Evolution of properties of parts during MIM and sintering of recycled oxide particles

Metal injection moulding (MIM) is an established process for high volume production of complex shaped metallic parts using commercially available feedstocks. The characteristics of parts after moulding, debinding, and sintering cannot be simply predictable from raw materials because the properties get altered with the process parameters and the corresponding levels of porosity during processing steps. In this study, physical properties, microstructure, and mechanical properties of the MIM parts have been characterised to understand the evolution of strength during various steps in MIM processing. Feedstocks with different binder loading show a considerable difference in physical as well as mechanical characteristics. During sintering of parts which have solid loading of grinding sludge, simultaneous in situ reduction and densification takes place, whereas only densification occurs in carbonyl iron parts. It is, therefore, possible to make complex shaped parts of different levels of porosity from downgraded shop floor metallic waste.     

Reduction of residual stress in montmorillonite/epoxy compounds

An epoxy resin was cured while in intimate contact with small amounts of epoxyphilic montmorillonites. It was determined that cured epoxy exists within the montmorillonite interlayer by the observation of very high interlayer spacings, even greater than 8 nm, Generally, epoxy compounds containing montmorillonites that had been swollen in the curing agent prior to curing exhibited larger interlayer spacings, especially among the non-dispersed montmorillonite layers. The maximum observed residual stress was reduced by greater than 50% in the epoxyphilic montmorillonite/epoxy compounds over that of the pure epoxy. The epoxyphilic montmorillonite/epoxy compounds generally exhibited higher values of glass transition temperature, flexural modulus, and ultimate flexural strength than the pure epoxy. The tyramine-montmorillonite compounds typically had the highest values overall.     

Mechanistic analysis of fatigue crack initiation in medium-density polyethylene

Kinetics parameters of craze evolution preceding fatigue crack initiation (FCI) in mediumdensity polyethylene (MDPE) pipe materials were determined and analysed within fracture mechanics theory. A single craze initially preceded the notch tip, a root craze, which subsequently became accompanied by a few side crazes. Crack initiation transpired after the craze-zone growth had reached its fully developed configuration. The length of the root craze of the fully developed zone was found to be equal to the length of the first discontinuous crack band on the fracture surface. The growth of the root-craze length and the crack-tip opening displacement (CTOD) followed a power law over the major portion (94%) of the FCI time. Measurable rupture of the craze material was only noted within the final portion of the FCI time and was associated with exponential increase of the CTOD. The Dugdale/Barenblatt model overestimated the craze length by 30% and underestimated the CTOD by 50% which was hypothesized to be due to multiple crazing at the notch tip.     

The specific enthalpy of fracture for beta Ti-15-3 alloy

Fatigue crack propagation (FCP) experiments were conducted on beta Ti-15-3 alloy under various loading conditions to examine the constancy of the specific enthalpy for fracture, advanced by the Crack Layer (CL) theory as a material parameter characteristic of its intrinsic toughness. The energy release rate and the irreversible work were determined from load-displacement curves during crack propagation. Microscopic and diffraction analyses were conducted to identify the damage mechanisms ahead of the crack tip. A damage zone whose geometry exhibited plane strain character at the initial stage of crack propagation was observed optically. The damage zone transformed into plane stress configuration when the crack reached half its critical length. Damage mechanisms involved slip lines and microcracking which is believed to ensue from intense accumulation of slip processes. The magnitude of microcracking became more weighty as the crack moved deeper into plane stress dominance. The damage preceding crack advance was quantitatively assessed as the crack resistance moment which is the volume of transformed material per unit crack extension. Application of the CL theory to the data generated under a wide range of applied stress levels gave rise to a constant value of the specific enthalpy of fracture, 20 MJ/m³. This value is in close agreement with the specific energy of slip lines computed from microstructural considerations.     

Effect of residual stress on crack propagation in MDPE pipes

Crack propagation behaviour in single edge notched specimens prepared from medium-density polyethylene (MDPE) pipe is examined under creep condition. The crack grown from an exterior notch (inbound) initiated faster than that grown from an interior notch (outbound). Subsequently, the outbound crack propagated monotonically to ultimate failure. The inbound crack showed anomalous behaviour involving two arrest stages prior to ultimate failure. The pipe is found to possess substantial residual stresses. The energy release rate for each case was calculated taking into account the respective residual stream distribution. The fact that the rates of crack propagation are not a unique function of the energy release rate indicates that the fracture is also influenced by morphological gradients imposed by processing conditions.     

Design of a grid service-based platform for in silico protein-ligand screenings

Grid computing offers the powerful alternative of sharing resources on a worldwide scale, across different institutions to run computationally intensive, scientific applications without the need for a centralized supercomputer. Much effort has been put into development of software that deploys legacy applications on a grid-based infrastructure and efficiently uses available resources. One field that can benefit greatly from the use of grid resources is that of drug discovery since molecular docking simulations are an integral part of the discovery process. In this paper, we present a scalable, reusable platform to choreograph large virtual screening experiments over a computational grid using the molecular docking simulation software DOCK. Software components are applied on multiple levels to create automated workflows consisting of input data delivery, job scheduling, status query, and collection of output to be displayed in a manageable fashion for further analysis. This was achieved using Opal OP to wrap the DOCK application as a grid service and PERL for data manipulation purposes, alleviating the requirement for extensive knowledge of grid infrastructure. With the platform in place, a screening of the ZINC 2,066,906 compound "drug-like" subset database against an enzyme's catalytic site was successfully performed using the MPI version of DOCK 5.4 on the PRAGMA grid testbed. The screening required 11.56 days laboratory time and utilized 200 processors over 7 clusters.     

Automated process planning method to machine A B-Spline free-form feature on a mill–turn center

In this paper, we present a methodology for automating the process planning and NC code generation for a widely encountered class of free-form features that can be machined on a 3-axis mill–turn center. The free-form feature family that is considered is that of extruded protrusions whose cross-section is a closed, periodic B-Spline curve. In this methodology, for machining a part with B-Spline protrusion located at the free end, the part is first rough turned to the maximum profile diameter of the B-Spline, followed by rough profile cutting and finish profiling with axially mounted end mill tools. The identification and sequencing of machining volumes is completely automated, as is the generation of actual NC code. The approach supports both convex and non-convex profiles. In the case of non-convex profiles, the process planning algorithm ensures that there is no gouging of the work piece by the tool. The algorithm also identifies when sections of the tool path lie outside the work piece and utilizes rapid traverses in these regions to reduce cutting time. This methodology presents an integrated turn–mill process planning where by making the process fully automated from design with no user intervention making the overall process planning efficient. The algorithm was tested on several examples and test parts using the unmodified NC code obtained from the implementation were run on a Moriseiki mill–turn center. The parts that were produced met the dimensional specifications of the desired part.     

Sound isolation by piezoelectric polymer films connected to negative capacitance circuits

Sound isolation has been achieved using a piezoelectric polymer film connected to a negative capacitance feedback circuit. A curved PVDF film was located in the middle of an acoustic tube and the transmission loss of sound through the film was determined in the audio frequency range. At any chosen frequency, the complete isolation of sound was achieved by adjusting the feedback, i.e. the complex capacitance of the circuit was matched precisely to that of the film.     

Nonlinear<Emphasis Type="Italic">I-V</Emphasis> characteristics study of doped SnO<Subscript>2</Subscript>

When tin oxide is doped with Sb₂O₃ and CoO, it shows highly nonlinear current (I)-voltage (V) characteristics. Addition of CoO leads to creation of oxygen vacancies and helps in sintering of SnO₂. Antimony oxide acts as a donor and increases the conductivity. The results are nearly the same when antimony oxide is replaced by tantalum oxide. The observed nonlinear coefficient, α = 30 and the breakdown voltage is 120 V/mm.