Effect of scanning path on temperature field in laser cladding

To explore effects of temperature field in laser cladding on structure of ceramic coating prepared by plasma spraying, a finite element model of continuous moving three-dimensional temperature field of laser cladded Al2O3-13wt.%TiO2 coating prepared by plasma spraying was constructed by the parametric design language of ANSYS finite element software to analyze temperature field during laser cladding. According to analysis results, it is very difficult to realize complete remelting of the whole preset ceramic coating during laser cladding when it is thick, which is related with the relatively low thermal conductivity of the ceramic materials. The whole coating can be divided into remelting zone, sintering zone and residual plasma spraying zone according to temperature field distribution in the zone of cladding. Given the optimal technological parameters, relatively thick remelting zone and sintering zone could be gained under the relatively low laser cladding power and relatively low scanning speed. Experimental results demonstrated that the ceramic coating after cladding formed remelting zone with small-sized and dense isometric crystals, sintering zone and lamellar residual plasma spraying zone. Moreover, the calculated results of thickness of the remelting zone and sintering zone conformed well to experimental values. This proved that the constructed finite element model is accurate and reliable.

The magnetostriction of the Fe82Ga15Al3 alloy, along the length and width, can be tailored by applying a magnetic field heat treatment. In this work, the Fe82Ga15Al3 sheet was cut from the directional solidified Fe82Ga15Al3 alloy with the ⟨100⟩ preferred orientation and was annealed at 720 °C for 30 min under a magnetic field of 800 Oe along the length direction with a heating and cooling rate of 100 °C/min. The magnetostrictive properties along the length and width directions were modified to λ// = 7 ppm and λ⊥ = −210 ppm from λ// = 210 ppm and λ⊥ = −10 ppm for the initial sample prior to the magnetic field heat treatment. The cellular-like magnetic domain structure was composed of parallel 180° stripe domains and vertical 90° domains observed using a magnetic-force microscope. The change in magnetostriction along parallel and perpendicular directions was mainly resulted from the rotation of the magnetic domain units.

Distribution of coarse aggregate and steel fibers in ultra-high performance concrete containing coarse aggregate (UHPC-CA) and their effect on the flexural performance

A 3D finite element method model is established for yoke-magnetization detection of a transverse defect on T-joint fillet weld and solved by the finite element software ANSOFT Maxwell (ANSYS, Canonsburg, PA). The leakage magnetic field around the transverse defect is obtained. The relationship between the width of transverse defect and leakage magnetic field signals is identified. The researchers found that the tangential component of magnetic flux leakage density, BX1, tends to be a parabolic distribution and reaches the maximum value near the center of the defect along the length direction. While BX1 shows a bimodal distribution, featuring two peaks near the edge of the defect and one peak valley at the center along the width direction, the normal component of magnetic flux leakage density, BZ1, is very different than that of BX1 along the width direction, presenting an approximate N-shape as a whole. The leakage magnetic field signals of the transverse defect on the fillet weld of the T joint will decay obviously when the scanning line is perpendicular to the weld surface over 0.5 mm. The results of numerical simulation can provide a theoretical foundation to detect and characterize various defects in the fillet weld.

In this article, a radio frequency identification (RFID) sensor tag for real-time health monitoring of the magnitude and direction of metal surface strain is presented. The chipless RFID sensor tag is composed of metal foil and F4B substrate, which is low-cost and works stably in harsh environments for a long time. Through highly sensitive strain monitoring, the risk can be predicted in the early stage of defect generation. The proposed tag includes a C-type resonator array, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> -type transmission line, and tag antennas. The C-type resonator has different sensitivities in the electrical length direction and width direction. Then, based on this characteristic, the resonator array creates a plurality of characteristic signatures containing strain information by optimizing the geometric parameters of the resonators. The strain information is transmitted to the tag antenna through the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> -type transmission line to complete the wireless communication between the tag and the reader. Finally, the performance of the strain monitoring system is verified by an experimental study. The experiment shows that the average sensitivity of the resonators is −4.94 and 1.14 kHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> in the electric length and width directions, respectively. When the strain is more than 150 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> , the relative error of magnitude is less than 12.7% and the absolute error of direction is less than 13.3°. Therefore, the proposed chipless RFID tag can monitor the amplitude and direction of strain with higher sensitivity and a simpler structure, for the key structures, such as the high-speed running gear.

The strain sensor based on microwave patch antenna is proposed to monitor structural strain in structural health monitoring. When patch antenna experiences deformation, the resonant frequency of patch antenna will shift. With these characteristics, the patch antenna can operate as both the strain-sensing element and communication component. This article chooses an RT-5880 rectangular patch antenna for strain measurement, focusing on its sensing performance. For distinguishing the influence of deformation in the antenna’s length direction and width direction, the numerical simulation is implemented, and then two kinds of laboratory experiments are conducted. The first approach is to paste antennas in longitudinal and transverse ways and solve the equation set. The other approach is to design another patch antenna with narrow width and compare the test results with the wide one. All results show that the influence of deformation in wide direction on sensitivity can be neglected, and the resonant frequency shift has a good linear relationship with the strain of antenna in length direction.

According to the finite difference method and thermal elastic-plastic theory, combining with martensitic phase transformation kinetics and considering the latent heat and microstructure stress, the temperature, microstructure, stress and strain fields are analyzed. The research indicates that at the beginning of cooling, there are great temperature differences in the direction of thickness and width; at the end of cooling, the temperature and microstructure fields become homogeneous, but the stress and strain field is seriously inhomogeneous. A larger plastic strain occurs on the surface and distributes inhomogeneously in the direction of width are the basic reasons of residual stress. A theoretical basis is provided for improving the offline heat treatment process by analyzing the reason of bad flatness.

斜齿轮轴齿面激光熔覆过程中温度场的数值分析

Stereolithography (SL) is one of the rapid prototyping (RP) systems that use liquid photopolymer resin as the raw material for building prototypes. The photopolymer type of the RP system employs lasers to selectively expose the surface of the liquid resin. The absorbance of energy leads to photo-polymerization that transfers the liquid resin into solid. Subsequently, the phenomenon of volume shrinkage is unavoidable, and the curl distortion changes with the different laser scan paths, even affecting the geometric profile of the final-parts. The volume shrinkage and curl distortion are the major causes that lead to poor accuracy of the built prototype. In order to understand and improve the curl distortion and the geometric profile, so as to find a simple and suitable laser scan path. This paper first of all uses simulation and experiment to explore the deformation and shrinkage during the process of photo-polymerization while the liquid resin uses a laser beam to carry out single line scanning or single layer scanning in liquid free surface, and further understands the final change of geometric profile. Secondly, it investigates into the curl distortion and changes of geometric profile occurred in the three-dimensional part by different scan paths. Finally, a simple, proper, and effective laser scan path planning is suggested to decrease the curl distortion, and promote the dimension accuracy and the profile of the final-parts. Besides, this paper also mentions the feasibility of multi-optical processing.

Research on the transformation mechanism of graphite phase and microstructure in the heated region of gray cast iron by laser cladding

Effect of laser cladding and laser-induction hybrid cladding coatings on the bending properties and fracture behavior of rails

Vibration and sound radiation of a piano soundboard (6-ft grand) were studied using modal analysis and surface intensity methods in the frequency region below 210 Hz. The first mode (49.5 Hz) looked like a trampoline. The second (76.5 Hz) and third (85.3 Hz) modes were the first breakup modes in the length direction. The fourth mode (116.1 Hz) showed the first breakup mode in the width direction. There were seven major resonances below 210 Hz with an average modal density of 1/25 Hz. The radiation was very inefficient below 90 Hz and the surface intensity method was not adequately accurate below this frequency. The radiation pattern (intensity distribution) showed some similarity to the forced vibration pattern for the lower-order modes (but not for the higher-order modes). On an average basis, the radiation efficiency (the ratio of the power radiated from the upper side of the soundboard to the mechanical input power) was approximately 15% above 100 Hz. A normalized radiation resistance was also used to evaluate the efficiency of radiation. A comparison of the normalized radiation resistance to the volume velocity confirmed that the interaction among the sound radiated from different areas on the soundboard is the major cause of the large fluctuation in the normalized radiation resistance.

Free vibration analysis of symmetrically laminated composite plates resting on Pasternak elastic support and coupled with an ideal, incompressible and inviscid fluid is the objective of the present work. The fluid domain is considered to be infinite in the length direction but bounded in the depth and width directions. In order to derive the eigenvalue equation, Rayleigh-Ritz method is applied for the fluid-plate-foundation system. The efficiency of the method is proved by comparison studies with those reported in the open literature. At the end, parametric studies are carried out to examine the impact of different parameters on the natural frequencies.

Injection molding PMMA microfluidic chips can significantly improve the efficiency of chips forming. However, due to the coexistence of macro and micro effects in the injection molding process, the thickness uniformity of molding substrates is poor, which will seriously affect the thermal bonding quality of chips. In this paper, the effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio and the quality of micro-channels was studied by experiments and simulations. The results show that when the following three conditions were satisfied during injection molding process, chips bonding ratio reaches to 93.9 % and the distortions of micro-channels caused by thermal bonding were acceptable. Firstly, the cover plates flatness error is smaller than 50–60 μm and substrates flatness error is smaller than 80–90 μm. Secondly, the maximum thickness difference of stack chips (cover plate stack with substrate) is smaller than 70–80 μm. Thirdly, chips thickness of the middle is larger than that of the two ends along their length direction and chips thickness distribute evenly along their width direction. These conclusions can be used for the parameters selection and moulds design during injection molding process of PMMA microfluidic chips.

Aiming at the problem that the machining accuracy of 45 steel rectangular thin-walled parts are difficult to ensure because of poor rigidity, poor manufacturability and easy machining deformation, it used the three-dimensional finite element method, determined the material model of 45 steel and established a prediction model of 45 steel rectangular thin-walled parts milling deformation. The prediction results display that the deformation of the workpiece shows obvious parabola in length direction and a linear decreasing trend in width direction. It verifies the correctness of the prediction model through milling experiments and provides the method and basis for the prediction and control of machining deformation of 45 steel thin-walled parts.