Volume 38, Issue 1

Tightness against media is a frequent requirement for technical components. Despite various standardized test procedures, failure regularly occurs during use. Often, no clear cause for failure can be determined afterwards. In this article, a new test setup is presented and applied, which allows an in-situ measurement during a mechanical load. A flow meter with a measuring range of 0.02 mL/min to 5 mL/min is used for this purpose. This makes it possible to determine leakage rates with time resolution and thus to identify the moment of failure or the causal failure load. This new method was applied directly to different aluminum inserts with a polyamide 66 (PA66) overmold. It was shown that no increase in leakage occurs until a maximum force is reached, even with multiple loads. This maximum force depends only on the pretreatment of the inserts and can be determined in a simple pull-out test independently of the test setup used here and can therefore be used for the design of assemblies. In the test, a maximum force of 100 N was achieved for untreated inserts, 140 N for adhesion promoter-coated parts and 600 N for etched inserts with a contact area of 48 mm 2 . With this results, a new link between adhesion and tightness can be shown, which of course is only valid for initial tight parts.

Injection molding of thin-walled plastic parts with minimum deformation in warpage and volume shrinkage is crucial for part quality. Simulation combined Latin hypercube sampling approach was used to research the effects of different process parameters on deformation. Then, random forest regression (RFR) is used to construct the mathematical relationship between process parameters and defects, such as warpage and volume shrinkage. The gaussian process is used as probabilistic surrogate model, while the probability of improvement is used as acquisition function to construct a Bayesian optimization for RFR’s hyperparameters, and the performance of random search is compared. In addition, the gradient boosting regression (GBR) and support vector regression (SVR) were also adopted to establish the prediction models, respectively. Comparing all the above prediction models, it can be found that the Bayesian optimized random forest regression (BO-RFR) has the highest accuracy. The Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is interfaced with the predictive models to find the optimum design parameters for the purpose of effectively predicting and controlling warpage and volume shrinkage. The results show that warpage is reduced by 66.03% while volume shrinkage is 46.20% after optimizing. The final finite element simulation and physical tests indicate that this proposed method can effectively achieve the multi-objective optimization of injection molding.

The rheological properties of biocomposites can change depending on the polymer, fiber type, fiber size and processing conditions. In this work, biodegradable PBS composites filled with raw and enzymatically treated date palm fibers were processed using an internal mixer. The influence of the processing conditions, namely filler concentration, rotor of the mixer rotational speed, as well as the type of the enzymatic fiber treatment on PBS (Poly Butylene Succinate)/date palm fiber composites were studied by measuring the torque and the temperature in real time during melt processing. A rheological analysis was also carried out by performing time and multi-wave-frequency sweeps. It was found that the stabilization torque increased with increasing fiber loading and rotor rotational speed, indicating a higher viscosity. An enhancement of the melting process occurred with modified fibers, which was explained by the decrease in the fiber diameter, denoting cellulose micro-fibrils separation by enzymes action. These composites were characterized by a better thermal resistance and mechanical stiffness compared to those based on raw fibers at the same loading rate.

The degradation of polyvinyl alcohol (PVA) has been investigated using ultrasonic (US) as well as microwave (MW) irradiation techniques with the approach of process intensification based on different additives, such as Titanium Dioxide (TiO 2 ), Sodium Lauryl Sulphate (SLS), Zinc Oxide (ZnO) and air. The effects of sonication time, initial polymer concentration, and temperature on the extent of reduction in viscosity have been thoroughly investigated using US as well as MW irradiation approaches. Basically, the degradation process has been optimized by utilizing two different ultrasonic reactors in a combined approach of ultrasonic horn and bath. The maximum extent of degradation of PVA was found to be 69.33% using MW irradiation with a required energy of 0.321 g/JL, and 62.47% using US horn with a required energy of 0.054 g/JL when operated at 0.1 g/L of TiO 2 catalyst. The combination of US horn and US bath results in same degradation as 0.1 g/L of TiO 2 catalyst with US horn. It has also been observed that the maximum degradation of PVA was obtained with a minimum treatment time of 3 min using MW irradiation, whereas the US horn required 40 min. Moreover, a lower extent of PVA degradation was obtained when additives were used, such as surfactants (SLS) and air. As a result, it can be inferred that the MW-assisted approach in the presence of process-intensifying additives/catalysts is the best approach for the degradation of PVA with a minimum energy consumption.

As a highly thermally conductive PPS that is lightweight and has excellent heat dissipation is expected to be applied in various products, its peculiar filling behavior can cause molding defects such as short shots and surface cracks. To address these challenges, it is important to elucidate the filling behavior and clarify the effects of cavity shape and molding conditions. Thus, we intend to visualize the filling behavior of the high-thermal-conductivity PPS. To achieve this goal, we develop an in-process visualization system to reveal both the thermal and kinetic behaviors of the resin while it fills the cavity. In the system, a sapphire prism glass is utilized in the mold for visualization because it exhibits high strength, high heat conduction, and high infrared transmittance. A high-speed visible camera for kinetic behavior and an infrared camera for thermal behavior are utilized. With the developed system, we successfully obtained for the first time the filling behavior of high-thermal-conductivity PPS. Visualization experiments prove that the temperature of the conventional PPS gradually decreases from the tip to the rear of the flow. However, the temperature of the high-thermal-conductivity PPS drops sharply from the tip of the flow to the rear, and breakage at the flow front near the cavity wall is generated. Our interpretation is that the flow front near the cavity wall can be easily broken when it is stretched, because the ductility of the high-thermal-conductivity PPS largely decreases because of the rapid temperature drop. To suppress the formation of this breakage, we modify the cavity shape and molding conditions, and verify its suppression effect.

Technical rubber or polymer profiles are often extruded while dragging them into a water bath. However, complex or heavy profiles may require additional guiding tools. For example, geometrically complex profiles, such as PVC-window frames, require the use of calibrators for satisfying severe geometric requirements, while heavy rubber profiles, such as D-shape fenders or tire treads, require a conveying belt mainly for being able to achieve the process. Within the context of numerical simulation of extrusion flows, such a guiding tool brings an additional downstream constraint to the kinematic equation which dictates the shape of the extrudate surface. In the present paper, we propose a simple engineering approach for modelling a conveyor belt used in rubber tire tread extrusion, and we apply it to the simulation of the extrusion flow for a 3D non-symmetric profile of a viscoelastic material.

In this work, the combined effects of fused filament fabrication (FFF) process parameters on the mechanical properties of 3D printed PLA products have been determined by focusing on the tensile strength at R 2  (97.29%). ASTM D638 test standard is used for the preparation of specimens for tensile tests. The optimization technique has been used to determine the optimal combinations of FFF process parameters for the validation of experimental tensile tests and computational fluid dynamics (CFD) simulations. From the results obtained the optimum cooling fan speed of 79.3%, extrusion temperature of 214.4 °C, printing speed of 75.9 mm/s, raster width of 0.4814 mm, and shell number 5 were determined with a 2.266% error of the tensile strength (45.06 MPa). SEM morphology examination shows that the fabricated part cooled at 80% cooling fan speed illustrates good inter-layer bond strength which is also confirmed by CFD temperature distributions analysis.

In the present work, a prototype was developed to observe the flow behavior of viscous fluids under free surface shear and determine an adhesion energy in this flow geometry. The geometry consists of an eccentric Couette cell (outer cylinder radius of 89.5 mm, inner cylinder radius of 43.75 mm and minimal gap of 3 mm) that can be used in two modes, where both cylinders can respectively rotate in the same or opposite directions. Cylinders are horizontal and short relatively to their diameters (30 mm long). Transparent windows allow in-situ flow observations. The design, development, and testing of the prototype with a model viscous fluid (silicone fluid with a 2.2 10 4  Pa.s Newtonian viscosity) are reported in this paper. The flow behavior of small fluid volumes (fill factor smaller than 15%) was investigated under co- and counter-rotating configurations to determine steady-state flow conditions. Stationary conditions were identified in the counter-rotating mode. The velocity conditions and resulting observations are studied and analysed. However, for the used silicone fluid, the bulk dissipative energy is much larger than the work of adhesive forces in the investigated regimes. The adhesion energy contribution could not be detected for this fluid.

This study used a hand layup process to create tri-layer hybrid composites composed of snake grass fiber (SGF) and jute fiber (JF). Two types of hybrid composites were investigated: jute/snake grass/jute (J/S/J) and snake grass/jute/snake grass (S/J/S). The fabricated composites were subjected to mechanical characterization and water absorption studies to verify their compatibility for various applications. The outcome revealed that the J/S/J hybrid sample shows the highest tensile and flexural strength at 68.46 and 78.62 MPa, respectively. This is due to stacking the maximum-strength JF as an exterior layer in the hybrid J/S/J sample. Meanwhile, the S/J/S composite shows a very high impact strength value of 4.45 kJ/mm 2 due to the placement of SGF at the outermost layer. It leads to absorbing more impact energy at sudden load applications. Water absorption studies revealed that the S/J/S composite absorbed more moisture than the J/S/J composite. Furthermore, the S/J/S composite exhibited greater biodegradability than the J/S/J composite based on soil burial experiments. From this study, it can be concluded that the J/S/J composite is suitable for structural applications because it has higher tensile and flexural qualities. In contrast, the S/J/S composite can be employed under damping conditions because it has better impact strength.

With a rotating mold core during the injection molding of fibre-reinforced plastics, the rotational shear caused by the rotation is superimposed on the injection-induced shear. This allows the fibre orientation in this area to be intentionally manipulated so that, for example, in the case of internal pressure loading, the fibres can be oriented in the tangential main loading direction. This paper deals with the impact of a rotating mold core on the fibre orientation and burst strength of short-and long-fibre-reinforced polypropylene. It is shown that the fibre orientation and strength can be significantly influenced for both short and long fibres, whereby increases in bursting strength of mostly over 80%, in some cases over 200%, could be achieved. The ultimate strength depends, among other things, on the wall thickness used and the fibre content. Major differences between the short-and long-fibre-reinforced polypropylene are less evident in the strength and more in the fibre orientation.

This paper presents the impact of accelerated aging on selected mechanical and thermal properties and VOC emission of polypropylene composites filled with glass fiber with different fiber contents. Due to their positive properties (good thermal and mechanical properties, low weight), glass fiber reinforced thermoplastics are becoming increasingly important. Fiber reinforced thermoplastics are mainly produced by injection molding and extrusion, whereby the extrusion compounding process is primarily used to prepare fiber-filled granulates while the injection molding process is used to manufacture products. In this study, short glass fiber reinforced thermoplastics (polypropylene) are produced on a twin screw extruder. Then, tensile test specimens are produced by injection molding. The glass fiber content is between 20 and 40 wt%. In order to investigate the long-term stability, the test specimens are artificially aged in accordance with ASTM 1980. The thermal, mechanical, and emission properties were evaluated by means of differential scanning calorimetry (DSC), tensile tests, and TDS-GC-MS analysis prior to and after accelerated aging. The objective of this study was to investigate the effects of thermal aging on crystallinity and mechanical properties and on VOC emission of glass fiber reinforced isotactic polypropylene.

The corner vortex phenomenon occurring in entry flow is relevant to both polymer rheology and polymer processing. The famous viscoelastic constitutive equations in numerical computations of fluid mechanics have always had limited relevance at low apparent shear rates. However, three-dimensional (3D) simulations of viscoelastic fluids have been rarely found in advanced rheology. Recently, the GNF-X (eXtended Generalized Newtonian Fluid) constitutive equation of the weighted shear/extensional viscosity developed in advanced rheology of complex fluids has been incorporated into state-of-the-art predictive engineering tools. Thereby, 3D numerical simulations of entry flow were performed for a LDPE (low-density polyethylene) melt. As a validation, the predicted vortex streamlines are in good agreement with related experimental observations. More importantly, the simulation results show the vortex growth with respect to apparent shear rates, contraction ratios, and inlet angles. In particular for extensional viscosity, the stronger extension hardening characteristic yields a large vortex size.