Heat Transfer Modeling of Oriented Sorghum Fibers Reinforced High-Density Polyethylene Film Composites during Hot-Pressing

A one-dimensional heat transfer model was developed to simulate the heat transfer of oriented natural fiber reinforced thermoplastic composites during hot-pressing and provide guidance for determining appropriate hot-pressing parameters. The apparent heat capacity of thermoplastics due to the heat of fusion was included in the model, and the model was experimentally verified by monitoring the internal temperature during the hot-pressing process of oriented sorghum fiber reinforced high-density polyethylene (HDPE) film composites (OFPCs). The results showed that the apparent heat capacity of HDPE accurately described its heat fusion of melting and simplified the governing energy equations. The data predicted by the model were consistent with the experimental data. The thermal conduction efficiency increased with the mat density and HDPE content during hot-pressing, and a higher mat density resulted in a higher mat core temperature. The addition of HDPE delayed heat transfer, and the mat had a lower core temperature at a higher HDPE content after reaching the melting temperature of HDPE. Both the experimental and simulated data suggested that a higher temperature and/or a longer duration during the hot-pressing process should be used to fabricate OFPC as the HDPE content increases.

Experimental and numerical study of the longitudinal and transverse residual stresses distribution in the constrained groove pressing process of pure copper sheets

In this research, the residual stresses distribution resulting from one of the severe plastic deformation methods called Constrained Groove Pressing in pure copper sheets has been studied experimentally and numerically. For this purpose, after the initial preparation of each sample, the mentioned process is applied to the samples up to three passes. After each pass, the residual stresses in these samples in both directions of their length and width have been measured experimentally. To measure the residual stresses in these samples, the contour method, which is a relatively new, effective, and accurate method in providing a two-dimensional residual stress map, has been used. The results indicate that the residual stresses on the surfaces of the samples are compressive and by moving towards the central layers of them, these stresses are converted into tensile residual stresses. The distribution of residual stresses along the length and width of the samples is reported to be relatively uniform. In another part of this research, numerical simulation of the Constrained Groove Pressing process in ABAQUS finite element software is discussed. In this simulation, Johnson–Cook model is used as a constitutive model. The average error of residual stress distribution between the simulation and contour method was about 18% which shown a good agreement.

Hot-pressing design of tubular polyester nonwoven lining material for pipeline rehabilitation

In view of the strength loss and dimension shrinkage of polyester nonwoven used for the sewage pipeline in the hot-pressing process, the response surface methodology was proposed to optimize the technological parameters of lining material. Select the temperature, time and pressure to enhance the hot-pressing process of lining material with the response value of the rate of dimensional change and tensile strength. The results showed that the temperature was 180°C, time was 3s, and pressure was 2.8MPa. Under this process, the rate of dimensional change was 4.23%, transverse tensile strength was 7.95MPa, and longitudinal tensile strength was 5.26MPa. It showed that the response surface methodology had practical application value, and provided a theoretical basis for the hot-pressing parameters of lining material with maximum tensile strength and minimum dimensional shrinkage. The paper also tested the adhesive strength, air permeability and water permeability of lining material under the optimal process, founding that the prepared material had excellent adhesive strength, air permeability, water permeability, and could meet the construction requirements of pipeline rehabilitation and the use requirements of conveying medium.