InformationWeek.com: News, analysis and research for business technology professionals, plus peer-to-peer knowledge sharing. Engage with our community.![]() Partner Perspectives. . Partner Perspectives.Partner Perspectives.White Papers. Current Issue. ![]() Digital Transformation Myths & Truths. Transformation is on every IT organization's to- do list, but effectively transforming IT means a major shift in technology as well as business models and culture. In this IT Trend Report, we examine some of the misconceptions of digital transformation and look at steps you can take to succeed technically and culturally.[Interop ITX 2. State Of Dev. Ops Report. The Dev. Ops movement brings application development and infrastructure operations together to increase efficiency and deploy applications more quickly. But embracing Dev. Ops means making significant cultural, organizational, and technological changes. ![]() This research report will examine how and why IT organizations are adopting Dev. Ops methodologies, the effects on their staff and processes, and the tools they are utilizing for the best results. Video. Sponsored Video. Slideshows. Twitter Feed. VideoCopilot Element 3D 2.2.2.2147 Final Release is a plugin for Adobe After Effects that allows using 3D geometries, duplicate them, applied materials, etc. J- Integral Calculation by Finite Element Processing of Measured Full- Field Surface Displacements. A key requirement in fracture mechanics research is to quantify the conditions that will propagate a crack. Fracture is a thermodynamic problem, and the strain energy release rate describes the potential elastic energy that is available to propagate the crack by increasing its surface area. In linear elastic materials, or when the small scale yielding condition is satisfied, the strain energy release rate can be represented by the stress intensity factor (SIF) that describes the crack’s stress field [1, 2, 3]. Even in cases where crack tip plasticity invalidates the small scale yielding condition, the strain energy release rate can be used as descriptor of the crack field [4]. Stress corrosion cracking and fatigue cracking also propagate under conditions that are controlled by such crack fields [5, 6, 7, 8]. As the strain energy release rate or SIF are descriptors of the crack’s elastic strain or stress field, it is essential to quantify the crack field in fracture mechanics experiments. The strain energy release rate can be measured directly from the work done to propagate a sub- critical crack [9], and it has long been the practice to calculate the SIF from the applied loads using analytical solutions or finite element methods with knowledge of the specimen geometry and applied load or displacement boundary conditions [1. Elastic- plastic fracture mechanics also enables the extraction of the SIF or strain energy release rate via measurements of the crack opening displacements [1. However, in some cases these standard solutions can be inadequate or inaccurate. For instance, residual stresses from manufacturing or crack closure following fatigue overloads, which may not be well quantified, can act against the applied loads that are the known boundary conditions; these effects are particularly important in stress corrosion [1. Uncertainties in the true boundary conditions acting on a crack, such as in a real engineering component or a small- scale mechanics test of non- standard geometry where factors such as friction and misalignment can be significant, may also prevent accurate calculation of the crack field [1. Consequently, there is an interest in defining the crack field by direct measurement of the deformation surrounding the crack. Typically, this deformation is measured between two successive observations that show the change in the field with a change in the applied load. Various approaches have been proposed, but such measurements are not routinely used since the analysis methods are quite complex and can be sensitive to measurement uncertainties. The most general method is the field fitting approach, which fits a theoretical field to the measured displacement field in order to retrieve the SIF. An early method by Chiang used speckle interferometry [1. SIF was estimated by relating the displacements at the Young’s fringes to the square root of their distance from the crack tip. Shortly afterwards, Huntley [2. SIF from a full field displacement field, obtained by double exposure laser speckle photography, via a least square fit to the Williams’ series. Other techniques to obtain the displacement field, such as the grid method [2. Big Pack of Elements 19888878 Videohive - Free Download After Effects TemplatesAfter Effects Version CC 2015, CC 2014 | Resizable | No Plugins | 182 MbWhat is inside? Ever notice how Christopher Nolan’s movies (Interstellar, Inception, The Prestige) feel like an anxiety attack? Well, maybe that’s overstating things a bit. But. Digital image correlation (DIC) is now widely used to measure displacement fields, due to its ease of use in a wide range of materials. Digital image correlation (DIC) is a method based on tracking of recognizable patterns between two images [2. An image of the surface is obtained in both original and deformed states, and a map of relative displacement vectors can be retrieved with a sub- pixel accuracy by considering subsets of the original image within the deformed image. This is typically done by maximization of a correlation coefficient (in the case where perfect correlation has unit coefficient). The correlation coefficient for each subset is optimised using rigid body displacement of the subset and the first- order displacement gradients describing the local deformation values of the subset [2. The second- order displacement gradient can also be included in the correlation analysis and has been shown to improve DIC accuracy [2. Image acquisition setups using one camera are able to determine in- plane displacements, with a requirement of negligible out of plane displacements unless confocal optics are used; such an example is presented by Fazzalari [2. With two- camera systems (stereo- DIC) [2. Since the early study by Sutton [2. DIC has increasingly been used in fracture research. For instance, DIC can be used to detect crack initiation; examples include the effect of strain state on high cycle fatigue initiation [2. Some early analyses used least- squares methods to fit the Williams’ series to the DIC results, and obtained the mode I SIF [3. The method has also been extended to mixed mode loading [3. However, the least- squares technique is quite sensitive to accurate definition of the crack tip location, as highlighted by Mc. Neill [3. 2]. Recently, specific terms of the Williams’ series (i. SIF calculation. The J- integral, independently developed by Cherepanov [3. Rice [4. 0] can be used to calculate the strain energy release rate directly from the strain field of a crack. Its formulation is defined as a contour path integral, which has zero value if no crack is present in the contour. The J- integral is contour independent, and the contour to evaluate the strain energy release rate of a crack must start and end from a traction- free surface, such as the crack surface. Often implemented as a line integral, the J- integral can be formulated as a surface or area integral using Green’s theorem, and this is convenient to implement in finite element analyses. An example of the direct evaluation of the J- integral from the measured crack field is the JMAN method [4. DIC measurements, and the implementation of other integrals with full- field displacement data can be found in the literature, such as [2. Importantly, these methods do not rely on fitting a presumed field (e. Williams’ series). A further advantage of using the J- integral method to obtain the strain energy release rate is that its calculation is quite robust to uncertainty in the crack tip position. In the case of a linear elastic analysis with small scale yielding, selection of the integration contours to exclude the plastic zone [4. Alternative formulations of the J- integral that are compatible with inelastic and plastic models have also been presented [4. The calculation of the area integral is implemented in standard finite element software packages to post- process the displacement fields that are obtained in simulations of cracked specimens or components; in Abaqus for instance, the virtual crack extension/domain integral method is applied [4.In this paper, we will show how an experimentally- measured displacement field may be imported directly into the finite element software, and post- processed similarly.An important factor that needs to be considered is the reliability of the data interpolations, which may be required when the meshes of the displacement field and the finite element simulation are differently optimised.Regular FE meshes can provide a poor description of the fields close to stress concentrations unless sufficiently refined, whereas the displacements measured by full- field methods such as digital image correlation (DIC) generally lie on a relatively coarse regular grid, although it is possible for DIC analysis to be tailored to retrieve displacement vectors at specific locations [4.Analysis of the displacement field requires knowledge of the deformation close to the crack.However, DIC can fail to determine the displacement vectors satisfactorily in the vicinity of edges or discontinuities in the displacement field, such as close to a crack [3. Ice Cream Sandwich For Droid Razr Release . For example, Réthoré proposed an algorithm based on enrichment of finite element- based DIC subsets [4. Poissant and Barthelat [4. DIC algorithm to allow the subsets to split along the crack path. These solutions are quite complex and are not yet generally applied, however, and it is quite common in DIC analysis to exclude those measurements in the vicinity of the crack (i. Consequently, data are missing from the crack tip region where the highest strains (i. In the context of the J- integral evaluation, data are also missing near to the traction- free surfaces of the crack.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |