Inverse Stress Relaxation and Viscoelastic Recovery of Multifilament Textile Yarns in Different Test Cycles
The article presents the results of the experimental research of inverse stress relaxation (IR) and viscoelastic recovery (VR) that take place in acetate and polyester multifilament yarns in dependance on the mechanical pre-history. The above-mentioned time-effects are investigated in two different – stress relaxation (R-) and creep (C-) testing cycles. The fact that inverse stress relaxation process takes place in Ctest cycle, i.e. after previous sustaining the specimen at constant load is experimentally confirmed. It is shown that viscoelastic recovery is the slower process than the inverse stress relaxation. At identical elongations of the yarns at the end of loading period the inverse relaxation and viscoelastic recovery processes go on similarly regardless of the character of testing cycle.
Research on Mechanism Analysis and Elimination Method for the Tufted Carpet Stop Mark
School of Mechanical Engineering, Donghua University, Shanghai 201620, China E-mail: xuyang@dhu.edu.cn Abstract The tufted carpet stop mark is an important factor affecting carpet final quality. It is closely related to the change in yarn tension caused by the tufting machine being improperly stopped and the yarn creep properties. The purpose of this paper is to develop a reasonable approach to eliminate the tufted carpet stop mark. Focusing on a typical tufting machine, the tufting equipment system and basic working principle of tufted carpet are briefly described. A yarn path flexing model which integrates yarn feeding parts, yarn guiders and the tufting needle for a typical tufting process is constructed. The yarn tension change is analysed along with the change in the yarn path. A Polypropylene yarn four-component model is used for analysing the relationship between tension and yarn creep properties. The creep property of polypropylene yarn under a certain tension is verified by experiments. According to the yarn tension change in different running positions of the tufting needle, a reasonable method of eliminating the stop mark which stops and restarts the machine in the highest position is put forward. Finally the experimental results prove that the method is effective and feasible.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.