Eva Nezbedova

Fracture behaviour of β-polypropylene as a function of processing conditions

The commercial grade of isotactic polypropylene (iPP) homopolymer (Mosten 58.412) was doped with different amount of β-nucleant (NJ Star NU-100). The fracture behavior of the β-iPP was examined on injection- and compression moulded specimens under dynamic load. The fracture toughness K Id and J Id , respectively, were used to describe the fracture behavior. The influence of processing conditions (the mould temperature and injection velocity) and the distance from the gate were also taken into the consideration. Structural changes during processing were characterized by DSC analysis. It was found that: (i) the amount of 0.03 % of β-nucleant gives the highest toughness (ii) the toughness of the β-iPP depends on the distance from the moulding gate and on the processing conditions (iii) the degree of crystallinity correlates with the fracture parameters.

Structural Changes, Evolution of Damage Parameters and Crack Propagation Behaviour in Welded Plastic Pipes

The microstructure as well as the local mechanical and fracture behaviour of welded joints in plastic pipes made form polyethylene and material zones outside of the welded joints have been analysed using recording microhardness testing, laser extensometry and crack resistance curve tests. In has been found that the mechanical basic properties and damage kinetics are clearly depending on the welding parameters and additional notching.

Effect of particles size on mechanical properties of polypropylene particulate composites

Purpose Polymeric particulate composites with thermoplastics, especially polypropylene (PP) matrix with mineral fillers, are of great practical importance due to their simple possibility of modifying mechanical properties and reducing the price/volume ratio of the resulting material. Both filler properties and interface properties have a great effect on the mechanical properties, primarily on stiffness and toughness, of the resulting composite material. Good final dispersion of the filler particles also plays a very important role. To reach the best adhesion and distribution of the particles, various procedures are carried out for activation of the particles. Therefore, the purpose of this paper is to investigate and discuss the effect of using plasma as a tool for treating commercially available CaCO3 nanoparticles in PP matrix. Design/methodology/approach The effect of the composite structure on its mechanical properties was studied from an experimental as well as a theoretical point of view. For an experimental study, four PP matrix were chosen. For use as filler, the commercially available precipitated surface-treated calcium carbonate was chosen. The composites were prepared with 5, 10, and 15 wt% of fillers. The sequence of expositions of plasma was chosen to verify the optimal treatment duration. The filler particles were characterized by several structure analytical methods. The composite mechanical properties were characterized by tensile, bending, impact, and creep tests. The deformation behavior of the three-phase composite with homogeneously distributed coated particles was numerically simulated on a microscopic scale. Findings The main conclusions of this work can be summarized as follows: with the use of plasma to the precipitated calcium carbonate, composites with well-dispersed particles can be prepared; the surface modification using plasma is done mainly by grafting –OH groups onto the particles’ surface; a synergetic effect of modifier enhancing the performance was observed; performance modifier increases the resistance against viscoelastic strain; and the size of the particles and their volume content generally lead to increase in the macro modulus of the composite. Originality/value Plasma, as a tool for treating the inorganic fillers, enables to destroy the agglomerates in composite, which is the basic way on how to optimally utilize the synergetic effect of composite with PP matrix.

Constraint effect on the slow crack growth in polyethylene

Purpose – From the practical point of view, most relevant damage to high density polyethylene (HDPE) structures is caused by slow crack growth. Therefore, detailed information about this type of damage is necessary. Experimental results transfer from specimens to real structure can be influenced by structure geometry (constraint). Therefore, the purpose of this paper is to investigate and discuss the effect of the constraint and relation between crack mouth opening displacement (CMOD) and crack length.Design/methodology/approach – The constraint effect is mainly effect of the structure geometry and can be quantified by T‐stress. Two different test specimens with different constraint level (T‐stress) were prepared: single edge notched specimen and modified single edge notch (SEN) specimen. The crack mouth opening displacement, crack tip opening displacement and crack length was measured.Findings – The main conclusions of this work can be summarized as: the slow crack growth rate in HDPE materials correspon...

Short-Term Stable Crack Propagation through Polyolefin Single- and Bilayered Structures - Influence of Welding, Composition and Direction of Crack Propagation

The overall stable crack initiation and propagation behaviour of specimens cut from plastic pipes that were composed of different polyolefin materials were investigated using concepts of elastic–plastic fracture mechanics including the crack propagation kinetics. The effect of specimen shape, orientation, welding, lading rate, composition/microstructure and direction of crack propagation on the crack resistance (R) behaviour of these materials has been thereby assessed.

Influence of adding poly(vinyl alcohol) fibres to poly(methyl methacrylate) matrix on the fracture behaviour of fibrereinforced composites

Abstract This paper reports on the relationship between structure and mechanical properties of poly(methyl methacrylate) (PMMA) reinforced with randomly oriented short poly(vinyl alcohol) (PVA) fibres. Special focus was on the effect of fibre content on the impact resistance of PMMA/PVA composites. Instrumented Charpy impact tests were carried out to characterize the impact resistance of PMMA/PVA composites. Linear elastics fracture mechanics was used to determine the dynamic critical strain energy release rate (GId) and the critical stress intensity factor (KId). Fracture surfaces were observed using scanning electron microscopy (SEM). Dynamic mechanical analysis was carried out to describe the viscoelastic response of the material. Finally, the behaviour of PMMA/PVA composites was interpreted using current short-fibre composite models. It was shown that a small amount of added PVA fibres (0.42 - 1.68 vol.-%) led to an increase of elastic modulus and yield stress under impact conditions. GId was also slightly increased, but KId remained unchanged. Good agreement was found between SEM observations and fracture toughness measured under impact loading.