Understanding of Excellent Mechanical Performance of 304L Manufactured by Optimal Selective Laser Melting (SLM) Conditions.

The optimal SLM conditions of 304L stainless steel were obtained by single factor and orthogonal tests. Results indicated that the optimal hardness (75 HRB) and Relative Density (RD 99.24%) could be obtained when the laser output power was 190 W, the scanning distance was 0.09 mm and the scanning speed was 800 mm/s. The microstructure of fish scales was uniform and compact with a few pores in the optimal sample. The fine particles were randomly distributed near the edge of the molten pool, and some preferred granular columnar crystal structures were formed. Abundant entanglement dislocations were observed between cell structures, forming dislocation clusters. Spherical nano-precipitates, rich in Si, Mn, and O, were also observed near cell structures. The mechanical properties of the specimens were highly anisotropic, and there were obvious necking and ductility at the tensile fracture.

A comparative study on improved Arrhenius-type and artificial neural network models to predict high-temperature flow behaviors in 20MnNiMo alloy.

The stress-strain data of 20MnNiMo alloy were collected from a series of hot compressions on Gleeble-1500 thermal-mechanical simulator in the temperature range of 1173 ∼ 1473 K and strain rate range of 0.01 ∼ 10 s(-1). Based on the experimental data, the improved Arrhenius-type constitutive model and the artificial neural network (ANN) model were established to predict the high temperature flow stress of as-cast 20MnNiMo alloy. The accuracy and reliability of the improved Arrhenius-type model and the trained ANN model were further evaluated in terms of the correlation coefficient (R), the average absolute relative error (AARE), and the relative error (η). For the former, R and AARE were found to be 0.9954 and 5.26%, respectively, while, for the latter, 0.9997 and 1.02%, respectively. The relative errors (η) of the improved Arrhenius-type model and the ANN model were, respectively, in the range of -39.99% ∼ 35.05% and -3.77% ∼ 16.74%. As for the former, only 16.3% of the test data set possesses η-values within ± 1%, while, as for the latter, more than 79% possesses. The results indicate that the ANN model presents a higher predictable ability than the improved Arrhenius-type constitutive model.

[Finite element analysis of a new shape memory alloy cervical hook for atlantoaxial instability].

The mechanics of a new shape memory alloy cervical hook for atlantoaxial instability was analyzed with finite element method on the basis of a three-dimensional model reconstructed from the images of CT scanning of an adult cadaveric upper cervical at 1-mm interval. The stress and displacement of every nodule and element in the course of deformation of the internal fixation were tested, and the results showed that the cervical hook was strong enough against tensile stress, which concentrates in the middle of the device. The pull was 237.58 N at the loading point. With such mechanical performance, this cervical hook can be reliable for correction of atlantoaxial instability.

[Distribution pattern of natural vegetation along moisture gradient at north edge of Ordos plateau: a preliminary study].

With Duguitala Township in the north part of Hangjin County as an example, this paper studied the spatial distribution pattern of natural vegetation along moisture gradient at the north edge of Ordos Plateau. The results showed that based on TWINSPAN classification, the communities were dominated by mesophytes and xerophytes, and there were some halophytes in some quadrats. The similarity indices of neighboring quadrats could reflect the mosaic pattern of different type communities, and thus, the diversity and complexity of communities along this gradient, which could be reconfirmed by DCA ordination. The CCA ordination for quadrats and geomorphological factors indicated that in this transitional region, the formation of vegetation's spatial distribution pattern was determined by moisture gradient, while the latter was controlled not by the distance from the main course of the Yellow River but by the change of micro-geomorphology. In the land exploitation of this region, relatively stable geo-morphological units should be taken into consideration, and large scale land exploitation through surface leveling should be avoided if shelterbelt measures and drainage and desalinizeation system were defective. This study would be helpful to the protection of natural vegetation and the integrated development of agriculture and animal husbandry.

[Study of three-dimensional computerized reconstruction and CT scanning with thin slice after filling hepatic duct system].

OBJECTIVE: To establish the modal of perfusing and casting in hepatic duct system and explore the methods of three dimensional reconstruction with CT scanning image after filling hepatic duct. METHODS: All canal of livers with integral porta hepatic were perfused with various filling material after pretreatment, then fixed and casted. Hepatic preparations that had been perfused were put into the model of modelling abdominal cavity and scanned with thin slice. The three dimensional duct structures of hepatic with three methods of MIP, SSD and computerized treatment. RESULTS: Fourteen hepatic samples were filled and casted. Nine hepatic samples were scanned with slice height 1.0 mm, all 2514 slice images and average 279 images. Five hepatic samples were scanned with slice height 3.0 mm, all 512 slice images and average 102 images. Intrahepatic vein and portal vein system of three dimensional reconstruction were seen clearly with MIP method. The three dimensional established three dimensional images with SSD method was shown much stronger than that of MIP method. The three dimensional images of hepatic solid and hepatic vein system were established with method of comperized treatment. Vary three dimensional shape of hepatic solid and hepatic vein was obtained through different direction rotational. CONCLUSIONS: The modal filled and casted hepatic duct system were practise. The images established three dimensional with methods of MIP, SSD and comperized treatment were seen clearly. The modal and images of thin slice CT scanning are a better method for researching hepatic duct system.