Determination of forces in high speed blanking using FEM and experiments

The increasing demand for micro-formed and stamped parts such as connectors in the electronic industry is forcing manufacturers to push the speed limit of conventional press technologies to improve throughput. Designing dies/tooling for higher speeds and obtaining extended tool life requires a thorough understanding of the process. This paper discusses an experimental study of the interaction between punch, stripper plate and sheet material at various blanking velocities up to 1600 mm/s. The effect of velocity on punching force is also studied. A methodology to obtain high strain and strain rate dependent material flow stress data using blanking test and finite element modelling is presented.     

A review of the tensile and fatigue responses of cellulosic fibre-reinforced polymer composites

ABSTRACT

The use of polymer-based composites has been gaining popularity in the industry over the last few decades. Their high strength to weight ratio and high fatigue resistance make these composites the preferred materials for a wide variety of applications. The current trend has inclined towards hybrid fibre reinforced composites owing to their outstanding characteristics compared to non-hybrid composites. Numerous research works have been conducted to study the fatigue life behaviour of such composite materials. This study addressed the monotonic and dynamic performance of non-hybrid and hybrid natural fibre based composite materials, and the factors that influence their fatigue performance, along with the stiffness decay of each composite material. Most studies have shown the superior potential of using natural fibres in place of synthetic fibres in those critical applications that involve tensile and cyclic loading.     

Control-Based Adaptive Middleware for Real-Time Image Transmission over Bandwidth-Constrained Networks

Real-time image transmission is crucial to an emerging class of distributed embedded systems operating in open network environments. Examples include avionics mission replanning over Link-16, security systems based on wireless camera networks, and online collaboration using camera phones. Meeting image transmission deadlines is a key challenge in such systems due to unpredictable network conditions. In this paper, we present CAMRIT, a Control-based Adaptive Middleware framework for Real-time Image Transmission in distributed real-time embedded systems. CAMRIT features a distributed feedback control loop that meets image transmission deadlines by dynamically adjusting the quality of image tiles. We derive an analytic model that captures the dynamics of a distributed middleware architecture. A control-theoretic methodology is applied to systematically design a control algorithm with analytic assurance of system stability and performance, despite uncertainties in network bandwidth. Experimental results demonstrate that CAMRIT can provide robust real-time guarantees for a representative application scenario.     

Biaxial load effects on the crack border elastic strain energy and strain energy rate

In a previous paper it was shown that the singular expressions for the elastic stress and displacements in the border region of a line crack are inadequate, generally speaking. This is nowhere more clearly demonstrated than for the case of the infinite sheet with a flat central crack, biaxially loaded along its outer boundaries. For this particular problem, the entire effect of the load applied parallel to the plane of the crack shows up in the generally discarded second (non-singular) terms of the series representations for the stresses and displacements. Omission of these contributions is, in effect, equivalent to denying the presence of the boundary load applied parallel to the crack and, consequently, leads to prediction of results at variance with experimental data.

In this paper we continue with further discussion of the same problem, focusing attention on the fact that the local elastic strain energy density and strain energy rate depend significantly on the biaxiality of the applied load.     

Crack border stress and displacement equations revisited

It is more or less accepted in fracture mechanics that the elastic stress and displacements very near to the tip of a plane line crack can be approximated with sufficient accuracy, for all geometries and outer boundary loading conditions, by. a one-parameter representation, i.e. strictly in terms of the stress intensity factors K_I and/or K_II. It is shown here that this presumption which appears to be reasonable on face value, quantitatively speaking, is nevertheless unacceptable as a general proposition. The reason lies with the quite arbitrary practice of omitting the second term of the series representation for the stresses, a contribution which is independent of distance from the crack tip. It is not difficult to show by way of specific examples how such omission can lead to error of serious qualitative nature in the prediction of stress and displacement related quantities of interest.     

Effect of Interlayer Thickness of Ion-Plated Pb-Coating on Its Life (SUS440C Substrates)

High-precision ball bearings (SUS440C) used in spacecraft mechanisms that are exposed to deep space vacuum are solid lubricated by thin, adherent Pb ion-plated coatings. The high reliability requirements with long endurance life of these mechanisms solely depend on the tribological aspects of this solid-lubrication coating. Since ion-plated, soft metallic coatings have a graded coating–substrate interface structure, a gradual change in mechanical, chemical and thermal properties is expected across the depth of the coating. This aspect of the interlayer plays a major role in determining the extent of optimum tribological properties of the coating. By improving the interlayer, both in terms of increased thickness and concentration of Pb, a corresponding improvement in the lubricity and endurance life of this Pb ion-plated coating on AISI 440C stainless steel (bearing material) can be assured. For this, a detailed examination of the interlayer of the ion-plated Pb film on the nano-micro level is mandatory. This report is focused on the cross-sectional examination of the interlayer by scanning electron microscopy. SUS440C steel disk specimens having similar properties as the bearing material and with a thin, ion-plated Pb coating processed under two different substrate bias conditions of ion-plating are used. The thickness of the Pb/steel interlayer and the elemental composition are analyzed using SEM and EDS respectively. The endurance life of the coatings is measured by repeated sliding wear tests with a pin-on-disk tester in vacuum. It is confirmed that with an increased thickness of the graded interfacial layer of the Pb ion-plated coating, the coating endurance life is extended remarkably.     

Determination of tensile,flexural properties and microstructural characterization of calcium carbonate filler reinforced polypropylene matrix composites

Calcium carbonate is one of the commonly used inorganic filler reinforcements in polypropylene matrix. In this research work, granules of chicken egg shell containing natural organic calcium carbonate resource has been introduced to reinforce in the polypropylene base material. The aim of this experimental study is to determine the tensile, flexural properties and to characterize the microstructures of granular chicken shell containing natural calcium carbonate reinforced in polypropylene. Chicken egg shells are crushed and sieved and granules of size 160μm are selected for reinforcement in the polypropylene matrix. The granules are then mixed with polypropylene base material with silane as a coupling agent proportionally in order to obtain four different proportions 10%, 20%, 30% and 40% on weight fraction basis with the aid of an extrusion machine. Experimental result have shown improvements in Tensile Modulus and Flexural Modulus of this newly processed natural organic calcium carbonate filler reinforced polypropylene composites, although it has not improved the tensile strength, flexural Strength and strain to fracture. The weight fraction ratio of the filler reinforced in the matrix which gave the highest tensile and flexural modulus is 20% and 10%, respectively.     

Experimental Evaluation of Friction and Wear Properties of Solid Lubricant Coatings on SUS440C Steel in Liquid Nitrogen

The friction and wear properties of the prevailing different solid lubricant coatings (Ion-plated Au, Ion-plated Ag and RF-sputtered PTFE on SUS440C stainless steel) used in the bearings of high-speed cryogenic-turbo-pumps of liquid rocket engines were experimentally evaluated in liquid nitrogen immersed conditions. Also the above experiments were carried out with two newly proposed solid lubricant coatings of sputter-ion-plated MoSTi and a new ion-plated Pb on SUS440C stainless steel. The friction coefficient and wear rates of the coatings of ion-plated Au, ion-plated Ag, RF-sputtered PTFE, the new ion-plated Pb and MoS₂Ti-SIP (with coating thickness of 0.7±0.1 μm) on SUS440C steel against SUS440C stainless steel ball in liquid nitrogen were compared. Worn surfaces were examined microscopically with a microscope and a profilometer for understanding the mechanisms of friction and wear and transfer film lubrication in liquid nitrogen. It is found that the newly proposed solid lubricant coatings are showing promising results for their use in liquid nitrogen immersed conditions. The sputter-ion-plated MoSTi coating on SUS 440C steel shows a minimum value of friction coefficient (μ=0.015) and wear rate (w_c=0.56 × 10⁻⁶ mm³/N m ) in liquid nitrogen.     

An analytical and experimental study of the plate tearing mode of fracture

Certain analytical and experimental aspects of the fracture of cracked thin plates subjected to pure twisting moments are examined. A simplified analytical and finite element approach to evaluate plate tearing mode stress intensity factors is proposed. A photoelastic study was also performed to observe the crack-tip fringe patterns and evaluate the plate tearing mode stress intensity factors. Although the observed fringe patterns differed considerably from the predictions obtained using Williams' analysis, they were much closer to the predictions obtained using Reissner's bending theory and the approach proposed in this paper. The finite-element study using the proposed method as well as the Kirchoff bending theory showed that the stress intensity factors obtained using the proposed method agree more closely with the photoelastic results.