基于Deepcrack网络的混凝土裂缝检测方法

混凝土结构裂缝对建筑安全构成了极大的潜在威胁,裂缝检测对建筑结构的维护具有重要意义,当前基于深度学习的裂缝检测针对提取裂缝细节的能力仍有待提高。因此,该文对Deepcrack网络进行优化,提出了基于金字塔分割注意力和全局上下文的混凝土裂缝检测算法PG-Deepcrack。首先,在编码器中提出双卷积-注意力并行模块,增加金字塔分割注意力分支为卷积层提供更丰富的多尺度裂缝信息;其次,为了捕获长距离依赖关系,并行模块操作后引入全局上下文模块,进一步提升网络对裂缝细节的表达能力;最后,在特征融合阶段利用全维动态卷积和GELU激活函数,对编解码器特征层联级融合,使网络更全面地保留不同尺寸的裂缝信息并提高模型的泛化性能。为验证网络模型的有效性,在Deepcrack数据集上与7个网络模型进行对比试验,所提出的网络表现了最佳性能,IoU达到了72.78%。

THE CONSTITUTIVE RELATION OF CRACK-WEAKENED ROCK MASSES UNDER AXIAL-DIMENSIONAL UNLOADING

An accurate and efficient numerical method for solving the crack-crack interaction problem is presented. The method is mainly by means of the dislocation model, stress superposition principle and Chebyshev polynomial expansion of the pseudo-traction. This method can be applied to compute the stress intensity factors of multiple kinked cracks and multiple rows of periodic cracks as well as the overall strains of rock masses containing multiple kinked cracks under complex loads. Many complex computational examples are given. The dependence of the crack-crack interaction on the crack configuration, the geometrical and physical parameters, and loads pattern, is investigated. By comparison with numerical results under confining pressure unloading, it is shown that the crack-crack interaction under axial-dimensional unloading is weaker than those under confining pressure unloading. Numerical results for single faults and crossed faults show that the single faults are more unstable than the crossed faults. It is found from numerical results for different crack lengths and different crack spacing that the interaction among kinked cracks decreases with an increase in length of the kinked cracks and the crack spacing under axial-dimensional unloading.

Discrete Element Modeling of Asphalt Concrete Cracking Using a User-def ined Three-dimensional Micromechanical Approach

We established a user-defined micromechanical model using discrete element method （DEM） to investigate the cracking behavior of asphalt concrete （AC）. Using the ＂Fish＂ language provided in the particle flow code in 3-Demensions （PFC3D）, the air voids and mastics in asphalt concrete were realistically built as two distinct phases. With the irregular shape of individual aggregate particles modeled using a clump of spheres of different sizes, the three-dimensional （3D） discrete element model was able to account for aggregate gradation and fraction. Laboratory uniaxial complex modulus test and indirect tensile strength test were performed to obtain input material parameters for the numerical simulation. A set of the indirect tensile test were simulated to study the cracking behavior of AC at two levels of temperature, i e, -10 ℃ and 15 ℃. The predicted results of the numerical simulation were compared with laboratory experimental measurements. Results show that the 3D DEM model is able to predict accurately the fracture pattern of different asphalt mixtures. Based on the DEM model, the effects of air void content and aggregate volumetric fraction on the cracking behavior of asphalt concrete were evaluated.

THREE-DIMENSIONAL ELLIPTIC CRACK UNDER IMPACT LOADING

The dynamic stress intensity factor of a three-dimensionalelliptic crack under impact loading is determined with the finiteelement method. The computation results can take into account theinfluence of time and the ratio of the wave speeds on the stressintensity factor. The present method is suitable not only forthree-dimensional dynamic crack, but also for three-dimensionaldynamic contact.

Interactions of penny-shaped cracks in three-dimensional solids

The interaction of arbitrarily distributed penny-shaped cracks in three-dimensional solids is analyzed in this paper. Using oblate spheroidal coordinates and displacement functions, an analytic method is devel- oped in which the opening and the sliding displacements on each crack surface are taken as the basic unknown functions. The basic unknown functions can be expanded in series of Legendre polynomials with unknown coefficients. Based on superposition technique, a set of governing equations for the unknown coefficients are formulated from the traction free conditions on each crack surface. The boundary collocation procedure and the average method for crack-surface tractions are used for solving the governing equations. The solution can be obtained for quite closely located cracks. Numerical examples are given for several crack problems. By comparing the present results with other existing results, one can conclude that the present method provides a direct and efficient approach to deal with three-dimensional solids containing multiple cracks.

Analysis of Three-dimensional Crack Propagation by Using Displacement Discontinuity Method

A technique for modelling of three-dimensional(3D)quasi-statically propagating cracks in elastic bodies by the displacement discontinuity method(DDM)was described.When the crack is closed,the Mohr-coulomb rule on the two contacted surfaces of the crack must be satisfied.A simple iterative method was adopted in order to consider three different states of cracks.Under the assumption that the advance of the point on the crack front would occur only in the normal plane which is through this edge point,the maximum energy release rate criterion is modified to be used as the criterion for the crack growth.With discretization,the process of crack propagation can be seen as the advance of the vertices of the crack front.The program MCP3D was developed based on these theories to simulate the 3D quasi-static crack propagation.A numerical example of a penny-shaped crack subject to tension and compression in an infinite elastic media was analyzed with MCP3D,and the results in comparison with others' show that the present method for 3D crack propagation is effective.

A MODE Ⅱ CRACK IN A TWO-DIMENSIONAL OCTAGONAL QUASICRYSTALS

The present study develops the fracture theory for a two-dimensional octagonal quasicrystals. The exact analytic solution of a Mode Ⅱ Griffith crack in the material was obtained by using the Fourier transform and dual integral equations theory, then the displacement and stress fields, stress intensity factor and strain energy release rate were determined, the physical sense of the results relative to phason and the difference between mechanical behaviors of the crack problem in crystal and quasicrystal were figured out. These provide important information for studying the deformation and fracture of the new solid phase.

A CLOSED FORM SOLUTION OF STRESS INTENSITY FACTORS FOR THREE DIMENSIONAL FINITE BODIES WITH ECCENTRIC CRACKS

In this paper, a new analytical-engineering method of closed form solution about stress intensity factors for three dimensional finite bodies with eccentric cracks is derived by means of energy release rate method. The results of stress intensity factors can be obtained. The results provided ir this method are in nice agreement with those of the famous alternating method by which only special cases can be solved.

A modified maximum tangential tensile stress criterion for three-dimensional crack propagation

The three-dimensional （3D） crack propagation is a hot issue in rock mechanics. To properly simulate 3D crack propagation, a modified maximum tangential tensile stress criterion is proposed. In this modified criterion, it is supposed that cracks propagate only at crack front in the principal normal plane. The tangential tensile stress at crack front in the principal normal plane in local coordinates is employed to determine crack propagation, which is calculated through coordinate transformation from global to local coordinates. New cracks will propagate when the maximum tangential tensile stress at crack front in the principal normal plane reaches the tensile strength of rock-like materials. Compared with the previous crack propagation criteria, the modified crack propagation criterion is helpful in calculating 3D crack stress intensity factor, and can overcome the limitations of propagation step determined by individual experiences in previous studies. Finally, the 3D crack propagation process is traced by element-free Galerkin method. The numerical results agree well with the experimental ones for a frozen resin sample with prefabricated 3D cracks.

The interaction between a screw dislocation and a wedge-shaped crack in one-dimensional hexagonal piezoelectric quasicrystals

Based on the fundamental equations of piezoelasticity of quasicrystal material,we investigated the interaction between a screw dislocation and a wedge-shaped crack in the piezoelectricity of one-dimensional hexagonal quasicrystals.Explicit analytical solutions are obtained for stress and electric displacement intensity factors of the crack,as well as the force on dislocation.The derivation is based on the conformal mapping method and the perturbation technique.The influences of the wedge angle and dislocation location on the image force are also discussed.The results obtained in this paper can be fully reduced to some special cases already available or deriving new ones.

CONVOLUTION OF THE IMPACT THREE-DIMENSIONAL ELASTO-DYNAMICS AND DYNAMIC STRESS INTENSITY FACTOR FOR AN ELLIPTIC CRACK

This paper presents a formulation for three-dimensional elasto-dynamics with an elliptic crack based on the Laplace and Fourier transforms and the convolution theorem. The dynamic stress intensity factor for the crack is determined by solving a Fredholm integral equation of the first kind. The results of this paper are very close to those given by the two-dimensional dual integral equation method.

A STUDY ON STRESS INTENSITY FACTORS AND SINGULAR STRESS FIELDS OF THREE-DIMENSIONAL INTERFACE CRACK

By using the finite-part integral concepts and limit technique,the hypersingular inte- grodifferential equations ofthree-dimensional(3D)planar interface crack were obtained; then thedominant-part analysis of 2D hypersingular integral was further usedto investigate the stress fields near the crack front theoretically,and the accurate formulae were obtained for the singular stressfields and the complex stress intensity factors.

INTERFACIAL CRACK ANALYSIS IN THREE-DIMENSIONAL TRANSVERSELY ISOTROPIC BI-MATERIALS BY BOUNDARY INTEGRAL EQUATION METHOD

The integral-differential equations for three-dimensional planar interfacial cracks of arbitrary shape in transversely isotropic bimaterials were derived by virtue of the Somigliana identity and the fundamental solutions, in which the displacement discontinuities across the crack faces are the unknowns to be determined. The interface is parallel to both the planes of isotropy. The singular behaviors of displacement and stress near the crack border were analyzed and the stress singularity indexes were obtained by integral equation method. The stress intensity factors were expressed in terms of the displacement discontinuities. In the non-oscillatory case, the hyper-singular boundary integral-differential equations were reduced to hyper-singular boundary integral equations similar to those of homogeneously isotropic materials.

Exact analytic solutions for an elliptic hole with asymmetric collinear cracks in a one-dimensional hexagonal quasi-crystal

Using the complex variable function method and the technique of conformal mapping, the anti-plane shear problem of an elliptic hole with asymmetric colfinear cracks in a one-dimensional hexagonal quasi-crystal is solved, and the exact analytic solutions of the stress intensity factors （SIFs） for mode Ⅲ problem are obtained. Under the limiting conditions, the present results reduce to the Griffith crack and many new results obtained as well, such as the circular hole with asymmetric collinear cracks, the elliptic hole with a straight crack, the mode T crack, the cross crack and so on. As far as the phonon field is concerned, these results, which play an important role in many practical and theoretical applications, are shown to be in good agreement with the classical results.

Prediction of Three Dimensional Crack Path Brittle Fracture in Weldment under Dynamic Load

Three dimensional dynamic stress intensity factors are analyzed for a curved crack with a second order perturbation method. The method is extended to obtain an approximate representation of a three dimensional dynamic stress intensity factors at the tip of a curved crack. Due to three dimensional curved crack growth the dynamic energy release rate can be calculated by using the Irwin＇s formula. A three dimensional curved crack in materials with inhomogeneous fracture toughness are considered. Paths of a brittle three dimensional curved crack propagating along a welded joint are predicted via the present method, where the effects of dynamic applied stresses, residual stresses, and material deterioration due to welding are taken into considerations.

炸药模拟裂纹宽度的CT检测与测量分析

炸药作为武器系统的核心部件,其内部结构质量直接关系到武器系统的可靠性,目前CT技术已被用于炸药试件的内部质量检测与评价研究,特别用于炸药试件内部裂纹的定性与定量分析中。然而选择不同的检测工艺参数会造成CT图像质量的变化,直接影响到后续定量表征的精度。通过在炸药试件表面加工不同宽度的标准尺寸线槽,再将其与相同规格的炸药试件对粘,以实现在炸药试件内部预制标准尺寸裂纹的目的。然后,改变检测参数与工艺条件,得到不同检测参数对试件裂纹宽度测量精度的影响规律,分析讨论了CT测量炸药试件(如尺寸小于10 mm的始发药等)裂纹宽度的最佳检测工艺条件。

动载下含表面裂纹岩石破坏的近场动力学模拟

为了研究动态加载下岩石表面裂纹的扩展,基于前期试验结果使用一种考虑压缩和拉伸强度比的弹塑性常规态基近场动力学模型进行数值试验。模拟动态加载下含不同角度和深度三维表面裂纹岩石的破坏过程。模拟结果表明,使用的近场动力学模型可以很好地模拟岩石三维裂纹的扩展和试样的破坏过程。通过近场动力学模拟可以得到与试验结果一致的强度变化规律。试样表面形成的裂纹深入试样内部一定深度,该深度与表面裂纹深度有关。试样内部产生的壳裂纹会与表面形成的裂纹连接形成复杂的三维裂纹。

涡轮叶片裂纹方位角的三维叶尖间隙动态响应特性研究

针对叶尖定时故障诊断方法在检测叶片裂纹时仅关注一维信息、提取故障特征有限的不足,利用叶尖间隙具有三维特征的特点,提出了航空发动机涡轮叶-盘-轴耦合系统的三维叶尖间隙(3D-BTC)有限元模型。以该模型为基础,分析了航空发动机涡轮叶片裂纹方位角对三维叶尖间隙的影响规律。首先,建立了航空发动机涡轮叶-盘-轴耦合系统有限元模型;其次,在叶片尾缘处引入贯穿裂纹,通过瞬态动力学分析计算了在不同横滚角、俯仰角裂纹作用下叶片的变形;最后,采用三维叶尖间隙计算方法获取了叶片三维叶尖间隙时域波形及频谱,研究了航空发动机涡轮叶片裂纹方位角的三维叶尖间隙动态响应特性。计算结果表明:裂纹的出现会降低叶片刚度,从而影响叶片的三维叶尖间隙;叶片三维叶尖间隙随裂纹横滚角的增大而减小,随裂纹俯仰角的增大先减小后增大;随着裂纹两类方位角变化,不同测点位置的叶尖径向间隙基本谐波分量峰值变化率的差值最大为6.1%,周向滑移角和轴向偏转角基本谐波分量峰值变化率的差值小于0.12%,可见综合三维叶尖间隙能够更准确地反映裂纹信息。

考虑残余应力影响的典型钢结构对接焊缝缺陷定位研究

对接焊缝为典型的钢结构焊缝形式,其位置处的裂纹和气孔型缺陷的准确检测对于钢结构维护有着重要的意义,使用磁记忆检测技术对焊缝裂纹和气孔型缺陷进行定位时,传统的零点极值理论由于焊接残余应力的影响,难以区分残余应力、焊接裂纹和气孔型缺陷所产生的磁信号,从而在实际检测中造成缺陷定位的误判和漏判,因此,从焊接裂纹和气孔型缺陷和残余应力所在区域磁信号产生机理的不同入手,开展考虑残余应力影响下的焊接裂纹和气孔型缺陷定位检测研究。首先对焊接残余应力与裂纹和气孔型缺陷产生磁信号的机理进行分析,提出采用三维磁模量梯度极值判定方式来区分残余应力与裂纹和气孔型缺陷产生的磁信号;其次再进行焊接缺陷有限元COMSOL模拟,将所得磁信号代入梯度极值特征公式中进行表征判断;最后为了验证模拟表征判断的准确性,人工制作焊接钢板,提取三维磁信号进行分析。研究结果表明,理论分析、数值模拟与试验结果相互吻合,三维磁模量梯度极值能定位焊接缺陷并定量表征缺陷的长度,且裂纹和气孔型的三维磁模量梯度值远远高于无缺陷残余应力区域的梯度值。

基于卷积神经网络和传感器数据的风力发电机转子断裂故障诊断

提出基于卷积神经网络和传感器数据的新能源风力发电机转子断裂故障诊断算法。根据转子运行状态与裂纹轴向刚度之间的关联关系,构建了发电机转子裂纹模型。对多个传感器采集的发电机转子振动数据进行融合处理后,将原始的一维数据转换为m×n二维矩阵的形式,利用多通道卷积神经网络对传感器数据信息进行分析,并将输出结果代入到发电机转子裂纹模型中,实现对转子断裂故障的诊断。在测试结果中,算法对不同数据源下的电机转子断裂故障诊断结果,误差稳定在0.03μm以内。