Impact testing of plastics: Present knowledge

This work takes a look at the present knowledge of the impact resistance of plastics. Two approaches are discussed and examined: the first is instrumented impact testing, and the second is that proposed by Williams and coworkers at Imperial College, London. The advantages of both are discussed and examined with particular reference to fracture mechanics analysis of impact data. It is shown that fracture mechanics gives a satisfactory theoretical assessment of the whole problem and many of the most important parameters of the material can now be determined by impact testing.     

Processing of product forms for the large-scale manufacturing of advanced thermoplastic composites

In the field of large-volume applications today, injection-moldable polymers, reinforced with short or long fibers, are used for semi-structural components. Additional use is made of glass mat thermoplastic sheets, for which the processing technologies have already been established in a large number of applications. Advanced thermoplastic composites based on highly aligned, continuous fibers represent, with their high fiber content, a big step in terms of mechanical performance and offer thermoplastic polymers the chance to become structural components. In spite of a great deal of work carried out in this category of materials, in particular with carbon fiber-based products for defense and aerospace applications, the business is still at an early stage of development due to the high price of intermediate products (small plants and not fully optimized production processes) and to embrionic manufacturing technologies for mess production applications. Conversion of the various continuous fiber reinforced thermoplastic materials into useful parts and components is dependent on the intermediate product forms: boardy tape, flexible two, fabric or sheet. Some general technologies exist for the thermoplastic composites and their subsequent processing methods; however, in many cases because of the peculiarity of these products (i.e. fabric deformation under stamping) they require different approaches. The scope of this work is to describe those methods that are most promising for large-volume applications, in particular products forms (containing powder) for post-shaping impregnation, and to analyze some of the fundamental mechanisms of flow and deformation that drive the processing behavior.     

Assessing the effect of containment measures on the spatio-temporal dynamic of COVID-19 in Italy

Nonlinear Dynamics - This paper aims at investigating empirically whether and to what extent the containment measures adopted in Italy had an impact in reducing the diffusion of the COVID-19...     

An experimental investigation of the shear behaviour of polyethylenes with different structures

Rheological properties in shear flow are presented for four different polyethylene samples: a high density, a linear low density and two low density polyethylenes manufactured using different techniques. Tests have been performed with the aid of capillary types of instrument equipped with capillaries of various lengths at three different temperatures. End correction factors have been determined and true flow curves obtained. Swelling ratios for both unannealed and annealed samples have been determined as well as the shear rate and shear stress at which irregularities begin. In some cases generalized plots have been prepared and in all cases the rheological response is discussed in terms of molecular characteristics, in particular the average molecular weight, molecular weight distribution and degree of branching.     

Particle filled polyolefins with high stiffness and toughness,as used for load bearing components

Mineral fillers have been used very often in the past for improving elastic modulus and temperature resistance of polyolefines, also to the detriment of impact resistance. Very recently it has been pointed out that good fracture toughness can be achieved if an appropriate mechanism is stimulated and a good bonding of the filler particles to the matrix is guarantied. This work shows some interesting results obtained in this field with HDPE (high density polyethylene) and kaolin. In particular the effect of filler content and of adhesion between matrix and filler is considered. A comparison is also made with literature data concerning filled polyolefines (HDPE and PP).     

J-integral analysis of ductile fracture of PP/EP rubber blends

The use of J-analysis to describe the ductile behaviour of PP/EP rubber blends is investigated. Two fundamental approaches are discussed and tested at low and high strain rate as a function of temperature.The results are presented with particular emphasis on the sensitivity of the parameters obtained by J-analysis to rubber content and particle size.