【正文】 ns in processing have developed at a rapid pace, the property data on microcellular foams has been slow in ing. The early publications on microcellular foams conjectured that the microcellular structure, believed to be on a scale that was smaller than the ‘critical flaw size’ for polymers, would enable these foams to retain their mechanical properties even as the density was reduced. No quantitative information on the critical flaw size was ever presented, nor was any property data presented in support of the hypothesis. This is likely to be due to the emphasis placed on process development, as opposed to property characterization, in the early years of evolution of this field. Over time, however, this conjecture has bee a myth that microcellular materials are as strong as the solid polymers but have a lower density, thus providing an opportunity to lower costs with no penalty in performance. The tensile property data [4] shows that the tensile strength of microcellular foams decreases in proportion to the foam density, and can be approximated quite well by the rule of mixtures. Thus a 50% relative density foam can be expected to have 50% of the strength of the solid polymer. Figure shows relative tensile strength as a function of relative foam density for a number of microcellular polymers. In this figure the relative tensile strength, is obtained by dividing the tensile strength of the foam by the tensile strength of the solid polymer. Similarly, the relative density is foam density divided by the solid polymer density. In Figure we have plotted the strength data on a specific basis. Thus the specific relative tensile strength for the foam of a given relative density is obtained by dividing the relative tensile strength by the relative density. Figure shows that on a specific basis, the tensile strength of microcellular foams is essentially constant over the entire range of foam densities. Unfortunately, similar data on conventional foams is not readily available for a direct parison with microcellular unique aspect of data in Figure is that in the relative density range of to , the microcellular foams represent novel materials for the engineer with properties not previously available. Most conventional foams fall eit her in the lowdensity region (relative density less than ) or belong in the structural foams category (relative density greater than ). The modulus of microcellular foams can be reasonably estimated by the GibsonAshby cubic cell model [5], which predicts that the relative tensile modulus equals the square of the relative density. The gas position in the cell may affect the long term thermal conductivity of the foams [6]. Microstructures, tensile strength, and thermal expansion properties for a number of low density foams have been reviewed by Williams and Wrobleski [7]. Fatigue and creep behaviours of microcellular polycarbonate foams have been investigated [810]. An interesting result from fatigue studies is that introduction of very small bubbles in PC, with less that 1% reduction of density, led to a thirtyfold increase in fatigue life pared to the solid PC. This might suggest a process similar to heat treatment of metals, where a PC part may be saturated with carbon dioxide at 5 MPa and then heated to say 60 186。 making consumer products perfectly suitable for recycling within the original polymer classification and allowing regrind material to reenter the process flow. The numerous cost and processing advantages have led to rapid global deployment of the MuCell process primarily in automotive, consumer electronics, medical device, packaging and consumer goods foams refer to thermoplastic foams with cells of the order of 10 181。編號： 畢業(yè)設(shè)計(jì) (論文 )外文翻譯 （ 譯 文） 學(xué) 院： 機(jī)電工程學(xué)院 專 業(yè)： 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 學(xué)生姓名： 學(xué) 號： 指導(dǎo)教師單位： 藝術(shù)與設(shè)計(jì) 學(xué)院 姓 名： 梁惠萍 職 稱： 講師 2021 年 5 月 15 日 The Effects of Mold Designon the Pore Morphology ofPolymers Produced withMuCell_ Technology ABSTRACT: In this study two molds were designed and used in MuCell_technology to generate implants with a porous structure. To arrive the desiredpore structure many process parameters were investigated for indicating theeffects of process parameters on the pore morphology. This process parameterinvestigation was performed on each mold respectively, so that the influencesof the mold design on the pore morphology have been researched by the sameprocess parameter setting. It was found that the mold design also had effectson the pore structure in MuCell_ technology. A proper mold design couldimprove the generated pore structure, such as porosity, pore diameter, andinterconnectivity. KEY WORDS: mold design, cell morphology, MuCell_, injection molding,medical implant, porous polymer, polyurethane. INTRODUCTION MuCell technology, as an effective microcellular injection moldingprocess, is widely used in automobile and furniture most cases, MuCell_ technology is used to save raw materials, but itis also used to produce implants with closed porous structure [1]. It usesCO2 as blowing agent, which is injected in the plasticization section ofthe injection molding machine (Figure 1). The blowing agent is injectedinto the polymer melt through the gas supply line and injector, in itssuper critical state, by the plasticization phase of the injection moldingmachine. After the plasticization the mixture of polymer melt and gas isinjected through the nozzle into the mold, where the foam structure canbe generated due to the quick pressure drop in the mold. The mainproducts which are produced today with MuCell_ technology have closedcellular foam [2–4]. The MuCell Microcellular Foam