Shear resistance of longitudinally stiffened panels — Part 2: Numerical parametric study

This paper presents the FE analysis of the influence of different parameters on the shear resistance of panels with different arrangements of longitudinal stiffeners. The studied parameters were the stiffener bending stiffness, the panel aspect ratio, the stiffener position, the web slenderness and the flange rigidity. Longitudinal stiffeners of trapezoidal shape were compared to open T-stiffeners. The former proved to be more efficient, since a larger panel resistance is achieved, for which in addition a smaller stiffness of trapezoidal stiffeners is needed. Different features of the new Eurocode rules were verified against the FEA results as well. Three different procedures for the determination of panel slenderness were tested and the reduction of stiffener bending stiffness, prescribed due to a better correlation with tests on open stiffeners, was verified for both closed and open stiffeners. The influence of bending moment was also considered and the verification of shear and bending interaction was discussed. Finally, the flange contribution to shear resistance was critically analysed.     

Fatigue performance characterisation of resistance-welded thermoplastic composites

This study investigates the fatigue performance of resistance-welded thermoplastic composites. Lap shear specimens consisting of unidirectional carbon fibre/poly-ether-imide (CF/PEI), unidirectional carbon fibre/poly-ether-ketone-ketone (CF/PEKK) and 8-harness satin weave fabric glass fibre/poly-ether-imide (GF/PEI) composites were resistance-welded using a metal mesh heating element. The specimens were fatigue-tested at various percentages of their static lap shear strengths at a load ratio R = 0.1 and frequency f = 5 Hz. The fatigue performances of resistance-welded semi-crystalline (PEKK) and amorphous (PEI) composites were compared and the failure modes of the specimens were described. The stiffness degradation was monitored during the tests in order to evaluate the damage accumulation in the specimens. Linear stress-life (S–N) curves were obtained for all three materials when plotted on a semi-log scale. Interlaminar failure modes, involving tearing of the heating element and damage to the adherends were observed. The indefinite fatigue lives of CF/PEKK and CF/PEI welded specimens were obtained at 25% of their static lap shear strengths. The indefinite fatigue life of the GF/PEI welded specimens was obtained at 20% of the static lap shear strength.     

Materials databases for the computational materials scientist

Until recently, many computational materials scientists have shown little interest in materials databases. This is now changing be-cause the amount of computational data is rapidly increasing and the potential for data mining provides unique opportunities for discovery and optimization. Here, a few examples of such opportunities are discussed relating to structural analysis and classification, discovery of correlations between materials properties, and discovery of unsuspected compounds.     

High-Resolution Volumetric Computation of Offset Surfaces with Feature Preservation

We present a new algorithm for the efficient and reliable generation of offset surfaces for polygonal meshes. The algorithm is robust with respect to degenerate configurations and computes (self‐)intersection free offsets that do not miss small and thin components. The results are correct within a prescribed ε‐tolerance. This is achieved by using a volumetric approach where the offset surface is defined as the union of a set of spheres, cylinders, and prisms instead of surface‐based approaches that generally construct an offset surface by shifting the input mesh in normal direction. Since we are using the unsigned distance field, we can handle any type of topological inconsistencies including non‐manifold configurations and degenerate triangles. A simple but effective mesh operation allows us to detect and include sharp features (shocks) into the output mesh and to preserve them during post‐processing (decimation and smoothing). We discretize the distance function by an efficient multi‐level scheme on an adaptive octree data structure. The problem of limited voxel resolutions inherent to every volumetric approach is avoided by breaking the bounding volume into smaller tiles and processing them independently. This allows for almost arbitrarily high voxel resolutions on a commodity PC while keeping the output mesh complexity low. The quality and performance of our algorithm is demonstrated for a number of challenging examples.     

Quality control engineering in automated ceramic tile production using a signal information content approach

The pressing process in the automated production of ceramic tiles is a complicated process that involves fully functional machinery and efficient coordination of the working crew. Quality control (QC) of the process relies on reasoning and acting on information coming from measured signals on the automated machinery. For QC, it is necessary to establish that these measurements are correct for the purpose of final product quality. In the process, tile batches are produced within a tolerable range of tile rejection. However, if the percentage of rejects rises above a certain threshold, e.g. 6%, the QC staff are responsible for finding the cause of the defect.The aim of this work is the investigation of a short-term information measure, expanded tessellation entropy, which can aid the QC staff in discovering the causes of deviations in the quality of batch production of ceramic tiles. This unique signal measure is calculable from as few as four consecutive machinery signal measurements, it is sensitive to small changes in the signal, and its computation is fast. Its noise sensitivity is tested for a set of four standard analytical process signals, with the addition of 1% random noise, and is shown to be robust with appropriate setting. The information measure is applied to measured process-machinery signals, and the results are compared with the QC signal that measures the tile rejection rate. An interpretation procedure is proposed and applied that reveals which signals are significant for increased tile rejection. The procedure is based on comparing signals and QC sequences with similar information code patterns. The results show that the defects are mainly due to human error, and that they usually start with improper furnace handling or uncompensated tile humidity. The method is compared to Shannon entropy, approximate entropy, Pearson correlation, and control charts, and it is shown to be superior for detection of faults in a setting where there is not much historical data available for statistical analysis, and where the quality of the process (percentage of rejects) is continuously measured as a target signal. In employing the proposed procedure, all of the QC defects were explained. The interpretation procedure is not fully automated at this moment. However, it is shown to be applicable to monitoring automated press machines in a ceramic tile plant, and thus preventing future defects. It can be applied to other similar automated industrial processes.     

Ligand‐Induced Dimerization of a Truncated Parallel MYC G‐Quadruplex

Binding of an indoloquinoline derivative with an aminoalkyl side chain to a truncated sequence from the MYC promoter region was studied through isothermal titration calorimetry (ITC). The targeted MYC3 sequence lacks 3′‐flanking nucleotides and forms a monomeric parallel quadruplex (G4) with a blunt‐ended 3′‐outer tetrad under the solution conditions employed. Analysis of ITC isotherms reveals multiple binding equilibria with the initial formation of a 1:2 ligand/quadruplex complex. Evaluation of electrophoretic mobilities as well as NMR spectral data confirm ligand‐induced dimerization of MYC3 quadruplexes with the ligand sandwiched between the two 3′‐outer tetrads. Additional ligand molecules in excess bind to the 5′‐outer tetrads of the sandwich complex. Such a ligand‐promoted G4 dimerization may be exploited for the controlled assembly or disassembly of G4 aggregates to expand on present quadruplex‐based technologies.     

Modelling an interplay of adoption determinants with respect to social Web applications used in massive online open courses

Universal Access in the Information Society - One of the major problems of using massive online open courses (MOOCs) commonly reported in the literature is the high dropout rate of students. Active...     

Condition-based spares ordering for critical components

It is widely accepted that one of the potential benefits of condition-based maintenance (CBM) is the expected decrease in inventory as the procurement of parts can be triggered by the identification of a potential failure. For this to be possible, the interval between the identification of the potential failure and the occurrence of a functional failure (P-F interval) needs to be longer than the lead time for the required part. In this paper we present a model directed to the determination of the ordering decision for a spare part when the component in operation is subject to a condition monitoring program. In our model the ordering decision depends on the remaining useful life (RUL) estimation obtained through (i) the assessment of component age and (ii) condition indicators (covariates) that are indicative of the state of health of the component, at every inspection time. We consider a random lead time for spares, and a single-component, single-spare configuration that is not uncommon for very expensive and highly critical equipment.     

High strength steel tension splices with one or two bolts

The paper presents experimental research of 38 tension splices with bolts in double shear. Steel grade S690 was used. The objective of the research was to determine ductility and resistance of such connections. The experimental resistance is compared to Eurocode provisions and a new bearing resistance formula is developed. The reliability assessment is given according to EN 1990, Annex D.     

Dynamic Optimization Model for Mining Equipment Repair by Using the Spare-Parts Inventory

We present the dynamic control system for the service rate in an M/M/1 queuing system, to optimize the inventory of critical repairable spare components for a fleet of mobile equipment in presence of an adjustable single server repair facility, namely, the repair rate can be expedited or slowed down. We consider the normal and expedited rates, when the faster repair rate implies higher repair costs. The repair rate selection depends on the number of units in operational condition; actual operating units plus stock on hand is generated at the moment of demand for a spare. The resulting optimal policy is to minimize the expected cost per unit time for the inventory system in the long run.