Analytic study on pure bending of metal sheets

In this work, analytical models of pure bending are developed to simulate a particular type of bend test and to determine possible errors arising from approximations used in analyzing experimental data. Analytical models proposed for steels include a theoretical solution of pure bending and a series of finite element models, based on the von Mises yield function, are subjected to different stress and strain conditions. The results show that for steel sheets the difference between measured and calculated results of the moment-curvature behaviour is small and the numerical results from the finite element models indicate that experimental results obtained from the test are acceptable in the range of the pure bending operation. Further for magnesium alloys, which exhibit unsymmetrical yielding, the algorithm of the yield function with a linear isotropic hardening model is implemented by programming a user subroutine in Abaqus for bending simulations of magnesium. The simulations using the proposed user subroutine extract better results than those using the von Mises yield function.<br /

A power-based approach to assess the barrelling test’s weak solution

Physical simulation of forming is an analytical-experimental branch of mechanical science. Carefully formulated models and their solutions are essential to interpret the simulation data meaningfully and to understand its underlying phenomena. Oversimplified models of deformation and their associated non-unique closed-form solutions are widespread due to the complex and path dependence nature of plastic deformation, its multi-layered governing equations and boundary conditions. Therefore, it is vital to critically evaluate these models at the kinematic level to ensure a reliable outcome

Experimental and numerical investigation of low pressure tube hydroforming on 409 stainless steel

Tube hydroforming has been widely used to produce automotive structural components due to the superior properties of the hydroformed parts in terms of their light weight and structural rigidity. Compared to the traditional manufacturing process for a closed-section member including stamping and followed by welding, tube-hydro forming leads to cost savings due to reduced tooling and material handling. However, the high pressure pumps and high tonnage press required in hydroforming, lead to increased capital investment reducing the cost benefits. This study explores low pressure tube hydro forming which reduces the internal fluid pressure and die closing force required to produce the hydroformed part. The experimental and numerical analysis was for low pressure hydro formed stainless steel tubes. Die filling conditions and thickness distributions are measured and critically analysed.<br /

Biomimetic porous titanium scaffolds for orthopaedic and dental applications

The development of artificial organs and implants for replacement of injured and diseased hard tissues such as bones, teeth and joints is highly desired in orthopedic surgery. Orthopedic prostheses have shown an enormous success in restoring the function and offering high quality of life to millions of individuals each year. Therefore, it is pertinent for an engineer to set out new approaches to restore the normal function of impaired hard tissues.Over the last few decades, a large number of metals and applied materials have been developed with significant improvement in various properties in a wide range of medical applications. However, the traditional metallic bone implants are dense and often suffer from the problems of adverse reaction, biomechanical mismatch and lack of adequate space for new bone tissue to grow into the implant. Scientific advancements have been made to fabricate porous scaffolds that mimic the architecture and mechanical properties of natural bone. The porous structure provides necessary framework for the bone cells to grow into the pores and integrate with host tissue, known as osteointegration. The appropriate mechanical properties, in particular, the low elastic modulus mimicking that of bone may minimize or eliminate the stress-shielding problem. Another important approach is to develop biocompatible and corrosion resistant metallic materials to diminish or avoid adverse body reaction. Although numerous types of materials can be involved in this fast developing field, some of them are more widely used in medical applications. Amongst them, titanium and some of its alloys provide many advantages such as excellent biocompatibility, high strength-to-weight ratio, lower elastic modulus, and superior corrosion resistance, required for dental and orthopedic implants. Alloying elements, i.e. Zr, Nb, Ta, Sn, Mo and Si, would lead to superior improvement in properties of titanium for biomedical applications.New processes have recently been developed to synthesize biomimetic porous titanium scaffolds for bone replacement through powder metallurgy. In particular, the space holder sintering method is capable of adjusting the pore shape, the porosity, and the pore size distribution, notably within the range of 200 to 500 m as required for osteoconductive applications. The present chapter provides a review on the characteristics of porous metal scaffolds used as bone replacement as well as fabrication processes of porous titanium (Ti) scaffolds through a space holder sintering method. Finally, surface modification of the resultant porous Ti scaffolds through a biomimetic chemical technique is reviewed, in order to ensure that the surfaces of the scaffolds fulfill the requirements for biomedical applications

Rooted Plantlet Production in a Vegetatively Reproductive Red Clover (\u3ci\u3eTrifolium pratense\u3c/i\u3e L.) cv. Astred

Vegetatively reproductive cultivars of red clover (Trifolium pratense L.) can produce clonal daughter plantlets under certain management and environmental conditions, which may improve sward persistency. Six trials involving spaced plants, pure swards or grazed mixed swards were conducted near Massey University, Palmerston North, New Zealand, from 1995 to 1998. Rooted plantlets counted in autumn of each year ranged from 5.8±1.6 to 43±5.1 rooted plantlets/parent plant for ungrazed spaced plants, and 0 to 1.8 rooted plantlets/parent plant for pure and mixed swards under grazing management. It is concluded that clonal, rooted plantlet production is highly variable in Astred depending on grazing management, environmental conditions and companion species, but offers a feasible replacement mechanism for maintaining red clover persistence in mixed and pure swards

Effects of Management Strategies on Seed Production and Seedling Recruitment in Birdsfoot Trefoil-White Clover Mixtures

The effects of grazing management on seed production, seed bank size and seedling emergence patterns of Trifolium repens cv. Zapicán (WC) and Lotus corniculatus cv. San Gabriel (BFT) oversown swards were evaluated. A complete randomized block design with 4 replicate blocks was used, in which 4 grazing strategies (grazing all year (SI), summer spelling for seed production (S2), winter rest plus summer spelling (S3) and autumn rest plus summer spelling (S4)), were combined with two defoliation severalties (4 and 10 cm height post-grazing residuals). Plots of 110 m2 were grazed monthly by sheep. Seed production, soil seed bank and seedling emergence were monitored from April 1998 to August 1999. In both species, summer spelling for seed production improved seed yield, especially in BFT. Severe defoliation (4 cm) reduced seed inputs drastically (46% in BFT and 64% in WC). 1000 seed weight was only affected by defoliation severity in WC (0.544 and 0.562 g for 4 and 10 cm height respectively). Potential seedling emergence, between June and December from soil seed bank, was 44 and 35% in BFT and WC, respectively. Seedling emergence of Lotus corniculatus increased under high seed production levels (S3), and also it was improved under intensive grazing during autumn and winter. There were no effects on Trifolium repens seedling emergence. Soil seed bank can preserve seedling recruitment rates in the short term, but maintenance of species balance will depend on seeding spelling management

Relationship between Canopy Closure and Pasture Production in Deciduous Tree Based Temperate Silvopastoral Systems

Experiments were carried out in New Zealand with 11 year-old alder (Alnus chordata) on lowland pasture, and with 30+ year-old poplar (Populus spp) on hill pasture. Alder tree shade decreased (P\u3c 0.001) tiller density and total herbage harvested, with the highest tiller density at the lowest shade level of 41% canopy closure (DifN 0.59). Net herbage accumulation (NHA) directly under a poplar canopy was 35% of the NHA of open pasture, but NHA in canopy gaps increased with gap size. These results suggested that keeping canopy closure percentage in the 40-50% range for a deciduous tree silvopastoral system, would maintain pasture production and tiller density at approximately two-thirds of that of unshaded pasture

Microstructure evolution modeling of square-diamond pass hot bar rolling of AISI 4135 steel

In this study, kinetics of the static (SRX) and metadynamic recrystallization (MDRX) of AISI4135 steel was investigated using hot torsion tests. Continuous torsion tests were carried out to determine the critical strain for dynamic recrystallization (DRX). The times for 50% recrystallization of SRX and MDRX were determined, respectively, by means of interrupted torsion tests. Furthermore, austenite grain size (AGS) evolution due to recrystallization (RX) was measured by optical microscopy. With the help of the evolution model established, the AGS for hot bar rolling of AISI4135 steel was predicted numerically. The predicted AGS values were compared with the results using the other model available in the literature and experimental results to verify its validity. Then, numerical predictions depending on various process parameters such as interpass time, temperature, and roll speed were made to investigate the effect of these parameters on AGS distributions for square-diamond pass rolling. Such numerical results were found to be beneficial in understanding the effect of processing conditions on the microstructure evolution better and control the rolling processes more accurately.<br /

Ti6Ta4Sn alloy and subsequent scaffolding for bone tissue engineering

Porous titanium (Ti) and titanium alloys are promising scaffold biomaterials for bone tissue engineering, because they have the potential to provide new bone tissue ingrowth abilities and low elastic modulus to match that ofnatural bone. In the present study, a new highly porous Ti6Ta4Sn alloy scaffold with the addition of biocompatible alloying elements (tantalum (Ta) and tin (Sn)) was prepared using a space-holder sintering method. Thestrength of the Ti6Ta4Sn scaffold with a porosity of 75% was found to be significantly higher than that of a pure Ti scaffold with the same porosity. The elastic modulus of the porous alloy can be customized to match that ofhuman bone by adjusting its porosity. In addition, the porous Ti6Ta4Sn alloy exhibited an interconnected porous structure, which enabled the ingrowth of new bone tissues. Cell culture results revealed that human SaOS2osteoblast-like cells grew and spread well on the surfaces of the solid alloy, and throughout the porous scaffold. The surface roughness of the alloy showed a significant effect on the cell behavior, and the optimum surfaceroughness range for the adhesion of the SaOS2 cell on the alloy was 0.15 to 0.35 mm. The present study illustrated the feasibility of using the porous Ti6Ta4Sn alloy scaffold as an orthopedic implant material with a specialemphasis on its excellent biomechanical properties and in vitro biocompatibility with a high preference by osteoblast-like cells.<br /