Generally, annealing is one of the important post-processing methods used to obtain injection molding products coupled with excellent comprehensive performance. Based on a series of experimental studies in this work, a systematic investigation was performed to research the annealing effect on crystalline structure and mechanical properties in long glass fiber reinforced polyamide 66 (LGF-PA66) composite. The composite was prepared by injection molding, using LGF-PA66 pellet with 50 wt % fiber content and 12 mm length. Composite samples were annealed in 120 8C to 200 8C range and then subjected to various tests at room temperature. Besides, the releasing strain during a specific temperature cycle was also investigated. Our results suggest that annealing treatment had a neglected impact on the crystallinity and crystal morphology of LGF-PA66 composite. However, with the increasing of processing temperature, annealing could strikingly promote the phase transition from g to a and the further growth of a 2 crystal in (010)/(110). In addition, annealing of LGF-PA66 composite resulted in a drastic increase in tensile and flexural properties and a reduction in impact strength, along with the transition of failure mode. The changes in mechanical properties were attributed to the crystal transition, strengthening of matrix performance, and the release of residual stress.

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The fatigue properties of T-joint of Q345 steel commonly used in construction machinery are studied. The fatigue life of T-joint with complete weld details is analyzed by nominal stress method and the equivalent structural stress method respectively, and compared with the test results. The results show that under the condition of stress ratio R=0.5, the fatigue crack of T-joint with complete weld details often occurs at the weld root of the arc extinguishing and propagate along the weld throat. In production, arc extinguishing should be avoided in key parts. The nominal stress method used to predict the fatigue life of T-joints with complete weld details is dangerous, while the fatigue life of T-joint analyzed by the equivalent structural stress method is basically consistent with the test results.

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Abstract. The scraper angle of milling machine has a direct effect on the milling efficiency. This research establishes the finite element model of scraper, and designs the cutting front angle and the cutting back angle as factor, impact force and the average force for orthogonal test of evaluation indexes. Through simulation analysis, the force is obtained at the different level. At the same time, the simulation results are verified by experiments. The results show that the simulation results of contact force in the X direction are close to the measured results, and prove the accuracy of the simulation results. The optimized scraper is that the cutting angle is 5.5°, and the cutting back angle is 9°. The impact force is minimum, and the resultant of average force and impact force is minimum. The optimization of scraper angle can effectively reduce the impact force and the average force, which provides guidance for the improvement of scraper.