Formability of high strength aluminium sheet

An initial review of the subject emphasises the need for improved fuel efficiency in vehicles and the possible role of aluminium in reducing weight. The problems of formability generally in manufacture and of aluminium in particular are discussed in the light of published data. A range of thirteen commercially available sheet aluminium alloys have been compared with respect to mechanical properties as these affect forming processes and behaviour in service. Four alloys were selected for detailed comparison. The formability and strength of these were investigated in terms of underlying mechanisms of deformation as well as the microstructural characteristics of the alloys including texture, particle dispersion, grain size and composition. In overall terms, good combinations of strength and ductility are achievable with alloys of the 2xxx and 6xxx series. Some specific alloys are notably better than others. The strength of formed components is affected by paint baking in the final stages of manufacture. Generally, alloys of the 6xxx family are strengthened while 2xxx and 5xxx become weaker. Some anomalous behaviour exists, however. Work hardening of these alloys appears to show rather abrupt decreases over certain strain ranges which is probably responsible for the relatively low strains at which both diffuse and local necking occur. Using data obtained from extended range tensile tests, the strain distribution in more complex shapes can be successfully modelled using finite element methods.Sheet failure during forming occurs by abrupt shear fracture in many instances. This condition is favoured by states of biaxial tension, surface defects in the form of fine scratches and certain types of crystallographic texture. The measured limit strains of the materials can be understood on the basis of attainment of a critical shear stress for fracture.

The effect of frequency and microstructure on corrosion fatigue crack propagation in high strength aluminium alloys

Fatigue crack growth in high strength aluminium alloy 7150 commercial plate material has been studied in both laboratory air and acidified aqueous salt solution. The aggressive aqueous environment enhanced fatigue crack growth rates by up to an order in magnitude compared to laboratory air. The enhancement in fatigue crack growth rate was accompanied by evidence of embrittlement in the crack path, involving both brittle intergranular and transgranular failure modes. Both the enhancement of fatigue crack growth rates and the extent of intergranular growth modes are dependent on cyclic frequency which, along with the absence of a similar frequency effect in a spray-formed version of the material with a significantly different grain structure, supports a mechanism of grain boundary hydrogen diffusion for intergranular corrosion fatigue crack growth. The convergence of corrosion fatigue crack growth rates at high ΔK in both spray-formed and conventional plate materials coincides with the operation of identical transgranular corrosion fatigue modes dependent on strain-controlled hydrogen diffusion ahead of the crack tip. © 1997 Acta Metallurgica Inc.

Steel–concrete–steel sandwich system in Arctic offshore structure: Materials, experiments, and design

The gravity based structure (GBS) with external Steel–Concrete–Steel (SCS) sandwich ice-resistant wall has been developed for the Arctic oil and gas drilling. This paper firstly reported the experimental studies on the mechanical properties of steel and concretes under Arctic low temperature. With the test data, design equations were developed to incorporate the influences of the low temperature on these mechanical properties. Two types of Arctic GBS structure with flower-conical SCS sandwich shell type and plate type of ice-resistant wall have been developed for the Arctic offshore structure. Besides the studies on the materials, two SCS sandwich prototype shells and plates were, respectively, prepared and tested under patch loading that simulated the localized ice-contact pressure. The structural behaviors of the SCS sandwich structure under patch loading were reported and discussions were made on the influences of different parameters on the structural behavior of the structure. Analytical models were developed to predict the punching shear resistances of the SCS sandwich structure through modifying the code provisions. The accuracies of the developed analytical models were checked through validations against 27 tests in the literature. Corresponding design procedures on resistances of SCS sandwich structure were recommended based on these discussions and validations.

Avaliação dos mecanismos de endurecimentoda liga AISI 300M submetida a diferentes ciclos de transformações martensíticas

Pós-graduação em Engenharia Mecânica - FEG

Características do aço API X70 utilizado em tubos de transporte de petróleo e gás

Having in mind that petroleum's history presents a huge growth, the exploration and production areas have been receiving lots of investments, in order to attend the increasing demand for gas and petroleum. Looking through that scenario, new technologies have been evolving in favor of discovering new natural petroleum deposits and act with effectiveness in truly deep waters without giving up the worldwide best operational security practices. The use of rigid pipes in marine installations have been rising quickly and, thanks to this reality, the many storage and pipe launching forms became study objects and are getting improved. The analysis of steel API X70 characteristics, proving that they are suitable for use in pipes developed to transport gas and petroleum is the theme of this presentation. A tensile test was conducted to determine the base metal's mechanical properties, draining's tension, traction's resistance, elasticity's modulus and maximum tension. An aspect that is concerning too is the metallographic analysis, in order to determine the studied iron's microstructure. Results of analyzes showed that the steel has high resistance, with good capacity for deformation and well defined yield point, concluding suitable for the application in question

Análise microestrutural e caracterização mecânica do aço AISI 4350 submetido a diferentes tratamentos térmicos

The multiphase steels are gaining increasing attention in scientific studies because of the different mechanical and microstructural properties that the material can achieve under different thermomechanical and heat treatments that can be submitted. In the present study, it was made a microstructural study thru the triple attack technic associated with optical microscopy and mechanical characterization of medium carbon AISI 4350 steel thru a tensile strength test, subjected to three routes of heat treatment: annealing, quenching and tempering and isothermal annealing. It was verified the predominance of ferrite-perlite constituent in the specimen annealed, martensitic in the quenched and tempered specimen and bainitic in the annealed isothermally specimen. The annealed material showed a higher ductility, while the hardened and tempered specimen showed the highest hardness and ultimately the bainitic specimen showed a combination of the two abovementioned mechanical properties. Thus, we proved that the multiphase steel SAE 4350 can be a versatile material with great potential for various industrial applications

Características do aço API X70 utilizado em tubos de transporte de petróleo e gás

Having in mind that petroleum's history presents a huge growth, the exploration and production areas have been receiving lots of investments, in order to attend the increasing demand for gas and petroleum. Looking through that scenario, new technologies have been evolving in favor of discovering new natural petroleum deposits and act with effectiveness in truly deep waters without giving up the worldwide best operational security practices. The use of rigid pipes in marine installations have been rising quickly and, thanks to this reality, the many storage and pipe launching forms became study objects and are getting improved. The analysis of steel API X70 characteristics, proving that they are suitable for use in pipes developed to transport gas and petroleum is the theme of this presentation. A tensile test was conducted to determine the base metal's mechanical properties, draining's tension, traction's resistance, elasticity's modulus and maximum tension. An aspect that is concerning too is the metallographic analysis, in order to determine the studied iron's microstructure. Results of analyzes showed that the steel has high resistance, with good capacity for deformation and well defined yield point, concluding suitable for the application in question

Análise microestrutural e caracterização mecânica do aço AISI 4350 submetido a diferentes tratamentos térmicos

The multiphase steels are gaining increasing attention in scientific studies because of the different mechanical and microstructural properties that the material can achieve under different thermomechanical and heat treatments that can be submitted. In the present study, it was made a microstructural study thru the triple attack technic associated with optical microscopy and mechanical characterization of medium carbon AISI 4350 steel thru a tensile strength test, subjected to three routes of heat treatment: annealing, quenching and tempering and isothermal annealing. It was verified the predominance of ferrite-perlite constituent in the specimen annealed, martensitic in the quenched and tempered specimen and bainitic in the annealed isothermally specimen. The annealed material showed a higher ductility, while the hardened and tempered specimen showed the highest hardness and ultimately the bainitic specimen showed a combination of the two abovementioned mechanical properties. Thus, we proved that the multiphase steel SAE 4350 can be a versatile material with great potential for various industrial applications

Strengthening of circular hollow steel tubular sections using high modulus CFRP sheets

This paper describes the behaviour of very high strength (VHS) circular steel tubes strengthened by carbon fibre reinforced polymer (CFRP) and subjected to axial tension. A series of tests were conducted with different bond lengths and number of layers. The distribution of strain through the thickness of CFRP layers and along CFRP bond length was studied. The strain was found to generally decrease along the CFRP bond length far from the joint. The strain through the thickness of the CFRP layers was also found to decrease from bottom to top layer. The effective bond length for high modulus CFRP was established. Finally empirical models were developed to estimate the maximum load for a given CFRP arrangement.

Influence of heat treatment on the strength and fracture behaviour of Fe-12Cr-6Al ferritic stainless steel

The changes in the tensile properties and fracture mode brought about by heat treatment of Fe-12Cr-6Al ferritic stainless steel have been studied. A favourable combination of high strength and good ductility is obtained by heating the material at 1370 K for 2 h followed by a water quench. The high-temperature treatment results in carbide dissolution as well as an increase in the grain size. The mechanism of strengthening has been evaluated from the apparent activation energy (28 kJ mol–1) and is identified to be the unpinning of dislocations from the atmosphere of carbon atoms. As the heat-treatment temperature is increased, the fracture behaviour changes from ductile to brittle mode and this is related to the changes in grain size and friction stress.