•Novel experimental data on mechanics of additively manufactured MJF PA12.•Fracture resistance assessed on V-Notched and Semi-circular bend cracked samples.•The ASED Theory provided a practical ...approach to assess load capacity of MJF PA12.
This study aims to study the fracture resistance of additively manufactured polyamide 12 (PA12), specifically when subjected to notches and cracks, and how it varies with the printing direction using Multi Jet Fusion (MJF). The methodology involved conducting tensile tests on V-notched samples, with a focus on different combinations of opening angle (0°-120°) and tip radius (0.2–2 mm). The findings revealed that the sensitivity to the notch opening angle decreased with an increase in the notch tip radius. Furthermore, the fracture resistance for different mode mixities was examined using semi-circular bend (SCB) specimens, with the crack angle varied between 0° and 53°. The results demonstrated two distinct fracture behaviours, namely brittle and ductile, depending on the crack angle. Theoretical analyses revealed that with appropriate tuning, average strain energy density (ASED) can predict the load capacity of notched and cracked PA12 parts manufactured with MJF, within an error range of ± 20 %.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Through the hydrogen bonding between polyamide 12 (PA12) and N, N′-dicyclohexylterephthalamide (DCHT) nucleator, the intentionally controlled self-assembly of DCHT and the crystallization behavior of ...isotactic polypropylene (iPP) matrix are investigated. The introduction of PA12 could severely postpone the condensation of DCHT vapor in iPP matrix due to the reduced vapor concentration. As a result, the nucleating efficiency of DCHT at lower concentration for example iPP/PA12/0.05DCHT even failed at a relatively higher final heating temperature Tf. Such a failure of nucleating efficiency could be recoverable after a step-cycle treatment at lower Tf, where the sublimation of DCHT can hardly occur. The changes from a cluster-like structure to a network structure driven by hydrogen bonding between DCHT and PA12 could be a reason of nucleation failure and recovery. This means that the nucleating efficiency of DCHT and crystallization of iPP could be tuned by controlling the absorption and release of DCHT vapor at the surface of PA12 particles. For iPP/PA12/0.5DCHT with a higher concentration of DCHT, the absorption of PA12 could only reduce the DCHT vapor concentration in the iPP melt and thus, the dendrite structure of DCHT shows more and thinner branches, which results in better nucleating efficiency of DCHT than that in iPP/0.5DCHT.
Display omitted
•The presence of PA12 could absorb DCHT vapor in iPP matrix and postpone its condensation.•The nucleation failure and recovery of DCHT could be regulated by step-cycle treatment.•The nucleating efficiency of DCHT could be tuned by controlling the absorption and release from PA12.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Additive manufacturing such as selective laser sintering (SLS) offers the strategies to create 3D complex components with desirable mechanical, electrical and thermal properties using the composite ...powders as feeding materials. This work proposes a new fabrication approach to preparing carbon nanotube (CNT) composite powders and utilizes them for SLS process. As compared with the hot-compression process, the SLS process could offer an effective method to fabricate the CNT/Polymer composite with electrically conductive segregated structures. At a small loading range of CNTs (<1 wt%), the laser-sintered composites exhibit significant improvements in the electrical conductivity up to anti-static and conductive range qualifying the applications in automobile and aerospace. However, the enhancement in thermal conductivity of laser-sintered composites is not comparable with that of hot-compressed ones. The process-structure-property relationships are further investigated to study the different processes induced microstructures and the underlying mechanism of thermal and electrical performances.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Visual inspection of components, subassemblies and final products is an essential step to ensure the quality control of ready-to-market electronic components. In many manufacturing plants, including ...Bosch Car Multimedia S.A., typically automated systems for automatic optical inspection (AOI) are implemented at several workstations to perform visual verification and validation in between critical production tasks. At Bosch Car Multimedia S.A., the AOI system includes a metallic support frame that accommodates a series of components for the function of AOI. The support frame is attached to a robotic arm for controlled movement. As the AOI is a rather fast-moving process, deformation of components may occur during monitoring due to the high acceleration of the robotic arm while operating. In addition to this issue, the existent AOI system includes a high number of components and connections which increase complexity for assembly and disassembly operations. This paper presents the redesign for enhanced performance and functionality of a AOI metallic support frame by resourcing to the generative design (GD) exploration method. Furthermore, additive manufacturing technology, based in selective laser sintering (SLS) of polymeric powders, was used for the production of a new lightweight and reliable version of an AOI support frame. The alternative AOI support frame configuration consists of a single consolidated polymeric component that enabled an overall weight decrease above 30% and a reduction of main components and total number of parts of approximately 89% and ∼77%, respectively.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Polyamide 12 is a popular material for manufacturing 3D printing powders, but the existing technologies require harsh processing conditions. This study suggests a new route to obtain powders via the ...thermally-induced phase separation of polyamide 12 – benzyl alcohol mixtures, which proceeds at ambient pressure without using highly toxic substances. The approach is based on the experimental phase diagram of this system constructed for the first time using an original optical method. The analysis of this diagram allows us to choose the concentration–temperature range suitable for the formation of polymer suspension. It appears that the mean size and dispersity of powders are more sensitive to the rate of cooling than to the composition of the initial polymer–solvent mixture. The parameters of the obtained powder (melting/crystallization temperature, degree of crystallinity, bulk density, and particle size distribution) are close to those of several trademarks, thus making our approach promising for practical realization.
Display omitted
•A new route to produce PA12 powders for SLS 3D printing is suggested•It is based on the phase diagram PA12 – BnOH constructed for the first time•Powder can be obtained at milder conditions than in the published patents•Sample powders possess characteristics similar to commercial analogues•Particle size distribution is very sensitive to the rate of cooling during TIPS
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Recently, the possibility of producing medium-to-large batches has increased the interest in polymer powder bed fusion technologies such as selective laser sintering (SLS) and multi jet fusion (MJF). ...Only scant data about the characterization of parts produced by MJF can be found in the literature, and fatigue behavior studies are absent. This study analyzes the material properties of Polyamide 12 (PA12) powders and printed specimens using both SLS and MJF technologies. The morphology, crystalline phases, density, porosity, dimensional accuracy, and roughness are measured and compared; tensile and fatigue tests are performed to assess the effect of the technologies on the mechanical behavior of the produced structures. In addition, lattice structure specimens obtained by different geometric modeling approaches are tested to understand the influence of modeling methods on the fatigue life. The PA12 powders printed by both SLS and MJF mainly show by X-Ray Diffraction γ-phase and a small shoulder of α-phase. The crystallinity decreases after printing the powders both in SLS and MJF technology. The printed parts fabricated using the two technologies present a total porosity of 7.95% for SLS and 6.75% for MJF. The roughness values are similar, Ra ≈ 11 µm along the building direction. During tensile tests, SLS samples appear to be stiffer, with a lower plastic deformation than MJF samples, that are tougher than SLS ones. Fatigue tests demonstrate higher dispersion for MJF specimens and an enhancement of fatigue life for both SLS and MJF printed lattice structures modeled with a novel geometric modeling approach that allows the creation of smoother surfaces at nodal points. Scanning electron microscopy on fracture surfaces shows a brittle failure for the SLS tensile specimens, a more ductile failure for the MJF tensile specimens, a crazing failure mechanism for the SLS fatigue tested samples, and a crack initiation and slow growth and propagation for the MJF fatigue tested samples.
Display omitted
•Comparison between PA12 Selective Laser Sintering and Multi Jet Fusion technologies.•Different failure mechanisms for SLS and MJF fatigue tested samples.•SLS bulk specimens behave better for stresses higher than 34 MPa.•MJF bulk specimens fatigue curve has a knee at 34 MPa.•Lattice structures modeled with Catmull–Clark algorithm have longer fatigue life.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Polyamide 12 (PA12) has found significant applications in the medical device industry, including its common use as an outer jacket layer in catheters. Like all polymers, PA12 can undergo degradation ...reactions, which compromise the mechanical and physical properties of the material. In this paper FTIR/ATR, 1H NMR, kinematic viscosity, GPC, DMA and DSC were used to characterize several PA12 catheter jackets. The results showed a decrease in elasticity when the PA12 molecular weight dropped below a critical value. Additionally, stress/strain measurements of dry and hydrated PA12 samples were used to investigate the plasticization effect of water on the properties of the material. An increase in elasticity was observed as the hydration of the samples increased, although the PA12 samples quickly dried back out to their initial stiff state. The PA12 extrusion conditions were also examined to determine how the selection of draw down ratio and air gap can affect the elastic properties of the final part.
•A reduction in the molecular weight of a Polyamide 12 (PA12) catheter jacket below a critical value resulted in fractures.•Hydrated PA12 samples of different molecular weight showed similar stress/strain curves contrary to the dry precursors.•Plasticization effect of water on PA12 is not permanent as the samples dry out back to their initial stiff state.•Processing conditions during extrusion should be carefully selected as they also affect the mechanical properties of PA12.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Display omitted
•Fatigue behaviour of Polyamide 12 through Kitagawa-Takahashi diagrams.•Best fatigue performance of polyamide 12 processed by SLS at 0° orientation.•Characteristic lengths did not ...display a trend with manufacturing technique.•El Haddad approach provides accurate predictions in physically short crack zone.•Fatigue map of Polyamide 12 depends on the manufacturing process.
This work deals with the mechanical and fatigue behaviour of polyamide 12 processed via Selective Laser Sintering and Injection Moulding. Apart from the analysis regarding the influence of the manufacturing technique, the effect of the layer orientation with respect to the direction of the applied load will be also analysed, since the additive manufacturing technique is a layer-wise technology that can induce anisotropy in the material. An extensive experimental program was carried out to determine the tensile, fracture, fatigue life and fatigue crack growth behaviours. The main novelty of this work lies, for the first time in polymers, in the use of the perspective of the Kitagawa-Takahashi diagrams for infinite fatigue life and by analogy their extension to failure.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Cold Spray is a solid deposition process that can expand the field of application of polymeric materials thanks to the build-up of a metallic coating that improves their electrical properties and the ...wear resistance, among others. The novelty of the Cold Spray deposition on polymers has as drawback the lack of processing models that allow to choose the manufacturing parameters and forecast the coatings and substrates properties. In this work, the influence of the processing parameters for Aluminium-Zinc coating build-up via Low Pressure Cold Spray on polyamide 12 additively manufactured via Fused Filament Fabrication was investigated. Several sets of processing parameters combinations were systematically modified to establish the deposition window, leading to a final set that allowed to determine the physical, microstructural, and mechanical properties of the coatings, and the physical and thermal properties of the polymeric substrate. For the fixed gas pressure of 0.45 MPa and gas temperature of 500 °C, the scanning speed and the powder mass flow rate had a strong influence. Thick coatings (around 850 μm in size) were achieved at high powder mass flow rate (26 g/min) at the expense of low bond strength (between 1 and 3 MPa). The surface roughness acquired the highest values in those samples where erosion took place, occurring this phenomenon at small standoff distances and low powder mass flow rate, and no finding any relationship with the transverse gun speed. The generation of an interface layer of mixed metallic particles polymeric substrate plays a key role in the subsequent metallic coating growth, with thicknesses that ranged from 30 μm to 200 μm. In the substrate, the crystallinity degree of the polyamide underneath the coating increased, evidence of a heat affected zone where temperatures around the crystallisation temperature were reached, that also promoted stretching of the polymeric substrate due to dilatational phenomena. All this accompanied of an overall decrease in the thickness of the PA12 coupon after coating build up deposition with the high powder mass flow rate. This evidence indicates that a large plastic deformation of the polymeric substrate at the most energetic combination of processing parameters took place.
Display omitted
•Effect of low-pressure cold spray parameters on 3D printed PA12 metallisation•Scanning speed and powder mass flow rate influenced the quality of the coating.•The interface layer plays a key role in the metallic coating growth.•Heat affected zone enhanced crystallinity of PA12 and led to dilatational phenomena.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
