Viscoelastic Equivalent Creep Behavior and Its Influencing Factors of Basalt Fiber-Reinforced Asphalt Mixture under Indirect Tensile Condition

The aim of this study is to further investigate the effect of different basalt fiber (BF) factors on the viscoelastic equivalent creep behavior of fiber-reinforced asphalt mixture (FRAM) under indirect tensile (IDT) condition. A two-dimension mesostructural model composed of different components including fiber mortar polymer and coarse particle aggregate is constructed via the section image processing for the IDT FRAM specimen, where BF is considered as random distribution in the mortar polymer. Furthermore, the stress distribution and equivalent creep of the IDT mesostructural model in simulation software are analyzed to discuss the influence of components on the creep behavior of FRAM. Moreover, the laboratory creep test of IDT specimens under 0% and 0.3% BF contents for FRAM is carried out to validate the simulated values. Research results indicate that the simulated creep deformation of the IDT mesostructural model is in agreement with that of the experiment. Finally, creep simulations are further conducted to discuss the effect of BF (e.g., fiber content, length-diameter ratio, and fiber modulus) and aggregate on the creep characteristic of FRAM. The increase of fiber content and length-diameter ratio has a significant reinforcing effect on the equivalent mechanical behavior, but the change in the modulus of fiber and aggregate has slight effects.

Experimental Study on Influence of Unloading Rate on Creep Characteristics of Marble under High Stress

In the engineering of high stress area, the measures to control the stability of surrounding rock by reducing excavation footage and excavation speed are to adjust the unloading rate of surrounding rock caused by excavation. In this study, unloading creep tests of marble under high stress conditions were carried out to study the effect of unloading rate. Research results showed that the axial and lateral instantaneous strain and creep strain of the sample increased with the increase of unloading rate; the lateral creep characteristic of marble under unloading condition was stronger than that of axial creep characteristic, and it was more obvious with the increase of unloading rate; the failure of specimens under unloading creep condition was mainly caused by the rapid increase of lateral strain, and the brittleness of rock was increasing with the increase of unloading rate. The Burgers model was used to describe the creep curves of specimens, and the variation of the parameters with the unloading rate was analyzed. The fitting results showed that the instantaneous elastic modulus E1, E'1 and the viscosity coefficients η1, η'1 all decreased with the increase of the unloading rate, which can be described by linear relationship within the unloading rate range of this experiment. Compared with the time of whole creep tests, the time for each specimen to enter the steady-state creep was similar, it was considered that the effect of unloading rate on η2/E2 and η'2/E'2 can be ignored.

Creep Characteristic of Sn1.0Ag0.7Cu Lead-Free Solders with Element Addition

In this study, creep properties of lead-free solders based on Sn1.0Ag0.7Cu were investigated. In the solders, germanium, nickel and bismuth were added to improve their mechanical properties. The effect of element addition on their microstructure and creep properties were studied. Creep properties were improved with the element addition. Creep rupture lifetime was the longest for SnAgCuBiNiGe, and that of SnAgCuBi was the second longest. It was made clear that a minimum creep strain rate is useful for lifetime prediction of the solders. An observation of microstructure was performed and coarsening of intermetallics after creep test was identified, resulting in creep rupture. It was found that the addition of bismuth hinders the coarsening of intermetallics and is effective to improve the creep properties of the solders.

Reduction of Fugitive Emissions From Bolted Flanged Connections by Using PTFE Blended Gasket

Gasket is the key element which determines the tightness of bolted flanged connection. PTFE blended gaskets which have recently been developed and come onto the market have a superior sealing performance as well as the chemical and temperature resistances and can contribute to reduce fugitive emissions. This paper deals with the sealing behaviors of the PTFE blended gasket and the tightness of a bolted flanged connection in which the gasket is used. The gasket is mainly composed of PTFE and graphite and has a high tightness and heat resistance up to 300 degree C. The creep characteristic is improved by the graphite filler. In this paper, the estimation method of the tightness of bolted flanged connections based on the sealing behavior of gasket is demonstrated. The estimated results are validated by experiments using a flange connection. It is shown that the leak rate below the tightness class 4 defined in the Room Temperature Tightness Test (ROTT, Pressure Vessel Research Council) can be obtained using the PTFE blended gasket.

Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 1 — Examination Plan

This paper describes the past preliminary examination results and the new characteristic examination plans of the thick laminated rubber bearing for the application to Sodium-cooled Fast Reactor (SFR). The preliminary examination focusing on mechanical characteristics such as shear modulus with a 1/8-scale model (ϕ= 200 mm) and creep characteristics with a 1/13-scale model (ϕ= 120 mm) were carried out [1]. With the basic mechanical characteristic examination, the basic design formulas were temporarily confirmed. Furthermore, to establish the creep prediction formula, the creep characteristic examination has been carried out and the creep amount during the plant life has been approximately predicted. To obtain the mechanical properties of thick laminated rubber bearing with the scale-effect, the basic mechanical characteristic examination, including the ultimate behavior test, with the 1/2-scale model (ϕ= 800 mm) will be planned to confirm design margin with clarifying the ultimate limit curve under the bi-axial loading such as shear strain and the normal stress. Moreover, the deterioration promoted examination will be planned. The object of this examination is intended to grasp the degree of aging that may be caused by environmental effects during the plant life. By the accelerated deterioration examination results, the influence by aging on the mechanical characteristic and ultimate behavior of the laminated rubber bearing could be evaluated.

Effectiveness of Retightening in Maintaining Higher Residual Bolt Loads and Tightness of Bolted Flanged Connections

Bolt loads reduce significantly after tightening of bolted flanged connections in which expanded PTFE (Polytetrafluoroethylene) gaskets are used. Bolts are often retightened after a while to compensate for the reduction of bolt loads in practice. The visco-elastic characteristic of PTFE gaskets is the main cause for the phenomenon. The flexibility of the bolt-flange system also affects the phenomenon. However, effects of the retightening on the residual bolt loads and the tightness of flanged connections have not been clarified yet. In this paper, an analytical model of a bolted flanged connection, in which the flanges, the bolts and the gasket are represented by spring constants, is proposed. The residual bolt forces and the deflection of the gasket were estimated based on the analytical model of the bolted flanged connection and a creep characteristic of the gasket. Thus, the relationship between gasket deflection and the tightness of the bolted flanged connection are clarified. Based on the analytical method, the effectiveness of retightening was discussed from the view points of the residual bolt load and the tightness.