Factors Influencing Fracture Toughness and Other Properties of Aluminum- Lithium Alloys PDF Download
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Author: T. H Sanders (Jr)
Publisher:
ISBN:
Category :
Languages : en
Pages : 282
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Book Description
An investigation was made to identify the microstructural features which control the fracture behavior of Al-Li alloys. Tensile, fracture toughness, and selected fatigue tests were conducted on candidate Al-Li alloys (Al-Mg-Li, Al-Cu-Li, and Al-Li). In all three alloy systems and most aging conditions investigated, the fracture mode was low energy, intergranular failure. Three microstructural features were considered to correlate with the intergranular failure--the shearable nature of the coherent Al3Li(delta') precipitates which leads to dislocation pile-ups at the grain boundaries; the growth of a solute depleted, precipitate free zone during aging, and the occurrence of the tramp elements sodium, potassium and sulfur presumably segregated in the grain boundaries. Furthermore, the hydrogen content of the alloys was also shown to be significantly higher than other high strength commercial alloys. All these features would contribute to the low toughness and would tend to promtoe intergranular failure.
Author: T. H Sanders (Jr)
Publisher:
ISBN:
Category :
Languages : en
Pages : 282
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Book Description
An investigation was made to identify the microstructural features which control the fracture behavior of Al-Li alloys. Tensile, fracture toughness, and selected fatigue tests were conducted on candidate Al-Li alloys (Al-Mg-Li, Al-Cu-Li, and Al-Li). In all three alloy systems and most aging conditions investigated, the fracture mode was low energy, intergranular failure. Three microstructural features were considered to correlate with the intergranular failure--the shearable nature of the coherent Al3Li(delta') precipitates which leads to dislocation pile-ups at the grain boundaries; the growth of a solute depleted, precipitate free zone during aging, and the occurrence of the tramp elements sodium, potassium and sulfur presumably segregated in the grain boundaries. Furthermore, the hydrogen content of the alloys was also shown to be significantly higher than other high strength commercial alloys. All these features would contribute to the low toughness and would tend to promtoe intergranular failure.
Author: R.J.H. Wanhill
Publisher: Elsevier Inc. Chapters
ISBN: 0128068507
Category : Technology & Engineering
Languages : en
Pages : 40
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Book Description
Most aluminium-lithium (Al–Li) alloy fatigue crack growth (FCG) data have been obtained for 2nd generation alloys, specifically under constant amplitude (CA) and constant stress ratio (CR) loading, and for long/large cracks. These data show the alloys in a favourable light, but this FCG ‘advantage’ essentially disappears under realistic flight simulation loading, and is also absent for short/small cracks. Furthermore, the FCG advantage is due to inhomogeneous plastic deformation, which has undesirable consequences for other important properties. These consequences have greatly restricted the use of 2nd generation alloys in aerospace structures. FCG data for 3rd generation Al–Li alloys are becoming more available. Many of the issues associated with 2nd generation alloys have been eliminated or greatly alleviated as a result of several changes, including reduced Li contents and innovative thermomechanical processing. Consequently, the FCG behaviour of 3rd generation alloys is more similar to that of conventional alloys. Nevertheless, the 3rd generation alloys tend to have better FCG properties than equivalent conventional alloys; and these and other improvements have already led to many aircraft applications.
Author: T.S. Srivatsan
Publisher: Elsevier Inc. Chapters
ISBN: 0128068485
Category : Technology & Engineering
Languages : en
Pages : 44
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Book Description
The emergence of Al–Li alloys as potential light metal, for safe use in a spectrum of aircraft structures and related aerospace applications has in recent years engendered an unprecedented widespread interest aimed at studying, understanding and improving their mechanical properties. In this chapter, we present and discuss some of the key aspects relevant to aluminum-lithium alloys, spanning the specific domain of precipitation kinetics as influenced by composition and heat treatment, intrinsic microstructural features and their effects, the fundamental mechanisms contributing to strength, ductility, fracture toughness, and overall anisotropy in mechanical properties of these alloys. The tensile behavior of representative first generation, second generation and third generation aluminum-lithium alloys is also presented and briefly discussed. Microstructural influences on mechanical properties are examined with specific reference to matrix microstructural features, dislocation-microstructural feature interaction, and matrix slip characteristics.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1064
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Book Description
Author: N Eswara Prasad
Publisher: Butterworth-Heinemann
ISBN: 0124016790
Category : Technology & Engineering
Languages : en
Pages : 596
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Book Description
Because lithium is the least dense elemental metal, materials scientists and engineers have been working for decades to develop a commercially viable aluminum-lithium (Al-Li) alloy that would be even lighter and stiffer than other aluminum alloys. The first two generations of Al-Li alloys tended to suffer from several problems, including poor ductility and fracture toughness; unreliable properties, fatigue and fracture resistance; and unreliable corrosion resistance. Now, new third generation Al-Li alloys with significantly reduced lithium content and other improvements are promising a revival for Al-Li applications in modern aircraft and aerospace vehicles. Over the last few years, these newer Al-Li alloys have attracted increasing global interest for widespread applications in the aerospace industry largely because of soaring fuel costs and the development of a new generation of civil and military aircraft. This contributed book, featuring many of the top researchers in the field, is the first up-to-date international reference for Al-Li material research, alloy development, structural design and aerospace systems engineering. - Provides a complete treatment of the new generation of low-density AL-Li alloys, including microstructure, mechanical behavoir, processing and applications - Covers the history of earlier generation AL-Li alloys, their basic problems, why they were never widely used, and why the new third generation Al-Li alloys could eventually replace not only traditional aluminum alloys but more expensive composite materials - Contains two full chapters devoted to applications in the aircraft and aerospace fields, where the lighter, stronger Al-Li alloys mean better performing, more fuel-efficient aircraft
Author:
Publisher:
ISBN:
Category : Power resources
Languages : en
Pages : 852
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Book Description
Author: K.V. Jata
Publisher: Elsevier Inc. Chapters
ISBN: 0128068434
Category : Technology & Engineering
Languages : en
Pages : 35
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Book Description
This chapter describes the development of crystallographic texture and its effects on mechanical properties in aluminum-lithium alloys. Crystallographic texture evolves during the forming of wrought products from cast ingots of Al-Li alloys and consequently affects the mechanical properties. Practical approaches to control the texture have been developed and have been successfully used in the products obtained from industrial-scale ingots. This texture tailoring has significantly reduced the yield strength anisotropy. In addition, theoretical approaches have been used to model the yield strength anisotropy of aluminum alloys in the presence of complex precipitates.
Author: G. Cavallini
Publisher:
ISBN:
Category :
Languages : en
Pages : 18
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Book Description
A research programme for the evaluation of the main characteristics of the newly developed Al-Li alloys has been undertaken under the sponsorship of the Italian National Research Council (C.N.R.). Many italian aeronautical Industries and Research Institutes take part in this programme, which comprises a large variety of experimental activities: static tests, fatigue tests, crack propagation tests, fracture toughness, corrosion susceptibility, formability, workability and other tests. Different producers (British Alcan, Cegedur Pechiney and Alcoa) provided the alloys tested in this programme; 2091, 8090 and 2090 alloys have been objects of investigation. The paper describes some of the results obtained so far in the C.N.R. programme and some results obtained by Aeritalia in its own programs. The results are relevant to fatigue tests carried out both on notched and unnotched specimens, under Constant Amplitude loading (R=0.1). Fatigue tests, together with structural (Transmission Electron Microscopy) and fractographic (Scanning Electron Microscope) studies, have been carried out also for assessing the influence of different ageing on both mechanical properties and failure modes of materials. Crack propagation tests were carried out under both C.A. loading and FALSTAFF sequence and are here presented, together with results from fracture toughness tests. Keywords: Alloys, Metallurgy, Italy, Fatigue(Mechanics), Fracture(Mechanics), Corrosion, Sodium sulfate, NA2S04, ASTMG69 Standard. (JG).
Author: Ramesh J. Kar
Publisher:
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 478
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Book Description
Author: N.J.H. Holroyd
Publisher: Elsevier Inc. Chapters
ISBN: 0128068523
Category : Technology & Engineering
Languages : en
Pages : 53
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Book Description
Industrial interest in wrought heat-treatable aluminium-lithium (Al–Li) based alloys dates back to around 1919 in Germany. However the exploitation of these alloys has historically been limited by their mechanical property anisotropy and concerns over their localized corrosion resistance and temperature stability. Recently, in the last ten years, alloy and process development has resulted in alloy compositions and thermomechanical treatments that potentially can overcome these issues. To put these developments in perspective we have reviewed the corrosion characteristics of first, second and third generation alloys with an emphasis on localized corrosion (intergranular and exfoliation) and stress corrosion cracking (SCC). Intergranular corrosion susceptibility of Al–Li–Cu and Al–Li–Cu–Mg alloys increases with copper content, and the depth of attack increases with ageing, i.e. UAPA~30 mm) further analysis of corrosion test results is required.
