Evaluation and consideration of local specimen material properties in lifetime prediction of short fibre reinforced PA6T/6I

To exploit the full material potential of short fibre reinforced PA6T/6I, specific component calculations including aniso- tropic material behaviour is necessary. For this, different failure criteria and fatigue models are used to describe the behaviour during a component service life. This paper deals with the determination and consideration of fibre orientations for failure criteria and fatigue calculations. Therefore, a novel method to determine fibre orientation (FO) distributions across injection moulded plates, is proposed. The developed method allows a forecast of FOs for different specimen extraction positions and angles on injection moulded plates by using only a few measured reference points. As a result, fatigue models can be calibrated with the strength values and the corresponding FO, calculated for fracture position. The performed tests show a non-negligible influence of failure positions, due to fibre orientation distributions along the specimens. So, the FO determination method delivers an improvement in strength values estimation.

Creep of particle and short fibre reinforced polyurethane rubber

Tensile stress–strain testing and creep testing have been carried out on a polyurethane rubber, at three temperatures, with and without either particulate or short fibre alumina reinforcement. A previous paper reported concerning composites with particulate reinforcement and the present work is focused on the effect of the fibres. The samples were made via a blending and extrusion process that produced a certain degree of fibre alignment (along the direction of loading). Prior milling procedures were used to produce fibres with two different ranges of aspect ratio (with averages about 10 and 16). When expressed as true stress–strain relationships, all materials exhibit approximately linear responses. The dependence of stiffness on the volume fraction and aspect ratio of the reinforcement was found to conform well to the Eshelby model predictions. Moreover, the creep behaviour of all of the materials can be captured well by a Miller–Norton formulation, using the average matrix stress predicted by the Eshelby model. A striking conclusion is that it is both predicted and observed that short fibres are much more effective in reducing the creep rate than is the case with particles.

An investigation of the tensile characteristics of printed handsheets

Purpose The purpose of this paper is to investigate the influences of fibre lengths and a given range of paper grammages on the fundamental properties of unprinted and printed papers by using mineral oil-based offset printing inks and also evaluate these results in terms of printing and tensile characteristics. Design/methodology/approach A design research approach has been based on the production of various laboratory handmade papers and their printing process with mineral oil-based offset printing inks. The analysis of mechanical and structural tests results of the unprinted and the printed papers have been evaluated. Findings This study is confirmed that the mineral oil-based offset printing inks can be easily applied to the surface of papers having different grammages and pulp contents. An increase was observed in the tensile index values of the papers with the printing process, and these increases were more evident (about 80%) particularly in low grammage papers having high short fibre content. Originality/value The originality of this work is based on understanding and comparing the effects of grammage and the effect of pulp contents (having long and short fibre) on tensile characteristics of printed and unprinted handsheets.

Reduced dispersibility of flushable wet wipes after wet storage

Scientific publications and newsfeeds recently focused on flushable wet wipes and their role in sewage system blockages. It is stated that although products are marked as flushable, they do not disintegrate after being disposed of via the toilet. In this work it is shown that wetlaid hydroentangled wet wipes lose their initially good dispersive properties during their storage in wet condition. As a consequence, we are suggesting to add tests after defined times of wet storage when assessing the flushability of wet wipes. Loss of dispersibility is found for both, wet wipes from industrial production and wipes produced on pilot facilities. We found it quite surprising that the wet wipes’ dispersibility is deteriorating after storage in exactly the same liquid they are dispersed in, i.e. water. This is probably why the effect of wet storage has not been investigated earlier. It is demonstrated that the deteriorating dispersibility of these wipes is linked to the used type of short cellulosic fibres — only wipes containing unbleached softwood pulp as short fibre component were preserving good dispersibility during wet storage. Possible mechanisms that might be responsible are discussed, e.g. long term fiber swelling causing a tightening of the fiber network, or surface interdiffusion.

Isolation of hydrodynamic parameters for the fibre length attrition in injection-moulded short-fibre polymer composites

A comprehensive study of the fibre breakage mechanisms during mould filling in injection moulding of short-fibre polymer composites requires the isolation of the main parameters promoting fibre length attrition. In this work, hydrodynamic parameters such as injection flow rate and residence time in the range of injection moulding were isolated, and their effect on fibre length attrition was studied. Fibre breakage was quantified by means of a capillary rheometer attached to an injection moulding machine minimising fibre-equipment interactions. Fibre breakage increased linearly as a function of injection flow rate in the range of 30–120 cm3.s−1. It was also found that residence time in the order of milliseconds had a significant effect on fibre breakage. The results shown that longer fibres had less breakage probability, which contradicts the buckling failure theory for brittle fibres in a simple shear flow. This result was attributed to the similar rotation period of the fibres in comparison with the test residence times.