RELATIONSHIP BETWEEN THE TENSILE AND STRESS RELAXATION BEHAVIOUR OF POLYPROPYLENE

The mechanical response of real polymers are basically of nonlinear character, therefore their behaviour patterns do not meet the idealized (linear) ones, especially in case of larger loads. Nevertheless, the linear viscoelasticity is often used successfully for describing the real behaviour in case of small or moderate loads. In this paper a way is sought and followed to estimate the real tensile load response by using the linear viscoelastic response given to the real relaxation stimulus and its relationship to the linear viscoelastic tensile load-strain curve and also by using some nonlinear transformations. Experiments were performed on PP as a test material and the stress relaxation behaviour, as well as the linear elastic and linear viscoelastic approximation of the tensile load-time curve were analysed. In order to demonstrate the applicability of this idea and to perform the numerical calculations a flexible function with three parameters was chosen to realize the nonlinear behaviour

UNTERSUCHUNG DER VERÄNDERUNGEN IN FADENS DIAMETER UND DREHUNGS-WINKEL BEI DER ZUG- UND DREHBEANSPRUCHUNG

The paper presents a method based on a special equipment and a projector microscope connected with an image processing system for measuring the diameter and the twist angle to study the cross-section contraction and the changes in the surface twist during tensile testing or twisting the yarns. As experimental studies polyester rayon yarn as well as ring-spun and rotor-spun yarns were tested and analysed. It is demonstrated how to use the results in modelling yarns

MODELLING THE BREAKING PROCESS OF TWISTED FIBRE BUNDLES AND YARNS

A brief description of a statistical modelling method is given to predict the total loading and breaking process of fibre bundles generated by the tensile test. Relationships between some normalized strength properties and the twist parameter of bundle, as well as the influence of the elastic part of the twist are examined by using the results of modelling an idealized structure of twisted fibre bundle. As an experimental study ring-spun and rotor-spun yarns are tested and their structure is analysed with the aid of comparing the measured and modelled breaking processes

Examination of the tensile state of fibers in braided fiber reinforced composite tubes

Braided composite rods and tubes offer a special possibility of structures tailored to loading. In this paper the contraction in the cross-section of a braided carbon/epoxy-acrylate tube is modelled and tested during tensile test. For the model the reinforcing fibrous structure was assumed to be located on the middle surface of the tube both before and during deformation. A hyperbolic type function was derived for describing the cross-section which was measured by a videoextensometer. The theory gave a good agreement with the measurements before neck-forming

Decellularised cartilage ECM culture coatings drive rapid and robust chondrogenic differentiation of human periosteal cells

The control of cell behaviour in an effort to create highly homogeneous cultures is becoming an area of intense research, both to elucidate fundamental biology and for regenerative applications. The extracellular matrix (ECM) controls many cellular processes in vivo, and as such is a rich source of cues that may be translated in vitro. Herein, we describe the creation of cell culture coatings from porcine decellularised hyaline cartilage through enzymatic digestion. Surprisingly, heat-mediated sterilisation created a coating with the capacity to rapidly and robustly induce chondrogenic differentiation of human periosteal cells. This differentiation was validated through the alteration of cell phenotype from a fibroblastic to a cuboidal/cobblestone chondrocyte-like appearance. Moreover, chondrogenic gene expression further supported this observation, where cells cultured on heat sterilised ECM-coated plastic displayed higher expression of COL2A1, ACAN and PRG4 (p 0.05) compared to non-coated plastic cultures. Interestingly, COL2A1 and ACAN expression in this context were sensitive to initial cell density; however, SOX9 expression appeared to be mainly driven by the coating independent of seeding density. The creation of a highly chondrogenic coating may provide a cost-effective solution for the differentiation and/or expansion of human chondrocytes aimed towards cartilage repair strategies

Research on Poverty Statistics in Pakistan Some Sensitivity Analyses

In the past, studies on poverty in a developing country like Pakistan have usually been based on an absolute (e. g. basic needs) concept of poverty see, e. g., Naseem (1977); Irfan and Amjad (1984); Ercelawn (1990) and Malik (1992). In this paperl we will state the case for using relative poverty thresholds, and present poverty statistics for Pakistan based on data from the Household Income and Expenditure Survey (1987-88). [Government of Pakistan (1988)]. The paper will also show the consequences of different choices in the assessment of the poverty threshold. In particular, instead of using one rather steep equivalence scale, as is the common practice in most studies, we will present poverty statistics based on three different -equivalence scales. The effects of choices with respect to the concept of resources and the measure of poverty, will also be examined. After a discussion of the concept of poverty (Section II), we compare the size and composition of the poor population using three relative poverty lines in Section III. In Section IV we present a number of sensitivity analyses, which show the effects of using different equivalence scales, using different indicators of household resources (income or total expenditures), and using measures of poverty different from the Head-count measure. The poverty incidence differentiated according to household characteristics is further analysed by means of cross-classification and logit analysis in Section V. Section VI presents some general conclusions