A model for the decohesion of aggregates of suspended particulate material in a binding matrix is developed. In the model cohesive zones which envelop each particle individually…
Abstract
A model for the decohesion of aggregates of suspended particulate material in a binding matrix is developed. In the model cohesive zones which envelop each particle individually are introduced at the particulate/binder interface. During progressive loading, the deterioration of the cohesive zones is initiated if constraints placed on the microstress fields are violated. In order for the material behavior to be energetically admissible, the deterioration of the material at a point is in the form of a reduction of the elasticity tensor’s eigenvalues at that point. The material within the cohesive zones deteriorates until the constraints are met. In order to isolate and study the effects of interfacial deterioration, outside of the cohesive zones, the material is unaltered. Mathematical properties of the model, as well as physical restrictions, are discussed. Numerical simulations are performed employing the finite element method to illustrate the approach in three‐dimensional applications.
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Jacek Ptaszny and Marcin Hatłas
The purpose of this paper is to evaluate the efficiency of the fast multipole boundary element method (FMBEM) in the analysis of stress and effective properties of 3D linear…
Abstract
Purpose
The purpose of this paper is to evaluate the efficiency of the fast multipole boundary element method (FMBEM) in the analysis of stress and effective properties of 3D linear elastic structures with cavities. In particular, a comparison between the FMBEM and the finite element method (FEM) is performed in terms of accuracy, model size and computation time.
Design/methodology/approach
The developed FMBEM uses eight-node Serendipity boundary elements with numerical integration based on the adaptive subdivision of elements. Multipole and local expansions and translations involve solid harmonics. The proposed model is used to analyse a solid body with two interacting spherical cavities, and to predict the homogenized response of a porous material under linear displacement boundary condition. The FEM results are generated in commercial codes Ansys and MSC Patran/Nastran, and the results are compared in terms of accuracy, model size and execution time. Analytical solutions available in the literature are also considered.
Findings
FMBEM and FEM approximate the geometry with similar accuracy and provide similar results. However, FMBEM requires a model size that is smaller by an order of magnitude in terms of the number of degrees of freedom. The problems under consideration can be solved by using FMBEM within the time comparable to the FEM with an iterative solver.
Research limitations/implications
The present results are limited to linear elasticity.
Originality/value
This work is a step towards a comprehensive efficiency evaluation of the FMBEM applied to selected problems of micromechanics, by comparison with the commercial FEM codes.
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Cong Yu, LongFei Qie, ShiKai Jing and Yan Yan
Orientation determination is an essential planning task in additive manufacturing (AM) because it directly affects the part quality, build time, geometric tolerance, fabrication…
Abstract
Purpose
Orientation determination is an essential planning task in additive manufacturing (AM) because it directly affects the part quality, build time, geometric tolerance, fabrication cost, etc. This paper aims to propose a negative feedback decision-making (NFDM) model to realize the personalized design of part orientation in AM process.
Design/methodology/approach
NFDM model is constructed by integrating two sub-models: proportional–integral–derivative (PID) negative feedback control model and technique for order preference by similarity to an ideal solution (TOPSIS) decision-making model. With NFDM model, a desired target is first specified by the user. Then, the TOPSIS decision model calculates the “score” for the current part orientation. TOPSIS decision model is modified for ease of control. Finally, the PID controller automatically rotates the part based on the error between the user-specified target and the calculated “score”. Part orientation adjustment is completed when the error is eliminated. Five factors are considered in NFDM model, namely, surface roughness, support structure volume, geometric tolerance, build time and fabrication cost.
Findings
The case studies of turbine fan and dragon head indicate that the TOPSIS model can be perfectly integrated with the PID controller. This work extends the proposed model to different AM processes and investigates the feasibility of combining different decision-making models with PID controller and the effects of including various evaluation criteria in the integrated model.
Originality/value
The proposed model innovatively takes the TOPSIS decision-making model and the PID control model as a whole. In this way, the uncontrollable TOPSIS model becomes controllable, so the proposed model can control the TOPSIS model to achieve the user-specified targets.
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Saeed Hatefi Ardakani, Peyman Fatemi Dehaghani, Hesam Moslemzadeh and Soheil Mohammadi
The purpose is to analyze the mechanical behavior of the arterial wall in the degraded region of the arterial wall and to determine the stress distribution, as an important factor…
Abstract
Purpose
The purpose is to analyze the mechanical behavior of the arterial wall in the degraded region of the arterial wall and to determine the stress distribution, as an important factor for predicting the potential failure mechanisms in the wall. In fact, while the collagen fiber degradation process itself is not modeled, zones with reduced collagen fiber content (corresponding to the degradation process) are assumed. To do so, a local weakness in the media layer is considered by defining representative volume elements (RVEs) with different fiber collagen contents in the degraded area to investigate the mechanical response of the arterial wall.
Design/methodology/approach
A three-dimensional (3D) large strain hierarchical multiscale technique, based on the homogenization and genetic algorithm (GA), is utilized to numerically model collagen fiber degradation in a typical artery. Determination of material constants for the ground matrix and collagen fibers in the microscale level is performed by the GA. In order to investigate the mechanical degradation, two types of RVEs with different collagen contents in fibers are considered. Each RVE is divided into two parts of noncollagenous matrix and collagen fiber, and the part of collagen fiber is further divided into matrix and collagen fibrils.
Findings
The von Mises stress distributions on the inner and outer surfaces of the artery and the influence of collagen fiber degradation on thinning of the arterial wall in the degraded area are thoroughly studied. Comparing the maximum stress values on outer and inner surfaces in the degraded region shows that the inner surface is under higher stress states, which makes it more prone to failure. Furthermore, due to the weakness of the artery in the degraded area, it is concluded that the collagen fiber degradation considerably reduces the wall thickness in the degraded area, leading to an observable local inflation across the degraded artery.
Originality/value
Considering that little attention has been paid to multiscale numerical modeling of collagen fiber degradation, in this paper a 3D large strain hierarchical multiscale technique based on homogenization and GA methods is presented. Therefore, while the collagen fiber degradation process itself is not modeled in this study, zones with reduced collagen fiber content (corresponding to the degradation process) are assumed.
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Ziming Zhou, Fengnian Zhao and David Hung
Higher energy conversion efficiency of internal combustion engine can be achieved with optimal control of unsteady in-cylinder flow fields inside a direct-injection (DI) engine…
Abstract
Purpose
Higher energy conversion efficiency of internal combustion engine can be achieved with optimal control of unsteady in-cylinder flow fields inside a direct-injection (DI) engine. However, it remains a daunting task to predict the nonlinear and transient in-cylinder flow motion because they are highly complex which change both in space and time. Recently, machine learning methods have demonstrated great promises to infer relatively simple temporal flow field development. This paper aims to feature a physics-guided machine learning approach to realize high accuracy and generalization prediction for complex swirl-induced flow field motions.
Design/methodology/approach
To achieve high-fidelity time-series prediction of unsteady engine flow fields, this work features an automated machine learning framework with the following objectives: (1) The spatiotemporal physical constraint of the flow field structure is transferred to machine learning structure. (2) The ML inputs and targets are efficiently designed that ensure high model convergence with limited sets of experiments. (3) The prediction results are optimized by ensemble learning mechanism within the automated machine learning framework.
Findings
The proposed data-driven framework is proven effective in different time periods and different extent of unsteadiness of the flow dynamics, and the predicted flow fields are highly similar to the target field under various complex flow patterns. Among the described framework designs, the utilization of spatial flow field structure is the featured improvement to the time-series flow field prediction process.
Originality/value
The proposed flow field prediction framework could be generalized to different crank angle periods, cycles and swirl ratio conditions, which could greatly promote real-time flow control and reduce experiments on in-cylinder flow field measurement and diagnostics.
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Wei Lu, Vivian W.Y. Tam, Heng Chen and Lei Du
Addressing global warming challenge, carbon emissions reduction potential of the construction industry has received additional attentions. The decoupling of construction industry…
Abstract
Purpose
Addressing global warming challenge, carbon emissions reduction potential of the construction industry has received additional attentions. The decoupling of construction industry and carbon emissions through policies, technologies and model innovations is an effective way for reducing environmental pollution and achieve eco-urban target. The paper aims to discuss these issues.
Design/methodology/approach
Within the scope of green building carbon emissions (GB-CO2) research, a large number of scientific literature has been published in construction discipline over the past few decades. However, it seems that a systematic summary of strategies, techniques, models and scientific discussion of future direction of GB-CO2 is lacking. Therefore, this paper carries out data mining on authoritative journals, identified the key research topics, active research areas and further research trends through visualization studies.
Findings
This study contributes to the body of knowledge in GB-CO2 by critically reviewing and summarizing: professional high-quality journals have a greater influence in the scope of research, developed countries and developing countries are all very concerned about sustainable buildings, and the current hot topics of research focus on the application of the life cycle models, energy efficiency, environmental performance of concrete material, etc. Moreover, further research areas that could expand the knowledge of cross-national long-term carbon mechanisms, develop comprehensive life cycle carbon emissions assessment models, build technical standards and tests for the sustainable building material and systems, and exploit multi-objective decision models considering decarbonizing design and renewable energy.
Originality/value
This study is of value in systematic insight the state-of-the-art of GB-CO2 research in the more recent decade. A more vividly and effectively method is documented in extending the traditional bibliometric review to a deeper discussion. This study can also benefit construction practitioners by providing them a focused perspective of strategy and technologies innovations for emerging practices in green building projects.
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Daiane Rossi, Fernando Henrique Lermen and Márcia Elisa Echeveste
This study aims to propose guidelines for developing circular products based on waste recovery that are aligned with sustainable production and consumption.
Abstract
Purpose
This study aims to propose guidelines for developing circular products based on waste recovery that are aligned with sustainable production and consumption.
Design/methodology/approach
A systematic literature review and case studies on circular product development were conducted. In total, 15 companies with products based on waste recovery and aligned with sustainable production and consumption goal were studied.
Findings
The results show the decisions and strategies applied at each stage of the new product development process, including the design for recycling, the use of waste as a raw material for products and the concern for reducing pollution and recovering end-of-life products.
Practical implications
The cases studied meet the goals of efficient use of natural resources and waste reduction by preventing, reducing, recycling and reusing waste. For practitioners, a set of guidelines is proposed to help companies develop circular products based on waste recovery.
Originality/value
Previous studies have not evaluated the new product development process and circularity from the institutional theory and waste valorization perspectives.
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Hayri Sezer, Joseph Tang, AMM Nazmul Ahsan and Sudhir Kaul
The purpose of this study is to develop a novel comprehensive three-dimensional computational model to predict the transient thermal behavior and residual stresses resulting from…
Abstract
Purpose
The purpose of this study is to develop a novel comprehensive three-dimensional computational model to predict the transient thermal behavior and residual stresses resulting from the layer-by-layer deposition in the direct metal laser sintering process.
Design/methodology/approach
In the proposed model, time integration is performed with an implicit scheme. The equations for heat transfer are discretized by a finite volume method with thermophysical properties of the metal powder and an updated convection coefficient at each time step. The model includes convective and radiative boundary conditions for the exposed surfaces of the part and constant temperatures for the bottom surface on the build plate. The laser source is modeled as a moving radiative heat flux along the scanning pattern, while the thermal gradients are used to calculate directional and von Mises residual thermal stresses by using a quasi-steady state assumption.
Findings
In this study, four different scanning patterns are analyzed, and the transient temperature and residual thermal stress fields are evaluated from these patterns. It is found that the highest stresses occur where the laser last leaves off on its scanning pattern for each layer.
Originality/value
The proposed model is designed to capture the layer-by-layer deposition for a three-dimensional geometry while considering the effect of the instantaneous melting of the powder, melt pool, dynamic calculation of thermophysical properties, ease of parametrization of various process parameters and the vectorization of the code for computational efficiency. This versatile model can be used for process parameter optimization of other laser powder bed fusion additive manufacturing techniques. Furthermore, the proposed approach can be used for analyzing different scanning patterns.
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Adnan Ibrahimbegović, Igor Grešovnik, Damijan Markovič, Sergiy Melnyk and Tomaž Rodič
Proposes a methodology for dealing with the problem of designing a material microstructure the best suitable for a given goal.
Abstract
Purpose
Proposes a methodology for dealing with the problem of designing a material microstructure the best suitable for a given goal.
Design/methodology/approach
The chosen model problem for the design is a two‐phase material, with one phase related to plasticity and another to damage. The design problem is set in terms of shape optimization of the interface between two phases. The solution procedure proposed herein is compatible with the multi‐scale interpretation of the inelastic mechanisms characterizing the chosen two‐phase material and it is thus capable of providing the optimal form of the material microstructure. The original approach based upon a simultaneous/sequential solution procedure for the coupled mechanics‐optimization problem is proposed.
Findings
Several numerical examples show a very satisfying performance of the proposed methodology. The latter can easily be adapted to other choices of design variables.
Originality/value
Confirms that one can thus achieve the optimal design of the nonlinear behavior of a given two‐phase material with respect to the goal specified by a cost function, by computing the optimal form of the shape interface between the phases.
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Lin Cheng, Pu Zhang, Emre Biyikli, Jiaxi Bai, Joshua Robbins and Albert To
The purpose of the paper is to propose a homogenization-based topology optimization method to optimize the design of variable-density cellular structure, in order to achieve…
Abstract
Purpose
The purpose of the paper is to propose a homogenization-based topology optimization method to optimize the design of variable-density cellular structure, in order to achieve lightweight design and overcome some of the manufacturability issues in additive manufacturing.
Design/methodology/approach
First, homogenization is performed to capture the effective mechanical properties of cellular structures through the scaling law as a function their relative density. Second, the scaling law is used directly in the topology optimization algorithm to compute the optimal density distribution for the part being optimized. Third, a new technique is presented to reconstruct the computer-aided design (CAD) model of the optimal variable-density cellular structure. The proposed method is validated by comparing the results obtained through homogenized model, full-scale simulation and experimentally testing the optimized parts after being additive manufactured.
Findings
The test examples demonstrate that the homogenization-based method is efficient, accurate and is able to produce manufacturable designs.
Originality/value
The optimized designs in our examples also show significant increase in stiffness and strength when compared to the original designs with identical overall weight.