Strain rate behaviour of thermoplastic polymers

Polymers are increasingly used in structures that have to withstand impact conditions. This thesis describes an investigation of strain rate properties at room temperature of four engineering polymers; polyethylene (high density, HDPE and ultra high molecular weight, UHMWPE), nylatron and polyetheretherketone (PEEK 150g). A split Hopkinson pressure bar (SHPB) system was used to study the response of these polymers in compression tests at high strain rates up to 10' S-1. Stress equilibrium in SHPB samples was studied theoretically by examining multiple reflection effects during the initial elastic loading of the polymers; this study proved very useful in the analysis of SHPB tests. To cover a wide range of strain rate, compression studies were also made at low strain rates (10-3 _10-2 S-1) using a Hounsfield screw machine. Viscoelastic models have been applied to these results. These models fit quite well with the experimental results of HDPE, UHMWPE, and nylatron, but not to the PEEK due to the yield drop in the stress - strain curves, especially at high strain rates. An exploding wire technique was used as an axial impulsive loading system for hollow cylindrical samples. An image converter camera at framing intervals of 21ls or 10 Ils recorded the radial expansion of the cylinder. The expanding cylinder was used as a driving system for a new technique called the freely expanding ring method, which was used to obtain the stress - strain behaviour of polymeric thin rings placed as a sliding fit on the cylinder. This method produced very high tensile strain rates up to fracture (> 10' S-1). Comparisons have been made between results obtained from the quasi-static, SHPB, and expanding ring tests. The freely expanding ring and SHPB results were in good agreement indicating similar tensile and compressive high strain rate behaviour. The mechanical properties of the above polymers are strongly dependent on strain rate. The Young's modulus and the flow stress increase with increasing strain rate. Nylatron showed high strain rate strain softening at high strain, this was due to the high temperature rise during loading, when the transition temperature (Tg) of the material (50 QC) was exceeded. However, the other materials showed continuous hardening behaviour. Plots of the flow stress at 5% and 10% strain vs log strain rate showed a linear increase up to a strain rate of about 103 S-1. Above 103 s-1, the stress rose more rapidly, but then showed significant drops for nylatron and PEEK. These drops in stress are probably due to both micro crack initiation in the sample and also high temperatures around the crack tips

High-speed photographic studies of blast wave impact phenomena

An exploding wire technique (EWT) is described, which provides high rates of loading by producing cylindrical blast waves of high reflection pressure with short duration. These waves have been used for internal impact of hollow polymeric cylindrical specimens. The EWT overcomes the small size restrictions of other high strain rate testing methods like the Split-Hopkinson pressure bar technique and drop weight. [Continues.

Superplastic behaviour of AZ91 magnesium alloy processed by high– pressure torsion

An investigation has been conducted on the tensile properties of a fine–grained AZ91 magnesium alloy processed at room temperature by high pressure torsion (HPT). Tensile testing was carried out at 423 K, 473 K and 573 K using strain rates from 1×10–1 s–1 to 1×10–4 s–1 for samples processed in HPT for N = 1, 3, 5 and 10 turns. After testing was completed, the microstructures were investigated by scanning electron microscopy and energy dispersive spectroscopy. The alloy processed at room temperature in HPT exhibited excellent superplastic behaviour with elongations higher than elongations reported previously for fine–grained AZ91 alloy produced by other severe plastic deformation processes, e.g. HPT, ECAP and EX–ECAP. A maximum elongation of 1308 % was achieved at a testing temperature of 573 K using a strain rate of 1×10–4 s–1, which is the highest value of elongation reported to date in this alloy. Excellent high–strain rate superplasticity (HSRSP) was achieved with maximum elongations of 590 % and 860 % at temperatures of 473 K and 573 K, respectively, using a strain rate of 1×10–2 s–1. The alloy exhibited low–temperature superplasticity (LTSP) with maximum elongations of 660 % and 760 % at a temperature of 423 K and using strain rates of 1×10–3 s–1 and 1×10–4 s–1, respectively. Grain–boundary sliding (GBS) was identified as the deformation mechanism during HSRSP, and the glide–dislocation creep accommodated by GBS dominated during LTSP. Grain–boundary sliding accommodated with diffusion creep was the deformation mechanism at high test temperature and slow strain rates. An enhanced thermal stability of the microstructure consisting of fine equiaxed grains during deformation at elevated temperature was attributed to the extremely fine grains produced in HPT at room temperature, a high volume fraction of nano ?–particles, and the formation of ?–phase filaments

Bioremediation of marine oil spill using beeswax

1227-1231Oil spills can have devastating environmental, economical, and social impacts. The use of bioremediation is a preferred technique for cleaning up oil spills because it facilitates the process of naturally converting oil into non-toxic byproducts without any further local environmental disruption. An experimental study was conducted to degrade marine oil spill using beeswax as a biostimulant for bioremediation and also to study the chemical variation. Beeswax, a nutrient source for proliferation of olephic (oil eating) bacteria, was added in intervals of five days and the corresponding dissolved oxygen (DO) was measured using Azide Winkler’s method. The recuperation of the DO concentration from 3.1 mg/l to 7.4 mg/l is an indication of the reduction in oil content. An oxygen sag curve and a graph showing temporal variation of chemical parameters such as nitrite, nitrate, and ammonium were plotted. During the period of study, the oil content reduced from 10 ml to 5 ml. As the addition of biostimulant resulted in an increase in the rate of bioremediation, the use of beeswax as a biostimulant appears to be an effective tool for the clean-up of oil-contaminated marine waters without adverse environmental impact

The use of polyurethane foams for the extraction of platinum (II) from hydrochloric acid solutions in the presence of tin (II) chloride

A preliminary investigation prior to the study of the extraction of platinum, was conducted on the Co(NCS)₄²⁻ /foam system to, (a) develop a suitable experimental apparatus in order to study the loading of platinum foams and (b) obtain fundamental kinetic and thermodynamic data concerning the sorption process. The sorption of platinum(II) as complexes of [Pt(SnCl₃)nCl₄-n]²⁻ and [Pt(SnCl₃)₅]³⁻ from hydrochloric acid solutions by polyurethane foams was examined in detail. Our studies show that the capacity of the foam to extract platinum depends on the following solution conditions of, temperature, initial platinum concentration, hydrochloric acid and hydrogen ion concentrations, the Sn:Pt ratio and the presence of interfering cations and anions. The rate of platinum sorption is shown to be dependent on temperature, initial platinum concentration, the Sn:Pt ratio and the mass of the foam. The foam's ability to selectively extract platinum from solutions containing platinum and certain base metals is examined. Results obtained show that in all cases almost complete extraction of platinum was achieved. Of all the base metals investigated only Cu(II) co-extracts to a small extent with the noble metal. In this work a procedure has been developed in which we are able to quantitatively recover both platinum and tin from loaded foams, by dissolving the polyurethane in warm nitric acid. A simple distillation allows for the satisfactory separation of platinum from tin

Suffolk Journal, Vol. 1, No. 5, 1/19/1937

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