Performances of conventional fiber reinforced composites are challenged in thermomechanical loading, when development of interlaminar stresses at the interface becomes the weakest link of the ...components. Development of functionally graded materials (FGMs) could lead to the reduction of such interlaminar failures, especially at high temperature applications. Therefore, these FGMs have a huge potential for use in many structural applications, particularly under thermomechanical loading. There has been a large number of works already reported on FGM components, starting from manufacturing to stress analysis of such components. Cracks in such FGM components may develop due to variety of reasons during service and need to be addressed while analyzing the performances of such components. This paper reviews the progress made till date on the analysis of structural components made of FGMs with a special emphasis on the analysis of cracked FGM components. In view of the potential use of components made of FGMs in a wide range of applications, it is important to understand the state of the art in this area. This paper thus provides a critical review of works reported in this area with an objective of providing the key challenges and future scopes of development in the direction of analysis of such structure for assessing safety in the presence of cracks.
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•Review on development of functionally graded materials (FGMs).•Review on the analysis of cracked structural components made of FGMs.•Key challenges and future scopes of development of FGMs in the presence of cracks.
The fundamental ideas for a nonlocal density functional theorycapable of reliably capturing van der Waals interactionswere already conceived in the 1990s. In 2004, a seminal paper introduced the ...first practical nonlocal exchange–correlation functional called vdW–DF, which has become widely successful and laid the foundation for much further research. However, since then, the functional form of vdW–DF has remained unchanged. Several successful modifications paired the original functional with different (local) exchange functionals to improve performance, and the successor vdW–DF2 also updated one internal parameter. Bringing together different insights from almost 2 decades of development and testing, we present the next-generation nonlocal correlation functional called vdW–DF3, in which we change the functional form while staying true to the original design philosophy. Although many popular functionals show good performance around the binding separation of van der Waals complexes, they often result in significant errors at larger separations. With vdW–DF3, we address this problem by taking advantage of a recently uncovered and largely unconstrained degree of freedom within the vdW–DF framework that can be constrained through empirical input, making our functional semiempirical. For two different parameterizations, we benchmark vdW–DF3 against a large set of well-studied test cases and compare our results with the most popular functionals, finding good performance in general for a wide array of systems and a significant improvement in accuracy at larger separations. Finally, we discuss the achievable performance within the current vdW–DF framework, the flexibility in functional design offered by vdW–DF3, as well as possible future directions for nonlocal van der Waals density functional theory.
Even though the influence of impact energy on the low velocity impact of laminated plate is well reported, the influence of relative mass of the impactor has not been addressed extensively. This work ...investigates the effect of impactor mass relative to that of target and other associated factors like impactor velocity and the target plate size on the impact response of a GLARE plate. A 3 D finite element analysis incorporating Newmark-β method and Hertzian contact is used considering appropriate contact stiffness to evaluate the contact force. Results show that the impactor mass significantly influences the contact force and interfacial delamination.
Finite element (FE) formulations have been developed for dynamic analysis of a functionally graded (FG) shaft having a transverse crack. Two nodded Timoshenko beam element with four degrees of ...freedom (DOFs) per node has been used where effects of translational and rotary inertia, transverse shear deformations, and gyroscopic moments are considered. Local flexibility coefficients (LFCs) of the cracked FG shaft are determined analytically as a function of crack size, power-law gradient index (k), and temperature using the Castigliano's theorem and Paris's equations which are used to compute the stiffness matrix in the FE analysis. Temperature dependent thermo-elastic material properties of the FG shaft are considered graded in the radial direction following power-law gradation. Using the present formulations, an FG shaft composed of zirconia (ZrO2) and stainless steel (SS) is considered and the forward and backward whirl frequencies and critical speeds are determined. Influences of crack size, power-law gradient index, slenderness ratio, and temperature gradient on the dynamic characteristics of the rotor-bearing system with an FG shaft have been studied. Results show that the power-law gradient index has significant influence on the whirl frequencies and critical speed both for cracked and un-cracked FG shaft and could be judiciously chosen in designing FG shafts.
•Finite element formulation for dynamic characteristics of cracked FG shafts is developed.•Modified stiffness of cracked FG shaft as a function of gradation index and temperature is computed.•Whirl frequencies and critical speeds of a rotor-bearing system with a cracked FG shaft depend on power law gradient.•In an FG shaft, power law gradient could be decided to achieve the desired dynamic characteristics.
The present paper investigates interfacial delamination in a GLARE fibre metal laminate having a central circular hole under multiple low-velocity impacts (LVIs) by cylindrical impactors. A full 3D ...finite element (FE) formulation is developed for analysing the response of GLARE under multiple cylindrical impacts using Hertzian contact law, and Newmark-β method is used for transient dynamic solution. Stresses and strains obtained from the FE analysis are used to assess the interfacial delamination. Influence of important parameters like length and radius of impactor, order of occurrence and location of impact on the extent of delamination have been studied. Results from the present analysis indicate that the outer aluminium thickness and impact interval between the successive impacts greatly influence the magnitude of contact force as well as delamination at the fibre-metal interfaces which initiates at free edges along the periphery of the hole.
•Finite element formulation for dynamic characteristics of FG shafts with multiple breathing cracks is developed.•Whirl frequencies and critical speeds of a rotor-bearing system with multiple cracked ...FG shaft depend on power law gradient.•In an FG shaft, power law gradient could be decided to minimize the undesirable effects in the event of multiple breathing cracks appearing during service.
Finite element (FE) formulation of a functionally graded (FG) shaft having multiple cracks has been presented to study the transverse vibration of such shafts in a rotor bearing system. Two nodded Timoshenko beam elements with four degrees of freedom (DOFs) per node are used to model cracked FG shaft considering the translational and rotary inertia, transverse shear deformations and gyroscopic moments. Local flexibility coefficients (LFCs) for the cracked FG shaft are derived using Paris's equation and Castigliano's theorem. Breathing effect of cracks has been considered taking into account the stiffness variation during rotation of the FG shaft. Zirconia (ZrO2) and stainless steel (SS) with temperature dependent material properties have been considered as the constituent materials of a radially graded FG shaft. Using the FE code developed, the forward and backward whirl frequencies and critical speeds of the cracked FG shaft are obtained to study the effects of important parameters and power law gradient index. Results show that besides being affected by the crack locations, orientations and size, the extent of percentage reductions in fundamental frequencies and critical speeds are also influenced by the power-law gradient index of the FG shaft. Therefore, from the view point of damage tolerant design of FG shafts, the choice of power-law gradient index has significant importance where multiple transverse cracks appear in the shaft during service.
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In this article, we present molecular dynamics study of the velocity autocorrelation function (VACF) of a Brownian particle. We compare the results of the simulation with the exact analytic ...predictions for a compressible fluid from T.S. Chow, J.J. Hermans, Physica
65
, 156 (1973) and an approximate result combining the predictions from hydrodynamics at short and long times. The physical quantities which determine the decay were determined from separate bulk simulations of the Lennard-Jones fluid at the same thermodynamic state point. We observe that the long-time regime of the VACF compares well the predictions from the macroscopic hydrodynamics, but the intermediate decay is sensitive to the viscoelastic nature of the solvent.
Alberta Stroke Program Early CT Score (ASPECTS) was devised as a systematic method to assess the extent of early ischemic change on noncontrast CT (NCCT) in patients with acute ischemic stroke (AIS). ...Our aim was to automate ASPECTS to objectively score NCCT of AIS patients.
We collected NCCT images with a 5-mm thickness of 257 patients with acute ischemic stroke (<8 hours from onset to scans) followed by a diffusion-weighted imaging acquisition within 1 hour. Expert ASPECTS readings on DWI were used as ground truth. Texture features were extracted from each ASPECTS region of the 157 training patient images to train a random forest classifier. The unseen 100 testing patient images were used to evaluate the performance of the trained classifier. Statistical analyses on the total ASPECTS and region-level ASPECTS were conducted.
For the total ASPECTS of the unseen 100 patients, the intraclass correlation coefficient between the automated ASPECTS method and DWI ASPECTS scores of expert readings was 0.76 (95% confidence interval, 0.67-0.83) and the mean ASPECTS difference in the Bland-Altman plot was 0.3 (limits of agreement, -3.3, 2.6). Individual ASPECTS region-level analysis showed that our method yielded κ = 0.60, sensitivity of 66.2%, specificity of 91.8%, and area under curve of 0.79 for 100 × 10 ASPECTS regions. Additionally, when ASPECTS was dichotomized (>4 and ≤4), κ = 0.78, sensitivity of 97.8%, specificity of 80%, and area under the curve of 0.89 were generated between the proposed method and expert readings on DWI.
The proposed automated ASPECTS scoring approach shows reasonable ability to determine ASPECTS on NCCT images in patients presenting with acute ischemic stroke.
In this article, results have been presented for the two-time correlation functions for a free and a harmonically confined Brownian particle in a simple shear flow. For a free Brownian particle, the ...motion along the direction of shear exhibit two distinct dynamics, with the mean-square-displacement being diffusive at short times while at late times scales as
t
3
. In contrast the cross-correlation 〈
x(t)y(t)
〉 scales quadratically for all times. In the case of a harmonically trapped Brownian particle, the mean-square-displacement exhibits a plateau determined by the strength of the confinement and the shear. Further, the analysis is extended to a chain of Brownian particles interacting via a harmonic and a bending potential. Finally, the persistence probability is constructed from the two-time correlation functions.
The physics of the pseudogap phase of high-temperature cuprate superconductors has been an enduring mystery over the past 30 years. The ubiquitous presence of the pseudogap phase in underdoped ...cuprates suggests that understanding it is key to unraveling the origin of high-temperature superconductivity. We review various theoretical approaches to this problem, emphasizing the concept of emergent symmetries in the underdoped region of those compounds. We differentiate these theories by considering a few fundamental questions related to the rich phenomenology of these materials. Lastly, we discuss a recent idea regarding two kinds of entangled preformed pairs that open a gap at the pseudogap onset temperature,
T
*
, through a specific Higgs mechanism. We review the experimental consequences of this line of thought.
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