Impact of modelling approximations in supply chain analysis – an experimental study

This paper presents a study of the comparison of the quality of results obtained at different levels of detail using a supply chain simulation. Analysis of supply chain is typically carried out using aggregated information to maintain the level of complexity of the simulation model at a manageable level. Advances in simulation have provided the ability to build comprehensive (detailed), modular models. The quantitative effect of detailed modelling on the corresponding analysis is investigated in this paper. A three-echelon supply chain is analysed using simulation models of varying levels of detail. Using each of these models, four sets of intensive experiments are performed. The first experiment intends to test whether the supply chain dynamics themselves depend on the modelling accuracy that represents the supply chain. The second and third experiments are conducted to test whether the effectiveness of the strategies employed to reduce the supply chain dynamics vary depending on the type (different detail) of model representing the supply chain. In the fourth experiment, statistical techniques are employed to identify which modelling aspect has the most influence on the supply chain dynamics. It is found that the approximations used in modelling, such as delays and capacity, have more impact on the outcome of supply chain analysis than end customer demand. Evidence that both the basic problem (supply chain dynamics) and the solution (strategy to reduce the dynamics) are greatly influenced by the modelling accuracy are presented.     

Tensile properties and plastic deformation modes ofβ Zr-Nb alloys

Tensile properties and plastic deformation modes of zirconium-niobium alloys were investigated at 290 and 77 K in the wide composition range from metastable to stable phase. Three types of plastic deformation modes, {332}113 twinning, {112}111 twinning and slip, were observed depending on alloy composition and temperature. {332}113 twinning, which occurs in metastable zirconium alloys, is related to the stability of phase to decomposition and leads to low yield stress and large elongation. On the other hand, {112}111 twinning, which appears in stable zirconium alloys, results from high critical stress for slip due to solution hardening and high Peierls stress and does not affect tensile properties significantly. The results obtained for zirconium-alloys are similar to those for titanium alloys, strongly suggesting that {332}113 twinning is an important plastic deformation mode which is common to phase alloys containing athermal phase.     

Gas-particle flow of cohesive aluminium powders during laser metal deposition – Experimental and numerical investigation

This paper investigates particle dynamics both inside and outside a Laser Metal Deposition nozzle of a Directed Energy Deposition processing head, i.e. a Laser Metal Deposition (LMD) nozzle, by way of high-speed imaging and particle tracking as well as through computer simulations that account for particle collision and van der Waals forces. It is shown that the particle accumulation phenomena observed experimentally with cohesive aluminium powders can be qualitatively reproduced numerically. It is also demonstrated that such computer simulations can yield the correct order of magnitude for particle velocities, which is rarely reported in the literature and usually unknown for any given LMD system. This work thus paves the way towards more accurate simulations of gas-particle flows in LMD nozzles, especially with cohesive powders.     

Diagonal compressive strength of masonry samples—experimental and numerical approach

Masonry is a structural material that presents a quite complex behaviour that depends on the mechanical and geometrical characteristics of the units, the mortar and the link between these two elements. In particular, the characterization of the shear behaviour of masonry elements involves proper experimental campaigns that make these analyses particularly expensive. The main objective of this paper is to present a case study on the characterization of the shear behaviour of masonry through a methodology that merges a small number of laboratory tests with computer simulations. The methodology is applied to a new masonry system that has recently been developed in Portugal, and involves a FEM numerical approach based on micro3D modelling of masonry samples using nonlinear behaviour models that are calibrated through a small number of laboratory tests. As a result, the characterization of the masonry shear behaviour trough this methodology allowed simulating, with reasonably accuracy, a large set of expensive laboratory tests using numerical tools calibrated with small experimental resources.     

An experimental–numerical study of moisture absorption in an epoxy

It is well known that moisture absorption impairs the mechanical and physical properties of polymers. Conventionally, the material’s hygric strains are described as the product of a constant coefficient of moisture expansion (CME) and moisture concentration. This hypothesis, however, has not been thoroughly examined experimentally. In this paper, the hygro-mechanical response of a DGBA based epoxy is reported as a function of moisture uptake. Cylindrical specimens are made of epoxy with an axially located optical fiber that contains a 23 mm Bragg grating sensor (FBG). Strain data from the sensor and from a micrometer are combined with experimental absorption curves to determine the resin’s CME. The data indicate that diffusion and CME depend on moisture. Analysis of the experiments is carried out by numerical simulations of heat transfer, moisture diffusion and elastic stress analysis of the single fiber composite. The simulated results correlate well with the experimental data.     

Effect of pulsed laser radiation on deformation band dynamics and discontinuous deformation in aluminum–magnesium Al-6%Mg alloy

The dynamics and morphology of deformation bands and the discontinuous deformation under local action of pulsed infrared fiber laser radiation on the surface of aluminum–magnesium Al-6%Mg alloy have been studied by high-speed video recording techniques. Conditions under which laser action leads to the formation of macrolocalized deformation bands and deformation jumps of several percent on the stress–strain diagram are experimentally established. A possible mechanism of this phenomenon is discussed.     

Localized strain and heat generation during plastic deformation in nanocrystalline Ni and Ni–Fe

Room temperature tensile testing was performed on a coarse-grained polycrystalline Ni (32 μm), a nanocrystalline Ni (23 nm) and two nanocrystalline Ni–Fe (16 nm) electrodeposits at two strain rates of 10^?1 and 10^?2/s. Strain localizations and local temperature increases were simultaneously recorded during tensile testing. For all materials, higher loads or higher strain rate generally resulted in higher peak temperature with the highest temperatures recorded in the fracture regions. The maximum temperature for the nanocrystalline materials was just over 80 °C, which is significantly below the reported temperatures for the onset of thermally activated grain growth. Therefore, the previously reported grain growth observed on similar materials after tensile deformation is likely not thermally activated but a stress-induced phenomenon. Despite the wide grain range from 16 nm to 32 μm, all samples exhibited similar strain localization behavior. Local strain variations initiated in the early stage of macroscopic uniform deformation, subsequent necking and fracture took place in the region of initial strain localization. While the coarse-grained polycrystalline Ni exhibited little strain rate sensitivity, gradually increased strain rate sensitivity was observed for the 23 nm Ni and the two 16 nm Ni–Fe samples, suggesting that both dislocation-mediated and grain-boundary-controlled mechanisms were operative in the deformation of the nanocrystalline Ni and Ni–Fe samples.     

Surface plastic deformation distribution and microstructural evolution in the compound rolling of Ti–50Al billet

Compound rolling, which uses two different roller profiles to create plastic strain variation in the surface of a material, is described in this study. Based on the local load theory, equipment for the plastic deformation on the surface of the rectangular billet has been produced. The compound rolling behavior of Ti–50Al billet has been studied using this equipment. In order to study the deformation distribution of compound rolling, the flow net method for strain measurement has been employed. The deformation differences between compound rolling and flat rolling have been investigated with the commercial finite element method (FEM) code DEFORM-3D. The microstructure and the hardness from the surface to the center of the Ti–50Al billet developed through compound rolling has been characterized. These results indicate that the compound rolling technique results in severe plastic deformation near the surface with limited strain towards the center of the billet. This can result in compound microstructures, with fine recrystallized grains in the near surface region and the original directionally solidified microstructures in the center, and improve the hardness on the surface of the billet significantly.     

Application of three­dimensional numerical simulation to analysis of development of deformation zone at beginning of aluminium extrusion process

Abstract

Understanding the thermomechanical phenomena that occur during aluminium extrusion with respect to the variations of temperature, flow stress, strain, and strain rate is of importance for process optimisation. Conventional analytical methods are restricted to the steady state stage of the process and thus cannot provide an insight into the dynamic changes taking place during the initial stage. In the present work, three­dimensional simulations using the finite element method were carried out to analyse the development of the deformation zone at the die front and the temperature evolution, before the process attains the steady state. The analysis revealed that a change in friction factor at the billet/container interface from 0.3 to 0.9 enlarges the dead metal zone. However, its size appears unaffected by a change of die orifice shape from round to square at the same reduction ratio. The increase in friction results in an increase of initial extrusion load of about 6%.     

Local plastic deformation in the vicinity of grain boundaries in Fe–3 mass% Si alloy bicrystals and tricrystal

Nanoindentation was used to study incipient plastic deformation in the vicinity of grain boundaries of different character in Fe–3 mass% Si alloy bicrystals and tricrystal. Pop-in events associated with the grain boundaries were observed in the load–displacement curves. From the pop-in hardness values, the critical stresses required to propagate the yield past the grain boundary were estimated to be in the range of approximately µ/400–µ/130 (where µ is the shear modulus) depending on the grain boundary character: the special boundaries usually had higher critical stresses than the general boundaries. A Hall–Petch (H–P) type relationship was found between the hardness and the distance of the indenter to the grain boundary. The H–P slopes obtained were approximately one order of magnitude lower than the macroscopic value of the H–P slope for the Fe–3 mass% Si alloy, and were generally lower for general grain boundaries than for special boundaries.     

Microstructure and microhardness of an AlFe alloy subjected to severe plastic deformation and aging

A nanocrystalline structure was produced in an Al-11 wt.% Fe alloy with the use of the novel technique of severe plastic deformahon of ingots by torsion under high imposed pressure. This technique allows a large departure of materials from equilibrium. The microstructure of the alloys was studied with the use of TEM and EDS. The severe plastic deformation led to solid solubility extension of iron in the aluminum matrix, dispersion and dissolution of second phase particles, grain size reduction into the nanometer range, and partial amorphization. Microhardness of the alloy increased substantially after the deformation due to the grain refinement and the solid solubility extension. Aging of the severe plastically deformed samples at 100 °C led to further increase of the microhardness due to the decomposition of the supersaturated solid solution and precipitation-induced hardening.     

Microcrack nucleation and its effect on the plastic deformation of FL γ-TiAl alloy

Microcracks and their effect on the plastic deformation of -TiAl alloy with fully lamellar microstructure (FL) at relatively low strain rate (1 × 10^–5/s) has been investigated. It is found that a large number of microcracks nucleate within the grains. The microcrack density increases with the increase of grain size. Most of the microcracks nucleate at the /₂ interfaces and gather at grains with soft-orientations. Based on the observation and analysis, a model of microcrack nucleation in FL -TiAl alloy is built up. The plastic elongation of -based TiAl alloys with FL microstructure changes non-monotonously with the increase of grain size, which results from cooperation of micro-deformations and microcracks.     

Integration of manufacturing and distribution networks in a global car company – network models and numerical simulation

Global supply chain practices and their effects have received considerable attention over the last two decades. In the recent past, the need for integration across supply chains has been identified as a key for effective and efficient operations of supply chains. This is observed with the increasing trend of collaborative partnerships among supply chain partners. This paper presents an integrated approach for manufacturing and distribution networks within the supply chain system of a global car company. The paper shows that the integration of manufacturing and distribution networks creates the environment for effective planning of many components and execution/follow-up of those plans. These components include materials, resources, operations/activities, suppliers and customers. The main features of the integration include component integration at individual networks via use of a central warehouse. This integration reduces various interfacing steps between partners and enables representations of relationships (component precedence, parent-component and component-component). The proposed integrated model is numerically tested using past data from one of Japan's auto-makers, based in the emerging economy of Thailand. The paper concludes that the integrated supply network eliminates the need for interfacing of individual networks and enables simultaneous planning of many components as well as forward planning of supply components in global supply chain operations. It also shows that the integrated approach is capable of providing visibility, flexibility, and maintainability for further improvement in the supply network environment.     

An experimental–numerical investigation of hydrothermal response in adhesively bonded composite structures

Water absorption and thermal response of adhesive composite joints were investigated by measurements and numerical simulations. Water diffusivity, saturation, swelling, and thermal expansion of the constituent materials and the joint were obtained from gravimetric experiments and strain measurements using embedded fiber Bragg grating (FBG) sensors. The mechanical response of these materials at different temperatures and water content was characterized by dynamic mechanical analysis. Thermal loading and water absorption in joint specimens were detected by monitoring the FBG wavelength shift caused by thermal expansion or water swelling. The measured parameters were used in finite element models to simulate the response of the embedded sensor. The good correlation of experimental data and simulations confirmed that the change in FBG wavelength could be accurately related to the thermal load or water absorption process. The suitability of the embedded FBG sensors for monitoring of water uptake in adhesive composite joints was demonstrated.     

Application of a dynamic numerical solution to high speed fracture experiments—I. analysis of experimental geometries

The application of a dynamic, generation mode, finite element program to the analysis of experimental geometries is reported. Particular attention is given to the DCB specimen, which is widely used in high speed fracture studies despite strong inertia effects, which are described. Finite strip and infinite plate results are also considered. Here, idealised cases are discussed, while in Part II the application of the analysis to experimental measurements, to derive propagating crack fracture resistance data, is reported.     

Pipeline failures in corrosive environments – A conceptual analysis of trends and effects

Pipeline corrosion is a major challenge facing many oil and gas industries today because of the enormous downtime associated with corrosion related failures. Fatigue stress initiation in pipelines has been attributed to corrosion defects whose growth is enhanced by cyclic loading caused by the operating pressure of the transported fluids. This work reviews the concept of oil and gas transmission pipeline failures in corrosive environment by highlighting the corrosion mechanisms, dominant stress corrosion cracking trends, hydrogen induced cracking and predominant models for burst pressure estimation. Fatigue stress failure trends of corroding pipelines were also explained whilst describing some pipeline manufacturing processes that increases the susceptibility to fatigue stress failure. Optimization framework for pipeline integrity assurance against corrosion fatigue failures was also shown to incorporate different steps that includes – strategic policy initiation, policy implementation, information analysis and reviews and implementation actions.     

Influence of damage on ultrasonic velocity and strength—analysis and experiments

Measurements of ultrasonic velocity in creep damaged material are reviewed. The influence of damage on ultrasonic velocity is analysed and the relation between them is derived. It is shown that measurements of ultrasonic velocity can be used to predict the remaining life. Measurements of ultrasonic velocity in a damaged beam are presented along with measurements of the ultimate strength. A relation is found to exist, between reductions in ultrasonic velocity and ultimate strength, which might be used to assess the load carrying capacity of a structural element.