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The concepts of solution error and optimal mesh in adaptive finite element analysis are revisited. It is shown that the correct evaluation of the convergence rate of the error norms involved in the error measure and the optimal mesh criteria chosen are essential to avoid oscillations in the refinement process. Two mesh optimality criteria based on: (a) the equal distribution of global error, and (b) the specific error over the elements are studied and compared in detail through some examples of application.

Stereolithography (SLA) is one of the most important techniques used in rapid prototyping processes. It has a great industrial interest because it allows for dramatic time savings with respect to traditional manufacturing processes. One of the main sources of error in the final dimensions of the prototype is the curl distortion effect owing to the shrinkage of the resin during the SLA process. Presents a study of the influence of different constructive and numerical parameters in the curl distortion, an analysis which was made using the computer code stereolithography analysis program, developed to model SLA processes using the finite element method. Also briefly presents this code.

The present contribution deals with the sensitivity analysis and optimization of structures for path‐dependent structural response. Geometrically as well as materially non‐linear behavior with hardening and softening is taken into account. Prandtl‐Reuss‐plasticity is adopted so that not only the state variables but also their sensitivities are path‐dependent. Because of this the variational direct approach is preferred for the sensitivity analysis. For accuracy reasons the sensitivity analysis has to be consistent with the analysis method evaluating the structural response. The proposed sensitivity analysis as well as its application in structural optimization is demonstrated by several examples.

Presents an approach for optimal design of geometrically non‐linear structures, using adaptive mesh refinement (AMR). The optimization technique adopted is based on the multi‐point approximation method. The finite element method is used for the structural analysis. Reformulation of the optimal design problem is applied to circumvent complications caused by the non‐linear behaviour of the structure. The latter may lead to bifurcations, limit points and/or significant reduction of the structural stiffness for individual intermediate designs generated by an optimization algorithm. Discretization errors are controlled using AMR. To reduce computational costs, the requested global and local discretization errors are not taken as fixed values but are specified on the basis of the current status of the optimization process. In the beginning relatively large errors are accepted, while as the process progresses discretization errors are reduced. The method is applied to thin‐walled structures with geometrically non‐linear behaviour.

The aim of this paper is to predict the optimum settings of the process parameters for selective laser sintering process.

A simulation model is prepared using author written subroutines in ANSYS^® Parametric Design Language (APDL™) environment. The simulation model is then run at the experimentally designed points using central composite design approach. Based on the observations, a response surface is generated for the density of a sintered part as a function of various process parameters.

The results indicate the optimum settings of the process variables to achieve a desired value of the density.

The developed simulation model can be used to predict the density of the final part with limited part geometries and may not be applicable for the complex shapes or with irregular features.

The parameter settings as predicted by the simulation model may not be reproduced exactly by the experimental readings.

The results of the simulation study concur with previous investigation by other researchers. Hence, the model can be suitably modified according to available data for different materials (amorphous and crystalline) taking the due considerations.

Additive manufacturing is today a viable industrial solution alongside traditional processes. Techniques like selective laser sintering (SLS) address the issues of digital production and mass customization in a variety of materials. Composite parts can be obtained with specific functional and mechanical properties. Building orientation during additive manufacturing often causes anisotropy of parts' properties that is still unspecified in technical information. The purpose of this paper is to investigate the mechanical performances and failure mechanisms of an aluminium‐filled polyamide and of a new alumina‐polyamide composite produced by SLS, in comparison with unfilled PA.

A specific focus is set on the evaluation of primary and secondary anisotropy in the case of metal or ceramic filler, as well as on the specific contribution of powder distribution modes and joining phenomena. Macroscopic mechanical tests and the observation of joining and failure micro‐mechanisms are integrated.

The results prove the absence of relevant anisotropy amongst specimens that are produced with the axis parallel to the plane of powder deposition. Samples whose axis is parallel to the growth direction Z, instead, reveal a significantly different response with respect to other orientations.

An original explanatory model is assumed and validated, based on an anisotropic distribution of the reinforcing particles during parts' production, which determines the efficacy of the strengthening mechanisms during crack propagation.

To investigate the “staircase effect”, which is one of the most significant manifestations of part inaccuracy in liquid‐based rapid prototyping (RP) processes, on multi‐layer RP parts made using a thick layer deposition and photo‐curing process in a stepless rapid prototyping (SRP) system.

The building of a five‐layer part is simulated layer by layer using a finite element method based on an incremental elastic model, to analyze the staircase effect due to shrinkage induced by polymerization and temperature variation. The influence of various factors such as layer thickness and intensity of incident UV light is studied. The results were verified experimentally.

Results show that the staircase amount increases 20 percent and 300 percent with light intensity increasing from 65 to 145 mW/cm² and layer thickness increasing from 0.2 to 2.0 mm, respectively. It is also found that the overall staircase is below 100 μm, which suggests that the SRP process improves surface quality greatly compared to other RP systems, and can provide enough accuracy for fabricating functional parts.

The results apply only to the material used in the work: an acrylate‐based photopolymer resin, C123, produced by Tianjin Chemical Co., China. Also, the thickness of the layers is fixed at 6 mm.

Provides a method to analyze the origin and amount of the staircase effect, upon which to better control the surface finish of RP parts. New materials and different layer thicknesses can be investigated using the same method.

Apart from the above practical implication, this paper establishes the parameters that influence the shrinkage of the material used in SRP.

The purpose of this paper is to elucidate the effect of part thickness and build orientation upon the type and magnitude of distortion in material jetting processes.

Specimens with high (10:1) aspect ratio were printed in two orientations (XY and YX) and three thickness values (1, 3 and 6 mm) and scanned with a white-light profilometer to quantify distortion.

The results of this paper indicate that 1-mm thick specimens always distorted following a wavy edge type, while thicker specimens (3- and 6-mm) always distorted following a reverse coil set. The factor thickness, when measured with the indices height of the highest peak (H) and profile radius (R), was shown to be statistically significant, with 3-mm specimens experiencing distortions of 57 and 51 per cent, respectively, more severe than those in 6-mm specimens. The thickness effect is attributed to the percentage of build layers that receive maximum energy exposure (61-72 per cent in 1-mm, 87-91 per cent in 3-mm and 93-95 per cent in 6-mm specimens). With respect to the thinner 1-mm specimens, the factor orientation was found to be statistically significant with distortion 114 per cent less severe in the YX orientation when measured by the H index.

This paper provides the first known description of build orientation and part thickness effects on dimensional distortion as a pervasive consequence of the curing process in photopolymerization and explores one of the most common defects encountered in additive manufacturing. In addition to the characterization of the type and magnitude of distortion, the contributions of this paper also include establishing the foundation for design guidelines aiming at minimizing distortion in material jetting.

This paper aims to study numerically the influence of the applied laser energy density and the porosity of the powder bed on the thermal behavior of the melt and the resultant instability of the liquid track.

A three-dimensional model was proposed to predict local powder melting process. The model accounts for heat transfer, melting, solidification and evaporation in granular system at particle scale. The proposed model has been proved to be a good approach for the simulation of the laser melting process.

The results shows that the applied laser energy density has a significantly influence on the shape of the molten pool and the local thermal properties. The relative low or high input laser energy density has the main negative impact on the stability of the scan track. Decreasing the porosity of the powder bed lowers the heat dissipation in the downward direction, resulting in a shallower melt pool, whereas pushing results in improvement in liquid track quality.

The randomly packed powder bed is calculated using discrete element method. The powder particle information including particle size distribution and packing density is taken into account in placement of individual particles. The effect of volumetric shrinkage and evaporation is considered in numerical model.

This paper aims to address the numerical simulation of additive manufacturing (AM) processes. The numerical results are compared with the experimental campaign carried out at State Key Laboratory of Solidification Processing laboratories, where a laser solid forming machine, also referred to as laser engineered net shaping, is used to fabricate metal parts directly from computer-aided design models. Ti-6Al-4V metal powder is injected into the molten pool created by a focused, high-energy laser beam and a layer of added material is sinterized according to the laser scanning pattern specified by the user.

The numerical model adopts an apropos finite element (FE) activation technology, which reproduces the same scanning pattern set for the numerical control system of the AM machine. This consists of a complex sequence of polylines, used to define the contour of the component, and hatches patterns to fill the inner section. The full sequence is given through the common layer interface format, a standard format for different manufacturing processes such as rapid prototyping, shape metal deposition or machining processes, among others. The result is a layer-by-layer metal deposition which can be used to build-up complex structures for components such as turbine blades, aircraft stiffeners, cooling systems or medical implants, among others.

Ad hoc FE framework for the numerical simulation of the AM process by metal deposition is introduced. Description of the calibration procedure adopted is presented.

The objectives of this paper are twofold: firstly, this work is intended to calibrate the software for the numerical simulation of the AM process, to achieve high accuracy. Secondly, the sensitivity of the numerical model to the process parameters and modeling data is analyzed.