球罐焊缝错边缺陷合于使用安全评定方法研究

针对目前GB/T 19624—2004没有明确球罐超标错边缺陷的评估方法,文章基于API 579合于使用原则,对某含焊缝错边超标缺陷的大型球罐进行了三级评定,重点对第三级评定中有限元数值方法进行了探讨,通过建立与实际错边情况相符的非对称三维实体模型,对错边缺陷高应力区进行了合于使用安全评定。研究成果可为今后同类缺陷问题的安全评定提供一种可行的解决方法。     

ANSYS子模型技术在LPG球罐设计检验中的应用

为了得到2 000m3LPG球罐的准确详细的应力分布情况和便于检验应力集中区域,建立了该球罐的简化模型,采用ANSYS软件在静态承载的工况下进行了有限元分析,明确了应力集中区域及应力值。利用子模型技术对局部区域进行了详细计算,并由板壳单元转化为实体单元。结果表明,该球罐结构强度满足设计要求,子模型切割边界选择正确,有效地为设计和检验提供了理论依据。     

开孔球罐的应力分析

利用解析法和有限元法(借助于ANSYS软件),对开圆孔的球罐进行应力分析.分别分析了球罐上同一位置不同半径的开孔和不同位置相同半径的开孔对应力集中的影响规律.结果发现,2种方法的结果比较接近;同时得出了一些结论,对合理的开孔提出了一些基本原则.     

基于ASME大型球罐有限元分析

利用有限元分析软件ANSYS对4000 m³大型球罐进行整体建模, 对其在不同操作工况下进行应力分析。同时研究球罐模型的建模方法、各种载荷的施加方法, 并采用ASME规范对球罐支柱和球壳连接处等多个部位进行应力评定, 总结出完整的应力分析方法, 从而为球罐的结构设计提供指导。经计算, 组合工况, 自重+设计压力+25%风载荷+地震载荷应力结果最大, 球壳上最大应力点发生在支柱与球壳连接处的最高点。球罐的最大应力值发生在支撑和球壳的连接部位, 说明支撑与球壳的连接处是薄弱点, 设计时应给予关注, 增加支柱与球壳连接长度能有效降低应力集中水平。     

3000m~3丙烯球罐多工况应力分析

以3 000 m3丙烯球罐为分析对象,分别建立整体有限元分析模型。考虑多载荷、多工况条件,计算获得球罐在不同工况下得应力分布规律。采用应力线性化方法对球罐进行应力评定。其有限元分析与评定方法为球罐的设计工作提供依据。     

基于金属磁记忆法的球罐支柱角焊缝缺陷检测方法

使用金属磁记忆方法对在用球罐支柱角焊缝进行检测,发现大部分支柱角焊缝存在应力集中指示区,且普遍分布于1#、2#检测部位,其中,2#支柱的应力集中最为明显。对支柱角焊缝进行常规检验,发现2#、9#、10#支柱存在超标裂纹,表明金属磁记忆法可用于常规检验之前以确定重点检测部位,使检测更具针对性,提高检验效率。采用有限元软件对承受工作压力、风压和雪压的球罐进行应力计算,发现最大von mises等效应力出现在2#球罐支柱角焊缝处,而该处应力满足球罐结构强度要求,经验证,检验发现的超标裂纹可能是由焊接所致。     

复合材料层合结构自由边效应实验研究

复合材料层合结构的自由边效应是复合材料结构总体破坏的主要因素之一.本文对复合材料层合结构自由边效应进行了实验研究,得到了自由边效应的分布规律,即层间应力在自由边界和载荷边界附近有明显的应力集中,在离开边界的地方应力集中现象很快消失.实验结果与数值模拟结果趋势基本一致,这一规律的发现可为复合材料制造工艺和工程应用提供指导.     

削边形式对筒体与封头过渡区应力分布的影响

利用ANSYS 16.0有限元分析软件,以半球形封头、椭圆形封头和无折边球形封头3种凸形封头为研究对象,通过改变削边长度和削边形式,得到其应力分布规律,并进行优化分析。结果表明:3种封头形式压力容器最大等效应力均集中于筒体和封头过渡区域;在相同尺寸和相同削边形式下,应力集中系数大小顺序为无折边球形封头>椭圆形封头>半球形封头;随着削边长度L的增加,椭圆形封头和无折边球形封头压力容器应力集中系数K均呈增大的趋势,对于半球形封头压力容器,削边长度L出现临界值;半球形封头压力容器优化效果最为明显。     

1500m3球壳板曲率超标球罐有限元应力分析与强度校核

对1500m3曲率超标球罐在水压试验和设计压力工况下进行了有限元应力分析计算,并根据应力分析设计方法进行了强度校核。结果表明应力强度合格,但最大应力点偏移到超标曲率最大点处。参考应力分析计算结果,提出了球壳板曲率超标球罐的处理措施。     

某压力容器现场组焊错边超差的对策

现场组焊压力容器经常出现焊缝错边超差的问题,由于这种几何形状突变将造成过高的应力集中,降低了容器壳体承载强度和疲劳强度。本文通过实例,在理论计算分析的基础上,讨论了采用某些工艺措施对抵消错边超差影响的可行性和局限性。     

Modeling of moisture‐induced stress in PMMA: A simple approach to consider sorption behavior in FEM

Moisture‐induced stresses in amorphous thermoplastics are studied in detail using the finite element method (FEM). The approach is based on the coefficient of moisture expansion which is derived from the sorption behavior (i.e., changes of mass, density and elastic properties). The required model parameters were obtained by isothermal diffusion and swelling experiments at different levels of relative humidity at room temperature. In the analysis, the evolutions of moisture‐induced stresses in a model system have been analyzed, i.e., drying sheets of poly(methyl methacrylate). The calculated stresses during drying are discussed with regards to the sorption models. Results indicate that these computational models are essential in capturing the accurate moisture‐induced stress. Finally, the simulation results were verified by three‐point bending. The implemented method shows the potential to predict environmental stress cracking due to humidity by FEM. This is important for the improved design of plastics parts. POLYM. ENG. SCI., 57:3–12, 2017. © 2016 Society of Plastics Engineers     

Neutron Diffraction and Finite-Element Analysis of Thermal Residual Stresses on Diffusion-Bonded Silicon Carbide-Molybdenum Joints

Various approaches can be used to minimize residual stresses in ceramic-metal joining, such as a refractory-metal interlayer in a hot-pressed joint. Nonetheless, it is still necessary to characterize the stresses at and near the interface between the interlayer and the ceramic, as a function of the hot-pressing parameters. This study combines two techniques to assess the stress distribution of hot-pressed silicon carbide-molybdenum joints: neutron diffraction and finite-element (FEM) analysis. The results demonstrate that the joining temperature greatly influences the final stress distribution, and that significant stress accommodation is achieved by controlling the cooling rate of the diffusion couples. FEM analysis provides a broad view of stress distribution profiles, whereas experimental stress values that are obtained via neutron diffraction allow a better assessment of the effects of parameters that are not easily reproduced using a mathematical model.     

Simulation of residual stress in thick thermal barrier coating (TTBC) during thermal shock: A response surface-finite element modeling

The current study demonstrates a well-designed response surface methodology (RSM), based on the generated dataset of finite element method (FEM) to establish an integrated model for simulation of residual stress distribution in a thick thermal barrier coating (TTBC). In this study, typical TTBCs were applied on Hastelloy X Nickel-based superalloy using air plasma spray technique followed by thermal cycling. The recorded stress data of Raman spectroscopy was employed to verify the proposed FEM model. A relatively good agreement was obtained between predicted residual stresses and measured ones. Verified FEM model was used to carry out the parametric studies to evaluate the effects of such various parameters as interface amplitude, wavelength, thermally grown oxide thickness and preheating temperature on the stress distribution in the TTBC during the thermal cycling. The computed data were subsequently used for the development of RSM model. In conclusion, experimentally verified numerical data was used to construct a statistical model based on RSM and successfully used to predict the residual stress distribution field in TTBC during thermal cycling. The obtained results of hybrid FEM- RSM model were in acceptable conformity with Raman spectroscopy measurements.     

Stress concentration coefficient in a composite double lap adhesively bonded joint

The main target of this paper is to investigate the effect of peak stress at the extremities of the adhesive layer of a bonded assembly subjected to dynamic shear impact. It is known, that under both static and dynamic loadings such joints endure at their extremities high level of stresses, an aspect known as edge effects. Double lap joint assembly was considered with unidirectional carbon–epoxy substrates and Araldite 2031 adhesive. To quantify this edge effect, a specific coefficient, named coefficient of stress concentration was defined: it is the ratio of the maximum shear stress to the average shear stress. This coefficient helps to calculate maximum strength of the joint since experimentally, only average shear stress could be measured. A numerical analysis at the midplane of the joint was carried out to investigate the effect of geometrical and material parameters on this stress concentration factor. It was found that this factor is constant with the time once the equilibrium is established. Moreover, this stress concentration coefficient decreases with higher Young's modulus of the adherents, lower Young's modulus of the adhesive, thicker and shorter adhesive layer. A unified parameter involving geometrical and mechanical parameters of the specimen was established to quantify this stress concentration factor.     

Analysis of the sensitivity to pressure and temperature of a membrane based SAW sensor

ABSTRACT

This paper presents a FEM analysis of a membrane-based Surface Acoustic Wave (SAW) sensor. The sensor is a 2.45GHz Reflective Delay Line (R-DL) based on Lithium Niobate (LiNbO₃). As the wave propagation time is much smaller than the typical time constant of the phenomena to be monitored (deformation, temperature change etc.), the analysis can be performed in three successive steps. First, a static FEM study of the complete sensor (housing included) is carried out, to compute the temperature, stress and strain fields generated in the sensitive area by the measured parameters (pressure, temperature, etc.). Then, a dynamic electro-mechanical study of the R-DL is performed. The simulation takes the previously computed fields into account, which makes it possible to compute the sensor sensitivity to the measured parameters. The model takes advantage of the periodicity of the components of the R-DL to compute phenomenological parameters (Coupling-of-Mode parameters), which can later on be used to compute the electrical response of the sensor (step 3). In this paper, we focus on the first two steps. The COM parameters are extracted, under simultaneous thermal and mechanical stresses. Especially, the sensor sensitivity is obtained from the evolution of the velocity, under various stress configurations.     

Conditional generative adversarial network driven approach for direct prediction of thermal stress based on two-phase material SEM images

A conditional generative adversarial network (cGAN)-driven approach for the direct prediction of thermal stress is proposed. Synthetic two-phase structure images of ceramic top coat (TC) with CaO–MgO–Al₂O₃–SiO₂ (CMAS) inclusions are established, and the TC matrix and CMAS inclusions are semantically segmented by grayscale. The thermal stresses of the two-phase structure are calculated using image-restoration finite element models (FEMs) under the isothermal process. The training database is established based on a small-scale original dataset of integral structures and their stresses. Each integral TC–CMAS structure and its corresponding stress distribution are partitioned into many local images, using which the cGAN model is trained. The model stresses are generated by the trained cGAN directly from the structure images. The deviations between the predicted stress and the FEM stress are small in most areas of the images. In terms of computing time, the proposed approach has higher stress evaluation efficiency than does the FEM.     

Progressive failure and experimental study of adhesively bonded composite single-lap joints subjected to axial tensile loads

Experimental tests and finite element method (FEM) simulation were implemented to investigate T700/TDE86 composite laminate single-lap joints with different adhesive overlap areas and adherend laminate thickness. Three-dimensional finite element models of the joints having various overlap experimental parameters have been established. The damage initiation and progressive evolution of the laminates were predicted based on Hashin criterion and continuum damage mechanics. The delamination of the laminates and the failure of the adhesive were simulated by cohesive zone model. The simulation results agree well with the experimental results, proving the applicability of FEM. Damage contours and stress distribution analysis of the joints show that the failure modes of single-lap joints are related to various adhesive areas and adherend thickness. The minimum strength of the lap with defective adhesive layer was obtained, but the influence of the adhesive with defect zone on lap strength was not decisive. Moreover, the adhesive with spew-fillets can enhance the lap strength of joint. The shear and normal stress concentrations are severe at the ends of single-lap joints, and are the initiation of the failure. Analysis of the stress distribution of SL-2-0.2-P/D/S joints indicates that the maximum normal and shear stresses of the adhesive layer emerge on the overlap ends along the adhesive length. However, for the SL-2-0.2-D joint, the maximum normal stress emerges at the adjacent middle position of the defect zone along the adhesive width; for the SL-2-0.2-S joint, the maximum normal stress and shear stress emerge on both edges along the adhesive width.     

Thermo-Mechanical Stresses and Mechanical Reliability of Multilayer Ceramic Capacitors (MLCC)

In this work, the effects of design parameters on the mechanical reliability of multilayer ceramic capacitors (MLCC) are evaluated by a board flex test. Using the finite element method (FEM), thermo-mechanical stresses that accumulated in the ceramic of MLCC during termination firing, soldering, and board flex test are determined by varying design parameters. The calculation results revealed that the sizes of Cu terminations are the parameters that affect the stress the most. The degree of sensitivity of the stress to the dominant parameters depends significantly on the thickness ratio of the MLCC to the board. Based on our investigation, better design rules are proposed and verified experimentally.     

新型螺杆挤出机螺杆强度的有限元分析

介绍了一种新型螺杆挤出机的原理及结构特点。对该新型挤出机的外螺杆建立了符合实际尺寸与形状的有限元模型，利用ansys有限元软件对其进行了应力分析。研究结果表明，安全系数达到3时。承受内外压力的特殊结构外螺杆危险截面的内外表面处。各主要应力值均小于许用应力，强度符合要求。从理论上证明了该螺杆在新的工作载荷条件下具备正常运转的能力。为该新型挤出机进一步的开发提供了保证，同时证明了有限元方法在强度分析中是可靠且高效的。     

Fracture and deformation mechanism of Ti(C,N)/TiAlSiN multilayer coating: FE modeling and experiments

Ti(C,N)/TiAlSiN multilayer coating was deposited on GTD450 using the Cathodic Arc PVD method to protect compressor blades from erosion damage. The fracture and deformation mechanisms of coating were investigated. To better observe fracture and deformation events and thus the need to apply high loads, Vickers microhardness test was performed and imprint diagonals were measured. Then, using SEM analysis, indent surfaces were investigated to observe crack initiation and deformation patterns at different loadings. It was found that crack initiated at the coating top surface (top surface of TiAlSiN layer) at a loading range of 250–500 mN. Cross-section SEM images of indent surfaces at lower loads revealed shear sliding and radial cracking below the indenter in the coating-substrate interface (bottom surface of Ti(C,N) layer). To better understand coating fracture and deformation, a 3D FE model was used to determine stress distribution in the coating. FEM results showed that maximum Von Mises stresses occur beneath the indenter and its edges, causing shear sliding to take place. Also, maximum principal stresses at lower loads take place beneath the indenter at the coating-substrate interface. As load increases, the maximum principal stress zone changes and is transferred to the coating top surface. Maximum principal stress was produced during the unloading process at the coating top surface or median plane and may cause lateral cracking. Experimental and FEM results were in good agreement.