Fracture Resistance Analysis of 3D-Printed Polymers

The Influence of Microstructural Arrangement on the Failure Characteristics of 3D-Printed Polymers: Exploring Damage Behaviour in Acrylonitrile Butadiene Styrene

This study investigated how printing conditions influence the fracture behaviour of 3D-printed acrylonitrile butadiene styrene (ABS) under tensile loading. Dog-bone-shaped ABS specimens were produced using the fusion filament fabrication technique, with varying printing angles. Tensile tests were conducted on pre-notched specimens with consistent pre-notch lengths but different orientations. Optical and scanning electron microscopies were employed to analyse crack propagation in the pre-notched specimens. In order to support experimental evidence, finite element computation was implemented to study the damage induced by the microstructural rearrangement of the filaments when subject to tensile loading. The findings revealed the simple linear correlation between the failure properties including elongation at break and maximum stress in relation to the printing angle for different pre-notch lengths. A more progressive damage was found to support the ultimate performance of the studied material. This experiment evidence was used to build a damage model of 3D-printed ABS that accounts for the onset, growth, and damage saturation. This damage modelling is able to capture the failure properties as a function of the printing angle using a sigmoid-like damage function and a modulation of the stiffness within the raster. The numerical results demonstrated that damage pattern develops as a result of the filament arrangement and weak adhesion between adjacent filaments and explains the diffuse damage kinetics observed experimentally. This study concludes with a topological law relating the notch size and orientation to the rupture properties of 3D-printed ABS. This study supports the idea of tailoring the microstructural arrangement to control and mitigate the mechanical instabilities that lead to the failure of 3D-printed polymers.

Tungsten Filled 3-Dimensional Printed Lung Blocks for Total Body Irradiation

PURPOSE

Lung blocks for total-body irradiation are commonly used to reduce lung dose and prevent radiation pneumonitis. Currently, molten Cerrobend containing toxic materials, specifically lead and cadmium, is poured into molds to construct blocks. We propose a streamlined method to create 3-dimensional (3D)-printed lung block shells and fill them with tungsten ball bearings to remove lead and improve overall accuracy in the block manufacturing workflow.

METHODS AND MATERIALS

3D-printed lung block shells were automatically generated using an inhouse software, printed, and filled with 2 to 3 mm diameter tungsten ball bearings. Clinical Cerrobend blocks were compared with the physician drawn blocks as well as our proposed tungsten filled 3D-printed blocks. Physical and dosimetric comparisons were performed on a linac. Dose transmission through the Cerrobend and 3D-printed blocks were measured using point dosimetry (ion-chamber) and the on-board Electronic-Portal-Imaging-Device (EPID). Dose profiles from the EPID images were used to compute the full-width-half-maximum and to compare with the treatment-planning-system. Additionally, the coefficient-of-variation in the central 80% of full-width-half-maximum was computed and compared between Cerrobend and 3D-printed blocks.

RESULTS

The geometric difference between treatment-planning-system and 3D-printed blocks was significantly lower than Cerrobend blocks (3D: -0.88 ± 2.21 mm, Cerrobend: -2.28 ± 2.40 mm, P = .0002). Dosimetrically, transmission measurements through the 3D-printed and Cerrobend blocks for both ion-chamber and EPID dosimetry were between 42% to 48%, compared with the open field. Additionally, coefficient-of-variation was significantly higher in 3D-printed blocks versus Cerrobend blocks (3D: 4.2% ± 0.6%, Cerrobend: 2.6% ± 0.7%, P < .0001).

CONCLUSIONS

We designed and implemented a tungsten filled 3D-printed workflow for constructing total-body-irradiation lung blocks, which serves as an alternative to the traditional Cerrobend based workflow currently used in clinics. This workflow has the capacity of producing clinically useful lung blocks with minimal effort to facilitate the removal of toxic materials from the clinic.

Performance of 3D printing biomimetic conch shell and pearl shell hybrid design composites under quasi-static three-point bending load

The failure process of biomimetic hybrid design composite composed of layers of conch shell and pearl shell was studied through quasi-static three-point bending experiments and numerical simulations. The biomimetic conch shell structure with inclined angles serves as the upper layer of the hybrid structure, while the biomimetic pearl shell structure with traditional brick and mud structure serves as the lower layer of the hybrid structure, forming a hybrid design structure. Four inclined angles were designed for the structural units of the conch shell, namely 15°, 30°, 45°, and 60°. Twenty-four specimens (six specimens for each inclined angle) were prepared using 3D printing technology using both soft and hard matrix materials. The influence of different inclined angles on the fracture strength, fracture toughness, and energy absorption of hybrid design structures was experimentally studied. The biomimetic hybrid design composite specimen with a notch is placed between two supporting rollers, and a loading indenter acts at mid-span. All twenty-four specimens were notched with a triangular tip and a rectangular bottom. A loading rate of 1 mm/min is used to avoid the viscoelastic effect of the composite materials. Details of the specimens, the experimental set-up and procedure are discussed in this paper. Complementary to the experimental studies, an extensive numerical investigation was carried out to study the influence of the aspect ratio of brick and mud units on the fracture initiation and failure of hybrid design structures. The causes of crack initiation and propagation, and failure modes in biomimetic hybrid design structures were postulated. These numerical findings help in reinforcing the experimental results and provide crucial information to enhance further research in this exciting area.

The Implementation of Neural Networks for Polymer Mold Surface Evaluation

This paper presents the measurement and evaluation of the surfaces of molds produced using additive technologies. This is an emerging trend in mold production. The surfaces of such molds must be treated, usually using laser-based alternative machining methods. Regular evaluation is necessary because of the gradually deteriorating quality of the mold surface. However, owing to the difficulty in scanning the original surface of the injection mold, it is necessary to perform surface replication. Therefore, this study aims to describe the production of surface replicas for in-house developed polymer molds together with the determination of suitable descriptive parameters, the method of comparing variances, and the mean values for the surface evaluation. Overall, this study presents a new summary of the evaluation process of replicas of the surfaces of polymer molds. The nonlinear regression methodology provides the corresponding functional dependencies between the relevant parameters. The statistical significance of a neural network with two hidden layers based on the principle of Rosenblatt's perceptron has been proposed and verified. Additionally, machine learning was utilized to better compare the original surface and its replica.

Box-Behnken modeling to quantify the impact of control parameters on the energy and tensile efficiency of PEEK in MEX 3D-printing

Currently, energy efficiency and saving in production engineering, including Material Extrusion (MEX) Additive Manufacturing, are of key importance to ensure process sustainability and cost-effectiveness. The functionality of parts made with MEX 3D-printing remains solid, especially for expensive high-performance polymers, for biomedical, automotive, and aerospace industries. Herein, the energy and tensile strength metrics are investigated over three key process control parameters (Nozzle Temperature, Layer Thickness, and Printing Speed), with the aid of laboratory-scale PEEK filaments fabricated with melt extrusion. A double optimization is attempted for the production by consuming minimum energy, of PEEK parts with improved strength. A three-level Box-Behnken design with five replicas for each experimental run was employed. Statistical analysis of the experimental findings proved that LT is the most decisive control setting for mechanical strength. An LT of 0.1 mm maximized the tensile endurance (∼74 MPa), but at the same time, it was responsible for the worst energy (∼0.58 MJ) and printing time (∼900 s) expenditure. The experimental and statistical findings are further discussed and interpreted using fractographic SEM and optical microscopy, revealing the 3D printing quality and the fracture mechanisms in the samples. Thermogravimetric analysis (TGA) was performed. The findings hold measurable engineering and industrial merit, since they may be utilized to achieve an optimum case-dependent compromise between the usually contradictory goals of productivity, energy performance, and mechanical functionality.

3D printing for customized carbon electrodes

Traditional carbon electrodes are made of glassy carbon or carbon fibers and have limited shapes. 3D printing offers many advantages for manufacturing carbon electrodes, such as complete customization of the shape and the ability to fabricate devices and electrodes simultaneously. Additive manufacturing is the most common 3D printing method, where carbon materials are added to the material to make it conductive, and treatments applied to enhance electrochemical activity. A newer form of 3D printing is 2-photon lithography, where electrodes are printed in photoresist via laser lithography and then annealed to carbon by pyrolysis. Applications of 3D printed carbon electrodes include nanoelectrode measurements of neurotransmitters, arrays of biosensors, and integrated electrodes in microfluidic devices.

Experimental Quantification of the Variability of Mechanical Properties in 3D Printed Continuous Fiber Composites

The material properties of 3D printed continuous fiber composites have been studied many times in the last years. However, only a minimal number of samples were used to determine the properties in each of the reported studies. Moreover, reported results can hardly be compared due to different sample geometries. Consequently, the variability of the mechanical properties (from one sample to the other) is a crucial parameter that has not been well quantified yet. In the present work, the flexural properties of 3D printed continuous carbon fiber/nylon composite specimens were experimentally quantified, using batches of 15 test specimens. In order to account for the possible influence of the quality of the prepreg filaments on the observed variability, three different filament rolls were used to manufacture the different batches. Also, two configurations were tested, with a fiber direction parallel (longitudinal) or perpendicular (transverse) to the main axis of the specimens. The results show moderate to high variabilities of the flexural modulus, flexural strength and maximum strain. The coefficient of variation was more than twice as high in the transverse case as in the longitudinal case.

Mathematical Modeling and Optimization of Fused Filament Fabrication (FFF) Process Parameters for Shape Deviation Control of Polyamide 6 Using Taguchi Method

Fused filament fabrication (FFF) is a layer-by-layer additive manufacturing (AM) process for producing parts. For industries to gain a competitive advantage, reducing product development cycle time is a basic goal. As a result, industries’ attention has turned away from traditional product development processes toward rapid prototyping techniques. Because different process parameters employed in this method significantly impact the quality of FFF manufactured parts, it is essential to optimize FFF process parameters to enhance component quality. The paper presents optimization of fused filament fabrication process parameters to improve the shape deviation such as cylindricity and circularity of 3D printed parts with the Taguchi optimization method. The effect of thickness, infill pattern, number of walls, and layer height was investigated as variable parameters for experiments on cylindricity and circularity. The MarkForged^® used Nylon White (PA6) to create the parts. ANOVA and the S/N ratio are also used to evaluate and optimize the influence of chosen factors. As a result, it was concluded that the hexagonal infill pattern, the thickness of 5 mm, wall layer of 2, and a layer height of 1.125 mm were known to be the optimal process parameters for circularity and cylindricity in experiments. Then a linear regression model was created to observe the relationship between the control variables with cylindricity and circularity. The results were confirmed by a confirmation test.

Redesign of the Geometry of Parts Produced from PBT Composite to Improve Their Operational Behavior

Parts produced from PBT-GF30 (70% polybutylene terephthalate +30% fiberglass) are very often used in car construction, due to the properties of this material. The current trend is to make parts with a shape designed to be as complex as possible, to take over many functions in operation. During the research, a part that is a component of the structure of car safety systems, and that must be completely reliable in operation, was analyzed. This piece has a complex shape that involves the intersection of several walls. Thus, the research aimed at establishing the optimal radius of connection between the walls (R), the ratio between the thickness of the intersecting walls (K) and the angle of inclination of the walls (α). The composite central design method was used to design the experiments. Both new parts and parts subject to an artificial aging process were tested. All parts were subjected to shear stress, to determine the load (L) and displacement (D) at which they break. In order to observe other changes in the properties of the parts, in addition to the mechanical ones, an analysis of the color of the new and aged parts was performed, as well as a topography of the surface layer in the breaking area. The design of the parts involved changes to the parameters of the injection process. In these conditions, a PBT-GF30 viscosity analysis was performed for new and artificially aged parts.

Autoclave sterilization of an in-house 3D-printed polylactic acid piece: biological safety and heat-induced deformation

AIMS

Fused filament fabrication 3D printing with polylactic acid filaments is the most widely used method to generate biomodels at hospitals throughout the world. The main limitation of this manufacturing system is related to the biomodels' temperature sensitivity, which all but prevents them to be sterilized using conventional methods. The purpose of this study is to define an autoclave temperature-resistant FFF-PLA 3D printing protocol to print 3D fractures biomodels during preoperative planning.

METHODS AND RESULTS

Six different printing protocols were established, each with a different infill percentage. Ten distal radius biomodels were printed with each protocol and each biomodel was subject to 3D scanning. The biomodels were subsequently autoclave-sterilized at 134 °C and subjected to a new scanning process, which was followed by a calculation of changes in area, volume and deformity using the Hausdorff-Besicovitch method. Finally, 192 polylactic acid models were produced using the printing protocol offering the greatest resistance and were contaminated with 31 common nosocomial pathogens to evaluate the effectiveness of sterilizing the model printed using the said protocol. Sterilization resulted in a mean deformation of the biomodel of 0.14 mm, a maximum deformity of 0.75 mm, and a 1% area and a 3.6% volume reduction. Sterilization of the pieces printed using the analyzed protocol was 100% effective.

CONCLUSIONS

The analyzed 3D printing protocol may be applied with any FFF-PLA 3D printer, it is safe and does not significantly alter the morphology of biomodels. These results indicate that 3D printing is associated with significant advantages for health centers as it increases their autonomy, allowing them to easily produce 3D biomodels that can be used for the treatment of fractures.

Mixed Mode Crack Propagation in Polymers Using a Discrete Lattice Method

The fracture behavior of polymeric materials has been widely studied in recent years, both experimentally and numerically. Different numerical approaches have been considered in the study of crack propagation processes, from continuum-based numerical formulations to discrete models, many of the latter being limited in the selection of the Poisson's coefficient of the considered material. In this work, we present a numerical and experimental analysis of the crack propagation process of polymethylmethacrylate beams with central and eccentric notches subjected to quasi-static three-point bending tests. The developed discrete numerical model consists of a regular triangular lattice model based on axial and normal interaction springs, accounting for nearest-neighbor interactions. The proposed model allows solving the above mentioned limitation in the selection of Poisson's coefficient, incorporating a fracture criterion defined by a bilinear law with softening that includes the fracture energy in the formulation and allows considering a progressive damage. One of the main objectives of this work is to show the capacity of this lattice to simulate quasi-static fracture problems. The obtained results show that the proposed lattice model is capable of providing results close to the experimental ones in terms of crack pattern, peak load and initial stiffening.

Security of 3D-printed polylactide acid piece sterilization in the operating room: a sterility test

INTRODUCTION

3D-printing technology has become very popular the last 10 years, and their advantages have been widely proved. However, its safety in the operating room after sterilization has not been evaluated. Thus, the use of 3D printing is still questioned. The aim of this work is to evaluate the security of polylactic acid (PLA) to print surgical models after its sterilization.

MATERIALS AND METHODS

One hundred and eighty-six PLA plates and 6 negative controls without microorganisms were seeded. After 10 days of culture, the PLA plates were randomized into three groups: A, B, and C. Group A underwent a sterilization process using an autoclave program at 134 °C. Group B was seeded in different culture media and group C was used to make crystal violet stains on the biofilms formed on the PLA. Mechanical properties of PLA after autoclave sterilization including, the breaking load, deformation and breaking load per surface were calculated.

RESULTS

Hundred percent of the group B showed monomicrobial growth. Stains performed on group C PLA showed biofilms in all PLA pieces. After sterilization, no pathogen growth was observed in group A during the culture observation period showing 100% sterilization effectiveness. A filling percentage of 5% obtained a breaking load of 6.36 MPa, and its elastic limit occurred after an elongation of 167.4%. A 10% infill was mechanically safe.

CONCLUSIONS

Autoclave sterilization of PLA-printed pieces is safe for the patient and mechanically strong for the surgeon. This is the first 3D-printing protocol described and evaluated to implement 3D-printing technology safely in the operating room.

SIGNIFICANCE AND IMPACT OF STUDY

This is the first 3D-printing protocol described to print and sterilize 3D biomodels using an autoclave showing its biological safety and its mechanical resistance.

Deformation Process of 3D Printed Structures Made from Flexible Material with Different Values of Relative Density

The main aim of this article is the analysis of the deformation process of regular cell structures under quasi-static load conditions. The methodology used in the presented investigations included a manufacturability study, strength tests of the base material as well as experimental and numerical compression tests of developed regular cellular structures. A regular honeycomb and four variants with gradually changing topologies of different relative density values have been successfully designed and produced in the TPU-Polyflex flexible thermoplastic polyurethane material using the Fused Filament Fabrication (FFF) 3D printing technique. Based on the results of performed technological studies, the most productive and accurate 3D printing parameters for the thermoplastic polyurethane filament were defined. It has been found that the 3D printed Polyflex material is characterised by a very high flexibility (elongation up to 380%) and a non-linear stress-strain relationship. A detailed analysis of the compression process of the structure specimens revealed that buckling and bending were the main mechanisms responsible for the deformation of developed structures. The Finite Element (FE) method and Ls Dyna software were used to conduct computer simulations reflecting the mechanical response of the structural specimens subjected to a quasi-static compression load. The hyperelastic properties of the TPU material were described with the Simplified Rubber Material (SRM) constitutive model. The proposed FE models, as well as assumed initial boundary conditions, were successfully validated. The results obtained from computer simulations agreed well with the data from the experimental compression tests. A linear relationship was found between the relative density and the maximum strain energy value.

Effect of Reconstruction Algorithm on the Identification of 3D Printing Polymers Based on Hyperspectral CT Technology Combined with Artificial Neural Network

Hyperspectral X-ray CT (HXCT) technology provides not only structural imaging but also the information of material components therein. The main purpose of this study is to investigate the effect of various reconstruction algorithms on reconstructed X-ray absorption spectra (XAS) of components shown in the CT image by means of HXCT. In this paper, taking 3D printing polymer as an example, seven kinds of commonly used polymers such as thermoplastic elastomer (TPE), carbon fiber reinforced polyamide (PA-CF), acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), ultraviolet photosensitive resin (UV9400), polyethylene terephthalate glycol (PETG), and polyvinyl alcohol (PVA) were selected as samples for hyperspectral CT reconstruction experiments. Seven kinds of 3D printing polymer and two interfering samples were divided into a training set and test sets. First, structural images of specimens were reconstructed by Filtered Back-Projection (FBP), Algebra Reconstruction Technique (ART) and Maximum-Likelihood Expectation-Maximization (ML-EM). Secondly, reconstructed XAS were extracted from the pixels of region of interest (ROI) compartmentalized in the images. Thirdly, the results of principal component analysis (PCA) demonstrated that the first four principal components contain the main features of reconstructed XAS, so we adopted Artificial Neural Network (ANN) trained by the reconstructed XAS expressed by the first four principal components in the training set to identify that the XAS of corresponding polymers exist in both of test sets from the training set. The result of ANN displays that FBP has the best performance of classification, whose ten-fold cross-validation accuracy reached 99%. It suggests that hyperspectral CT reconstruction is a promising way of getting image features and material features at the same time, which can be used in medical imaging and nondestructive testing.