The lagging of the viscoelastic body
because of the engineering plastics are polymers, generally exist and heat-resistant properties of the problem, affected by the temperature on the mechanical properties of the plastic extremely large. If for metal working temperature 20 ℃, material mechanical performance is not affected by any basic, while plastic otherwise, if use working temperature 20 ℃, material mechanical performance will be greatly reduced. Even lose bearing capacity and failure.
because of ultra-high molecular weight polyethylene heat resistance is poor, thermal deformation temperature is low, so the mechanical parts made of ultra-high molecular weight polyethylene design must consider its heat capacity, this is because the viscosity of the elastomer polymer not only low thermal deformation temperature of heat resistance is poor, and the contact surface of mechanical parts, besides of friction heating and heating energy consumption, the lagging behind of viscoelastic body and combined with the plastic machinery, mechanical properties are decline with the rise of temperature.
through chemical modification, physical modification and other measures to improve the heat distortion temperature of the plastic, so as to improve its thermal capacity, engineering plastics used in the machine is mainly suitable for small load and low speed working condition, his failure mainly wear failure and heat. Due to the condition of higher temperature caused by the plastic parts strength, hardness, stiffness caused by the sharp decline in failure. When designing plastic parts to consider not only strength, rigidity, heat resistance and wear resistance, etc. , also consider plastic hysteresis energy consumption.
in the plastic parts of the surface of the work, in addition to like friction heat production, on the surface of the metal parts and lagging heating energy consumption, as people to the design of plastic mechanical parts still follows method of metal parts, often ignore the heat capacity of plastic parts, plastic parts failure. With the progress of science, the new engineering plastics materials, application scope expands unceasingly, therefore, the study of plastic hysteresis energy consumption has great theoretical significance and practical application value.
before calculating hysteresis energy consumption, lagging behind the lag refers to the deformation load, this is due to the injection molding processing of polymer viscoelastic body, after loading molecules to rearrange, need a certain amount of time, to meet the hooke's law ideal elastomer in linear range when the stress/strain curve of the loading and unloading stress/strain curve is a coincidence, both for viscoelastic body don't overlap. The size of the hysteresis energy consumption and the stress and the strain is directly proportional to the phase Angle.
in the design of plastic parts to attach great importance to the heat capacity, thermal failure figure, that is to say, the higher heat distortion temperature of plastic material, the heat deformation temperature of the first point is not necessarily plastic material carrying capacity is high, so said, because the two materials of the friction coefficient of different, after the energy consumption, thermal conductivity, etc. , these factors affect thermal capacity. So for engineering plastics researchers only increase heat distortion temperature of the material is not enough, also thought to reduce the friction coefficient and the energy consumption, increase the heat transfer coefficient of lag and so on.
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