Finite Volume Method for the Launch Safety of Energetic Materials

It is important to examine the ignition of energetic materials for launch safety. Given that there is a paucity of experimental tests, numerical simulations are important for analysing energetic materials. A computer program based on the finite volume method and viscoelastic statistical crack mechanics model is developed to study the ignition of energetic materials. The trends of temperature and stress of energetic materials subjected to projectile base pressure are studied by numerical examples. The results are compared with those in an extant study, which verified the correctness of the proposed method. Additionally, the relationships between the temperature increase and nonimpact ignition of energetic materials were analysed. The results show that when the temperature at the bottom of the explosive rises to a certain value, it will cause the explosive to ignite. This research has significance to the study of the base gap of explosives, and it provides a reference for launch safety evaluation of energetic materials.

Nonsingular Gradient Solutions in Crack Mechanics and the Concept of Stress Concentration

We consider the fracture mechanics problem for the finite and semi-infinite cracks in the gradient elasticity. Local stress fields that define the fracture the strength of materials are found as solutions of the inhomogeneous Helmholtz equations in which the inhomogeneity is determined by classical stresses. To construct solutions, the radial factors method and the Papkovich-Neuber representation are used. It is shown that, in problems of crack mechanics. We show that the local stresses in the vicinity of crack tips are non-singular, have the form characteristic of stress concentration, and depend only on the level of acting stresses and the scale parameter, which is found as a result of mechanical testing of material samples.

Impact Strength of Composite Materials Based on EN AC-44200 Matrix Reinforced with Al2O3 Particles

The paper presents the results of research of impact strength of aluminum alloy EN AC-44200 based composite materials reinforced with alumina particles. The research was carried out applying the materials produced by the pressure infiltration method of ceramic preforms made of Al2O3particles of 3-6μm with the liquid EN AC-44200 Al alloy. The research was aimed at determining the composite resistance to dynamic loads, taking into account the volume of reinforcing particles (from 10 to 40% by volume) at an ambient of 23°C and at elevated temperatures to a maximum of 300°C. The results of this study were referred to the unreinforced matrix EN AC-44200 and to its hardness and tensile strength. Based on microscopic studies, an analysis and description of crack mechanics of the tested materials were performed. Structural analysis of a fracture surface, material structures under the crack surfaces of the matrix and cracking of the reinforcing particles were performed.

Failure Stress in Notched Paper Sheets

In this work the crack initiation stress of notched specimens of filter paper is studied. The paper in the microstructure has a random array in their fibers while macroscopically it behaves anisotropically. The self-affine crack mechanics is used to study the size effect in the tensile behavior of this kind of paper under the presence of several conditions of geometrical notches. While in the traditional fracture mechanics the crack initiation stress is a material parameter when is reached a critical level at the crack tip, in the self-affine crack mechanics, depends moreover of the resulting tortuosity of the crack. Four geometrical arrangements in two sizes we considered: centered circular notch, centered lineal notch, sided circular notches and without notch at 10 and 300 mm width with a relation 2a/w = 0.25 under the same loading conditions. In this, the without notch specimens present the higher stress, all other notched specimens presented a similar crack initiation stress about 1 % of difference among them, and the crack growth is not affected by the geometry of notch. In spite of this difference, no one of the specimens reach the theoretical stress concentration of 3 such as predicted the classical stress theory.

Fatigue Limit Prediction of the Matrix of 17-4PH Stainless Steel Based on Small Crack Mechanics

The experimentally obtained fatigue limit of high strength steel is generally a value reduced by inherent flaws, and such a value does not characterize the resistance of the matrix of high strength steel to cyclic loading. To investigate the fatigue limit of the matrix, fatigue tests of 17-4PH stainless steel were performed. 17-4PH stainless steel showed a distinct dual-stage S-N curve: one stage corresponding to high stress where crack initiated at the surface and another stage corresponding to low stress where crack initiated from the subsurface inclusion (Al2O3). Based on small crack mechanics, a model was proposed to predict the fatigue limit of the matrix of 17-4PH stainless steel and its validity has been discussed.