Microstructure and Mechanical Behaviour of Ultrafine Grained Al-4wt%Cu-(2.5-10) Vol.% SiC Metal Matrix Composites Produced by Powder Compact Forging

Ultrafine grained Al-4wt%Cu-(2.5-10) vol.% SiC metal matrix composite powders were produced from a mixture of Al, Cu and SiC powders using high energy mechanical milling (HEMM). The composite powders produced were first hot pressed at 300°C with a pressure of 240 MPa to produce cylindrical powder compacts with a relative density in the range of 80-94% which decreased with increasing the SiC volume fraction. Powder compact forging was utilized to consolidate the powder compacts into nearly fully dense forged disks. With increasing the volume fraction of SiC from 2.5% to 10%, the average microhardness of the forged disks increased from 73HV to 162HV. The fracture strength of the forged disks increased from 225 to 412 MPa with increasing the volume fraction of SiC particles from 2.5 to 10%. The Al-4wt%Cu-2.5vol.%SiC forged disk did not show any macroscopic plastic yielding, while the Al-4wt%Cu-(7.5 and 10)vol.% SiC forged disk showed macroscopic plastic yielding with a small plastic strain to fracture (~1%).

Elastic-Plastic Pull-In Strength and Damage Analyses of Steel Catenary Risers in Deepwater

This paper presents the strength and damage results based on elastic-plastic analysis to address the design feasibility of pulling in a steel catenary riser (SCR) through a pull tube with various bend configurations in a Spar. The example riser system contains an SCR of typical size, a tapered stress joint, a vertical pull tube with multiple bend sections, guide supports for the pull tube, and the associated pull head and pull chain connected to the top of the riser. The design methods discussed in the paper include: (1) Modeling of riser and pull tube in ABAQUS for strength analysis of the SCR; (2) Strain-based strain-life method to assess the associated fatigue damage; and (3) Strain-based Level 3B ECA design method to derive the critical surface flaw sizes for weld qualification of the SCR inside the pull tube. Comparisons are also presented between results derived from elastic and elastic-plastic analysis methods. The pull-in load on the example SCR increases with the water depth as well as the number and curvature of the bends on the pull tube. Calculated riser pull-in loads are about 11% to 51% higher than the submerged weight of the SCR. The elastic-plastic analysis shows small plastic zone and also small plastic strain on the example SCRs passing through pull tubes of a large bend radius of 125 ft. It also shows large plastic zone but small plastic strain on the SCR in a triple-bend pull tube with a small bend radius of 70 ft. The overall fatigue damage caused by cyclic plastic straining on the example SCRs due to pull in is lower than 3.3%. The allowable surface flaw sizes for the example SCRs are on the order of a × 2c = 8 × 10mm and 2.5 × 40mm for low aspect-ratio and high aspect-ratio surface flaws, respectively. Critical flaw sizes determined by Level 2A ECA are about 25% smaller than the flaw sizes based on Level 3B ECA for low aspect-ratio surface flaws. The specified maximum allowable flaw sizes are not very sensitive to the pull tube configuration and the water depth under the present study. The strength and damage analyses of SCR from other installation methods such as reeling are not included in this paper.

Some thermodynamic aspects of viscoplasticity of ferromagnetic

The paper deals with viscoplasticity of ferromagnetic materials. Tensor representation is applied to a set of evolution equations comprising the plastic stretching and residual magnetization tensors. Small magneto elastic strains of isotropic insulators are considered in detail in two special cases of finite as well as small plastic strain. A special emphasis is given to piezomagnetism effects in the case of uniaxial cycling strain. Vakulenko's irreversible thermodynamics is applied to irreversible magnetic phenomena by means of a hereditary evolution function. Purely mechanical as well as purely magnetic irreversible phenomena are considered in detail.

Creep of a Hollow Sphere

Using internal stress arising from a spherically symmetric, finite plastic strain, creep of a hollow sphere subjected to inner and outer pressures, and also thermal stress, is discussed. If computer-aided numerical calculation method is used, creep is easily followed up to a finite plastic strain range including initial transient creep, whatever type of creep law is employed. If assumed in a steady state, creep rate, stress, small plastic strain leading to a stress state in steady creep, and another small plastic strain relaxing thermal stress are analytically obtained. Numerical method is also applicable to creep relaxation. Further, the origin of residual stress after unloading is clarified.