Geometry of “developable cones”

When a thin disc is supported on the rim of a bowl, and its centre is pushed down by a finger, it adopts a characteristic conformation, known as a “developable cone”, and sketched in Fig. 1(a): the main, broadly conical, shape can only form if about one-quarter of the disc buckles upwards. There is a curved intersection between the two parts, which takes the form of a crescent-shaped “crease” near its apex, but with the flanking regions less tightly deformed. The “developable cone” is a recurring motif in a wide range of physical situations—crumpling, buckling, draping—and its mechanics provides a key to understand the phenomena, whether the disc deforms in the elastic or the plastic range. The task of this paper is to study only geometrical features of the “developable cone”. The first step is to replace the actual crease (Fig. 1(a)) by an idealised “sharp” crease (Fig. 1(b)). The second step is to study the apparently “large-rotation” problem of kinematics by means of an adaptation of the classical “yield-line” pattern of folding, but with a crucial added constraint that springs from Gauss's analysis of inextensional deformation. We illustrate the method via a graded sequence of examples, and we close with a discussion.     

Making the practically impossible “Merely difficult”—Cryogenic FIB lift‐out for “Damage free” soft matter imaging

The preparation of thinned lamellae from bulk samples for transmission electron microscopy (TEM) analysis has been possible in the focussed ion beam scanning electron microscope (FIB‐SEM) for over 20 years via the in situ lift‐out method. Lift‐out offers a fast and site specific preparation method for TEM analysis, typically in the field of materials science. More recently it has been applied to a low‐water content biological sample (Rubino 2012). This work presents the successful lift‐out of high‐water content lamellae, under cryogenic conditions (cryo‐FIB lift‐out) and using a nanomanipulator retaining its full range of motion, which are advances on the work previously done by Rubino (2012). Strategies are explored for maintaining cryogenic conditions, grid attachment using cryo‐condensation of water and protection of the lamella when transferring to the TEM. Microsc. Res. Tech. 79:298–303, 2016. © 2016 Wiley Periodicals, Inc.     

Elastic contact with a “donut”-shaped asperity

The laser-textured surfaces used for the touchdown area of computer hard-disks are sometimes covered with asperities consisting of a crater surrounded by a raised rim; contact with the read-head takes place over the rim of the crater, colloquially referred to as a “donut”. In order to analyse the load/compliance relation or the stiction to be expected in contact of hard disks, a number of authors have proposed load/compliance relations for contact between such a single doughnut and a plane, usually as simple modifications of the Hertz line contact equations. In this note simple, asymptotically correct, relations for a ring asperity are derived and verified by direct solutions. In particular, the relation between elastic deflection and load is approximately δ=(W/π²RE^*)[ln(16R/b)+0.5)].     

The “SOMSEM”—An SEM-based scanning optical microscope

No one form of microscopy is ideal for all applications and, in general, significant advances are made by correlating several techniques. In this paper, a scanning optical microscope is discussed which is based on the SEM and is entirely compatible with it. This new hybrid instrument, known as the SOMSEM, has been demonstrated using a converted SEM specimen stage and a standard Cambridge Stereoscan 250 Mk II microscope. The operating principles have been verified, and silicon MOS (metal oxide semiconductor) devices have been successfully imaged using the OBIC (optical beam induced current) mode thus avoiding electron beam damage. Potential applications and future developments are briefly discussed.     

The “primary integrity parameters” — Design parameters for safety systems

This paper discusses the Primary Integrity Parameters (PIPs) - design attributes that, as a group, determine the level of safety integrity achieved by a Programmable Electronic System (PES). These parameters include redundancy level, failure rates and modes, diagnostic coverage factor, common cause failure rates, on-line manual test interval/duration, maintainability and security. The paper demonstrates that the level of safety provided by a PES is not simply a factor of any one of these attributes, but is determined by the total combination of the PIPs. Examples are given to show the dependency of the system safety on each of the parameters.     

High availability systems for safety and performance—the “coverage” factor

High Availability Systems are needed in many applications not only for safety purposes but also good economic performance. “Coverage” is a measure of how well the automated testing in such systems detects failures. The coverage factor is considered by many to be the most important measure of availability in fault tolerant architectures. The control system designer can create better logic control systems by understanding the “hows” and “whys” of coverage.     

Kinematic hardening analysis of ratchet strain in the “pulley test”

The classical Bree problem—which represents an uniaxial model of a thin tube subjected to combined internal pressure and cyclic thermal stress across its wall—can be simulated by means of the pulley test in which a wire or strip specimen is subjected to combined steady tensile stress and cyclic bending stress. In this paper, accumulation of ratchet strain in the pulley test is investigated using a linear kinematic hardening material model from which perfect plasticity can be generated as a special case. The results of the investigation show that asymptotic ratchet strains are linearly related to the excess in mean stress σ_D above its value σ*_D at the ratchetting limit regardless of the thermal stress amplitude. Comparisons with test results on copper wire specimens—which exhibit non-linear hardening rate—confirm the qualitative validity of this simple relation. Deviations between theory and experiment are attributed to metallic cyclic creep. Further, perfect plasticity results are shown to be well predicted by a linearized lower bound estimate.     

Identification of flexible characteristics of a mechanical system based on “passive” experimentation

The paper presents a method of identifying the flexible non-linear characteristics of a mechanical system. For this purpose we used the Fokker-Planck equation and on this basis the criterion function has been built.The proposed method does not impose any restrictions on the character of non-linearities or the dimension of the system.The present method determines the non-linear characteristics of elasticity and damping of the objects while in use.The results obtained from identification of the non-linear dissipative force that is caused by the dry friction of a mechanical system such as a freight car are presented here as a computational example. The results, which are based on the passive experiment results, confirm the efficiency of the method.     

Comparative authentication of three “snow lotus” herbs by macroscopic and microscopic features

“Snow lotus” is a famous Chinese Materia Medica derived from species of the genus Saussurea (Compositae). To differentiate three representative easily‐confused snow lotus herbs, namely, Saussurea involucrata (Kar. et Kir.) Sch.‐Bip, Saussurea laniceps Hand.‐Mazz., and Saussurea medusa Maxim., macroscopic features of the three herbs were systemically observed, and microscopic features were compared by using ordinary light microscopy, polarized light microscopy and scanning electron microscopy (SEM). The results indicate that, as for macroscopic identification, capitula situation and arrangement, and as for microscopic identification, pollen grains, nonglandular hairs, glandular hairs, and cells of inner surface of the microdiodange can be used to authenticate the three snow lotus herbs. Comprehensive table comparing the characteristics were presented in this study. SEM has been found to provide a number of unique characteristics of pollen grains. Based on the observation of pollen grains, evolution sequence of the three species was speculated. The present method was proven to be efficient, convenient, simple, and reliable, which was successfully applied to the authentication of three snow lotus herbs. Microsc. Res. Tech.1 77:631–641, 2014. © 2014 Wiley Periodicals, Inc.     

“EDGE TOUGHNESS” AND MATERIAL PROPERTIES RELATED TO THE MACHINING OF DENTAL CERAMICS

Seven dental ceramic compositions, including zirconia, glass-infused alumina, polycrystalline alumina, porcelain and three different machinable glass ceramics (MGC's) were tested for edge flaking. The chosen load range encompassed the forces typically associated with machining operations for these materials. The results were examined with regard to material properties and the applicability of a parameter defined as “edge toughness” to machin-ability. It was determined that a non-linear low-load chipping relationship may be more relevant to machinability than the “edge toughness” parameter calculated from the high-load linear region.     

Temperature distribution over contact area and “hot spots” in rubbing solid contact

Experiments intended to understand thermal phenomena in a sliding contact were performed and their results are presented. Asperities in contact were found to undergo the pulse effect of the temperature approaching the melting point of one of the friction members. It was noted that the temperature higher than the melting point can be generated in the sapphire–aluminium and sapphire–polyethylene pairs. Temperature distributions over both the contact area and the local heat source are considered.