Rate Of Decrease In Strength Research Articles

Experimental Study on Water Absorption and Weakening of Silurian Argillite

The objective was to analyse the water absorption and weakening of a Silurian argillite taken from the northwest of Hubei Province, China. Some experiments were conducted including measurement of the change in water absorption, the microstructure of the minerals, the porosity, and the strength of argillite samples, at different water absorptions, by scanning electron microscope, powder X-ray diffraction analysis, and needle penetration test. The results indicate that argillite was soaked in water for up to 0.5 days, water absorption rates were fast and the amount absorbed was large. At the same time, the rate of strength decrease was high and significant loss of strength was observed. Argillite soaked in water for 0.5 to 180 days had an increased water absorption at a slower rate, and the strength tended to be stable over time. The relationship between strength and water absorption was established: the strength decreases in the form of negative exponential function with increasing water absorption. Finally, the micro-mechanical model shows that, the decrease of attractive force of mineral grains and the increase in the force acting between mineral grains and the pore water are the main reason why this degree of water-weakening appeared in the argillite.

A replacement of chromate coating for adhesive bonding of stainless steel in a corrosive environment

For adhesive bonding of stainless steel to itself, a surface treatment involving chromates is used. However, chromates are environmentally unfriendly so a replacement is being sought. In this paper, an alternative to chromate was investigated. The standard test method, ASTM D 1002, was used to measure the failure load of adhesively bonded stainless steel samples. A general-purpose epoxy adhesive was used. To simulate marine exposure, adhesively bonded samples were placed in a 5% salt spray for extended periods of time, up to five weeks. Results indicated that the initial shear strength of adhesive joints prepared with a traditional chromate preparation was 25% greater than the new, alternative coating. However, more importantly, the rate of decrease in strength with salt spray exposure was greater for the chromate than for the alternative. After 21 days, both bonding surface treatments had the same strength. However, after this period of time, the alternative was stronger than the chromate treatment, indicating that the alternative was a more durable coating. An adhesive/adherent coated system was investigated using a finite element method in order to investigate the influence of adhesive thickness between the adhesive and the adherent, and the residual stress in the adhesive layer. Keywords: Adhesive, Alternative Coating, Crevice Corrosion, Potentio-Dynamic, Salt Spray.

Hierarchical Order of Influence of Mix Variables Affecting Compressive Strength of Sustainable Concrete Containing Fly Ash, Copper Slag, Silica Fume, and Fibres

Experiments have been conducted to study the effect of addition of fly ash, copper slag, and steel and polypropylene fibres on compressive strength of concrete and to determine the hierarchical order of influence of the mix variables in affecting the strength using cluster analysis experimentally. While fly ash and copper slag are used for partial replacement of cement and fine aggregate, respectively, defined quantities of steel and polypropylene fibres were added to the mixes. It is found from the experimental study that, in general, irrespective of the presence or absence of fibres, (i) for a given copper slag-fine aggregate ratio, increase in fly ash-cement ratio the concrete strength decreases and with the increase in copper slag-sand ratio also the rate of strength decrease and (ii) for a given fly ash-cement ratio, increase in copper slag-fine aggregate ratio increases the strength of the concrete. From the cluster analysis, it is found that the quantities of coarse and fine aggregate present have high influence in affecting the strength. It is also observed that the quantities of fly ash and copper slag used as substitutes have equal “influence” in affecting the strength. Marginal effect of addition of fibres in the compression strength of concrete is also revealed by the cluster analysis.

단면결손에 따른 고장력볼트 체결부의 내하력 변화에 관한 연구

This study conducted a static tensile test in order to prevent the lowering of load carrying capacity caused by critical sections made by over bolt holes in the base plate and the cover plate of steel member joints using high-tension bolts. The change of the load carrying capacity of joints was examined by comparison of the maximum load on joint fracture obtained from the tensile test with critical section rate and design strength. According to the results, the rate of decrease in strength was higher when the critical section rate was high, and in particular, decrease in strength was affected much more by critical sections in the base plate than by those in the cover plate. In high-tension bolt joints using over bolt holes for the base plate and the cover plate, load carrying performance was somewhat lower than that in joints using standard bolt holes, but the maximum tensile strength on facture was over 15% higher than design fracture strength. According to the results of this study, the use of over bolt holes in high-tension bolt joints had an insignificant effect on the lowering of load carrying capacity, so the allowance of over bolt holes in the joints of steel members is expected to enhance to the economy and efficiency of the works.

DEVELOPMENT RESEARCH FOR AN ACRYLIC CONTINUOUS FILAMENT

The conditions for modifying a thermo-contractible acrylic continuous filament to stretch yarns by the air-jet false twist method were investigated, and the stretch yarns obtained by the optimum condition as well as the fabrics knitted out of the yarns were compared with those of poly (vinyl chloride) and poly (ethylene terephthalate).The factors taken up in the experiments of the modifying conditions were (A) temperature of the heater, (B) distance between the air-jet nozzle and the hook below it, (C) velocity of winding, (D) pressure of compressed air, (E) rate of overfeeding, and two-factor interactions A×C and D×C. The characteristic properties measured were strength, elongation, rate of fulling, elongation ratio of crimp, elasticity of crimp, and residual twist. An orthogonal divided 313 type experiment gave the following results:1. In principle, when the combination of level of factors gives the larger false twists, the higher values can be obtained on the rate of fulling and on the elongation ratio of crimp of the stretch yarn. It is inevitable, however, that the strength and the elongation of the stretch yarns is deteriorated. On the conditions in which the extreme twists are given, on the contrary, the elongation ratio of crimp becomes lower because of insufficient untwist. In general, less false twist is required for acrylic filaments than that of poly (vinyl chloride).2. Compared with the stretch yarns of poly (vinyl chloride) and poly (ethylene terephthalate), the acrylic stretch yarns have lower strength and elongation, higher rate of decrease in strength, and lower elasticity of crimp. Compared in knitted fabrics, the acrylic ones have the highest value of bulkiness after fulling, though the value becomes lower after scouring because the fabrics are elongated. The compressive elasticity of the acrylic knitted fabrics is about the same as those of poly (vinyl chloride) and poly (ethylene terephthalate), or superior after fulling as well as scouring.3. Worn as an under wear, the acrylic stretch yarns do not give the feeling of power to human body as do those of poly (ethylene terephthalate) that have larger elongation ratio of crimp.

A Model for the Deterioration in Strength of Materials Due to Fungal Attack

Many materials used by industries are subject to fungal attack and the conditions to which they are subjected are frequently favourable to the growth of fungi. The result of fungal attack is usually that the material gradually loses its strength and eventually disintegrates; but it may actually become useless long before such an advanced stage is reached. On the other hand, due to slow decrease in strength the material may serve its purpose for a long time even though it is being attacked by fungi. Laboratory studies of the rate of decrease in strength under different conditions are, therefore, of considerable importance. Development of a mathematical model for the loss of strength due to fungal attack seems desirable for at least two reasons. They are:

41—Effect of Humidity on the Tensile Behaviour of Grey, Scoured, Mercerised and Chemically Modified Cotton

Load-extension curves of a folded cotton yarn, which had been scoured or mercerised, then tendered to various degrees by oxidation, acid or heat, have been determined at relative humidities ranging from 9% to 100% (wet state).The strength and breaking extension of the grey yarn increase steadily with relative humidity, but the scoured and mercerised yarns give maximum values at about 85% r.h., and this maximum moves to lower relative humidities as the tendering increases. For the most highly tendered materials, the strength decreases with increase in relative humidity and, for the highly tendered mercerised yarn, the rate of decrease in strength is almost identical with that for a regenerated cellulose staple fibre yarn. The results are compared with data obtained by Turner for weathered cotton fabrics.Breaking load tests on fibres taken from the chemically modified yarns show that the strength-humidity relationship for the fibres is determined by the average length of the molecules, and that most of the ...