A modified micromechanical approach to determine flow stress of work materials experiencing complex deformation histories in manufacturing processes

2007 ◽  
Vol 49 (7) ◽  
pp. 909-918 ◽  
Author(s):  
S. Anurag ◽  
Y.B. Guo
Keyword(s):  
Flow Stress ◽  
Manufacturing Processes ◽  
Complex Deformation ◽  
Micromechanical Approach

A Micromechanical Approach to Determine Flow Stress of Work Materials Experiencing Complex Deformation Histories in Manufacturing Processes

2006 ◽  
Author(s):  
S. Anurag ◽  
Y. B. Guo
Keyword(s):  
Flow Stress ◽  
Constitutive Model ◽  
Strain Rate ◽  
Test Data ◽  
High Strain ◽  
Dislocation Motion ◽  
Manufacturing Processes ◽  
Strain Rates ◽  
Complex Deformation ◽  
Micromechanical Approach

Work materials experience a broad range of strains, strain rates, and temperatures in many manufacturing processes such as machining, forming, etc. Strain rate has an important effect on the yield and flow stress of work materials, especially metals, since at higher strain rates there is less time for thermally-activated events; consequently, it is equivalent to a lowering of the temperature of the materials. On the other hand, it is also true that, for high strain rate deformations such as metal cutting, adiabatic plastic flow may produce significant temperature changes in the materials. Flow stress is significantly affected by the strain rate history; hence, mechanical behavior may not be fully described in terms of a mechanical equation of state relating the instantaneous stress, strain, strain rate, and temperature. Based on the concept of dislocation mechanics, a micromechanical approach has been explored to determine flow stress at high strain rates by combining athermal stress (the long-range barriers to dislocation motion) and thermal stress (the short-range temperature and strain rate-dependent barriers to dislocation motion). The SHPB (split Hopkinson pressure bar) compression test data of Aluminum 6061-T6 and titanium Ti6Al-4V in literature over a temperature range of 77K–1000K was used for this purpose. Based on the baseline test data, the constitutive model describing the flow stress was developed. The constitutive model was further modified and extended to predict flow stress above the critical temperature. The corresponding model predictions were compared with the experimental data, attaining good agreement.

Dynamic Mechanical Behavior of Titanium Ti-6Al-4V at Transient Large Deformation Manufacturing Processes

2007 ◽  
Author(s):  
J. Sun ◽  
Y. B. Guo
Keyword(s):  
Flow Stress ◽  
Mechanical Behavior ◽  
Large Deformation ◽  
Large Deformations ◽  
Model Parameters ◽  
Manufacturing Processes ◽  
Strain Rates ◽  
Dynamic Mechanical ◽  
Dynamic Mechanical Behavior ◽  
Jc Model

Titanium Ti-6Al-4V alloy has been widely used in the aerospace, biomedical, automobile and petroleum industries. However, Ti-6Al-4V is a typical difficult-to-process material owning to its unique physical and mechanical properties which are characterized by low thermal conductivity, low modulus of elasticity, and high yield strength at elevated temperatures. The rapidly rising demand for titanium components demands more efficient manufacturing processes. Material property of Ti-6Al-4V plays an important role in process design and optimization especially for transient large deformations processes such as forming and machining. However, the dynamic mechanical behavior is poorly understood and accurate predictive models have yet to be developed. To obtain meaningful results which reflect the physical mechanisms of large deformation processes, it is essential to study the dynamic mechanical behavior of Ti-6Al-4V. The Johnson-Cook (JC) model has shown to be effective for modeling strain-hardening behavior of metals and it is numerically robust and can easily be used in finite element simulation models. However, the determination of JC model parameters is determined mostly based on split Hopkinson bar pressure (SHPB) test at isothermal conditions, which is very different from those of transient large deformations characterized by quick and high temperature changes. This study focuses on the dynamic mechanical behavior of titanium in transient manufacturing processes. The mechanical behavior of Ti-6Al-4V at large strains and strain rates beyond the isothermal conditions has been studied using the JC model coupled with the adiabatic condition. Heat fraction coefficient and temperature parameter have great effect on Flow stress-strain relationship. A significant drop of the flow stress occurs at large deformations with high strain rates. The flow stress sensitivity to JC strength model parameters was also investigated. The effect of pressure-stress ratio on material failure strain has shown the material may exhibit super plasticity before failure at hydro compression mode.

Dislocation structures around SiO2 Particles in aged Cu-Cr-SiO2

1978 ◽  
Vol 36 (1) ◽  
pp. 594-595
Author(s):  
N.J. Long ◽  
M.H. Loretto ◽  
C.H. Lloyd
Keyword(s):  
Flow Stress ◽  
Single Crystals ◽  
Room Temperature ◽  
Thin Foil ◽  
Age Hardening ◽  
Dispersion Strengthening ◽  
Accurate Picture ◽  
The Matrix ◽  
Very High ◽  
Good Agreement

IntroductionThere have been several t.e.m. studies (1,2,3,4) of the dislocation arrangements in the matrix and around the particles in dispersion strengthened single crystals deformed in single slip. Good agreement has been obtained in general between the observed structures and the various theories for the flow stress and work hardening of this class of alloy. There has been though some difficulty in obtaining an accurate picture of these arrangements in the case when the obstacles are large (of the order of several 1000's Å). This is due to both the physical loss of dislocations from the thin foil in its preparation and to rearrangement of the structure on unloading and standing at room temperature under the influence of the very high localised stresses in the vicinity of the particles (2,3).This contribution presents part of a study of the Cu-Cr-SiO2 system where age hardening from the Cu-Cr and dispersion strengthening from Cu-Sio2 is combined.

Precipitate coarsening during hot-compression testing of NiAl + 2 at.% Nb

1986 ◽  
Vol 44 ◽  
pp. 598-599
Author(s):  
W. M. Sherman ◽  
K. M. Vedula
Keyword(s):  
High Temperature ◽  
Flow Stress ◽  
Weight Ratio ◽  
Constant Strain Rate ◽  
Hot Compression ◽  
Compression Testing ◽  
Second Phase ◽  
Precipitate Coarsening ◽  
High Temperature Mechanical Properties ◽  
Ordered Intermetallic

The strength to weight ratio and oxidation resistance of NiAl make this ordered intermetallic, with some modifications, an attractive candidate to compete with many superalloys for high temperature applications. Recent studies have shown that the inherent brittleness of many polycrystalline intermetallics can be overcome by micro and macroalloying. It has also been found that the high temperature mechanical properties of NiAl can be enhanced through the addition of Nb by powder metallurgical techniques forming a dispersed second phase through interdiffusion in a polycrystalline matrix. A drop in the flow stress is observed however in a NiAl-2 at.% Nb alloy after 0.2 % strain during constant strain rate hot compression testing at 1025°C. The object of this investigation was to identify the second phase and to determine the cause of the flow stress drop.

Impact of fiber structure on edge-wicking of highly-sized paperboard

TAPPI Journal ◽  
2018 ◽  
Vol 17 (08) ◽  
pp. 437-443
Author(s):  
Lebo Xu ◽  
Jeremy Meyers ◽  
Peter Hart
Keyword(s):  
Fiber Surface ◽  
Manufacturing Processes ◽  
Paper Machine ◽  
Liquid Penetration ◽  
Fiber Structure ◽  
Cut Edge ◽  
Local Fiber

Coffee edge-wicking testing was conducted on two groups of highly-sized paperboard manufactured at two mills with similar manufacturing processes, but with vastly different local fiber sources. Although the Hercules size test (HST) indicated similar internal size levels between the two types of board, the edge-wicking behavior was noticeably different. Analysis of fiber structure revealed that the board with more edge-wicking had fibers with thicker fiber walls, which kept the fiber lumen more open after pressing and drying on a paper machine. It was demonstrated that liquid penetration through voids between fibers in highly-sized paperboard was limited, because the fiber surface was well protected by the presence of sufficient sizing agent. Nevertheless, freshly exposed fiber walls and lumens at the cut edge of the sheet were not protected by sizing material, which facilitated edge-wicking. The correlation between fiber structure and edge-wicking behavior was highlighted in this work to inspire development of novel sizing strategies that protect the freshly cut edge of the sheet from edge-wicking.

An Overview of 300 mm SOI Starting Wafer Quality and Its Yield Detractors

2005 ◽  
Author(s):  
Pei Y. Tsai ◽  
Junedong Lee ◽  
Paul Ronsheim ◽  
Lindsay Burns ◽  
Richard Murphy ◽  
...  
Keyword(s):  
Integrated Circuits ◽  
Device Fabrication ◽  
Sampling Plan ◽  
Silicon On Insulator ◽  
Manufacturing Processes ◽  
Circuit Performance ◽  
Characterization Techniques ◽  
Wafer Manufacturing

Abstract A stringent sampling plan is developed to monitor and improve the quality of 300mm SOI (silicon on insulator) starting wafers procured from the suppliers. The ultimate goal is to obtain the defect free wafers for device fabrication and increase yield and circuit performance of the semiconductor integrated circuits. This paper presents various characterization techniques for QC monitor and examples of the typical defects attributed to wafer manufacturing processes.

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