Strain Limit of Extra Galvannealed InterstitialFree and Bake Hardened Steel Sheets Under Different Stress Conditions

The formability of bake hardened steel （thickness 0.82 mm）, and the extra galvannealed IF steel （thickness 0.82 mm） have been studied. The suitability of the above steels for forming applications has been critically examined. The microstructure, tensile properties, and formability parameters of the above sheet metals were determined. The manufacturing process of the steels and the significance with reference to its formability were studied.     

Surface replication studies of small bores

Replication is one of the best methods available for studying the surface characteristics of small bores of diameter 3 mm or less. This paper deals with the detailed statistical analysis of the digitised profile of the original surface and its film replicas. Analysis shows that this method can be successfully used for the assessment of small bores of medium coarse surfaces     

Thermomagnetic studies of (Co0.93Fe0.07)75−x Cr x Si15B10 metglas

Thermomagnetization measurements have been carried out on the Co-Fe-Cr-Si-B metglas up to 7.5 at% Cr. For the Co₇₀Fe₅Si₁₅Si₁₀ metglas, application of magnetic field has been found to influence the process of crystallization. Thermal annealing of this alloy at temperaturesT _c<T _a<T _cr leads to a decrease in the value ofT _c due to chemical short-range ordering (CSRO) and topological short-range ordering (TSRO). Introduction of chromium into the above alloy reduces the saturation magnetization and Curie temperature of the alloy at the rate of 5.55 emu gm^–1 and 41 K per at% Cr, respectively. These are explained due to the antiparallel coupling of the 3 d electrons of iron and cobalt atoms with those of chromium and to a deterioration in the strength of ferromagnetic exchange interactions between Co-Co, Co-Fe and Fe-Fe magnetic pairs.     

Patching Processor Design Errors with Programmable Hardware

Equipping processors with programmable hardware to patch design errors lets manufacturers release regular hardware patches, avoiding costly chip recalls and potentially speeding time to market. For each error detected, the manufacturer creates a fingerprint, which the customer uses to program the hardware. The hardware watches for error conditions; when they arise, it takes action to avoid the error. Overall, our scheme enables an exciting new environment where hardware design errors can be handled as easily as system software bugs, by applying a patch to the hardware     

Analysis of fracture limit curves and void coalescence in high strength interstitial free steel sheets formed under different stress conditions

Void formation, which is a statistical event, depends on inhomogeneities present in the microstructure. The analysis on void nucleation, their growth and coalescence during the fracture of high strength interstitial free steel sheets of different thicknesses is presented in this article. The analysis shows that the criterion of void coalescence depends on the d-factor, which is the ratio of relative spacing of the ligaments (δd) present between the two consecutive voids to the radius of the voids. The computation of hydrostatic stress (σ_m), the dominant factor in depicting the evolution of void nucleation, growth and coalescence and the dimensional analysis of three different types of voids namely oblate, prolate and spherical type, have been carried out. The ratio of the length to the width (L/W) of the oblate or prolate voids at fracture is correlated with the mechanical properties, microstructure, strains at fracture, Mohr’s circle shear strains and Triaxiality factors. The Lode angle (θ) is determined and correlated with the stress triaxiality factor (T), ratio of mean stress (σ_m) to effective stress (σ_e). In addition, the Void area fraction (V _a), which is the ratio of void area to the representative area, is determined and correlated with the strain triaxiality factor (T_o).     

Influence of mechanical milling and thermal annealing on electrical and magnetic properties of nanostructured Ni-Zn and cobalt ferrites

The present article reports some of the interesting and important electrical and magnetic properties of nanostructured spinel ferrites such as Ni_0.5Zn_0.5Fe₂O₄ and CoFe₂O₄. In the case of Ni_0.5Zn_0.5Fe₂O₄, d.c. electrical conductivity increases upon milling, and it is attributed to oxygen vacancies created by high energy mechanical milling. The real part of dielectric constant (?′) for the milled sample is found to be about an order of magnitude smaller than that of the bulk nickel zinc ferrite. The increase in Néel temperature from 538 K in the bulk state to 611 K on the reduction of grain size upon milling has been explained based on the change in the cation distribution. The dielectric constant is smaller by an order of magnitude and the dielectric loss is three orders of magnitude smaller for the milled sample compared to that of the bulk. In the case of cobalt ferrite, the observed decrease in conductivity, when the grain size is increased from 8–92 nm upon thermal annealing is clearly due to the predominant effect of migration of some of the Fe³⁺ ions from octahedral to tetra-hedral sites, as is evident from in-field Mössbauer and EXAFS measurements. The dielectric loss (tan δ) is an order of magnitude smaller for the nano sized particles compared to that of the bulk counterpart.     

Effect of annealing on formability of aluminium grade 19000

Forming limit diagrams are used by the stampers to solve sheet metal forming problems. In practice, sheet metals have been subjected to various combinations of strain. Necking during sheet metal forming, sets the limit to which the sheet metal can be formed. Forming limit diagram is an effective tool to evaluate the formability of sheet metal in various strain conditions. The information upon the formability of the sheet metal is important for both sheet metal manufacturers and users. In this work, a study has been made on the formability of aluminium 19000 grades annealed at three different temperatures namely 160 °C, 200 °C and 300 °C for sheet thickness of 2.00 mm. The tensile properties and formability parameters were experimentally evaluated and they are related to forming limit diagram. Strain distribution profiles obtained from the forming experiment have been analyzed. The fractured surface of the formed samples were viewed using scanning electron microscope (SEM) and the SEM images were correlated with fracture behaviour and formability of sheet metal. The sheet which is annealed at 300 °C has been found to possess good drawability and stretchability compared to other two annealed sheets.     

Comparison of workability strain and stress parameters of powder metallurgy steels AISI 9840 and AISI 9845 during cold upsetting

A complete experimental investigation on the workability behaviour of nickel–chromium–molybdenum steel grades namely AISI 9840 and AISI 9845 of powder metallurgy preforms was performed. Cold upsetting of aforesaid composites with different aspect ratios namely 0.42, 0.63 and 0.93 was carried out with graphite lubricant and the formability behaviour of the preforms under triaxial stress-state condition was determined. A new formability strain parameter was proposed, evaluated and compared with formability stress parameter for all the above said preforms. The characteristics of various stress and strain ratio parameters with respect to relative density were also analyzed and presented for comparison.     

Effect of annealing on combined forming, fracture and wrinkling limit diagram of Aluminium 5086 alloy sheets

In this work, a combined forming, fracture and wrinkling limit diagram have been experimentally evaluated for Aluminium 5086 alloy sheet annealed at three different temperatures namely 200, 250 and 300°C. With the help of the above diagrams, the safe range which avoids necking, fracture and wrinkles during forming of Aluminium 5086 alloy sheets were examined and the effect of annealing temperature on this range and other parameters namely microstructure, tensile properties and formability parameters were studied.