Prediction and measurement of residual stresses in injection molded parts

Residual stresses were predicted by a flow analysis in the mold cavity and residual stress distribution in the injection molded product was measured. Flow field was analyzed by the hybrid FEM/FDM method, using the Hele Shaw approximation. The Modified Cross model was used to determine the dependence of the viscosity on the temperature and the shear rate. The specific volume of the polymer melt which varies with the pressure and temperature fields was calculated by the Tait’s state equation. Flow analysis results such as pressure, temperature, and the location of the liquid-solid interface were used as the input of the stress analysis. In order to calculate more accurate gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise direction was predicted in two cases, the free quenching and the constrained quenching, under the assumption that the shrinkage of the injection molded product occurs within the mold cavity and that the solid polymer is elastic. Effects of the initial flow rate, packing pressure, and mold temperature on the residual stress distribution was discussed. Experimental results were also obtained by the layer removal method for molded polypropylene.     

Confocal microscopy measurement of the fiber orientation in short fiber reinforced plastics

To determine three-dimensional fiber orientation states in injection-molded short fiber composites a CLSM (Confocal Laser Scanning Microscope) is used. Since the CLSM optically sections the composites, more than two cross-sections either on or below the surface of the composite can be obtained. Three dimensional fiber orientation states can be determined with geometric parameters of fibers on two parallel cross-sections. For experiment, carbon fiber reinforced polystyrene is examined by the CLSM. Geometric parameters of fibers are measured by image analysis. In order to compactly describe fiber orientation states, orientation tensors are used. Orientation tensors are determined at different positions of the prepared specimen. Three dimensional orientation states are obtained without the difficulty in determining the out-of-plane angles by utilizing images on two parallel planes acquired by the CLSM. Orientation states are different at different positions and show the shell-core structure along the thickness of the specimen.     

林业剩余物棒状燃料的成型技术研究

对不同林业剩余物的棒状燃料的成型技术进行研究,重点分析进料间隙和进料速度对不同材性、粒度的林业剩余物的成型效果.结果表明：1）所有的林业剩余物只要将其含水率控制在15％～25％之间,最大粒度的宽、厚规格不超30 mm,通过调整进料间隙和速度均可加工成棒状燃料.2）进料间隙与原料粒度呈负相关,进料速度又与进料间隙呈负相关.即木屑、竹屑等粒度小的物料进料间隙要大,可调至4～5 mm,进料速度应控制在中速或中速以下（电机频率为6Hz或6 Hz以下）;而杂灌、油茶果壳等粒度较大的物料进料间隙要小,可调至1～3 mm,进料速度应控制在较高速或高速间（电杌频率为8～11 Hz）.3）成型燃料的密度取决于成型时的压力.通过选用孔长径比大的环模或控制进料间隙和进料速度来调节成型时的压力,可使不同林业剩余物的棒状燃料密度达到1 g/cm3以上.4）原料的物质组成和性质是成型燃料热值的决定因素.锯末、竹屑的棒状燃料热值在4 000 kcal/kg左右,而杂灌和油茶果壳一般在4 000 kcal/kg以下.     

面包质构特性测定方法的研究(Ⅵ)——面包硬度与感官评价的关系及压缩速度对面包硬度测定值的影响

用不同品质面粉制作面包样品并进行感官评价和质构特性测定,主要考察了面包感官评价和面包硬度测定值的关系及压缩速度对面包硬度测定值的影响.实验结果表明,面包感官评价总分与面包体积和面包纹理结构都有线性正相关的关系,面包硬度测定值与面包感官评价总分具有很强的相关性.不同面粉材料和不同探头测定位置都有随着压缩速度的增大、面包硬度测定值呈先增后减再增大的规律,探头测定位置为中上时在压缩速度100mm/min时出现硬度测定值的峰值,而在压缩速度为140 mm/min时出现硬度测定值的谷值,探头测定位置为中下时的硬度测定值峰谷值的压缩速度比前者分别大40 mm/min.     

碳纳米管改性的蜡基复合粘结剂

通过熔融共混将功能化的碳纳米管引入到蜡基粘结剂中,得到碳纳米管改性的复合粘结剂.扫描电镜（SEM）显微照片显示,功能化的碳纳米管能均匀分散在粘结剂基体中.偏光显微照片和热性能分析结果表明,碳纳米管的加入能有效地提高粘结剂的结晶度和热稳定性,进而改善生坯在脱脂时的保形性.碳纳米管与粘结剂的非共价键结合有助于碳纳米管的均匀分散,更可能有利于复合材料成型后的脱脂.     

纤维素单独成型及燃烧特性研究

以纤维素为成型原料,利用万能试验机进行纤维素成型试验,研究物料含水率、成型温度及成型压力对成型颗粒品质影响,利用扫描电镜观察纤维素成型颗粒内部结构,热重分析仪分析纤维素粉末及成型后颗粒燃烧特性。结果表明,一定范围内增加纤维素含水率、成型压力及成型温度,可提高颗粒品质,含水率为14%~29%、成型压力为3~4 k N、成型温度为100℃时效果最好;纤维素粉末及纤维素颗粒主要失重部分在挥发分燃烧阶段,纤维素成型后会升高燃烧反应起始温度,提高燃烧最大速度时温度。建立燃烧动力学模型,结果表明,纤维素活化能较低,且遵循动力学一级和二级规律。     

Strength attributes and compaction susceptibility of Brazilian Latosols

In this study, strength attributes and compaction susceptibility of the main classes of Brazilian Latosols (Oxisols), under native vegetation, were studied using the load bearing capacity models relating precompression stress, compression index and water potential through statistical regression models. These models were developed based on the results of the analysis of undisturbed soil samples collected at the B horizon at the different sites. The results showed that the maximum value of the compression index was 0.53 for the Acric Red Latosol, indicating its higher susceptibility to soil compaction. The Dystrocohesive Yellow Latosol had the highest load bearing capacity, while the Acric Red Latosol had the lowest one. The Dystrocohesive Yellow Latosol due to its high load bearing capacity and bulk density (mechanical resistance) behave similarly to hardsetting soil, in which the plants root system has severe physical restrictions to explore deeper horizons during the dry periods. Differences in the load bearing capacity and compaction susceptibility were found to be influenced by soil structure which is associated with clay mineralogy in these very weathered-leached soils and water potential. The study also showed that soil compression index is influenced by water potential and clay mineralogy also. Our work has laid a foundation for estimation of compaction susceptibility of Latosols.     

冲击压实技术在高速公路加宽扩建中的应用

针对高等级公路加宽扩建工程中冲击压实技术应用问题,以吉黑公路拉林-五常-省界加宽扩建工程项目为依托,通过现场测得压实度和高程值,分析了冲击压实遍数与压缩变形、压实度的关系,以及冲击压实遍数对不同深度处压实度的影响,得出了该路段处的合理冲击压实遍数,并且提出了减少新路基工后沉降与变形的措施.采用简易贯入试验对冲击压实后路基的压实效果进行评价.研究成果对该地区路基的大面积机械化施工有重要的参考价值和指导意义.     

基于3D-CDF（2,2）和3D SPIHT的序列图像压缩编码研究

研究了3D DWT和3D SPIHT算法,用CDF（2,2）双正交小波为帧内小波变换的小波基,考虑到边界延拓效应,时间维小波变换也选用CDF（2,2）双正交小波为时间维小波变换的小波基,实验结果表明算法对于视频序列图像压缩是非常有效的,其压缩效果明显优于基于3D-DCT的压缩编码算法.