Mechanical relaxations of poly(vinylidene fluoride) and some of its copolymers

The dynamic mechanical properties of poly(vinylidene fluoride) have been studied under isochronal conditions and the effect of thermal treatment examined. The results are compared with a product of different molecular weight distribution. The study also included the mechanical relaxation spectra of copolymers of vinylidene fluoride and chlorotrifluoroethylene at four compositions and four frequencies as a function of temperature. The thermodynamic parameters associated with the main relaxations were determined and the results discussed on the basis of available information on the drgree of crystallinity, copolymer heterogeneity, and main chain flexibility.     

Block copolymers of polycarbonates with several hydroxy-terminated elastomers to yield thermoplastic elastomers for higher service temperature

The synthesis of block copolymers and the study of their morphology were undertaken to find improved thermoplastic rubbers for service at elevated temperatures. The basis was the extraordinary properties possessed by ABA-type block copolymers in which the terminal blocks are polystyrene and the central block is either polyisoprene or polybutadiene. In these systems it has been well established that the unusual properties are a result of domain formation in which the hard and the soft blocks aggregate separately into distinct phases. The hard segment is thought to act both as a crosslink and as a filler. Block copolymers were synthesized with different soft and hard segments. The effects of these segments and of their properties on the morphology and the stress-strain properties of the block copolymers were measured and evaluated. Electron microscopy and birefringence were used to determine the morphology. It was found that the glass transition temperatures of the segments, the bulk of the monomer unit in the glassy segment, and the morphology determined the strength of the material. Some of the materials prepared have tensile strengths of 0.1 kg/cm² or more at temperatures in excess of 180°C and therefore appear promising as elastomers for service at elevated temperatures.     

The fracture of rubber-modified polystyrene

This paper reports a successful attempt to apply the theories of fracture mechanics to the failure of impact polystyrene in air. The results show that linear elastic fracture mechanics is limited to correlating crack initiation data but that both maximum load and initiation data can be correlated using a constant crack opening displacement criterion calculated from the Dugdale model. The results are supported by similar calculations made from experiments with two other commercially important plastics: PVC and polycarbonate. The toughness of these materials and that of PMMA, polystyrene, and poly(ethylene terephthalate) are compared in terms of Rice's contour integral, J.     

Some observations on the fracture of poly(ethylene terephthalate) film

Recent work on the applications of linear elastic fracture mechanics to the problem of ductile tearing and fracture of poly(ethylene terephthalate) film is reviewed. It is shown that, even for a brittle plastic, there can be no direct correlation between the amount of slow crack growth and stress intensity factor. The Dugdale model, combined with a constant crack opening displacement criterion, is then used to correlate both initiation and final fracture results for poly(ethylene terephthalate) film extended in the extrusion direction. Also, the model is able to justify the use of linear elastic fracture mechanics for a limited range of crack initiation results.     

Performance analysis of planar hybrid matrix arrays

An analysis is presented of overall aperture efficiency, weight, and control power requirements for hybrid matrix arrays in synchronous satellite applications. An array is described which is mounted on a 7-foot aperture in a triangular grid fashion and fed by a hybrid matrix consisting of 3-port building blocks which in turn are fed by 9-port matrices. The beam crossover loss is minimized by beam combining at the outputs of the 9 ports. Component losses are analyzed, and residual array gains are calculated for the 7-foot aperture as a function of operating frequency. It is concluded that arrays of this type are practical for net gains of up to 30 dB.     

Void-swelling in 20% cold-worked FV548 austenitic stainless steel irradiated with 22 MeV C2+ ions or 46.5 MeV Ni6+ ions

A study has been made of the void-swelling behaviour of 20% cold-worked FV548 steel irradiated with 22 MeV C²⁺ or 46.5 MeV Ni⁶⁺ ions in the Harwell Variable Energy Cyclotron after room-temperature pre-injection with 10 ppm helium. The dose dependence of void-swelling under 46.5 MeV Ni⁶⁺ irradiation at 500 and 600°C, and the temperature dependence of void-swelling of specimens irradiated with 22 MeV C²⁺ ions in the range 500–650°C have been established. In addition the temperature dependence of void-swelling in specimens aged for 1000 h at 650° C before irradiation has also been studied. Subsidiary annealing experiments have demonstrated the high recovery resistance of the 20% cold-worked structure in FV548, compared with types 316 and 321 steels.The void-swelling behaviour is interpreted in terms of the balance between the dislocation and NbC point defect sink strengths and the observed resistance to recovery of the cold-worked structure in FV548.     

A quasi-reduction method for estimating matrix reduction times

A concise modified reduction method is presented, justified, coded in FORTRAN and applied. It estimates the time needed to reduce a stiffness matrix K to upper triangular form K^Δ. Allowance can be made for the use of band matrix methods and/or sparse matrix methods and/or sub-structures. The method can be integrated into large programs to check, automatically, the relative efficiency of alternative node numberings and solution methods. It can also be used as an educational tool to give experience of efficient ways of numbering nodes and using sub-structures. Finally, a band matrix method FORTRAN listing illustrates one of several ways in which the reduction of K can be speeded up by using the method presented.It is assumed that K can be partitioned into Ns × Ns sub-matrices, some of which are null while the others are densely populated. (When appropriately analysed, most structures readily satisfy this requirement.) The method takes about (1/N³_S) of the time estimated. It also gives the position of null N_s × N_s sub-matrices within K^Δ.     

Oxidation states of four sulfurs of rhodopsin before and after bleaching

The action of n-dipropylacetate (nDPA) is related to the dose. In low doses, nDPA improved the number of conditioned responses with negative reinforcement. In higher doses, the drug inhibited spontaneous and conditioned behaviour. An nDPA produces an increase in gamma-aminobutyric acid (GABA) brain level, results are discussed in relation to the inhibitory action of GABA in the central nervous system.