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In order to meet the needs of the mother and fetus during pregnancy, the various systems in the body have more or less changed. However, because of individual differences,some pregnant women may suffer from metabolic syndrome such as type 2 diabetes(T2D) mellitus, lipid disorder, and hypertension, which will affect the health of mothers and the development of nervous and cardiovascular systems of their offspring. Therefore, controlling various metabolic abnormalities is beneficial to improve pregnancy outcomes.

Among the manufacturing methods of high performance gradient functional materials, laser additive manufacturing technology can achieve the materials with gradient microstructure and property through precisely controlling the powder feeding and corresponding process adjustment, providing a new way to prepare high performance gradient functional materials more conveniently and efficiently. The basic principles and classification of laser additive manufacturing technology for high performance gradient functional materials were introduced in this paper, and the research progress in manufacturing high performance gradient functional materials by laser additive manufacturing technology at home and abroad was summarized. Furthermore, the shortcomings of this research field in material selection, process optimization and process monitoring were proposed, and its future research directions, such as the establishment of standard systems, in-depth theoretical research and the development of new manufacturing systems, were prospected, which provide guidance for the research of laser additive manufacturing technology for high performance gradient functional materials.

With the development of basic theoretical research and equipment, laser additive manufacturing technology is widely used in the manufacture of large complex components. However, the internal stress in laser additive manufacturing process tends to result in distortion and cracking. Stress and deformation control has become an urgent issue in laser additive manufacturing process. In this paper, research progress of residual stress in laser additive manufacturing was reviewed from various aspects such as residual stress forming mechanism, test methods, control measures. Furthermore, the main problems and research directions were proposed for the research of stress and deformation control technology, which provides guidance for the research of "shape control" in laser additive manufacturing.

In the case of preheating and non-preheating, the rapid prototyping system of high-power fiber laser and electromagnetic induction heating equipment was used to fabricate 12CrNi2 alloy steel. The microstructure of the molded parts was observed under a scanning electron microscope, and the hardness test of different parts was conducted using the Victorinox hardness tester. The tensile properties in different directions were tested using the universal material testing machine. This study investigated the effect of preheating on the microstructure, hardness, and tensile properties of laser melting deposited 12CrNi2 alloy steel in different directions. The obtained results show that the microstructure of the single-channel molten pool without preheating is lath martensite, and the molten pool of block-shaped forming parts is tempered martensite and bainite mixed structure. No obvious structural difference between XOZ and YOZ sections is observed. However, the overall hardness of the YOZ cross section is larger than that of the XOZ cross section. Large-scale macroscopic crack defects appear in both sections, and the mechanical properties are poor. Under preheating conditions, bainite transformation occurs in the molten pool because of the decrease in the temperature gradient. The single-channel molten pool shows an excellent bainite structure. No tempered martensite transformation in the molten pool of block-shaped forming parts, mainly granular bainite, is observed. Cross-sectional hardness distribution is more uniform with preheating than without preheating. High tensile strength and low plasticity are detected in the tensile and overlap directions. The tensile strength is up to 1189 MPa, the yield strength is 951 MPa, and the elongation is only 2.8%. No obvious anisotropy in performance is observed. Preheating can reduce the temperature gradient in the molten pool, reduce the thermal stress, effectively control the crack defects, promote the homogenization of the microstructure, reduce the anisotropy of the microstructure and properties, and improve the mechanical properties of the alloy steel forming parts.

Based on acoustoelastic theory, stress measurement of laser cladding coating with Rayleigh wave was investigated.The acoustoelastic formula for evaluation of stress in laser cladding coating was simplified by means of Taylor series expansion method.Combined with the static load tensile test, acoustoelastic coefficients were determined.The results show that the variation rate of Rayleigh wave signal velocity in Fe314 alloy coating increases linearly with the increase of stress.When tensile stress is greater than 495MPa, the variation rate of Rayleigh wave signal velocity does not change linearly any more.Based on the analysis of ultrasonic propagation theory and microstructure of laser cladding coating, the changing rule of acoustoelastic curve and its influence mechanism on stress measurement were analyzed, the inhomogeneous deformation of anisotropic laser cladding coating is the main cause of the "wave-type" fluctuation of acoustoelastic curve in high stress stage.Results show that anisotropic tissue effect can affect the result of stress measurement;the penetration in laser cladding layers can be ignored. By fitting the acoustoelastic curve, anisotropic tissue effect factor is determined.The experimental results show the maximum relative error in stress measurement is 4.4%, the method can realize the nondestructive evaluation of the stress in laser cladding coating.

Based on Lcr wave acoustoelastic theory, the influence mechanism of blind-hole on stress evaluation with Lcr wave was discussed. Combined with equivalent method, the blind-holes with different diameters were preset, the difference in time of flight between Lcr wave was calculated by cross correlation coefficient function, the Lcr wave acoustoelastic coefficient was determined with linear fitting function, the influence mechanism of blind-hole diameter on Lcr wave acoustoelastic coefficient was clarified based on the elastic plastic deformation theory and stress concentration theory of hole. The results show that when the diameter of blind-hole is different, the change rule of the difference in time of flight between Lcr wave is basically the same as stress increases, the difference in time of flight between Lcr wave increases linearly as stress increases, while the nonlinear feature is also gradually obvious, the maximum stress in linear stage is less than the yield strength of specimen, the Lcr wave acoustoelastic coefficient decreases gradually as blind-hole diameter increases, and it tends to be constant. The analysis shows that the stress concentration is seen as the main reason for above results, anisotropic structure of specimen and blind-hole depth are also the important reasons for that.

The temperature field of FeCrNiCu alloy forming layers of continuous wave(CW) and pulsed laser remanufacture was analyzed using the non-contact infrared thermometer.The general rule of temperature field distribution of molten pool and heat-affected zone of the two modes was obtained. The pulsed laser process superiority in heat input, forming deformation control and reducing the temperature in molten pool and heat-affected zone was vilidated. The results show that during pulsed laser forming the peak temperature in the heat-affected zone is 730.4-810.5℃,the peak temperature in the molten pool is 998.7-1383.4℃,which are all obviously lower than the same process of the CW mode; the temperature-rise rate and cooling rate of pulsed laser are higher, which is helpful to the forming of fine grain structures and good mechanical performance; the forming experiment also further verifies more narrow heat-affected zone in pulsed laser process.

In order to eliminate the noise which exists in ultrasonic detection signal and improve the diagnostic accuracy of defects inside the material, the method of de-noising ultrasonic signal by applying adaptive threshold(EAT) based on entropy theory is put forward in this paper. The searching algorithm of best wavelet packet basis adopting Shannon entropy is analyzed. The state of signal with noise is characterized by entropy and the threshold of wavelet packet decomposed in different scales is determined according to the entropy of the wavelet packet energy spectrum. Experiment of processing ultrasonic signal which comes from Steyr engine crankshaft with flaws has been implemented. Information that characterizes defect size and location could be extracted accurately from the processing results. The result indicates that the proposed EAT method has better de-noising performance and it has benefit to enhancing the degree of accuracy for quantitatively analyzing the defect inside material. [ABSTRACT FROM AUTHOR]