Heat Transfer Study of the In-situ Automated Fiber Placement (AFP) for Thermoplastic Composites

With more and more use of composites in engineering applications, the need for automated composites manufacturing is evident. The use of automated fiber placement (AFP) machine for the manufacturing of thermoplastic composites is under rapid development. In this technique, a moving heat source (hot gas torch, laser, or heat lamp) is melting the thermoplastic composite tape and consolidation occurs in situ. Due to the rapid heating and cooling of the material, there are many issues to be addressed. First is the development of the temperature distribution in different directions which gives rise to temperature gradients. Second is the quality of the bond between different layers, and third is the rate of material deposition to satisfy industrial demand. This thesis addresses the first issue. The temperature distribution affects the variation in crystallinity, and residual stresses throughout the structure as it is being built. The end result is the distortion of the composite laminate even during the process. In order to address this problem, first the temperature distribution due to a moving heat source needs to be determined. From the temperature distribution, the development and distribution of crystallinity, residual stresses and deformation of the structure can then be determined. As the first phase of the work, this thesis investigates the temperature distribution due to a moving heat source for thermoplastic composites, without considering the material deposition. A finite difference (FD) code based on the energy balance approach is developed to predict the temperature distribution during the process. Unidirectional composite strips are manufactured using AFP and fast-response K-type thermocouples are used to determine the thermal profiles in various locations through the thickness of the composite laminate subjected to a moving heat source. It is shown that temperature variations measured experimentally during the heating pass, using thermocouples embedded into the composite substrate, underneath layers of the composite material, are consistent with the generated thermal profiles from the numerical model. The temperature distribution, both in the direction of the tape and through-thickness direction can be predicted numerically. It should be noted that the convective heat transfer coefficient employed in the thermal analysis of the process plays an important role in the heat transfer mechanism. Information from the literature shows values of h that vary from 80 W⁄(m^2.K) to 2500 W⁄(m^2.K). This large range can provide a great degree of uncertainty in the determination of important quantities such as temperature distributions and residual stresses. The reason for these large differences can be due to the differences in the process parameters in each of the studies. The process parameters can include the flow rate of the hot gas, the gas temperature, the distance between the nozzle exit and the surface of the composite substrate, the angle of the torch with respect to the surface of the substrate etc. The purpose of the final part of this thesis is to investigate the effect of different AFP process parameters on the convective heat transfer coefficient and to propose a procedure for the determination of the h value according to the particular experimental setup

Rapport général du TC202 Géotechnique pour les infrastructures de transport

Today’s needs of urban transportation including roads, railways, airports and harbours demand significant resources for infrastructure development in view of rapid and efficient public and commercial (freight) services. In most cases, authorities have had difficulties in meeting these service demands due to the rapidly growing public, industrial, mining and agricultural sectors in many parts of the world. In order to maximise efficiency and to reduce the costs of maintenance, sound technical knowledge is required. This general report presents major technical advancements around the globe encompassing 33 articles from 19 countries and it is classified into 6 key categories, namely: compaction and subgrade improvement, laboratory testing, theoretical advancements and contributions to design, applications of geosynthetics, numerical modelling and field performance evaluation.De nos jours, les besoins en transports urbains (routes, chemins de fer, aéroports aériens et maritimes) nécessitent d’importantes ressources pour le développement des infrastructures en vue d’assurer des services commerciaux rapides et efficaces. Dans la plupart des cas, en raison de la croissance rapide des secteurs public, industriel, minier et agricole, les autorités se trouvent confrontées à des difficultés pour atteindre les services escomptés. Un savoir technique est alors nécessaire en vue de maximiser l’efficacité et de réduire le coût d’entretien. Le présent rapport général expose les avancées techniques majeures à travers le monde synthétisant 33 articles émanant de 19 pays ; six thèmes clés sont classés : compactage et amélioration des assises, expérimentation en laboratoire, développements théoriques et contributions au dimensionnement, applications des géosynthétiques, modélisations numériques et évaluation des performances sur le terrain.(undefined

Mesoscale Calculations of the Dynamic Behavior of a Granular Ceramic

Mesoscale calculations have been conducted in order to gain further insight into the dynamic compaction characteristics of granular ceramics. The primary goals of this work are to numerically determine the shock response of granular tungsten carbide and to assess the feasibility of using these results to construct the bulk material Hugoniot. Secondary goals include describing the averaged compaction wave behavior as well as characterizing wave front behavior such as the strain rate versus stress relationship and statistically describing the laterally induced velocity distribution. The mesoscale calculations were able to accurately reproduce the experimentally determined Hugoniot slope but under predicted the zero pressure shock speed by 12%. The averaged compaction wave demonstrated an initial transient stress followed by asymptotic behavior as a function of grain bed distance. The wave front dynamics demonstrate non-Gaussian compaction dynamics in the lateral velocity distribution and a power-law strain rate–stress relationship

Emerging technologies for the non-invasive characterization of physical-mechanical properties of tablets

The density, porosity, breaking force, viscoelastic properties, and the presence or absence of any structural defects or irregularities are important physical-mechanical quality attributes of popular solid dosage forms like tablets. The irregularities associated with these attributes may influence the drug product functionality. Thus, an accurate and efficient characterization of these properties is critical for successful development and manufacturing of a robust tablets. These properties are mainly analyzed and monitored with traditional pharmacopeial and non-pharmacopeial methods. Such methods are associated with several challenges such as lack of spatial resolution, efficiency, or sample-sparing attributes. Recent advances in technology, design, instrumentation, and software have led to the emergence of newer techniques for non-invasive characterization of physical-mechanical properties of tablets. These techniques include near infrared spectroscopy, Raman spectroscopy, X-ray microtomography, nuclear magnetic resonance (NMR) imaging, terahertz pulsed imaging, laser-induced breakdown spectroscopy, and various acoustic- and thermal-based techniques. Such state-of-the-art techniques are currently applied at various stages of development and manufacturing of tablets at industrial scale. Each technique has specific advantages or challenges with respect to operational efficiency and cost, compared to traditional analytical methods. Currently, most of these techniques are used as secondary analytical tools to support the traditional methods in characterizing or monitoring tablet quality attributes. Therefore, further development in the instrumentation and software, and studies on the applications are necessary for their adoption in routine analysis and monitoring of tablet physical-mechanical properties

Modifications to Johanson\u27s roll compaction model for improved relative density predictions

Johanson’s roll compaction model [J.R. Johanson, A rolling theory for granular solids, ASME Journal of Applied Mechanics E32 (1965) 842–848] is modified to improve its predictions of a compacted ribbon’s relative density. Previous work has shown that the maximum roll pressure and ribbon relative density predicted by the Johanson model are not only larger than those predicted from finite element method (FEM) simulations, but also unphysical in some cases. This over-prediction is due to a one-dimensional flow assumption in the Johanson model. Real powder velocity profiles within a roll compactor are non-uniform. Johanson’s analysis is modified in this work to include a mass correction factor to account for the improper one-dimensional flow assumption, similar to what was proposed by Bi et al. [M. Bi, F. Alvarez-Nunez, F. Alvarez, Evaluating and modifying Johanson\u27s rolling model to improve its predictability, J Pharm Sci. 103 (2014) 2062-2071]. Unlike Bi et al.’s work, however, an empirical curve fit accounting for the mass correction factor’s dependence on position is included in the current analysis. The fit has two fitting parameters, which can be determined from online measurements. Predictions of the average relative density at the minimum gap width from the modified Johanson model are compared to predictions from two-dimensional FEM models and the errors are found to be approximately 5% larger than the FEM predictions. The unmodified Johanson model over-predicts the FEM results by around 50%. Comparisons to published experimental data also show good agreement. This modified Johanson model can be used in control schemes to provide much better estimates of ribbon relative density in roll compaction operations

Prediction Of The Stress At The Inlet Of The Nip Region In A Roll Compactor

The stress at the inlet nip region of a roll compactor (i.e., feeder outlet stress) is a necessary input parameter for existing powder roll compaction models; however the nip region inlet stress is poorly understood and difficult to directly measure. The inability to specify the nip region inlet stress on a roll compactor limits comparisons between powder roll compaction models and experimental results. Therefore, this thesis investigates the application of a solid plug model to a powder feed screw of a roll compactor in order to predict the stress at the inlet nip region. The feeder outlet stress predictions of the Solid Plug models developed by Tadmor et al. (1972), Campbell et al. (1995), and Hyun et al. (1997a) were compared to experimental results. Each of the Solid Plug models under-predicted the experimentally measured feeder outlet stress by orders of magnitude. Potential reasons why the Solid Plug models poorly predicted the experimental results are the accuracy of the friction coefficient measurements and the assumed values for the stress ratios. The friction coefficients could not be completely defined because the surface finish of the feed screw and barrel were unknown, and the stress ratios were assumed to equal one based on the kinetic theory of granular material (Lun, 1991). The sensitivity of the Solid Plug models to the following input parameters: friction coefficients, stress ratio, and stress-density relationship are investigated. Adjusting the friction coefficients or stress ratios, such that the stress-density relationship predicts a density greater than the lower density limit, is shown to cause the Solid Plug models\u27 feeder outlet stress predictions to rapidly increase and become more sensitive to the mass flow rate. In most cases, varying the friction coefficients or stress ratios by 10% caused the feeder outlet stress predictions to vary by a factor from two to ten. The Solid Plug models\u27 poor predictions of the experimental results are also likely due to assuming constant material parameters such as the friction coefficients and stress ratios. The sensitivity of the Solid Plug models to the material input parameters and the effects of the stress-density relationship show that small changes in the material parameters due to the variation in stress along the length of the feed screw could have a significant impact on the Solid Plug models\u27 feeder outlet stress predictions. The friction coefficients and stress ratios necessary for the Solid Plug models to accurately predict the experimental results were determined. The fitted parameters varied significantly from the initial values input because the initial feeder outlet stress predictions were orders of magnitude below the experimental results. Due to the sensitivity of the Solid Plug models to several input parameters and the poor comparisons between the Solid Plug models\u27 feeder outlet stress predictions and experimental results, the Solid Plug models, as presented in the literature, do not lend themselves to predicting the nip region inlet stress applied to the powder roll compaction models. In addition to applying the Solid Plug models to a powder feed screw, the Solid Plug models\u27 derivations were extended to determine a relationship between the feeder torque and the feeder outlet stress. The derivations predict qualitatively the linear relationship between the feeder torque and feeder outlet stress observed experimentally, but quantitative predictions are orders of magnitude different. Although the Solid Plug models\u27 predictions of feeder outlet stress are not applicable to powder roll compaction models, experimentally measuring the feeder torque-outlet stress relationship and measuring the feeder torque on a roll compactor would allow for the feeder outlet stress to be predicted. Determination of the feeder outlet stress allows for real time processing and complete comparisons between the powder roll compaction models and experimental results