Papers by Keyword: Thermal Degradation

Abstract: Hot forging of nickel-based superalloys involves severe thermo-mechanical loading of the forming dies due to the high strength of these materials, even at elevated temperatures. Under industrial production conditions, forging dies are subjected to repeated heating-cooling cycles, which progressively degrade the mechanical properties of the tool steel and increase the risk of die plastic deformation. Reliable assessment of die performance therefore requires material characterisation that accounts for both temperature effects and service-induced degradation. In this work, an H13 tool steel used in an industrial hot forging application (nickel-based superalloy case study), was experimentally and numerically investigated in both its raw and service-degraded conditions. Hardness measurements, microstructural analysis, uniaxial compression tests, and quasi-static tensile tests were carried out from room temperature up to 600 °C. An artificial degrading heat treatment was applied to reproduce the mechanical state of the most degraded die regions, and the resulting data were used to quantify the temperature-dependent reduction in yield strength with service exposure. Finite element simulations of the industrial forging process were then carried out using deformable dies to evaluate temperature evolution and stress levels in critical die regions. The risk of die plastification was assessed by comparing simulated von Mises stresses with the experimentally determined temperature-dependent yield strengths for the raw and degraded conditions. The results show a significant reduction in yield strength due to both increasing temperature and service-induced degradation, leading to a substantially higher risk of die plastic deformation under production conditions. The study underlines the importance of incorporating degraded material properties into tool design and process assessment, and motivates improved cooling systems to enhance tool life and process stability.

Abstract: The major concern of the polymers is their degradation in the presence of thermal, mechanical or oxidative stressors even in the normal operating conditions. Life prediction of polymers e.g. insulations, jackets is vital for the continuous working of power plants. In this novel study, the accelerated aging procedure for the life estimation of EPDM and silicone rubber blend (ESB) in thermo-oxidative environment has been proposed. The procedure used the Arrhenius model and laboratory accelerated aging to predict the life of ESB. 50% elongation at break (EAB) was declared as the end-of-life criterion for this study. Thermal stability of the ESB has been investigated by monitoring infrared spectrum, mass loss curve, activation energy, melting point, density, tensile strength and shore hardness before and after thermal aging. The investigation showed that in addition to a loss in EAB, a considerable decrease in the activation energy, tensile strength and shore hardness has been observed. The life was calculated at three accelerated aging temperatures i.e. 130,140 and 150 °C and then this data was extrapolated to lower temperatures. The estimated life at 100 °C was found to be 282 days. This predictive approach is useful in determining the life of various polymeric materials and to build confidence for the use of certain polymers in the required service conditions.

Abstract: The effect of polyketone thermal processing duration on the rheological properties of the melts and the physical and mechanical characteristics of the samples, obtained by injection and compression molding methods, is studied.

Abstract: This work investigates the mechanical behavior of a PCLIGHT type of polycarbonate (PC). PC samples display interesting results after thermal degradation at different temperatures. Samples of PC in sheet form were exposed for a period of 5 hours at temperatures of 50, 100, 150 e 200°C. After, thermogravimetric test, flexural, impact and tensile tests were performed. The results show that the samples treated at 200oC has their mechanical performance affected this indicates that the temperature acts on the PC embrittlement behavior. Thus, it can be inferred that temperatures above 150oC can negatively influence the mechanical behavior of the polycarbonate indicating that this material should not be used in association with high temperatures.

Abstract: This work investigates the mechanical behavior of a PCLIGHT type of polycarbonate (PC). PC samples display interesting results after thermal degradation at different temperatures. Samples of PC in sheet form were exposed for a period of 5 hours at temperatures of 50, 100, 150 e 200°C. After, thermogravimetric test, flexural, impact and tensile tests were performed. The results show that the samples treated at 200oC have their mechanical performance affected. This indicates that the temperature acts on the PC embrittlement behavior. Thus, it can be inferred that temperatures above 150oC can negatively influence the mechanical behavior of the polycarbonate indicating that this material should not be used in association with high temperatures.

Abstract: A study on polymer-ceramic composite, CaCu₃Ti₄O₁₂ (CCTO) embedded in epoxidised natural rubber (ENR-25) were successfully fabricated through mixing method using an internal mixer and two-roll mill followed by hot-pressed via compression moulding for a potential electronic device such as a flexible capacitor. CCTO powders were successfully synthesised through a solid-state reaction and calcined at 900 °C for 12 hours. The ENR-25 was blended with 0, 20, 40, 60, 80, 100, and 120 phr (part per hundreds of rubber) of CCTO powders. Thermal stability and degradation are crucial properties for the composite based polymer. Therefore, thermogravimetric and differential scanning calorimetry (TGA/DSC) used to find out the thermal reaction and degradation mechanism of CCTO/ENR-25 composites. Besides, dynamic mechanical analysis (DMA) also used to investigate glass transition temperature (T_g) and storage modulus. TGA/DSC showed a two-step degradation mechanism with increasing thermal stability over increasing filler content of CCTO and only showed a major endothermic reaction. However, for DMA there is no significant difference in T_g value between each composite but showed high storage modulus up to 4398 MPa for 120 phr. High storage modulus indicates the high stiffness of the composite. In conclusion, the addition of filler content will show high thermal stability, storage modulus, and stiffness of CCTO/ENR-25 composites.

Abstract: The problems of reducing combustibility and increasing fire resistance of some polymer building materials are considered. And the toxicity of the gaseous products of their thermal degradation was evaluated both individually and in various combinations with each other. The features of thermal degradation and the loss of mechanical properties under the influence of a flame of polymer building materials were studied. The following samples were used: water pipes based on polyethylene; Tarkett linoleum, Ondex roofing products, Rolvaplast PVC profile panels; structural panels of the company "Polygal"; facing tile based on phenol-formaldehyde oligomers. The processes occurring during pyrolysis and combustion are considered, the results of a study of the combustibility and mechanical properties of polymer building materials based on polyethylene, polyvinyl chloride, polycarbonate, phenol-formaldehyde and epoxy oligomers under the influence of a flame are presented. For the studied building polymer materials, the products of pyrolysis and combustion were studied; their ignition and self-ignition temperatures, and also the flame propagation velocity were measured. The data on the toxicity of the products of their combustion, both individually and under combined action, are summarized. Also, for the studied polymer building materials, the losses of heat resistance, toughness, and flexural strength under the influence of a flame were studied. Thermogravimetric analysis of Rolvaplast PVC panels and Poligal polycarbonate panels allowed us to determine the maximum temperatures and activation energies of the polymer decomposition process. It was concluded that if the material is recognized as non-combustible or slow-burning, it will not always be fire resistant, since its strength and thermal properties can sharply decrease already in the first seconds of flame exposure.

Abstract: Thermal degradation of the composite constituted by high density polyethylene (HDPE) and microencapsulated red phosphorus (MRP) were studied using thermogravimetric (TG) data obtained at different heating rates. The kinetic models and parameters of the thermal degradation of MRP/HDPE composite were evaluated by FWO, KAS and IKP method. It indicates that the activation energy E of 4 % MRP/HDPE composite is higher than HDPE for three methods. MRP could improve the thermal stability and slow down the thermal degradation of HDPE. With adding MRP, the degradation mechanism of HDPE is changed and the degradation rate decreases.

Abstract: The paper provides the results of failure analysis of the air intake pipe in the truck compressor. The thermal studies were carried out to identify a material, and to analyze the thermal oxidative degradation caused by excessively high operating temperatures. The study of the vehicle component part showed that it was made from polypropylene block copolymer. Analysis of the thermo-physical properties of the warranty polypropylene part showed that the thermal degradation led to a higher polymer crystallization and, as a result, a lower molecular mass due to high temperatures. The results of the thermal studies showed that the polypropylene part was subjected to excessively high operating temperatures which caused the thermal degradation and, as a result, catastrophic failure of the material.

Abstract: Wood is preferably used in civil engineering for load bearing structures and facing elements. However, its disadvantage is low resistance to degradation factors, even when exposed to high temperature. Mineralization of wood matrix, for example by organosilanes, is one possibility of increasing the durability against weathering and against water exposition. In this work, the influence of the mentioned mineralization substances on the thermal degradation of solid wood is verified by means of thermal analysis.