Search

Flexible polishing technology is widely used in the precision machining of aero-engine blisk blades. It has become one of the important research contents of flexible polishing technology to systematically study the flexible polishing process and understand the connotation of the microscopic morphology of the polished surface. In this paper, the flapwheel is used as a flexible abrasive tool, and the spatial kinematics model for the abrasive grains on the surface of the flapwheel and the geometric interference model for the abrasive grains and workpiece are established by transforming the spatial geometric coordinates. Based on the surface topography model for the abrasive tool, MATLAB software was used to simulate the micro topography generation process of the flexible polishing surface with flapwheel as abrasive tool, and the three-dimensional topography of the workpiece surface and its influence law under different process parameters were obtained. The polishing experimental results verified the simulation algorithm correctness and effectiveness.

The fiber reinforced resin-based composite materials have the characteristics of high specific modulus and strength, impact resistance, creep resistance, and seismic resistance, which are widely used in the aviation, automotive, and marine industries. As one of the advanced composite material forming technologies, the fiber placement can manufacture the large-curvature composite parts with the high efficiency, high quality, high repeatability and low cost. The rubber compaction roller will deform under the pressure, in which the deformation will increase the contact area between the pressure roller and the substrate, and improve the interlaminar bonding degree. Due to the different deformation of the compaction roller caused by the different laying pressures, the deformation process of the fiber compaction roller was analyzed. By establishing the pressure stress distribution model for the compaction roller, the contact pressure, the downward deformation of the compaction roller and the deformation contact area between the compaction roller and the substrate are obtained. The mapping relationship among the contact curves of the substrate is verified by using the experiments.

With their high specific stiffness, corrosion resistance and other characteristics, especially their outstanding performance in product weight loss, fiber-reinforced resin matrix composites are widely used in the aviation, shipbuilding and automotive fields. The difficulties in minimizing defects are an important factor in the high cost of composite material component fabrication. Fiber steering is one of the typical means of producing composite parts with increased strength or stiffness. However, fiber waviness is an important defect induced by fiber steering during the fiber placement process. Meanwhile, the laying speeds of the inner and outer tows along the path width direction are different during the fiber steering process, resulting in different interlaminar bond strengths. Therefore, the fiber waviness and uneven interlaminar bonding strength during fiber steering not only affect the dimensions of a composite product, but also influence the mechanical properties of the part. This study aims to reduce fiber waviness and improve interlaminar bonding uniformity along the path width direction using a multi-piece compaction roller. By analyzing the mechanism of the generation of fiber waviness, the interlaminar bonding strength for each tow during fiber steering is investigated. Through analyzing and optimizing the compaction force, laying temperature and laying velocity during fiber steering experiments, the optimization approach is verified. [ABSTRACT FROM AUTHOR]

Background: Intravoxel incoherent motion (IVIM) parameters derived from iZOOM diffusion-weighted imaging (DWI) can be used to quantitatively identify malignant thyroid nodules. However, the criteria are not standardized. Purpose: To determine IVIM parameter values derived from iZOOM DWI that can differentiate malignant from benign thyroid nodules. Material and Methods: Forty-two patients with 46 pathologically confirmed thyroid nodules. All patients underwent preoperative examinations with conventional and iZOOM DWI. A three-dimensional region of interest was drawn on multiple slices to cover the entire nodule. IVIM parameters (D, pure diffusion; f, perfusion fraction; and D*, pseudodiffusion) were measured. The IVIM parameters of the malignant and benign thyroid nodules were compared using independent samples t - tests, a multiple logistic regression, and receiver operating characteristic (ROC) curve analysis. Results: D, D*, and f exhibited good reproducibility. The D and f values in the malignant nodules (D = [0.72 ± 0.14] × 10−3 mm2/s, [29.94 ± 7.36] %) were significantly lower than those in benign nodules (D = [1.23 ± 0.35] × 10−3 mm2/s, [36.00 ± 8.35] %). The D value achieved the highest area under curve (0.939). The optimal cut-off value for D was 0.87 × 10−3 mm2/s (sensitivity = 95.83%, specificity = 90.91%, positive predictive value [PPV] = 92.00%, negative predictive value [NPV] = 95.24%, and accuracy rate = 93.48%). The area under ROC curve (AUC) of D combined with the f value did not significantly differ from that of D. Conclusion: IVIM parameter D derived from iZOOM DWI may be helpful in differentiating malignant from benign thyroid nodules. [ABSTRACT FROM AUTHOR]