Similitude of sandwich panels with a ‘soft’ core in buckling

The paper presents the similarity analysis of a sandwich unidirectional panel with a transversely flexible core under buckling loads. The governing equations are those used in the high-order analysis of sandwich panels with a ‘soft’ core. The study derives the similitude conditions in the case of external in-plane compressive loads that yield buckling of the panel with and without imperfections. In the first part, the buckling analysis is presented and it is based on the linearized version of the governing equations of the non-linear geometrical bending equations. The presentation includes an analytical proof of the applicability of similarity for the buckling of a sandwich panel with identical faces and a numerical demonstration of the response when full similarity and partial similarity exist. The effects of full and partial similarity are presented for a panel with imperfections.     

Modifications to the ‘directional simulation in the load space’ approach to structural reliability analysis

‘Directional simulation in the load space (DS-LS)’ is a simulation-based technique used to perform reliability analysis of structures subjected to time-invariant or time-variant random loads. To perform DS-LS a location must first be chosen for an ‘origin of simulation’. The origin may be positioned in either the safe or failure region of the load space, and its precise location (with respect to these regions) influences the DS-LS formulation needed to evaluate reliability correctly. The current formulation requires the origin to be positioned in the safe region. However, even for simple structures, the ‘exact’ location of the safe and failure region is not always known explicitly ‘a priori’. Modifications to allow for the possibility of positioning the origin not only in the ‘safe’ region but in the ‘failure’ region are proposed in this paper. Some numerical examples involving one or more stationary continuous Gaussian loads and the simulation of directions by ‘Monte Carlo’ and ‘the hyperspace division method’ are presented to demonstrate the validity of the proposed formulations. Some comments on convergence are made.     

‘Expert information’ versus ‘expert opinions’. Another approach to the problem of eliciting/ combining/using expert knowledge in PRA

In the traditional approach to eliciting expert knowledge for use in risk assessment and decision analysis, the expert is asked for his opinion about, say, the numerical value of some unknown parameter λ. This opinion is then expressed as a point estimate, λ_i, or a probabilistic estimate, P_i(λ). Much attention and debate is then given, in the traditional approach, to methods of weighing and combining the opinions from the individual experts.The present paper advocates another approach in which we ask each expert, instead, for his body of evidence, E_i, relevant to the value of λ. In this way, the approach first arrives at a consensual body of evidence, E − {E_i}, and second, at a consensual curve p(λ|E) that expresses our knowledge about λ based on that body of evidence.The essential difference between this ‘expert information’ approach and the traditional ‘expert opinion’ approaches may be captured in the slogan: lsWeigh evidence, not experts!’     

A simple approximate expression for finite life fatigue behaviour in the presence of ‘crack‐like’ or ‘blunt’ notches

In this note, we explore the possibility of simple extensions of the heuristic El Haddad formula for finite life, as an approximate expression valid for crack‐like notches, and of the ‘Luká? and Klesnil’ equation for blunt notches. The key starting point is to assume, in analogy to the Basquin power‐law SN curve for the fatigue life of the uncracked (plain) specimen, a power law for the ‘finite life’intrinsic El Haddad crack size. The approach has similarities with what recently proposed by Susmel and Taylor as a Critical Distance Method for Medium‐Cycle Fatigue regime. Reasonable agreement is found with the fatigue data of Susmel and Taylor for notches, and in particular the error seems smaller in finite life than for infinite life, where these equations are already used. In these respects, the present proposal can be considered as a simple empirical unified approach for rapid assessment of the notch effect under finite life.     

A proposal to establish ‘packaging science’

To make packaging truly beneficial to human beings, it is important to help people learn more about the great variety of packaging materials and packaging techniques. In applying that knowledge, certain ethics should be observed by those engaged in packaging activities. The first step in achieving this task is to recognize what constitutes the packaging sciences, and from the results of various investigations a system of packaging sciences has been produced. Packaging science, as we have organized it, consists of the three major fields of packaging sociology, packaging materials science and packaging technology. With regard to the ethics that should form the backbone for the varied packaging activities, we propose that a Packaging Charter be established, incorporating the basic spirit and the ideas outlined herein.     

Complicating the ‘logic of design’

A ‘logic of design’ was outlined by March in 1976. Since then it has gained wide acceptance among designers and recently has been used in several knowledge-based systems of design. This paper makes a suggestion for extending the model by taking into consideration the logical nature of the laws in the argument form. This focus on the logical nature of laws brings out interesting and subtle differences in the inference process which are lost in the current analysis. It also results in some interesting complications. It means that it is no longer adequate to talk of the three phases of design — performance prediction, knowledge acquisition, and design generation — in the simple categories of deduction, induction and abduction, respectively. In particular, it means that performance prediction is not necessarily (or even usually) a deductive inference.     

Accelerated ‘relaxation’ or direct solution? Future prospects for fem

‘Dynamic’ or ‘viscous’ relaxation procedures have not gained much popularity in finite element analysis in which the direct (Gaussian elimination) solution dominates. Reasons for this are various—the most important being the rather slow convergence generally achieved for such procedures. However, it is possible to accelerate this quite dramatically and a method of doing so is shown in this paper. With the use of such acceleration and the inherent advantages of greatly reduced storage requirements and simplicity of programming, relaxation procedures promise an exciting possibility for the solution of large two- and three-dimensional problems in both linear and nonlinear ranges.     

Continuous Taguchi—a model-based approach to Taguchi's ‘quality by design’ with arbitrary distributions

Statistical experimental design has been used in ‘off-line’ quality control to determine the optimal settings for a system even when the mathematical model is known. Taguchi demonstrated how signal-to-noise ratios could be used to improve the performance of a system through variance minimization. However, these statistical methods often do not use the full distribution information that may be available. Proposed in this paper is an extension and complement to Taguchi's use of experimental design and signal-to-noise ratios for known system models. The use of a probability transformation method with the mathematical system model will allow designers to perform parameter and tolerance design simultaneously using a method of ‘fast integration’. The result is a new method in the field of ‘quality by design’, which we call continuous Taguchi, that can handle both linear and non-linear systems, with components of any distribution type, with or without correlation of the variables. In addition, an interpretation of Taguchi's classification of factors is given in the context of our full distribution method. © 1998 John Wiley & Sons, Ltd.     

A shell problem ‘highly sensitive’ to thickness changes

In general, shell structural problems can be identified to fall into one of the categories of membrane‐dominated, bending‐dominated and mixed shell problems. The asymptotic behaviour with a well‐defined load‐scaling factor shows distinctly into which category a given shell problem falls. The objective of this paper is to present a shell problem and its solution for which there is no convergence to a well‐defined load‐scaling factor as the thickness of the shell decreases. Such shells are unduly sensitive in their behaviour because the ratio of membrane to bending energy stored changes significantly and indeed can fluctuate with changes in shell thickness. We briefly review the different asymptotic behaviours that shell problems can display, and then present the specific problem considered and its numerical solution using finite element analysis. Copyright © 2003 John Wiley & Sons, Ltd.     

‘Flaw matrix’ and its application to some ceramics

An improved method for the prediction of fatigue life and/or failure strength of ceramics is proposed, which is especially useful for ceramics whose failure strength does not follow Weibull statistics and for the prediction of failures with a low probability. It was shown that various types of failure data such as fatigue life, failure strength and short time failure strength are all useful for the prediction of failures. Experimental verification of the method is given for various types of ceramics and stressing processes.     

‘Violation’—does HRA need the concept?

Violations are part of a complex matrix of judgmental behavior. The term violation is an indicator of the possibility of recent judgment errors but more so of latent errors in management and/or design. The effect of investigations in this arena do indicate a need for an extension of the classic slip/mistake taxonomy of human reliability analysis. The note attempts to initiate this extension.