Assessment of debonding in GFRP joints using damage identification techniques

Pultruded sections are used in many different civil engineering applications involving FRP composites, including a number of footbridges. These sections are typically joined through adhesive bonding and/or mechanical interlock. The joint is clearly critical to load transfer and the avoidance of unintended failure modes. As a contribution towards studying damage identification and assessment in FRP joints, this paper examines the dynamic performance of bonded GFRP pultruded sections. Experimental testing and FE modelling were employed to model damage in the joints and to assess whether debonding can be detected through differences in the dynamic characteristics – namely frequencies and mode shapes – of the components. Debonding in the joints was simulated by progressively reducing their bonded area. Four damage identification techniques (based on modal curvature, flexibility, damage index and the curvature of the flexibility-based uniform load surface) were used to assess damage. The results show that significant damage has to be present before debonding can be identified through changes in resonant frequencies and mode shapes. Once such levels are present, damage identification techniques can be applied effectively to locate damage. It is concluded that vibration-based damage assessment methods should be used in conjunction with other non-destructive evaluation techniques.     

Sensitivity analysis of a small‐volume objective heat stability evaluation test for recombined concentrated milk

To quantify the stability towards heat coagulation, an objective test method was developed. The combined use of emulsion preparation by microfluidisation and heat stress by immersion of capped samples in an oil bath enabled small‐volume heat stability evaluation of milk formulations. From experimental data, it became obvious that a heating period of about 9 min was necessary for the samples to acquire the requested temperature (i.e. 121 °C). Similarly, both viscosity and particle size analyses showed an increased aggregation tendency when samples were heated for longer than 10 min, whereby their positioning and the cooling medium seemed to have an insignificant effect.     

The effect of construction pattern and unit interlock on the structural behaviour of block pavements

The maintenance or even replacement of cracked pavements requires considerable financial resources and puts a large burden on the budgets of local councils. In addition to these costs, local councils also face liability claims arising from uneven or cracked pedestrian pavements. These currently cost the Manchester City Council and Preston City Council around £6 million a year each. Design procedures are empirical. A better understanding of the interaction between paving blocks, bedding sand and subbase was necessary in order to determine the mode of failure of pavements under load. Increasing applied stress was found to mobilise “rotational interlock”, providing increased pavement stiffness and thus increased load dissipation resulting in lower transmitted stress on the subgrade. The indications from the literature review were that pavements are designed to fail by excessive deformation and that paving blocks remained uncracked at failure. This was confirmed with experimental data which was obtained from tests on segments of pavements that were laid/constructed in a purpose built test frame in the laboratory.     

Critical insulation thickness of a rectangular slab embedded with a periodic array of isothermal strips

We address the problem of two-dimensional heat conduction in a solid slab embedded with a periodic array of isothermal strips. The surfaces of the slab are subjected to a convective heat transfer boundary condition with a uniform heat transfer coefficient. Similar to the concept of critical insulation radius, associated with cylindrical and spherical configurations, we show that there exists a critical insulation thickness, associated with the slab, such that the total thermal resistance attains a minimum, i.e. a maximum heat transfer rate can be achieved. This result, which is not observed in one-dimensional heat conduction in a plane wall, is a consequence of the non-trivial coupling between conduction and convection that results in a 2D temperature distribution in the slab, and a non-uniform temperature on the surface of the slab. The findings of this work offer opportunities for improving the design of a broad range of engineering processes and products.     

Slide attacks and LC-weak keys in T-310

T-310 is an important Cold War cipher (Cryptologia 2006). In a recent article (Cryptologia 2018), researchers show that, in spite of specifying numerous very technical requirements, the designers do not protect the cipher against linear cryptanalysis and some 3% of the keys are very weak. However, such a weakness does not necessarily allow breaking the cipher because it is extremely complex and extremely few bits from the internal state are used for the actual encryption. In this article, we finally show a method that allows recovering a part of the secret key for about half of such weak keys in a quasi-realistic setting. For this purpose, we revisit another recent article from Cryptologia from 2018 and introduce a new peculiar variant of the decryption oracle slide attack with d?=?0.     

Shape factor and shape optimization for a periodic array of isothermal pipes

We address the problem of two-dimensional heat conduction in a solid slab embedded with a periodic array of isothermal pipes of general cross-section. The objective of this work is two-fold: to develop a numerical procedure through which we can obtain the shape factor associated with a given configuration and, to develop a numerical shape optimization algorithm through which we can compute shapes that extremize the transport rate. The shape factor is obtained by first transforming the periodic array of pipes into a periodic array of strips using the generalized Schwarz–Christoffel transformation and, subsequently, by developing an integral equation of the first kind for the temperature gradient using the boundary element method. The integral equation is solved both numerically and analytically/asymptotically with excellent agreement between the results. The shape optimization problems, which are formulated with respect to the parameters of the generalized Schwarz–Christoffel transformation, are solved numerically to compute the shape that maximizes the cross-sectional area and the shape that minimizes the perimeter of the cross-section, given the shape factor and the distance between two consecutive pipes. It is inferred that the problems are adjoint to the transport rate minimization and transport rate maximization problems, respectively. The optimal shapes are computed numerically and validated with available analytical and numerical results for a single pipe. Furthermore, motivated by the analytical result, we propose a parametric set of equations that describe well the optimal shapes. The versatility of the Laplace equation suggests that similar formulations have applications in continuum mechanics, electricity, hydraulics and drug reduction.     

Computation of metastable phases in tungsten-carbon system

Metastable phase equilibria in the W-C system are presented in the vicinity of the metastable reactions involving W₂C, WC_1−x , and WC. Metastable phase boundaries were obtained by reproducing the stable boundaries using optimized Gibbs energy formulations and extrapolating them into regions of metastability. Four metastable reactions were obtained: a metastable congruent melting reaction of WC at 3106 K, a metastable eutectic reaction between WC_1−x and graphite at 2995 K, a metastable eutectic reaction between W₂C and WC at 2976 K, and a metastable eutectic reaction between W₂C and graphite at 2925 K. The reaction enthalpies and entropies associated with these transitions are also computed using the available Gibbs energy data. Furthermore, possible kinetic paths that could lead to metastability are discussed.     

Desktop video conferencing in the organisation

While the potential advantages of video conferencing are appealing, the technology has not been implemented in more than a handful of organisations. This is likely to change in the future as video conferencing moves to the desktop. This paper examines the issues surrounding the area and, in particular, attempts to determine the impact of video conferencing on organisations. A framework is provided for understanding desktop video conferencing in the organisational context, and the relative benefits of and problems in the use of desktop video conferencing are discussed. Finally, a number of suggestions are made on how organisations may reconcile the implications of utilising desktop video conferencing technology.     

Threshold counters with increments and decrements

A threshold counter is a shared data structure that assumes integer values. It provides two operations: changes the current counter value from v to v+1, while returns the value v/w, where v is the current counter value and w is a fixed constant. Thus, the operation returns the “approximate” value of the counter to within the constant w. Threshold counters have many potential uses, including software barrier synchronization. Threshold networks are a class of distributed data structures that can be used to construct highly-concurrent, low-contention implementations of shared threshold counters. In this paper, we give the first proof that any threshold network construction of a threshold counter can be extended to support a operation that changes the counter value from v to v−1.     

Distributed parameter thermal controllability: a numerical method for solving the inverse heat conduction problem

This paper addresses the inverse heat conduction problem encountered in thermal manufacturing processes. A numerical control algorithm is developed for distributed parameter conduction systems, based on Galerkin optimization of an energy index employing Green's functions. Various temperature profiles of variable complexity are studied, using the proposed technique, in order to determine the surface heat input distribution necessary to generate the desired temperature field inside a solid body. Furthermore, the effect of altering the iterative time step and duration of processing time, on the convergence of the solution generated by the aforementioned method is investigated. It is proved that despite the variations in numerical processing, the iterative technique is able to solve the problem of inverse heat conduction in the thermal processing of materials. Copyright © 2004 John Wiley & Sons, Ltd.