Modeling structure property relationships using finite elements and high energy X-rays

Mechanical design with structural materials has been well-served by traditional methods for linking microstructure to mechanical properties using image-based data and mechanical testing. Modern “micrographs” might include three-dimensional microstructural models with spatially resolved orientation and/or chemical composition. Regardless of the level of detail, however, image-based data contain no information regarding the mechanical response of the aggregate. Often the connections between the microstructure and resulting mechanical properties are derived by intuition and inference. This highly empirical process is one of the reasons that materials design and selection are such time and resource-intensive process. The creation of mathematical models of the microstructure – ones based on functional accuracy – was the motivation of the Integrated Computational Materials Engineering report and the Materials Genome Initiative. Once deemed “reliable” such models could be employed to conduct costly “microstructural iterations” to optimize properties. This discussion describes a method for studying structure–property relations using a finite element representation of the crystal and subcrystal scale microstructure. A key aspect of the methodology is a set of high energy X-ray diffraction experiments with in situ mechanical loading and heating designed to provide crystal-scale micromechanical material response data. Bringing the experimental and simulated data into coincidence builds trust in the model and its ability to enable optimizations during the material design process. Examples employing various experimental methods and functional material representations are described examining a range of engineering materials

Efficient prediction of axial load-bearing capacity of concrete columns reinforced with FRP bars using GBRT model

The behavior of concrete columns reinforced with fiber reinforced polymer (FRP) bars is different from conventional reinforced concrete columns due to the mechanical properties of FRP bars. This study develops a novel machine learning (ML) model, namely gradient boosting regression tree (GBRT), for efficiently predicting the axial load-bearing capacity (ALC) of concrete columns reinforced with FRP bars. A data base containing 283 experimental results is collected to develop the ML model. Seven code-based and empirical-based equations are also included in comparison with the developed ML models. Moreover, we also propose a multiple linear regression (MLR)-based formula for calculating the ALC of the FRP-concrete column. The performance results of GBRT model are compared with those of published formulas and the proposed MLR-based formula. Statistical properties including , , and  are calculated to evaluate the accuracy of those predictive models. The comparisons demonstrate that GBRT outperforms other models with very high  values and small . Moreover, the influence of input parameters on the predicted ALC isevaluated. Finally, an efficient graphical user interface tool is developed to simplify the practical design process of FRP-concrete columns

The impact of process parameters on mechanical properties of parts fabricated in PLA with an open-source 3-D printer

Purpose - This study aims to quantify the ultimate tensile strength and the nominal strain at break (f) of printed parts made from polylactic acid (PLA) with a Replicating Rapid prototyper (Rep-Rap) 3D printer, by varying three important process parameters: layer thickness, infill orientation and the number of shell perimeters. Little information is currently available about mechanical properties of parts printed using open-source, low-cost 3D printers. Design/methodology/approach - A computer-aided design model of a tensile test specimen was created, conforming to the ASTM:D638. Experiments were designed, based on a central composite design. A set of 60 specimens, obtained from combinations of selected paramers, was printed on a Rep-Rap Prusa I3 in PLA. Testing was performed using a JJ Instruments - T5002-type tensile testing machine and the load was measured using a load cell of 1,100 N. Findings - This study investigated the main impact of each process parameter on mechanical properties and the effects of interactions. The use of a response surface methodology allowed the proposition of an empirical model which connects process parameters and mechanical properties. Even though results showed a high variability, additional ideas on how to understand the impact of process parameters are suggested in this paper. Originality/value - On the basis of experimental results, it is possible to obtain practical suggestions to set common process parameters in relation to mechanical properties. Experiments discussed in the present paper provide a variety of data and insight regarding the relationship among the main process parameters and the stiffness and strength of fused deposition modeling-printed parts made from PLA. In particular, this paper underlines the shortage in existing literature concerning the impact of process parameters on the elastic modulus and the strain to failure for the PLA. The experimental data produced show a good degree of compliance with analytical formulations and other data found in literature.Peer reviewe

Mechanical properties and melting conditions of beeswax for comb foundation forming

The melting conditions and the mechanical properties of beeswax after melting process were investigated in thisstudy. The study variables of melting process were hot water temperature, propeller speed and time. The empirical model ofbeeswax melting efficiency was then established. The melting conditions were optimized based on the melting efficiencyand color of beeswax and were found at the hot water temperature in range of 98°C -100°C, propeller speed in range of 40-90r/min and time in range of 12-15 min. The beeswax was solidified at the different cooling rates. The compression testswere performed at condition of 60% strain to characterize the mechanical behavior of beeswax. The constitutive equationfor hyperelastic material was employed for beeswax. The two forms of the constitutive equation showed a better fit to theexperimental data and the optimized material parameters were obtained. The rolling beeswax sheets were simulated underthe different conditions of pressure angle, velocity and friction coefficient in order to determine the effect of the variables onthe mechanical properties of beeswax sheet. The stress and deformation distributions across the beeswax sheet including theforces acting on the contact interfaces were examined. The pressure angle was found to be the most effective variable on thestress distribution. The maximum pressure angle of 11° was found to provide the non-defect beeswax sheet. This presentmodel for beeswax sheet rolling provides the understanding of the stress and deformation distributions and has been utilizedto design the rolling for comb foundation forming

Environmental Feedback in an Iterative Design-process

This paper is an account of a practice-led project carried out during an “architects’ residence” in Kielder in the North of the UK, between 2003-2006. It describes how a systems-based approach was applied to cycle through the design-process iteratively. The aim was to fabricate an object embodying a mechanical mechanism that would visibly respond to the diurnal cycle of environmental change found in microclimates in Kielder. An evaluation of the object’s behaviour was carried out based on environmental metrics. The iterative process of building and monitoring prototypes suggests a design methodology that incorporates “as-built and operated” evidence into the design process. Initially, the design of the object was investigated using virtual models that served as descriptions of the finished object due to be placed on sites in Kielder. In an iterative approach to design with physically fabricated prototypes, there is the opportunity to capture and use feedback to develop the design and location of a prototype in the subsequent iteration. This paper discusses the methodology implemented in a case-study project and how information returning across the real-to-virtual threshold became design intelligence used in the next iteration. The collection of empirical data by “design probes” [Sheil and Leung, 2005] was coupled with a computer simulation; two feedback loops were identified, one informing model validation the other, objective validation. An iterative methodology is proposed to revise objectives, to re-model solutions, to re-synthesise outcomes and to re-locate on-site between iterations based on feedback from the ’as-built and operated’ data

Heat Transfer And Mechanical Design Analysis Of Supercritical Gas Cooling Process Of CO2 In Microchannels

An extensive review of the literature indicates a lack of systematic study of supercritical CO2 gas cooling and no prior work on CO2/oil mixture in supercritical region, suggesting a lack of fundamental understanding of supercritical gas cooling process and a lack of comprehensive data that would help quantify the performance potential of CO2 microchannel heat exchangers for engineering applications. This dissertation presents a systematic and comprehensive study on gas cooling heat transfer characteristics of supercritical CO2 in microchannels. Semi-empirical correlation is developed for predicting heat transfer performance of supercritical CO2 in microchannels. The effect of oil addition on heat transfer performance has been experimentally investigated as well. It is shown that presence of lubricant oil mixed with supercritical CO2 in the heat exchangers can substantially affect heat transfer and pressure drop coefficients. Because of the outstanding performance of supercritical CO2 and its promising potential as a substitute for current refrigerants, attention has been paid to the design of CO2 microchannel heat exchangers. The extensive review of the literature also indicates no previous study in systematically developing a simulation model for structural design of microchannel heat exchangers. The dissertation extends the research to the mechanical design analysis of microchannel heat exchangers. A finite-element method (FEM) based mechanical design analysis of tube-fin heat exchangers is carried out to develop a simulation model of the heat exchangers. The solid modeling and simulation scheme can be served as a guide for mechanical design of CO2 heat exchangers. Experiments are conducted to validate the developed models as well

Design: One, but in different forms

This overview paper defends an augmented cognitively oriented generic-design hypothesis: there are both significant similarities between the design activities implemented in different situations and crucial differences between these and other cognitive activities; yet, characteristics of a design situation (related to the design process, the designers, and the artefact) introduce specificities in the corresponding cognitive activities and structures that are used, and in the resulting designs. We thus augment the classical generic-design hypothesis with that of different forms of designing. We review the data available in the cognitive design research literature and propose a series of candidates underlying such forms of design, outlining a number of directions requiring further elaboration

The role of the user and the society in new product development

Within the knowledge-based economy several institutions are involved in product innovation processes. Literature study has shown that the most researched and cited are the industry-universitygovernment relations, presented in the Triple Helix model of institutional relations within new product development (NPD). Based on a case study of the Academic Virtual Enterprise, we have put the sole input of these institutions in NPD into question. We have tested and supported the claim that the user and the society are equal partners in the product innovation process. We have put forward the Fourfold Helix model that features a new formation of institutional relations where special focus is placed on the involvement of the user and the society in NPD

Review on the prediction of residual stress in welded steel components

Residual stress after welding has negative effects on the service life of welded steel components or structures. This work reviews three most commonly used methods for predicting residual stress, namely, empirical, semi-empirical and process simulation methods. Basic principles adopted by these methods are introduced. The features and limitations of each method are discussed as well. The empirical method is the most practical but its accuracy relies heavily on experiments. Mechanical theories are employed in the semi-empirical method, while other aspects, such as temperature variation and phase transformation, are simply ignored. The process simulation method has been widely used due to its capability of handling with large and complex components. To improve its accuracy and efficiency, several improvements need to be done for each simulation aspect of this method