scholarly journals Development of Microstructures with Improved Cryogenic Toughness Through Local Variations in Stress State: Aluminum-Lithium Alloys

1990 ◽  
Vol 186 ◽  
Author(s):  
K. T. Venkateswara Rao ◽  
R. O. Ritchie
Keyword(s):  
Stress State ◽  
Sheet Material ◽  
Thin Sheet ◽  
Local Stress ◽  
Cryogenic Temperatures ◽  
Aluminum Lithium ◽  
Thin Sheet Material ◽  
Local Stress State ◽  
Crack Tip Constraint ◽  
Induced Changes

AbstractMicrostructurally-induced changes in the local stress state (triaxial constraint) and their effect on fracture-toughness behavior are examined at ambient and cryogenic temperatures in an Al-Li-Cu-Zr alloy, processed in the form of 12.7 mm-thick "naturally laminated" plate containing aligned-weak interfaces and 1.6 mm-thin unlaminated sheet. It is shown that marked improvements in long-transverse (L-T) toughness can be achieved in the plate material at cryogenic temperatures by promoting through-thickness delamination along these interfaces, which relaxes local constraint and promotes a fracture-mode transition from global plane strain to local plane stress. Conversely, in thin sheet material, the absence of such interface delamination leads to a reduction in toughness with decrease in temperature, consistent with the greater degree of crack-tip constraint.

To the Influence of the Deformation Speed on Hardening Process during the Cold Sheet Forming

2018 ◽  
Vol 284 ◽  
pp. 513-518 ◽  
Author(s):  
Sergey A. Tipalin ◽  
Michael A. Petrov ◽  
N.F. Shpunkin
Keyword(s):  
Sheet Metal Forming ◽  
Metal Forming ◽  
Sheet Material ◽  
Thin Sheet ◽  
Hardening Process ◽  
Deformation Speed ◽  
Thin Sheet Material ◽  
Simulation Results ◽  
Hardening Curve ◽  
Material Forming

The accuracy of the simulation results of stamping processes of thin sheet material depends on the correct properties’ specification, namely stamping ability. Experiments have been carried out and the influence of the deformation speed on the hardening exponent during cold sheet metal forming was studied. It was found out, that strain changed 100 times can influence the strain grade of the hardening curve of about 10%. This regularity has been taken into consideration prior to the calculation in any CAE-software for material forming.

Investigation of Constraint Effects on Fracture Toughness for CC(T) Specimens

2004 ◽  
Author(s):  
Dieter Siegele ◽  
Igor Varfolomeyev ◽  
Kim Wallin ◽  
Gerhard Nagel
Keyword(s):  
Fracture Toughness ◽  
Crack Tip ◽  
Temperature Shift ◽  
Local Stress ◽  
Significant Loss ◽  
Reference Temperature ◽  
T Stress ◽  
Local Stress State ◽  
Constraint Effects ◽  
Crack Tip Constraint

Within the framework of the European research project VOCALIST, centre cracked tension, CC(T), specimens made of an RPV steel were tested and analysed to quantify the influence of local stress state on fracture toughness. The CC(T) specimens demonstrate a significant loss of crack tip constraint resulting in a considerable increase in fracture toughness as compared to standard fracture mechanics specimens. So, the master curve reference temperature, To, determined on the basis of CC(T) tests performed in this study is about 43°C lower than To obtained on standard C(T) specimens. Finite element analyses of the tests revealed that the above experimental finding is in a good agreement with the empirical correlations between the reference temperature shift and the crack tip constraint as characterised by the T-stress or Q parameter (Wallin, 2001; Wallin, 2004). The results of this work are consistent with a number of other tests performed within the VOCALIST project and contribute to the validation of engineering methods for the crack assessment in components taking account of constraint.

An Investigation on Deformation-Based Micro Surface Texturing

2011 ◽  
Author(s):  
Rui Zhou ◽  
Jian Cao ◽  
Kornel Ehmann ◽  
Chun Xu
Keyword(s):  
Sheet Material ◽  
Thin Sheet ◽  
Surface Texturing ◽  
Channel Depth ◽  
Surface Textures ◽  
Numerical Studies ◽  
Micro Channels ◽  
Thin Sheet Material ◽  
Wear Reduction ◽  
Final Profile

Micro surface textures have various applications, such as friction/wear reduction and bacteria sterilization. Deformation-based micro surface texturing has the potential of economically creating micro surface textures over a large surface area. A novel desktop micro surface texturing system is proposed for efficiently and economically fabricating micro channels on the surface of thin sheet material for micro fluid and friction/wear reduction applications. Both experimental and numerical studies were employed to analyze the problems of the flatness of the textured sheet, the uniform of the channel depth and pile-ups built up during the micro surface texturing process. The results demonstrated a clear relationship between relative velocity of the upper and lower rolls and the flatness of the textured sheet and the final profile of the micro channels.

Reinforced Plastics for Jet Lift Engines

1967 ◽  
Vol 71 (677) ◽  
pp. 355-365 ◽  
Author(s):  
H. E. Gresham ◽  
C. G. Hannah
Keyword(s):  
Sheet Material ◽  
Thin Sheet ◽  
Economic Factor ◽  
Specific Strength ◽  
Reinforced Plastics ◽  
Thin Sheet Material ◽  
Good Heat Resistance ◽  
Ply Orientation ◽  
Rain Erosion ◽  
Good Heat

Summary:—Extensive use of reinforced plastics has contributed significantly to the success of small VTOL engines, notably the Rolls-Royce RB 162 series in whose compressors it has been possible to demonstrate their versatility and ruggedness. The choice of reinforced plastics for such obvious reasons as lightness, specific strength and corrosion resistance has been fully justified, while apparent deficiencies in stiffness and rain erosion resistance have not proved embarrassing.Considerable use has been made of epoxy resin pre-impregnated sheet incorporating non-woven parallel aligned glass fibre, in particular the “Scotchply” series of “pre-pregs”. Exceptionally high fibre contents have been achieved, resulting in higher strengths and moduli than are usual with glass-reinforced plastics and furthermore, since Scotchply has proved so uniform in composition and ply thickness it has been possible to precision-mould most components with such accuracy that machining is eliminated—a major economic factor. Further economies have been achieved by minimising press curing times by the use of latent catalytic type hardeners for the resin systems which, in addition, confer long storage life and good heat resistance. The use of very thin sheet material has allowed much ply orientation within laminates, resulting in substantial and controllable variations in anisotropy, allowing properties to be tailored more nearly to meet the conditions imposed.

Measurement of Monotonic Biaxial Elastoplastic Stresses at Notch Roots

1991 ◽  
Vol 58 (4) ◽  
pp. 916-922 ◽  
Author(s):  
W. N. Sharpe
Keyword(s):  
Effective Stress ◽  
Notch Root ◽  
Sheet Material ◽  
Thin Sheet ◽  
Strain Curve ◽  
Local Stress ◽  
Uniaxial Stress ◽  
Maximum Deviation ◽  
Principal Stresses ◽  
Interferometric Technique

Biaxial principal strains were measured at the roots of notches in aluminum specimens with a laser-based interferometric technique. Interference patterns from three tiny indentations spaced 150 or 200 micrometers apart in an orthogonal pattern were monitored with a microcomputer-controlled system. Elastoplastic strains up to one percent were measured in real time with a resolution of 25 microstrain. Procedures were developed for computing the two principal stresses from the incremental strain data using J2-flow theory. The validity of the computations was checked by computing the stresses in smooth tensile specimens. Anisotropy in the thin sheet material leads to errors in the computed lateral stresses (which should be zero), but the maximum deviation of the computed effective stress from the uniaxial stress is only five percent. Three kinds of double-notched specimens were prepared to vary the amount of constraint at the notch root. These were tested under monotonic tensile loading and the biaxial notch-root strains recorded. There is considerable variation among the strains once the elastic limit is passed. This is due primarily to the local inhomogeneity of plastic strain, since the gage length of the measurement is only a few times larger than the grain size of the material. Local biaxial stresses were computed from the measured strains for the three cases. The nature of the material’s stress-strain curve tends to smooth out the variations among tests, particularly when the effective stress is computed. It is discovered that the local stress predicted by the Neuber relation agrees very closely with the measured local effective stress.

A New Coolant Supply Method Using a Coolant Flow Guided Flexible Sheet Attracted to a Wheel Surface

2005 ◽  
Vol 291-292 ◽  
pp. 227-232 ◽  
Author(s):  
Kiyoshi Suzuki ◽  
Shinichi Ninomiya ◽  
Manabu Iwai ◽  
Yoshiaki Shishido ◽  
Tetsutaro Uematsu
Keyword(s):  
Flow Rate ◽  
Sheet Material ◽  
Thin Sheet ◽  
Coolant Flow ◽  
New Method ◽  
Coolant Flow Rate ◽  
Nozzle Outlet ◽  
Wheel Surface ◽  
Profile Grinding ◽  
Thin Sheet Material

To improve the characteristic of the floating nozzle method, a new coolant supply method using a coolant flow guided flexible sheet was developed. In this method, all the coolant supplied from the nozzle outlet can surely be directed immediately to the grinding point, because the coolant flow guided flexible sheet made of a thin sheet material is attracted to the wheel surface automatically, and confines the coolant between the wheel surface and the sheet. Therefore, the coolant can be completely prevented from deviating away from the grinding point. In fact, when the coolant flow rate of 4 l/min was supplied from the upper part of the wheel by using this method, the amount of coolant that reached the grinding point was 18 times higher than the case of only the floating nozzle method. It was clarified that this method had the effect to improve the grinding performance. Furthermore, this new method has a possibility of the wide application such as in profile grinding and cam grinding.

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