Demagna Koffi

Damage Characterization of Bio and Green Polyethylene–Birch Composites under Creep and Cyclic Testing with Multivariable Acoustic Emissions

Despite the knowledge gained in recent years regarding the use of acoustic emissions (AEs) in ecologically friendly, natural fiber-reinforced composites (including certain composites with bio-sourced matrices), there is still a knowledge gap in the understanding of the difference in damage behavior between green and biocomposites. Thus, this article investigates the behavior of two comparable green and biocomposites with tests that better reflect real-life applications, i.e., load-unloading and creep testing, to determine the evolution of the damage process. Comparing the mechanical results with the AE, it can be concluded that the addition of a coupling agent (CA) markedly reduced the ratio of AE damage to mechanical damage. CA had an extremely beneficial effect on green composites because the Kaiser effect was dominant during cyclic testing. During the creep tests, the use of a CA also avoided the transition to new damaging phases in both composites. The long-term applications of PE green material must be chosen carefully because bio and green composites with similar properties exhibited different damage processes in tests such as cycling and creep that could not be previously understood using only monotonic testing.

Formulation and tensile characterization of wood–plastic composites Polypropylene reinforced by birch and aspen fibers for gear applications

This study reports the effects of wood fibers and 3 wt% maleic anhydride-grafted polypropylene used as coupling agent on the tensile properties of polypropylene/wood composites. Compounding was done in a roller-based internal batch mixer followed by compression molding. Our findings show that both birch and aspen wood fibers improve the elastic modulus and the tensile strength of composites, and the chemical treatment improves the fiber–matrix interface. A comparison of experimental results’ elastic modulus with micromechanics theoretical models shows that the Lavengood–Goettler model is closer to experimental data. Also the results showed that the polypropylene/wood composites’ elastic modulus exceeds high-performance thermoplastics commonly used in gears manufacturing. Thus, the price of polypropylene/wood fibers makes it a viable alternative for similar application.

Study of lignin dispersion in low-density polyethylene

A maximum of 20% (w/w) lignin was used as a filler in low-density polyethylene (LDPE), together with 3–6% maleic anhydride-grafted LDPE as compatibilizer and 3–10% copper(II) sulphate pentahydrate (CuSO4·5H2O) as lignin’s dispersing agent. The resulting composites were investigated for both their mechanical properties and their melting point following the ASTM standards as well as their behaviour was compared with neat LDPE. The results reveal that addition of compatibilizer significantly improved the mechanical properties of lignin, yielding closer values to those of neat LDPE. In fact, the addition of 3% maleated polyethylene induced a 37% increase of the Young’s modulus, whilst 3% CuSO4·5H2O provides a good lignin dispersion. The above observations are further supported by the scanning electron micrographs of the blend specimens. Finally, the differential scanning calorimetry analysis revealed that the melting temperature and the crystallinity of LDPE slightly increase with the addition of 3% CuSO4·5H2O.

Optimized use of cooling holes to decrease the amount of thermal damage on a plastic gear tooth

The full potential of plastic gear usage is limited by not only poor mechanical properties but also equally poor temperature limits and poor heat conduction properties. Cooling holes were developed to decrease the amount of thermal damage on the contact surface. These cooling holes promote increased stress and tooth deflection, thus exerting a negative effect. This article compares various cooling holes for plastic gear configurations and proposes novel cooling holes. Thermal and mechanical simulations that consider specific aspects of plastic gear meshing were performed. The main objective of this article was to verify the best methods for reducing thermal damage through cooling holes. The results indicate the best compromise between the temperature reduction and the mechanical properties of the new tooth geometry. The results also indicate that the simple variations in the cooling holes proposed can improve tooth performance.

Modeling and Prediction of Mechanical Behavior of Plastic Gears in Simulated Wear Situation

The present work shapes a normal plastic gear and simulates the corresponding worn one in order to predict its mechanical behavior in operation depending on the wear. To predict the mechanical behavior of plastic gears, a modeling of the gears has been done under SOLIDWORKS. Then with ALGOR, which uses the FEM, we studied two types of gear. A normal tooth of each type of gear has been net as well as the corresponding worn tooth. We opted for the study of two cases of charge. The first (case 1) corresponds to the application of strength to the head of the tooth (Fig. 2) and the second (case2) at the pitch point of the tooth (Fig. 3). We noticed the stresses and deformations on the nodes located on the right profile of the tooth, the first node is taken at the head of the tooth. The wear has been assumed uniform on the right profile from the head to the root. The tooth has been assumed embedded at the root. We obtained some results which could allow the prediction of the number of revolutions to breaking off, knowing the wear according to this cycle.