Reduced-size Specimens Research Articles

A probabilistic stress-life model supported by weakest link principle and highly-stressed volume/surface area concepts

This article introduces a probabilistic fatigue model that combines the principles of the weakest link theory with the highly-stressed volume (HSV) or highly-stressed surface area (HSSA) concepts to estimate stress-life (P-S-N) curves for both unnotched (smooth) and notched large-scale specimens, for any prescribed failure probability. By incorporating probabilistic models, P-S-N curves corresponding to lower probabilities of failure can be obtained. The integration of HSV or HSSA with the weakest link principle enhances the estimation of fatigue strength for real elements or components, which often require testing with reduced-size specimens. The proposed model is verified by experimental fatigue data from the literature, specifically involving unnotched and notched cylindrical specimens subjected to different constant amplitude loadings. The results demonstrate the robustness and effectiveness of the model in estimating characteristic P-S-N curves at lower probabilities of failure.

Comparison of varied specimen geometry for simplified VECD test with pulse-rest period

The viscoelastic continuum damage (VECD) model has become one of the promising methods for interpretation of asphalt mixture’s fatigue and damage behavior based on real physical responses, while asphalt mixture performance tester (AMPT) is the current standardized facility used for VECD characterization test. Since there is a trend to reduce the specimen size used in AMPT tests while maintaining the accuracy of test results, this paper investigated AMPT specimens’ geometry effect on VECD tests and the resultant damage characteristic curves when rest period is inserted after each load cycle (pulse-rest). A series of specifically designed dynamic modulus tests and simplified VECD (S-VECD) tests are conducted on three different sample geometries. The results have agreed with existing findings of that, in comparison to standard sizes, small specimen can produce reasonably accurate dynamic modulus master curves at low to medium temperatures, with the variation at higher temperature found to be caused by fluctuation of loading measurement. Remarkably, at both temperatures (12 and 20°C), a reduced size specimen is able to produce reasonably accurate damage characteristic curves either with 0.3s pulse-rest period or without rest period. Else, the small size specimen demonstrates high likelihood of controlled failure location within the measuring range. The results increase confidence of using reduced specimen size for VECD and rest period healing research by AMPT, with benefit of saving significant experimental time and material consumption.

Experiment Study on Compressive Membrane Action of Slab Strips Restrained by Shear Walls

Subjecting to the compressive membrane action (CMA), the ultimate load capacity of the reinforced concrete (RC) slab with lateral restraint would be improved obviously. Test of 12 one-way slab specimens restrained by shear-walls was carried out to investigate the properties of the slab strips’ compressive membrane action. The reduced-size specimens were designed to keep the ratios of shear-walls’ restraint stiffness to slab strips’ flexural stiffness unchanged. One horizontal testing instrument was first used to record the development of the slabs’ lateral restraint forces. The ultimate loads of slab strips with certain lateral restraint stiffness gave an average 38.3% rise from the calculations of upper-bound method. Though the increment of slab’s ultimate load was due to the additional moment formed by the lateral restraint force, the results showed that the peak of lateral force lagged of the slab strips’ ultimate load, which was different from the previous hypothesis. Various parameters which affect the development of CMA were also investigated, such as the shear-wall’s thickness, axial load on the walls, the slab strips’ span-height ratio and reinforcement percentage.

On the Identification of Critical Damage Mechanisms Parameters to Predict the Behavior of Charpy Specimens on the Upper Shelf

Abstract The use of sub-sized Charpy-V specimens to monitor the mechanical properties of reactor pressure vessel (RPV) steels is receiving increasing attention. It is motivated by the fact that a smaller amount of material can be used to obtain the fracture properties, which can be of great economical interest when dealing with activated materials. Prior to use reduced-size specimens, investigations are still necessary to verify that the properties obtained from sub-sized specimens are comparable to those obtained from standard size specimens. Amongst the approaches that are available, the local approach to failure, which combines a description of the material microstructure (void density, distance between inclusions…) and empirical observations, is a promising way to investigate the transferability of mechanical properties. It has been successfully used to describe the macroscopic behavior of a wide range of cracked or notched specimens and components of various dimensions but restricted so far to quasi-static loading conditions. The results discussed in the paper are focused on the upper shelf behavior of the French RPV material, equivalent to the American ASTM A508 Cl.3 material. Modeling of the material is achieved using the Rousselier coupled damage constitutive equations. This model is implemented in CAST3M, a general-purpose finite element code developed by the French Atomic Energy Agency. Comparisons between the numerical results and the experimental observations are given and the computed local temperature elevations and plastic strain rates discussed to explain the behavior of the specimens.

火力プラント部材のミニチュアクリープ試験法による余寿命評価

In order to develop and validate a procedure of creep rupture tests using miniature specimens in estimating the remaining life of fossil power plant parts, a method to make the miniature specimens was investigated first. Then the accelerated stress-rupture tests were performed on the miniature specimens to predict the remaining creep life of Cr-Mo-V, 21/4Cr-Mo and 11/4-1/2Mo steels.The results obtained are summarized as follows:(1) The miniature specimens could be produced by either only machining, or welding the grips at the ends of specimen and then machining them. The miniature specimen sized into 2mm dia.×30mm was suitable as a reduced size specimen.(2) The creep curve and rupture life of the miniature specimens tested in argon were similar to those of the conventional size specimens in air. The fracture mode of the miniature specimens was also consistent with that of the conventional size specimens.(3) On a graph of temperature vs. logtr, the creep rupture data of Cr-Mo-V, 21/4Cr-Mo and 11/4Cr-Mo steels were represented with an iso-stress line, respectively. Each iso-stress line moved parallel with the stress level. It was found that the miniature specimens could be used in the short time iso-stress creep line extrapolation method to predict the remaining creep life.(4) The present method was found to be applicable to the parts subjected to long-term service. It is considered that the creep life evaluation based on this method is very useful because of its convenience and reliability.