension loading the creep strain accumulated in a fixed time-period at a given stress level is always higher during loading than during unloading. Continued cycling causes an exhaustion of creep ratchetting which depends on the stress-rate. Periods of creep and relaxation introduced during completely reversed plastic cycling show that the curved portions of the hysteresis loop exhibit most of the inelasticity. In the straight portions, creep and relaxation are small and there exists a region commencing after unloading where the behavior is similar to that at the origin for virgin materials. This region does not extend to zero stress.The results are at variance with creep theory and with viscoplasticity theories which assume that the yield surface expands with the stress. They support the theory of viscoplasticity based on total strain and overstress.     

Power-law creep and residual stresses in a carbopol gel

We report on the interplay between creep and residual stresses in a carbopol microgel. When a constant shear stress σ is applied below the yield stress σ _y, the strain is shown to increase as a power law of time, γ(t) = γ ₀ + (t/τ) ^α , with an exponent α = 0.39 ± 0.04 that is strongly reminiscent of Andrade creep in hard solids. For applied shear stresses lower than some typical value σ _c ? 0.2σ _y, the microgel experiences a more complex, anomalous creep behavior, characterized by an initial decrease of the strain, that we attribute to the existence of residual stresses of the order of σ _c that persist after a rest time under a zero shear rate following preshear. The influence of gel concentration on creep and residual stresses are investigated as well as possible aging effects. We discuss our results in light of previous works on colloidal glasses and other soft glassy systems.     

Direct method of solving the boundary-value problem of relaxation of residual stresses in a hardened cylindrical specimen under creep conditions

A direct method of solving a boundary-value problem for a surface-hardened cylindrical specimen affected by a tensile load under creep conditions is proposed. Relations for estimating the kinetics of the stress-strain state in the hardened layer are obtained. The adequacy of the solution is verified by experimental data on relaxation of residual stresses in the hardened layer of a cylindrical specimen made of éI 691 steel at T = 400°C. The calculated and experimental residual stresses are demonstrated to be in good agreement.     

Determination of transient and residual thermal-hardening stresses in steel plates

Summary Diagrams for determining weight fractions of pearlite and martensite, transient and residual thermal-hardening stresses are numerically evaluated and analysed for steel plates. Kinetics of phase transformation and the accompanying volumetric dilatation are taken into account. The diagrams enable the evaluation of proportions of individual constituents and phases, determination of relative volumetric changes due to phase transformations, and estimation of transient and residual stresses. The results are obtained and compared for Lomakin's theory and the Hildenwall model.

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Bestimmung der transienten und bleibenden Härtespannungen in Stahlplatten

Übersicht Für Stahlplatten werden durch numerische Berechnung Diagramme zur Bestimmung der Gewichtsanteile von Perlit und Martensit sowie der transienten und bleibenden thermischen Härtespannungen ermittelt und interpretiert. Die Kinetik von Phasentransformationen und die damit einhergehende Volumenänderung werden berücksichtigt. Die Diagramme erlauben sowohl die Bestimmung des Anteils jeder Phasenkomponente als auch der relativen Volumenänderung infolge Phasentransformationen und eine Abschätzung der transienten und permanenten Eigenspannungen. Die Ergebnisse nach Lomakin's Theorie und dem Modell von Hildenwall werden verglichen.

     

Crack propagation under mode II dominance at stainless steel–epoxy interfaces with residual stresses and micro-scale roughness

This report describes investigations of grain boundary groove effects on mode II dominated interface fracture. The study focused on a specific interface between stainless steel and an epoxy adhesive. First, a finite element model was developed to simulate residual stresses and crack propagation. Second, the simulation results were compared with the experimental results from a previous study (Kanerva et al., 2013. Eng. Fract. Mech. 99, 147-158). Additional measurements were performed using atomic force microscopy. Based on the simulation, a 100-fold toughening effect due to the grain boundaries was determined. Implementation of flaws, in the form of interfacial voids, decreased the toughening effect by 35% and increased the mode II dominance significantly. The work underlines the practical importance of complete wetting by the adhesive and its necessary adherence to the grain boundary groove walls.     

A study on the relief of residual stresses in weldments with explosive treatment

Explosive treatment is an efficient and economical technique in reducing welding residual stresses. The whole course of residual stress reduction is investigated both numerically and experimentally, in order to discover the mechanism of the explosive treatment and optimizing the technique. It is proved that the reflection and superposition of stress waves aroused by explosive loading lead to redistribution and remarkable reduction of welding residual stresses. Moreover, the optimum working conditions, such as detonator shape, width, location, explosive loading and velocities, are also discussed. The numerical results and the experimental ones are in reasonable agreement with each other.     

Stress relaxation,creep, and internal stresses in high density polyethylene filled with calcium carbonate

The effect of filling high density polyethylene (HDPE) with calcium carbonate (up to 50% by weight) on the stress relaxation and the creep in uniaxial extension at room temperature was investigated. The addition of CaCO₃ was found to have a strong influence on the flow behaviour of HDPE. In particular, it was observed that the internal stress level, calculated from relaxation data, increased markedly with the filler content. The reduction in creep rate of the filled samples suggested that the CaCO₃-particles induce a change in the structure of the HDPE-interphase close to the filler surface. This was supported by dynamic mechanical measurements performed at low temperatures on swollen HDPE-CaCO₃ samples.     

Effect of thermal exposure on the residual stress relaxation in a hardened cylindrical sample under creep conditions

This paper describes the effect of thermal exposure (high-temperature exposure) (T = 675?C) on the residual creep stress relaxation in a surface hardened solid cylindrical sample made of ZhS6UVI alloy. The analysis is carried out with the use of experimental data for residual stresses after micro-shot peening and exposures to temperatures equal to T = 675?C during 50, 150, and 300 h. The paper presents the technique for solving the boundary-value creep problem for the hardened cylindrical sample with the initial stress–strain state under the condition of thermal exposure. The uniaxial experimental creep curves obtained under constant stresses of 500, 530, 570, and 600 MPa are used to construct the models describing the primary and secondary stages of creep. The calculated and experimental data for the longitudinal (axial) tensor components of residual stresses are compared, and their satisfactory agreement is determined.     

Influence of seawater and residual stresses on fatigue crack growth in C---Mn steel weld joints

Results are presented on fatigue crack growth of weld joints made of C---Mn structural steel plates in both air and seawater. Tests were conducted to identify the behavior at different locations of the joints as the frequency, R-ratio and electrochemical potential are varied. Residual stresses in specimens with welds are evaluated to analyse the fatigue crack growth behavior. Satisfactory predictions are obtained by accounting for residual stresses and crack closure.     

三轴应力状态下混凝土的一种新强度准则

提出了一种新的三轴应力状态下的混凝土强度准则,它的理论基础是最小耗能原理.对不同的混凝土材料和不同的受力状态,该文给出的强度准则与实验值均吻合较好.     

A parametric study of CaCO3 scaling in AISI 316 stainless steel tubes

 The formation of undesirable layer of deposits on the heat-transfer surface is defined as fouling. These deposits present a major problem in the operation and maintenance of heat exchangers, particularly in cooling-water systems. It has been generally observed that the deposits in such systems consist mainly of calcium carbonate (CaCO₃), which has inverse solubility characteristics. An experimental study was carried out to determine the effect of tube surface temperature, Reynolds number, tube diameter and salt concentration on the growth of CaCO₃ scale. In this paper, effects of some of these parameters on fouling growth are discussed. The effect of CaCO₃ concentration on the scale growth is compared with the ionic diffusion model presented by Hasson. The variation of the fouling thickness along the length of the heat exchanger is also illustrated. Furthermore, dimensionless parameters are introduced to present the fouling resistance data collected during the experimental study. Received on 14 June 2000     

A novel scheme for the approximation of residual stresses in arterial walls

In this contribution, a novel approach for the modeling of residual stresses in human arteries is proposed. The starting point in a variety of contributions is the opening angle of the section of an artery as a consequence of a longitudinal cut. In contrast to this, we focus directly on the current stress state within the arterial wall. To be more precise, we analyze the gradients of suitable invariant stress measures in thickness direction of the arterial wall. As an underlying optimization criterion, we assume that these gradients have to be smoothed between their inner and outer margins of the individual layers in an appropriate way. In order to do this, we define suitable radial sections for the media and adventitia, where this condition has to be enforced independently. The efficiency of the proposed model is demonstrated by means of a patient-specific cross section of a diseased artery in a two-dimensional simulation.     

Elevated-temperature creep and relaxation of torsion-tension members

Based on the assumption that each material satisfies the condition for isotropic hardening for a von Mises material, an incremental solution is developed to predict axial-strain creep curves and maximum shearing-strain creep and relaxation curves for solid circular torsion-tension members subjected to proportionate and nonproportionate stepped loading including creep in tension and relaxation in torsion. Test data are obtained from torsion-tension members made either of annealed OFHC copper at 800°F (427°C) or hot-rolled SAE 1045 steel at 950°F (510°C). The loading histories include either four stepped proportionate load changes, four stepped nonproportionate load changes, or torsion-tension loading in which the axial load remains constant and the torsional load is allowed to relax during two loading periods of the test. Each test duration is about 100 h. Good agreement is indicated between the predicted and measured creep and relaxation curves.     

On the sensitivity of interconversion between relaxation and creep

The interconversion equation of linear viscoelasticity defines implicitly the interrelations between the relaxation and creep functions G(t) and J(t). It is widely utilised in rheology to estimate J(t) from measurements of G(t) and conversely. Because different molecular details can be recovered from G(t) and J(t), it is necessary to work with both. This leads naturally to the need to identify whether it is better to first measure G(t) and then determine J(t) or conversely. This requires an understanding of the stability (sensitivity) of the recovery of J(t) from G(t) compared with that of G(t) from J(t). Although algorithms are available that work adequately in both directions, numerical experimentation strongly suggests that the recovery of J(t) from G(t) measurements is the more stable. An elementary theoretical rationale has been given recently by Anderssen et al. (ANZIAM J 48:C346–C363, 2007) for single exponential models of G(t) and J(t). It explicitly exploits the simple algebra of such functions. In this paper, corresponding bounds are derived that hold for arbitrary sums of exponentials. The paper concludes with a discussion, from a practical rheological perspective, about the implications and implementations of the results.     

Measurement of favorable residual stresses in polycarbonate

Research in this laboratory has been directed toward the production and effects of beneficial residual stresses in plastics. Such stresses have been shown to have a dramatic effect on the impact strength and fatigue life of polycarbonate samples. For example, thermal quenching, in water or liquid nitrogen, of samples heated above their glass-transition temperature, resulted in an increase in the mean fatigue life of the material by as much as 20 times over that of annealed material. This increase is attributed in large part to the introduction of compressive stresses on the surfaces of the samples. This paper concentrates on methods used to measure residual stresses in the surface of the material and on the variation of these stresses with time after treatment. Three measurement techniques are described: (1) material slicing, (2) photoelastic fringe displacement and (3) the ASTM hole-drilling method. The advantages, limitations and comparative results of these three methods are described and analyzed. Paper was presented at the 1986 SEM Spring Conference on Experimental Mechanics held in New Orleans, LA on June 8–13.     

Experimental determination of residual stresses in paperboard

A method for the experimental determination of the through-thickness residual stress distribution in paperboard is presented. The successive removal of thin layers from strips of board through surface grinding changes the stress-state and the bending stiffness resulting in a changed curvature, which is measurable. From tests of strips in both in-plane directions, stress distributions can then be evaluated using the Treuting-Read method. Geometrically nonlinear effects at the large deformations taking place are avoided through a proper choice of strip dimensions. Typical results are presented and factors influencing the accuracy of the determination are thoroughly discussed.