Measurements of inverse creep in polyester multifilament yarns
Creep and Inverse creep are the important fundamental properties of textile materials. These properties determine the relaxation behaviour of the product. We have designed and fabricated an instrument which can measure the creep and inverse creep. The instrument consists of a Trans - Receiver unit interfaced with Embedded System along with the Personal Computer. Existing technique for measuring inverse creep does not measure the instantaneous extension or contraction. The newly fabricated instrument, can measure the instantaneous extension and contraction of the yarn up to an accuracy of 0.02%. This can be measured after every 500 μs. The position of the yarn, which is to be hanged, is vertical. The 'Electronic Timer Unit', replaces a meter scale. Set up is improved by using electronic utilities. The capability is enhanced to next level of time and distance resolutions. Automation enables to have flexibility of time from microseconds to minutes. Data is stored in different text files. Different samples of Polyester multifilament yarn were used in the experiment. The length and the load were altered. Change in stress lead to instantaneous extension or contraction followed by creep or inverse creep. This can sensed by the sensor and further stored in the memory of the Computer. The percentage creep and inverse creep were measured and have been reported in this present paper
Elastic Recovery and Inverse Relaxation of Polyester Staple Fiber Rotor Spun Yarns
We have studied the elastic recovery and inverse relaxation phenomena of polyester staple fiber rotor spun yarns. Better fiber orientation obtained with a drawing passage before spinning results in higher permanent deformation and lower delayed elastic recovery of the yarn. Yarn twist has little influence on elastic characteristics. The stress produced in the yarn when strained at 10% is higher when fibers are straighter and lower when twist increases. The inverse relaxation effect increases with the level of orientation of the fibers in the yarn.
Microstructure of the solder-casting zone in bridges of dental gold alloys.
The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.