A small sealed Ta crucible for thermal analysis of volatile metallic samples

Differential thermal analysis on metallic alloys containing volatile elements can be highly problematic. Here we show how measurements can be performed in commercial, small-sample, equipment without modification. This is achieved by using a sealed Ta crucible, easily fabricated from Ta tubing and sealed in a standard arc furnace. The crucible performance is demonstrated by measurements on a mixture of Mg and MgB$_2$, after heating up to 1470$^{\circ}{\rm C}$. We also show data, measured on an alloy with composition Gd$_{40}$Mg$_{60}$, that clearly shows both the liquidus and a peritectic, and is consistent with published phase diagram data

Nondestructive Evaluation of Damage and Degradation of Mechanical Properties in Composite Panels Subjected to Impact

Materials. The materials used in this research were T300/5208 unidirectional graphite/epoxy composite panels supplied by the Army Materials Technology Laboratory. The panels were in square form of 12 in. by 12. in. with nominal thicknesses of 0.042 in. (7-ply) and 0.144 in. (24-ply) respectively. All of the panels were subjected to c-scan examination for uniformity and integrity. The properties of the material are presented in Table 1. A schematic of the unidirectional composite is shown in Fig. 1.</p

Multi-axial fatigue damage models of fiber reinforced composites

ABSTRACT Fiberglass reinforced composites are extensively used in various structural components. In order to insure their structural integrity, their monotonic and fatigue properties under multiaxial stress fields must be understood. Combined in-phase tension/torsion loading is applied to [±45º] 4 Eglass/epoxy composite tubes under monotonic and fatigue conditions to determine the effects of multiaxial loading on its failure. Various monotonic and fatigue damage criteria are proposed. These models considered failure mode (failure plane), the energy method and the effective stress-strain method. It is observed for the majority of experiments, the failure initiated at the outer lamina layer at 45º to the tube axis. A damage criterion for multiaxial monotonic loading is proposed considering both normal and shear stress contributions on the plane of failure. The experimental data show an excellent agreement with this proposed model for various loading conditions. Other failure models are currently under investigation utilizing the stresses and strains at the composite laminate as well as stress and strain at the outer lamina layer. Multiaxial fatigue failure models are proposed considering again the plane of failure. Since the plane of the failure is subjected to mean and cyclic stresses (shear and normal) and mean and cyclic strains (shear and normal), the fatigue damage models consider the contributions of these stresses and strains to the fatigue life of the composite tube. In addition to the fatigue damage model based on the plane of failure, a multi-axial fatigue failure model is proposed considering the mean and cyclic energy during fatigue experiments. The experimental data show a good correlation between the proposed damage parameters and fatigue life of specimens with some scatter of the data. Other fatigue failure models are currently under investigation considering the loading frequency and visco-elastic properties of the composite. INTRODUCTION Fiber reinforced composites are extensively used in manufacturing of various components such as high-pressure vessels, aerospace structures, transmission shafts in automobiles, support structures, etc. Traditional materials are being replaced by composites due to their high strength to weight ratio, corrosion resistance and cost. Increase use of composite structures has led to the need for models to determine their monotonic and their fatigue characteristics under multiaxial stress fields. There are numerous papers reporting fatigue damage models in isotropic materials under multiaxial fatigue loadings. However, these models are not suitable for evaluating fatigue life of anisotropic fiber reinforced composites. There is relatively little literature on the damage accumulation and the effect of multi-axial loading on the fatigue life of composite materials. Found [1] proposed a conservative failure criterion for chopped fiber reinforced composites, woven fabric reinforced composite and fabric reinforced composites under bi-axial static and fatigue loading conditions. He suggested a conservative estimate for design purposes where the failure in the tension/tension quadrant is given by a circular arc and by a straight line in the tension/compression quadrant. The proposed failure models are given as