Experimental Study of Concrete Subjected to Explosive Loading

The main subject of this paper is to demonstrate the response of structural concrete to different imposed strain rates. Attention is focused on the strain rate about 10^-2 s ^-1>, where some technical difficulties are experienced when an exact determination of mechanical properties for quasi-brittle materials is attempted. The design of a measurement system, which realizes computer acquisition, analysis, and graphic representation of data, is also presented.     

Rat and human pancreatic islet cells contain a calcium ion independent phospholipase A2 activity selective for hydrolysis of arachidonate which is stimulated by adenosine triphosphate and is specifically localized to islet beta-cells

The recent demonstration that myocardial Ca(2+)-independent phospholipase A2 exists as a complex of catalytic and regulatory polypeptides that is modulated by ATP has suggested a novel mechanisms through which alterations in glycolytic flux can be coupled to the generation of eicosanoids which facilitate insulin secretion. To determine the potential relevance of this mechanism, we examined the kinetic characteristics, substrate specificities, and cellular locus of phospholipase A2 activity in pancreatic islets. Rat pancreatic islets contain a Ca(2+)-independent phospholipase A2 activity which is optimal at physiologic pH, preferentially hydrolyzes phospholipid substrates containing a vinyl ether linkage at the sn-1 position, and prefers arachidonic acid compared to oleic acid in the sn-2 position. Rat islet Ca(2+)-independent phospholipase A2 activity is inhibited by the mechanism-based inhibitor (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one and is stimulated by ATP. Purification of beta-cells from dispersed pancreatic islet cells by fluorescence-activated cell sorting demonstrated that beta-cells (but not non-beta-cells) contain Ca(2+)-independent, ATP-stimulated phospholipase A2 activity. Remarkably, clonal RIN-m5f insulinoma cells, which possess a defect in glucose-induced insulin secretion, contain a Ca(2+)-independent phospholipase A2 which is not modulated by alterations in ATP concentration. Collectively, these results and those of an accompanying paper [Ramanadham et al. (1993) Biochemistry (following paper in this issue)] implicate Ca(2+)-independent phospholipase A2 as a putative glucose sensor which can couple alterations in glycolytic metabolism to the generation of biologically active eicosanoids and thereby facilitate glucose-induced insulin secretion.     

Analysis of the Process of Explosion Braze-Welding of Heat Exchanger Tube Plates

The process of kinematic braze-welding of thin-walled tube plates and tubular elements in making heat exchangers is considered. The process is simulated by the high-velocity contact interaction of coaxial cylinders with a thin layer of high-strength amorphous solder between them. The inner cylinder expands by the action of explosive pulse load. When solving the thermoelastoplasticity problem, the dynamic properties of the material are taken into account. This process has been experimentally investigated using test specimens.     

Study of Dry and Wet Cement Mortar Dynamic Properties

We performed dynamic tests and studied the dynamic properties under compression of dry and wet cement mortar specimens using the Hopkinson split pressure bar method. As a result, we determined the fracture stresses and their dependence on the applied loading growth rate. It is noteworthy that the strength characteristic of wet material under study is less by 10–15% as compared to the dry one.     

Pulse current treatment effect on the strength of reinforcing steel and its weld joint under impact loading

We present results of static and impact tension tests of as-received reinforcing steel specimens, specimens with weld joints in their test portion, as well as specimens pretreated by high-density pulse current. As test results demonstrate, an increased strain rate enhances strength, and the pulse current treatment greatly influences the strength and plasticity of a defect-containing weld metal under static and impact tension. Translated from Problemy Prochnosti, No. 3, pp. 89–96, May–June, 2009.     

Theoretical-Experimental Analysis of Structural Components Separation upon Local Impulse Loading

Separation of structural components is considered as a high-speed directed local destruction of an object in the area of a specially applied concentrator. Elements in the form of plates and shells of arbitrary curvature have been taken as destruction objects. Calculations have been made by explicit finite-element methods. Results of the investigation performed have found practical applications.     

Dynamic Testing of Reinforced Glass Fibre–Epoxy Composite at Elevated Temperatures

We present experimental analysis of the deformation, strength and failure of tubular specimens, made of woven reinforced glass fibre–epoxy composite. The specimens were subjected to uniaxial tensile testing with the average strain rates from 10^-5 s^-1 to 20 s^-1. Tests were performed at room and three elevated temperatures, up to the temperature corresponding to the phase transformation of the matrix.     

THERMOPLASTIC ANALYSIS OF NORMAL IMPACT OF LONG CYLINDRICAL SPECIMEN: EXPERIMENT AND COMPARISON WITH THE NUMERICAL CALCULATION

The objective of this paper is to compare the temperature and the deformation fields in the cylindrical specimens (e.g., aluminum alloys), determined in the Taylor impact tests, with the numerical solutions. The temperature and deformation fields are caused by dynamic plastic deformation at high strain rates in the presence of finite strains. It is assumed that the process is locally adiabatic and associated with the axisymmetric deformations. Additionally, within the framework of Mandel's formalism, the general adiabatic plastic flow laws are derived for isotropic rate-dependent solids. They reduce to a simple form for the considered problem. The testing stand was based on the Hopkinson's pressure bar system and AGA thermovision set. The details of the experiment and the analysis of the experimental results are presented. The experimental results are compared with the numerical solutions.