Physical Interlocking Research Articles

Magnetic alignment in powder magnet processing

A strong magnetic field is used to align single-crystal powder particles in the process of producing sintered powder permanent magnets, including hard ferrites and rare-earth permanent magnets. The applied magnetic field aligns the easy direction of magnetization of each particle, owing to strong crystalline anisotropy. Shape anisotropy, existence of particles containing multigrains, and physical interlock between particles reduce the degree of alignment. This study provides a quantitative analysis of magnetic alignment in powder magnet processing. We assume (1) the powder particle is a single crystal; (2) it has the shape of an oblate spheroid and its short axis is the easy direction of magnetization; and (3) the applied magnetic field is strong enough to overcome the resistance of alignment. By applying the minimum-energy principle, it was concluded that the necessary and sufficient condition for a complete magnetic alignment is that the magnetocrystalline anisotropy constant K1 of the particles is greater than its shape anisotropy constant Ks, provided the applied magnetic field is strong enough. When Ks≳K1+2K2, the angle between the short axis of the oblate particle and the direction of applied magnetic field is 90°, and when K1≤Ks≤K1+2K2, the angle is arcsin√(Ks−K1)/2K2.

The effect of metals on the processing of LLDPE through a slit die

The effect of surfaces on the rheology and processing of polymers is a newly developing area of research. In this work, a stainless steel slit die was used with a variety of inserts of other metals, at the exit. The viscosity measured with the slit die was well predicted by the generalized Maxwell model containing a damping function with parameters determined from separate shear experiments. The viscosity was not affected by different metal type at the die exit. However, there was a marked increase in exit pressures for flow over brass inserts at the die exit. This effect coincided with the production of a porous, copper‐rich brass surface and it was shown that this was the result of surface dezincification. This was postulated to cause increased adhesion between the LLDPE and the brass via physical interlocking at the porous surface which subsequently increased the exit pressure.

Reactive extrusion of poly(vinyl chloride) compounds with polyethylene and with ethylene‐vinyl acetate copolymers

AbstractThe mechanical properties of poly(vinyl chloride)/polyethylene blends can be improved by a reactive extrusion process in the presence of an organic peroxide and a coupling agent. With a judicious loading of dibenzoyl peroxide and triallyl isocyanurate coupling agent, such blends generally exhibit significantly greater ultimate tensile strengths and dynamic moduli. The nature of the sample posttreatment after compression molding is shown to have a major impact upon the relative magnitude of these differences. Evidence is also presented to suggest that such improvements result from a superior physical interlocking between blend components, rather than through the formation of co‐crosslinked graft segments (which would, presumably, impart a compatibilization effect). Similar extrusion trials with a poly(vinyl chloride)/poly(ethylene‐stat‐vinyl acetate) mixture revealed a general worsening of material properties with increasing dibenzoyl peroxide levels. These observations can be rationalized by examination of the degradation reactions that likely occur in these reacting systems.

Modification of the Interfacial Zone Between Aggregate and Cement Paste

ABSTRACTIn order to improve the properties of concrete, the composition and structure of the interfacial zone must be modified. This may be done by pretreating the inert aggregate with special reagents to form a reactive surface, which will then react with the cement paste, resulting in an enhancement of the bond strength between cement paste and aggregate through the combination of the physical, chemical and mechanical interlocking effects. A cylindrical hole was drilled in a limestone cake and the surface of the hole coated with special solutions; cement slurry was then poured into the hole and the specimens were cured in a fog room. The shearing strength was determined to evaluate the effect of the aggregate pretreatment on the bond strength. The mechanical strength, porosity, electric conductivity of the concrete, orientation degree of the Ca(OH)2 and morphology in the interfacial zone were also examined. It was found that the compressive and flexural strengths increased, and the bond strength between aggregate and cement paste also increased; the porosity, average pore size, number of large harmful pores, electric conductivity and the orientation index of the Ca(OH)2 decreased.

Role of fibre surface?matrix combination in carbon fibre reinforced epoxy composites

The effect of surface treatment of carbon fibres with concentrated as well as dilute nitric acid on the mechanical properties of carbon fibres has been reported. The role of the fibre—matrix interface in carbon fibre reinforced epoxy resin composites has been studied. Composites have been made both with untreated and surface treated carbon fibres and epoxy resin Araldite LY556 with different hardeners. Mechanical properties as well as fracture behaviour of these composites suggest that it is the physical interlocking between the fibres and the matrix, along with some chemical bonding between the two, and not the pure chemical bonding which yield better composites.

Systems to ensure the correct application of wedge filters

In a treatment where a wedge filter is used, the dose given may be in error by as much as a factor of two if the wrong wedge is used, or if the correct wedge has its thin end incorrectly orientated with respect to the treatment field. It is, therefore, considered necessary to provide a physical interlock to ensure that the radiotherapists' instructions are correctly carried out. It transpires that the details of such a system depend on whether or not an applicator is used and the two possibilities will be considered separately. If the treatment to be considered is one where an applicator would normally be used (e.g. a small field, beam-directed treatment at 250 kV), it is usual in this hospital to mount the wedge filter in a special applicator. On the face of this applicator are two pegs. The distance between these is peculiar to the wedge filter in the applicator and the position of the eccentric peg specifies its thin end. If two suitable holes are bored in the wax seating of a patient's beam direction ...