Effects of process parameters on compressive property of FDM with ABS

Purpose This work aims to investigate the interaction effects of printing process parameters of acrylonitrile butadiene styrene (ABS) parts fabricated by fused deposition modeling (FDM) technology on both the dimensional accuracy and the compressive yield stress. Another purpose is to determine the optimum process parameters to achieve the maximum compressive yield stress and dimensional accuracy at the same time. Design/methodology/approach The standard cylindrical specimens which produced from ABS by using an FDM 3D printer were measured dimensions and tested compressive yield stresses. The effects of six process parameters on the dimensional accuracy and compressive yield stress were investigated by separating the printing orientations into horizontal and vertical orientations before controlling five factors: nozzle temperature, bed temperature, number of shells, layer height and printing speed. After that, the optimum process parameters were determined to accomplish the maximum compressive yield stress and dimensional accuracy simultaneously. Findings The maximum compressive properties were achieved when layer height, printing speed and number of shells were maintained at the lowest possible values. The bed temperature should be maintained 109°C and 120°C above the glass transition temperature for horizontal and vertical orientations, respectively. Practical implications The optimum process parameters should result in better FDM parts with the higher dimensional accuracy and compressive yield stress, as well as minimal post-processing and finishing techniques. Originality/value The important process parameters were prioritized as follows: printing orientation, layer height, printing speed, nozzle temperature and bed temperature. However, the number of shells was insignificant to the compressive property and dimensional accuracy. Nozzle temperature, bed temperature and number of shells were three significant process parameters effects on the dimensional accuracy, while layer height, printing speed and nozzle temperature were three important process parameters influencing compressive yield stress. The specimen fabricated in horizontal orientation supported higher compressive yield stress with wide processing ranges of nozzle and bed temperatures comparing to the vertical orientation with limited ranges.

The shear and compressive yield stress of fibrillated acacia pulp fiber suspensions

The degree of interactions between fibers and the tendency of fibers to form flocs play an important role in effective unit operation in pulp and paper industry. Mechanical treatments may damage the structure of the fiber cell wall and geometrical properties, and ultimately change the fiber-fiber interactions. In this study, the gel crowding number, compressive and shear yield stress of fibrillated acacia pulps were investigated, and the results showed that the gel crowding number of the refined pulp samples ranged from 8.7 to 10.7, which were much lower than that of un-refined pulps. As the concentration increased, both the compressive yield stress {P_{y}} and shear yield stress {\tau _{y}} of all suspensions increased accordingly, and the yield stress was found to depend on a power law of the crowding number. Moreover, the values of {\tau _{y}}/{P_{y}} were also examined and the variation of {\tau _{y}}/{P_{y}} became largely dependent on the fiber morphology and mass concentration.

A new cooperative model for the prediction of compressive yield stress of polycarbonate nanocomposites considering strain rate, temperature, and agglomeration

In this study, a new model was proposed to predict the compressive yield stress of polycarbonate nanocomposite reinforced by nanoparticles at different strain rates, temperatures, and filler contents. In addition, the proposed model makes it possible to calculate the critical filler content for which the agglomeration phenomena occur. For the validation of the model, a series of experiments were performed. At first, the modified nanoclay Cloisite 20A masterbatch was produced by a direct method using extrusion machine, and the graphene oxide masterbatch was produced by the solvent method. Then the composite samples were produced using the injection-molding process, and the compressive tests were performed at three temperatures under quasi-static and dynamic loadings using a universal testing machine and split Hopkinson pressure bar. The coefficients of the proposed modified cooperative model were calculated using the experimental results. The observations showed that the presented model could correlate the compressive yield stress of polycarbonate nanocomposites to strain rate, temperature, and filler content with sufficient accuracy. Furthermore, the agglomeration of nanoparticles in polymer matrix which is a critical issue in fabrication of the advanced nanocomposites is predictable by using the current model.

Thermal Stability of Nickel-Base Alloys

The thermal stability of three Ni-base samples was assessed at 1850F (1010°C) and 2000F (1093°C) in ambient air as a function of exposure time ranging from 500 to 2000 hrs. Assessments of thermal stability of the samples were made using weight change, oxidation, microstructural evolution, and post-exposure mechanical properties such as Vickers microhardness and compressive yield stress. The three samples included bare Alloy “A” (9Cr-6Al-1.5Hf), Alloy “A” with an overlay coating, and bare Alloy “B” (12Cr-3Al), were not much different in compositions. At 1850F, oxidation as measured by weight change was insignificant up to 2000 h in all the three samples. At 2000F, however, noticeable weight change occurred, increasing linearly with time all in the three samples. The oxidation penetration from surface to matrix for these samples was more intense when exposed to above 1000 hours, forming various oxides, gamma-prime (γ′) depletion zones, and TCP phases. The size and area fraction of γ′ precipitates were determined as a function of temperature and exposure time. Post-exposure mechanical properties were also assessed through Vickers hardness and compressive yield stress. A maximum change in Vickers hardness was about 10% at both temperatures up to 2000 hrs. The change in compressive yield stress was more pronounced than the change in Vickers hardness as a function of thermal exposure and time.