Deformation and fracture behaviour of plate specimens subjected to underwater explosion—a review

Behaviour of plate specimens subjected to underwater explosion is of interest to metal forming community and ship designers. The break down of the original molecule of an explosive into product molecules associated with the evolution of large amount of heat generates a shock front in the water medium, followed by a gas bubble pulsation. The interaction of the shock wave with a plate imparts energy to it, which is dissipated in the form of deformation. The intensity of explosion determines whether a plate undergoes elastic deformation, yielding, plastic deformation or fracture. When the deformation is in the elastic range, the stress developed in the plate is given as a function of the material and shock wave parameters. As the intensity of explosion progressively increases, the elastic to plastic transition occurs over a specific shock factor. Plastic deformation is predicted as a function of geometric and material properties of the plate and shock pulse impulse. Deflection-time history reveals the reloading effects of the shock wave. As the deforming plate absorbs maximum energy, depending on its strength and ductility, it undergoes fracture. Terminal strain to fracture is considered as the criterion for explosive shock performance of ship materials.     

Improvements in microstructure homogenization and mechanical properties of diffusion-alloyed steel compact by the addition of Cr-containing powders

The use of diffusion-alloyed powders for fabricating powder metal parts, despite alleviating the segregation problem of the alloying elements while retaining good compressibility, still cannot attain homogeneous microstructure in as-sintered products. The presence of soft Ni-rich areas and pores causes poor mechanical properties compared to those of wrought steel counterparts. This study investigated the effects of adding 0.5 wt pct Cr, which was introduced in the 316L stainless steel powder form, on the microstructure and mechanical properties of diffusion-alloyed Fe-4Ni-1.5Cu-0.5Mo-0.5C (Metal Powder Industries Federation (MPIF) FD-0405) steels. The results show that weak Ni-rich areas were present in the Cr-free specimen when sintered at 1120 °C and 1250 °C. These areas were lean in carbon because of the strong repelling effect between Ni and C. With the addition of 316L powders, the Cr was uniformly distributed and helped eliminate the soft Ni-rich areas, particularly in specimens sintered at 1250 °C. The distribution of carbon also improved. With a more uniform distribution of Ni and C, and more homogeneous microstructure, which consisted mainly of bainite and martensite, the mechanical properties of the Fe-4Ni-1.5Cu-0.5Mo-0.5C diffusion alloy steels were improved significantly.     

Robust and reliable estimation via Unscented Recursive Nonlinear Dynamic Data Reconciliation

The quality of process data in a chemical plant significantly affects the performance and benefits gained from activities like performance monitoring, online optimization and control. Since many chemical processes often exhibit nonlinear dynamics, techniques like Extended Kalman Filter (EKF) and Nonlinear Dynamic Data Reconciliation (NDDR) have been developed to improve the data quality. There are various issues that arise with the use of either of these techniques: EKF cannot handle inequality or equality constraints, while the NDDR has high computational cost. Recently a recursive estimation technique for nonlinear dynamic processes has been proposed which combines the merits of EKF and NDDR techniques. This technique, named as Recursive Nonlinear Dynamic Data Reconciliation (RNDDR), provides state and parameter estimates that satisfy bounds and other constraints imposed on them. However, the estimate error covariance matrix in RNDDR is computed in the same manner as in EKF, that is, the effects of both nonlinearity and constraints are neglected in the computation of the estimate error covariance matrix.

A relatively new method known as the Unscented Kalman Filter has been developed for nonlinear processes, in which the statistical properties of the estimates are computed without resorting to linearization of the nonlinear equations. This leads to improved accuracy of the estimates. In this paper, we combine the merits of the Unscented Kalman Filter and the RNDDR to obtain the Unscented Recursive Nonlinear Dynamic Data Reconciliation (URNDDR) technique. This technique addresses all concerns arising due to the presence of nonlinearity and constraints within a recursive estimation framework, resulting in an efficient, accurate and stable method for real-time state and parameter estimation for nonlinear dynamic processes.     

Estimation of mobile speed and average received power in wirelesssystems using best basis methods

A new method is presented for estimating the mobile speed and the average received power in general wireless propagation environments. The locally stationary received signal is expanded in a local exponential basis using best basis methods of wavelet analysis. An estimate of the time-varying Doppler power spectrum is obtained together with an estimate of the maximum Doppler frequency, which is proportional to the mobile speed. The average received power is then estimated by integrating the time-varying spectrum. Simulations demonstrate good tracking of variable mobile speed and average received power for a wide range of angular distributions of incident power. The estimator is shown to perform significantly better than an adaptive averaging method described in the literature. The speed and average power estimates are also used to detect the corner effect in urban cellular systems to improve handoff performance and reduce the call dropping rate     

Limit Strains Comparison during Tube and Sheet Hydroforming and Sheet Stamping Processes by Numerical Simulation

Hydroforming is a manufacturing process that uses a fluid medium to form a component by using high internal pressure. Tube and sheet hydroforming has gained increasing interest in the automotive and aerospace industries because of its many advantages such as part consolidation, good quality of the formed parts etc. The main advantage is that the uniform pressure can be transferred to every where at the same time. Forming limit is the limit of the component up to that extent it can be formed safely. While analyzing hydroforming process, it is often assumed that the limit strains are identical as that of stamped sheet metal of equivalent material properties. It is not clear if such an assumption is valid. In this paper the forming limit strains during hydroforming is predicted. A series of tube bulge tests for tube hydroforming and limiting dome height test for sheet hydroforming and sheet stamping processes are simulated by a commercial finite element solver to predict the limit strains. Numerical simulation of forming limit strains in tube hydroforming with different internal pressure and different simulation set up with or without axial feeding, while in sheet hydroforming and sheet stamping, by changing the specimen geometry are considered to develop wide range of strain paths in the present work. The effects of process conditions on the forming limit strains are detailed. The comparison of limits strains during hydroforming and stamping processes is presented. Prediction of limits strains is based on a novel thickness based necking criterion.     

A cohesive finite element formulation for modelling fracture and delamination in solids

In recent years, cohesive zone models have been employed to simulate fracture and delamination in solids. This paper presents in detail the formulation for incorporating cohesive zone models within the framework of a large deformation finite element procedure. A special Ritz-finite element technique is employed to control nodal instabilities that may arise when the cohesive elements experience material softening and lose their stress carrying capacity. A few simple problems are presented to validate the implementation of the cohesive element formulation and to demonstrate the robustness of the Ritz solution method. Finally, quasi-static crack growth along the interface in an adhesively bonded system is simulated employing the cohesive zone model. The crack growth resistance curves obtained from the simulations show trends similar to those observed in experimental studies     

Cardamom — production,technology, chemistry,and quality

Cardamom, Eleltaria cardamomum Maton var. Miniscula Burkill (Fam. Zingiberaceae) known as true or lesser cardamom is the widely cultivated variety and important in the world trade. It occupies a high second or third place in world trade, being a high priced spice. It belongs to the sweet spices group and is used predominantly to flavor sweets, baked goods, and coffee, particularly in the Arab countries. This monograph critically reviews the post‐harvest handling and processing and the chemistry of the volatiles. The components contributing to the characteristic aroma for which the spice is valued are specifically considered. Gas chromatographic analysis for quality control and attempts at evaluating the aroma quality by sensory profile are discussed in relation to regional varieties, and processing variables. The areas in which further research is required are indicated. The botanical and cultivation aspects and production and trade of the different growing and consuming regions are briefly considered. Available information on other “cardamoms” from related species and genera are summarized.     

Retailer’s sourcing strategy under consumer stockpiling in anticipation of supply disruptions

We study a retailer’s sourcing strategy under consumers’ stockpiling behaviour and the factors associated with the selection of an optimal strategy in multi-tier supply chains in the presence of supply disruption risk. Stockpiling behaviour occurs when consumers attempt to mitigate the negative impact of a supply shortage. We prove that those behaviours become stronger if consumers have experienced similar problems before and weaker as more inventories are hoarded. Based on these findings, numerical analysis is carried out to compare the superiority of single sourcing versus dual sourcing from retailer’s perspective. Our results suggest that the superiority is highly dependent on factors such as supplier’s volume flexibility, retailer’s purchasing price, and supplier reliability.