D. Karalekas and D. Rapti
This paper presents an experimental study undertaken to determine the polymerisation‐induced residual stresses generated in stereolithography (SL) built test specimens, by using…
Abstract
This paper presents an experimental study undertaken to determine the polymerisation‐induced residual stresses generated in stereolithography (SL) built test specimens, by using the hole‐drilling strain gage method of stress relaxation. Experimentally measured strains, using special three‐element strain gage rosettes, were input into the blind‐hole analysis to calculate the induced residual stresses. The mechanical properties of resin specimens fabricated by the solidification process using an epoxy based photopolymer and post‐cured under ultraviolet (UV) and thermal exposure were determined and incorporated into the subsequent drill‐hole analysis. The effect of the pre‐selected fabrication parameters (hatching space and curing depth) and subsequent by the post‐curing procedure (UV, thermal curing) on the magnitude of the recorded strains is also presented.
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J. Giannatsis, V. Dedoussis and D. Karalekas
The purpose of this paper is to investigate the applicability and effectiveness of Stereolithography rapid prototyping to the field of scale modelling for architectural design…
Abstract
The purpose of this paper is to investigate the applicability and effectiveness of Stereolithography rapid prototyping to the field of scale modelling for architectural design evaluation and demonstration purposes. Two scale models concerning a modern renovated track and field sports facility and a reconstructed ancient stadium are examined. Both models were constructed by assembling together resin parts fabricated with Stereolithography instead of milling. Critical issues encountered during the building phase of the two models are addressed and presented in detail. Comments are made on the CAD requirements of the parts geometry, on the part building and the post‐processing phases as well as on the end achieved accuracy. Problems associated with the computational time, related to the 3‐D solid modelling, and with the physical properties of the parts, are also discussed. The present Stereolithography methodology is compared to conventional model building techniques by investigating efficiency and productivity factors, quality matters and time requirements.
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Anthony A. D’Amico, Analise Debaie and Amy M. Peterson
The aim of this paper is to examine the impact of layer thickness on irreversible thermal expansion, residual stress and mechanical properties of additively manufactured parts.
Abstract
Purpose
The aim of this paper is to examine the impact of layer thickness on irreversible thermal expansion, residual stress and mechanical properties of additively manufactured parts.
Design/methodology/approach
Samples were printed at several layer thicknesses, and their irreversible thermal expansion, tensile strength and flexural strength were determined.
Findings
Irreversible thermal strain increases with decreasing layer thickness, up to 22 per cent strain. Tensile and flexural strengths exhibited a peak at a layer thickness of 200 μm although the maximum was not statistically significant at a 95 per cent confidence interval. Tensile strength was 54 to 97 per cent of reported values for injection molded acrylonitrile butadiene styrene (ABS) and 29 to 73 per cent of those reported for bulk ABS. Flexural strength was 18 to 41 per cent of reported flexural strength for bulk ABS.
Practical implications
The large irreversible thermal strain exhibited that corresponding residual stresses could lead to failure of additively manufactured parts over time. Additionally, the observed irreversible thermal strains could enable thermally responsive shape in additively manufactured parts. Variation in mechanical properties with layer thickness will also affect manufactured parts.
Originality/value
Tailorable irreversible thermal strain of this magnitude has not been previously reported for additively manufactured parts. This strain occurs in parts made with both high-end and consumer grade fused deposition modeling machines. Additionally, the impact of layer thickness on tensile and flexural properties of additively manufactured parts has received limited attention in the literature.
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Karina Puebla, Karina Arcaute, Rolando Quintana and Ryan B. Wicker
The purpose of this paper is to investigate the effects of aging, pre‐conditioning, and build orientation on the mechanical properties of test samples fabricated using…
Abstract
Purpose
The purpose of this paper is to investigate the effects of aging, pre‐conditioning, and build orientation on the mechanical properties of test samples fabricated using stereolithography (SL) and a commercially available resin.
Design/methodology/approach
American Society for Testing and Materials (ASTM) Standard D638 Type I specimens were manufactured in a Viper si2 SL system using WaterShed™ 11120 resin. The specimens were manufactured in two different build setups, designed to fit batches of 18 or 24 specimens with different build orientations. The specimens were randomly tested in tension, and a design of experiments (DOE) was used to determine the effect of aging (4, 30 or 120 days), pre‐conditioning (ambient, desiccant, or ASTM recommended conditioning), and build orientation (flat, on an edge, or vertical) on the ultimate tensile stress (UTS) and elastic modulus (E) of SL fabricated samples. Additionally, the fractured samples were imaged using scanning electron microscopy (SEM) to characterize the fractured surfaces.
Findings
Results showed that aging, pre‐conditioning, and build orientation each had an effect on the mechanical properties of the SL samples. In general, the samples aged at the shortest time frame (4 days) and the samples preconditioned according to ASTM recommendations had the lowest values of UTS. Regarding the effect of build orientation, the specimens built flat (with layers oriented along the thickness of the sample) had the lowest UTS and E values and the mechanical properties were statistically different from those built vertically or on an edge. The specimens built in the vertical orientation (with layers oriented along the length of the sample) had the highest values of UTS and E, yet the mechanical properties of the samples built on an edge (with layers oriented along the width of the sample) were not statistically different from the samples built vertically. SEM images of the fractured specimens showed fracture surfaces typical of polymers with a mirror zone and changes in surface texture from smooth to coarse.
Research limitations/implications
The research was limited to a single commercially available resin. Through a statistical DOE approach, statistically significant differences in mechanical properties of SL fabricated samples were found as functions of aging, pre‐conditioning, and build orientation. These results can assist the ASTM F42 Committee with developing test standards specific to SL and the additive manufacturing community.
Originality/value
The statistical analyses presented here can help identify and classify the effects of fabrication, storage, and conditioning parameters on mechanical properties for SL fabricated parts. Understanding how the mechanical properties of SL resins are affected by different parameters can help improve the use of SL for a variety of applications including direct manufacturing of end‐use products.
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The objective of this study is to investigate the use of a fibre Bragg grating (FBG) sensor for measuring of curing strains that develop during the solidification of a…
Abstract
Purpose
The objective of this study is to investigate the use of a fibre Bragg grating (FBG) sensor for measuring of curing strains that develop during the solidification of a photocurable resin used in 3D microfabrication.
Design/methodology/approach
The followed approach consists of embedding a 1,300 nm FBG into a cylindrical specimen, fabricated into a transparent mould, being exposed to ultraviolet laser light. The further development of the cure induced strains under thermal treatment was also studied by post‐conditioning the cylindrical specimen in an oven at 70°C.
Findings
The experimental results demonstrate the capability of the FBG sensor to provide useful information on the strain build‐up during laser solidification and their post‐cure evolution under the presence of a thermal environment.
Research limitations/implications
Future work should involve the use of smaller diameter FBG sensors in microstereolithography built parts.
Practical implications
It is shown that considerable cure strains are developed at the end of the photo‐polymerisation process that eventually can affect the structural resolution of final parts fabricated by microstereolithography.
Originality/value
The presented method can be used to investigate other photopolymers used in micro‐stereolithography.
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Engineering design optimisation of products and investigating the influence of various critical design parameters on their operational performance has been a complex task. Despite…
Abstract
Engineering design optimisation of products and investigating the influence of various critical design parameters on their operational performance has been a complex task. Despite the recent development of sophisticated computer hardware and software tools, increasing the use of computer‐based simulation methods and virtual prototypes, the product development process could be sharply aided by the implementation of rapidly available physical models of the products' conceptual designs. Such rapid prototyping models could be used for experimental evaluation and validation purposes, where critical aspects of the product can be investigated, tested and refined. The objective of this study was to investigate the prospect, and demonstrate the ability, of obtaining engineering data through experimental testing of stereolithography built models. This paper reports on the experimental data obtained from the two application examples studied: a consumer food metal container and an engine intake port component.
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Rui Yan, Yuye Wang, Pengjun Luo, Yangbo Li and Xiaochun Lu
The limited strength of polylactic acid (PLA) hinders its extensive engineering applications. This paper aims to enhance its strength and realize diverse applications.
Abstract
Purpose
The limited strength of polylactic acid (PLA) hinders its extensive engineering applications. This paper aims to enhance its strength and realize diverse applications.
Design/methodology/approach
Here, the continuous fiber reinforced PLA composites are fabricated by a customized fused filament fabrication three-dimensional printer. Uniaxial tensile and three-point flexural tests have been conducted to analyze the reinforcement effect of the proposed composites. To unveil the adhering mechanism of optic fiber (OF) and PLA, post failure analysis including the micro imaging and morphology have been performed. The underlying mechanism is that the axial tensile strength of the OF and the interfacial adhesion between PLA and OF compete to enhance the mechanical properties of the composite.
Findings
It is found that 10%–20% enhancement of strength, ductility and toughness due to the incorporation of the continuous OF.
Originality/value
The continuous OFs are put into PLA first time to improve the strength. The fabrication method and process reported here are potentially applied in such engineering applications as aerospace, defense, auto, medicine, etc.
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Huaqing Hu, Ketai He, Tianlin Zhong and Yili Hong
This paper aims to propose a method to diagnose fused deposition modeling (FDM) printing faults caused by the variation of temperature field and establish a fault knowledge base…
Abstract
Purpose
This paper aims to propose a method to diagnose fused deposition modeling (FDM) printing faults caused by the variation of temperature field and establish a fault knowledge base, which helps to study the generation mechanism of FDM printing faults.
Design/methodology/approach
Based on the Spearman rank correlation analysis, four relative temperature parameters are selected as the input data to train the SVM-based multi-classes classification model, which further serves as a method to diagnose the FDM printing faults.
Findings
It is found that FDM parts may be in several printing states with the variation of temperature field on the surface of FDM parts. The theoretical dividing lines between different FDM printing states are put forward by traversing all the four-dimensional input parameter combinations. The relationship between the relative mean temperature and the theoretical dividing lines is found to be close and is analyzed qualitatively.
Originality/value
The multi-classes classification model, embedded in FDM printers as an adviser, can be used to prevent waste products and release much work of labors for monitoring.
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Wilco M.H. Verbeeten, Miriam Lorenzo-Bañuelos, Rubén Saiz-Ortiz and Rodrigo González
The purpose of the present paper is to quantify and analyze the strain-rate dependence of the yield stress for both unfilled acrylonitrile-butadiene-styrene (ABS) and short carbon…
Abstract
Purpose
The purpose of the present paper is to quantify and analyze the strain-rate dependence of the yield stress for both unfilled acrylonitrile-butadiene-styrene (ABS) and short carbon fiber-reinforced ABS (CF-ABS) materials, fabricated via material extrusion additive manufacturing (ME-AM). Two distinct and opposite infill orientation angles were used to attain anisotropy effects.
Design/methodology/approach
Tensile test samples were printed with two different infill orientation angles. Uniaxial tensile tests were performed at five different constant linear strain rates. Apparent densities were measured to compensate for the voided structure. Scanning electron microscope fractography images were analyzed. An Eyring-type flow rule was evaluated for predicting the strain-rate-dependent yield stress.
Findings
Anisotropy was detected not only for the yield stresses but also for its strain-rate dependence. The short carbon fiber-filled material exhibited higher anisotropy than neat ABS material using the same ME-AM processing parameters. It seems that fiber and molecular orientation influence the strain-rate dependence. The Eyring-type flow rule can adequately describe the yield kinetics of ME-AM components, showing thermorheologically simple behavior.
Originality/value
A polymer’s viscoelastic behavior is paramount to be able to predict a component’s ultimate failure behavior. The results in this manuscript are important initial findings that can help to further develop predictive numerical tools for ME-AM technology. This is especially relevant because of the inherent anisotropy that ME-AM polymer components show. Furthermore, short carbon fiber-filled ABS enhanced anisotropy effects during ME-AM, which have not been measured previously.
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Paschalis Charalampous, Ioannis Kostavelis and Dimitrios Tzovaras
In recent years, additive manufacturing (AM) technology has been acknowledged as an efficient method for producing geometrical complex objects with a wide range of applications…
Abstract
Purpose
In recent years, additive manufacturing (AM) technology has been acknowledged as an efficient method for producing geometrical complex objects with a wide range of applications. However, dimensional inaccuracies and presence of defects hinder the broad adaption of AM procedures. These factors arouse concerns regarding the quality of the products produced with AM and the utilization of quality control (QC) techniques constitutes a must to further support this emerging technology. This paper aims to assist researchers to obtain a clear sight of what are the trends and what has been inspected so far concerning non-destructive testing (NDT) QC methods in AM.
Design/methodology/approach
In this paper, a survey on research advances on non-destructive QC procedures used in AM technology has been conducted. The paper is organized as follows: Section 2 discusses the existing NDT methods applied for the examination of the feedstock material, i.e. incoming quality control (IQC). Section 3 outlines the inspection methods for in situ QC, while Section 4 presents the methods of NDT applied after the manufacturing process i.e. outgoing QC methods. In Section 5, statistical QC methods used in AM technologies are documented. Future trends and challenges are included in Section 6 and conclusions are drawn in Section 7.
Findings
The primary scope of the study is to present the available and reliable NDT methods applied in every AM technology and all stages of the process. Most of the developed techniques so far are concentrated mainly in the inspection of the manufactured part during and post the AM process, compared to prior to the procedure. Moreover, material extrusion, direct energy deposition and powder bed processes are the focal points of the research in NDT methods applied in AM.
Originality/value
This literature review paper is the first to collect the latest and the most compatible techniques to evaluate the quality of parts produced by the main AM processes prior, during and after the manufacturing procedure.