Search results

The purpose of this study is to understand how printing parameters and subsequent annealing impacts porosity and crystallinity of 3D printed polylactic acid (PLA) and how these structural characteristics impact the printed material’s tensile strength in various build directions.

Two experimental studies were used, and samples with a flat vs upright print orientation were compared. The first experiment investigates a scan of printing parameters and annealing times and temperatures above the cold crystallization temperature (T_cc) for PLA. The second experiment investigates annealing above and below T_cc at multiple points over 12 h.

Annealing above T_cc does not significantly impact the porosity but it does increase crystallinity. The increase in crystallinity does not contribute to an increase in strength, suggesting that co-crystallization across the weld does not occur. Atomic force microscopy (AFM) images show that weld interfaces between printed fibers are still visible after annealing above T_cc, confirming the lack of co-crystallization. Annealing below T_cc does not significantly impact porosity or crystallinity. However, there is an increase in tensile strength. AFM images show that annealing below T_cc reduces thermal stresses that form at the interfaces during printing and slightly “heals” the as-printed interface resulting in an increase in tensile strength.

While annealing has been explored in the literature, it is unclear how it affects porosity, crystallinity and thermal stresses in fused filament fabrication PLA and how those factors contribute to mechanical properties. This study explains how co-crystallization across weld interfaces is necessary for crystallinity to increase strength and uses AFM as a technique to observe morphology at the weld.

This study aims to investigate the impact of layer thickness, extrusion temperature, extrusion speed and build plate temperature on the tensile strength, crystallinity achieved during fabrication (herein, in-process crystallinity) and mesostructure of Poly(lactic acid) specimens. Both tensile strength and in-process crystallinity were optimized and verified as the function of processing parameters, and their relationship was thoroughly examined.

The four key technological parameters were systematically varied as factors on three levels, using the statistically designed experiment. Surface response methodology was used to optimize tensile strength and crystallinity for the given ranges of input factors. Optimized factor settings were used in a set of confirmation runs, where the result of optimization was experimentally confirmed. Material characterization was performed using differential scanning calorimetry and X-ray diffraction analysis, while the effect of processing parameters on mesostructure was examined by scanning electron microscopy.

Layer thickness and its quadratic effect are dominant contributors to tensile strength. Significant interaction between layer thickness and extrusion speed implies that these parameters should always be varied simultaneously within designed experiment to obtain adequate process model. As regards, the in-process crystallinity, extrusion speed is part of two significant interactions with plate temperature and layer thickness, respectively. Quality of mesostructure is vital contributor to tensile strength during FDM process, while the in-process crystallinity exhibited no impact, remaining below the 20 per cent margin regardless of process parameter settings.

According to available literature, there have been no previously published investigations which studied the effect of process parameters on tensile strength, mesostructure and in-process crystallinity through systematic variation of four critical processing parameters.

Rapid tooling has numerous advantages when prototyping injection molded components, but the effects of the tooling on the resulting part properties are often overlooked. The purpose of this paper is to consider the effect of tooling on the final part properties and morphology.

Digital polyacrylonitrile-butadiene-styrene (ABS) tooling and aluminum tooling were used to mold test specimens from isotatic polypropylene (iPP). Tensile behavior, impact strength, shrinkage, surface roughness and porosity were evaluated for both sets of samples. Additionally, differential scanning calorimeter (DSC) and wide-angle X-ray scattering (WAXS) were used to assess the crystallinity of the samples.

Characterization of the molded parts showed that slower cooling rates in the Digital ABS inserts promoted the formation of ß-PP, while this crystal structure was not found in the parts molded using aluminum tooling. Additionally, parts molded on the digital ABS inserts exhibited higher mold shrinkage and SEM images identified microscopic shrinkage voids within the material. The change in morphology and the presence of voids significantly affected the tensile behavior with the parts molded in Digital ABS, which broke with little cold drawing and exhibited higher tensile moduli and higher yield strengths.

The results show that the choice of rapid tooling technique plays an important role on determining the properties of the final parts.

Previous studies have not characterized the effect of rapid tooling on the morphology of the molded articles fully or over a variety of processing conditions. This study builds on prior work by using both WAXS and DSC to characterize morphological changes over a wide range of processing conditions and comparing results to mechanical property and shrinkage data.

Additive manufacturing (AM) methods such as material extrusion (ME) are becoming widely used by engineers, designers and hobbyists alike for a wide variety of applications. Successfully manufacturing objects using ME three-dimensional printers can often require numerous iterations to attain predictable performance because the exact mechanical behavior of parts fabricated via additive processes are difficult to predict. One of that factors that contributes to this difficulty is the wide variety of ME feed stock materials currently available in the marketplace. These build materials are often sold based on their base polymer material such as acrylonitrile butadiene styrene or polylactic acid (PLA), but are produced by numerous different commercial suppliers in a wide variety of colors using typically undisclosed additive feed stocks and base polymer formulations. This paper aims to present the results from an experimental study concerned with quantifying how these sources of polymer variability can affect the mechanical behavior of three-dimensional printed objects. Specifically, the set of experiments conducted in this study focused on following: several different colors of PLA filament from a single commercial supplier to explore the effect of color additives and three filaments of the same color but produced by three different suppliers to account for potential variations in polymer formulation.

A set of five common mechanical and material characterization tests were performed on 11 commercially available PLA filaments in an effort to gain insight into the variations in mechanical response that stem from variances in filament manufacturer, feed stock polymer, additives and processing. Three black PLA filaments were purchased from three different commercial suppliers to consider the variations introduced by use of different feed stock polymers and filament processing by different manufacturers. An additional eight PLA filaments in varying colors were purchased from one of the three suppliers to focus on how color additives lead to property variations. Some tests were performed on unprocessed filament samples, while others were performed on objects three-dimensional printed from the various filaments. This study looked specifically at four mechanical properties (Young’s modulus, storage modulus, yield strength and toughness) as a function of numerous material properties (e.g. additive loading, molecular weight, molecular weight dispersity, enthalpy of melting and crystallinity).

For the 11 filaments tested the following mean values and standard deviations were observed for the material properties considered: p_a = 1.3 ± 0.9% (percent additives), M_w = 98.6 ± 16.4 kDa (molecular weight), Ð = 1.33 ± 0.1 (molecular weight dispersity), H_m = 37.4 ± 7.2 J/g (enthalpy of melting) and = 19.6 ± 2.1% (crystallinity). The corresponding mean values and standard deviations for the resulting mechanical behaviors were: E = 2,790 ± 145 MPa (Young’s modulus), E’ = 1,050 ± 125 MPa (storage modulus), S_y = 49.6 ± 4.93 MPa (yield strength) and U_t = 1.87 ± 0.354 MJ/m^³ (toughness). These variations were observed in filaments that were all manufactured from the same base polymer (e.g. PLA) and are only different in terms of the additives used by the manufacturers to produce different colors or different three-dimensional printing performance. Unfortunately, while the observed variations were significant, no definitive strong correlations were found between these observed variations in the mechanical behavior of the filaments studied and the considered material properties.

These variations in mechanical behavior and material properties could not be ascribed to any specific factor, but rather show that the mechanical of three-dimensional printed parts are potentially affected by variations in base polymer properties, additive usage and filament processing choices in complex ways that can be difficult to predict.

These results emphasize the need to take processing and thereby even filament color, into account when using ME printers, they emphasize the need for designers to use AM with caution when the mechanical behavior of a printed part is critical and they highlight the need for continued research in this important area. While all filaments used were marked as PLA, the feedstock materials, additives and processing conditions created significant differences in the mechanical behavior of the printed objects evaluated, but these differences could not be accurately and reliably predicted as function of the observed material properties that were the focus of this study.

The testing methods used in the study can be used by engineers and creators alike to better analyze the material properties of their filament printed objects, to increase success in print and mechanical design. Furthermore, the results clearly show that as AM continues to evolve and grow as a manufacturing method, standardization of feedstock processing conditions and additives would enable more reliable and repeatable printed objects and would better assist designers in effectively implementing AM methods.

In this study, a three‐dimensional (3D) flow model is used to approximate the crystallinity gradients of slowly crystallizing polymers developed in the injection molding process. A generalized second order parallel splitting formula is constructed to achieve both the accuracy and efficiency of the computation. Calculated values of flow‐wise (flow‐thickness plane) and width‐wise (width‐thickness plane) crystallinity distributions are obtained and compared with experimental results. The structure‐oriented simulation method developed is not only capable of describing moldability parameters, but is also able to predict the characteristics of ultimate properties of the final products.

The amount of radiated energy is known to be a crucial parameter in powder-bed additive manufacturing (AM) processes. The role of irradiance in the multijet fusion (MJF) process has not been addressed by any previous research, despite the key role of this process in the AM industry. The aim of this paper is to explore the relationship between irradiance and dimensional accuracy in MJF.

An experimental activity was carried out to map the relationship between irradiance and dimensional accuracy in the MJF transformation of polyamide 12. Two specimens were used to measure the dimensional accuracy on medium and small sizes. The experiment was run using six different levels of irradiance. For each, the crystallinity degree and part density were measured.

Irradiance was found to be directly proportional to part density and inversely proportional to crystallinity degree. Higher irradiance leads to an increase in the measured dimensions of parts. This highlights a predominant role of the crystallisation degree and uncontrolled peripherical sintering, in line with the previous literature on other powder-bed AM processes. The results demonstrate that different trends can be observed according to the range of sizes.

This paper aims to establish an appropriate annealing method, which is necessary for shape stability and to evaluate their potential degradation performance of 1-, 3- and 5-layer material extruded polylactic-acid specimens by enhancing their thermal and mechanical properties.

The distortion of each layered printed specimen subjected to degradation was calculated in x- and y-direction. Each layered specimen was subjected to annealing at 70°C, 80°C and 90°C for 2 h and at 80°C for 1, 4, 8 and 16 h. Thermal, molecular weight and mechanical properties were calculated using, differential scanning calorimetry, gel permeation chromatography and tensile testing machine, respectively.

In the x-direction, distortion was 16.08 mm for one-layer non-annealed printed specimens and decreased by 73% and 83% for 3- and 5-layer, respectively, while each layered non-annealed specimen subjected to degradation at 37°C for one month. Within the outlined study, annealing treatment enhances properties such as the degree of crystallinity (%χ) up to 34%, Young’s modulus (E) by 30% and ultimate tensile strength by 20% compared to the non-annealed specimens.

The future research accomplishments will be concentrated on the design, development and optimisation of degraded biomedical implants using material extrusion thin films including drug delivery system and fixation plates.

The printed thin specimens subjected to degradation were investigated. This research developed a new understanding of the effect of the annealing temperature and time on the mechanical, thermal and molecular weight properties for each layered specimen.

The purpose of this article is to discuss the tribological behavior of polytetrafluoroethylene (PTFE) and property changes imposed by wear tests.

Long-duration dry wear tests were carried out in a sliding bearing on shaft tribometer. Differential Scanning Calorimetry (DSC) and Fourier Transformed Infrared Spectroscopy (FTIR) analyses were performed in the PTFE in its original condition and after the tests.

The wear products merged in multilayer films and were expelled out of the test sequence. Through DSC and FTIR analyses in the polymeric material, before and after tests, it was possible to verify an increase of the crystallinity degree of PTFE, as well as absence of crystalline fusion of the material. The wear products presented changes in the infrared spectra, which suggests the occurrence of some bonds of hydrogen and oxygen.

It was verified on correlation that fibril mechanism, which occurred during PTFE wear, and its crystallinity degree increase. Also, analysis of PTFE wear products showed CO and CH bonds, which were imposed by wear test.

The purpose of this paper is to understand the influence of reinforced fiber length over material‐plastic energy of deformation, clogging, crystallinity, and correlates with the friction and wear behavior of polypropylene (PP) composites under multi‐pass abrasive condition. Also to identify wear mechanisms of glass fiber reinforced PP materials under various abrasive grit sizes and normal loads.

Multi‐pass abrasive wear tests were performed for unreinforced, short, and long glass fiber reinforced PP (LFPP) on a pin on disc machine under three different normal loads and two different abrasive grit sizes for a constant sliding velocity. Measured wear volume was correlated with the plastic energy of deformation by carrying out a constant load indentation test using servo hydraulic fatigue test system. Clogging behavior of test materials was examined with the aid of online wear measurement and wear morphology. Test materials crystallinity was estimated with the aid of X‐ray diffraction investigation and correlated with abrasive wear performance.

Fiber reinforcement in a PP material is found to improve the plastic deformation energy and crystallinity which results in improved abrasive resistance of the material. Increase in reinforced fiber length is found to improve the material cohesive energy and hence the wear resistance. Reinforcement is found to alter the material clogging behavior under multi‐pass condition. Fiber reinforcement is found to reduce the material coefficient of friction, and increase in reinforced fiber length further reduces the frictional coefficient.

Friction wear tests using pin on disc equipment is carried out in the present investigation. However, in practice, part geometry may not be always equivalent to simple pin on disc configuration.

The paper's investigation results could help to improve the utilization of LFPP material in many structural applications.

Influence of reinforced fiber length over multi‐pass abrasive wear performance of thermoplastic material, and online wear measurement to substantiate clogging behavior is unique in the present multi‐pass abrasive investigation.

This study aims to motivate the application of some low-cost minerals in synthesizing nanoparticles as effective additives on the performance of liquid crystal (LC) hydroxypropyl cellulose (HPC) nanocomposite film, in comparison with carbon nanoallotrope.

Metallic nanoparticles of vanadium oxide, montmorillonite (MMT) and bentonite were synthesized and characterized by different techniques (Transmission electron microscopy [TEM], X-ray diffraction [XRD] and Fourier transform infrared [FTIR]). While the XRD, FTIR, non-isothermal analysis thermogravimetric analysis, mechanical analysis, scanning electron microscope and polarizing microscope were techniques used to evaluate the key role of metallic nanoparticles on the performance of HPC-nanocomposite film.

The formation of nanoparticles was evidenced from TEM. The XRD and FTIR measurements of nanocomposite films revealed that incorporating the mineral nanoparticles led to enhance the HPCs crystallinity from 14% to 45%, without chemical change of HPC structure. It is interesting to note that these minerals provide higher improvement in crystallinity than carbon nanomaterials (28%). Moreover, the MMT provided film with superior thermal stability and mechanical properties than pure HPC and HPC containing carbon nanoparticles, where it increased the E_a from 583.6 kJ/mol to 669.3 kJ/mol, tensile strength from 2.25 MPa to 2.8 MPa, Young’s modulus from 119 MPa to 124 MPa. As well as it had a synergistic effect on the LC formation and the birefringence texture of the nanocomposites (chiral nematic).

Hydroxylpropyl cellulose-nanocomposite films were prepared by dissolving the HPC powder in water to prepare 50% concentration, (free or with incorporating 5% synthesized nanoparticles). To obtain films with uniform thickness, the prepared solutions were evenly spread on a glass plate via an applicator, by adjusting the thickness to 0.2 mm, then air dried.

These minerals provide higher improvement in crystallinity than carbon nanomaterials (28%), moreover, the MMT and bentonite provided films with superior thermal stability than pure HPC and HPC containing carbon nanoparticles. The mineral nanoparticles (especially MMT nanoclays) had a synergistic effect on LC formation and the birefringence texture of the nanocomposites (chiral nematic).

This study presents the route to enhance the utilization of claystone available in El-Fayoum Province as the precursor for nanoparticles and production high performance LC nanocomposites.

This study presents the route for the valorization of low-cost mineral-based nanoparticles in enhancing the properties of HPC-film (crystallinity, thermal stability, mechanical strength), in comparison with carbon-based nanoparticles. Moreover, these nanoparticles provided more ordered mesophases and, consequently, good synergetic effect on LCs formation and the birefringence texture of the HPC-films.