A large orthotropic plate with misfit pin under arbitrarily oriented biaxial loading

The problem of misfit (interference or clearance) pin in a large orthotropic plate was solved earlier by the authors for biaxial loading in the principal directions of orthotropy. Here, a more general case of arbitrarily oriented loading is considered. The most important aspect of the problem studied is the partial contact at the pin-hole interface. The solution is obtained by extending the use of ‘inverse technique’ which was successfully applied earlier by the authors to problems of pins in isotropic and orthotropic domains. The loss of symmetry because of the arbitrary orientation of loading makes the problem more complex. Additional parameters are then involved in the inversion of the problem for the solution. Numerical results are presented primarily for a smooth interference fit pin in a typical orthotropic plate.

Photoelastic determination of stress intensity factors in patched cracked plates

n this paper, the influence of patch parameters on stress intensity factors in edge cracked plates is studied by employing transmission photoelasticity. Edge cracked plates made of photo-elastic material are patched on one side only by E glass-epoxy and carbon-epoxy unidirectional composites. The patch is located on the crack in such a way that the crack tip is not covered. Magnified isochromatic fringes are obtained by using a projection microscope of magnification 50, converted into a polariscope. Irwin's method is used to compute stress intensity factors from photoelastic data. The reduction in stress intensity factors is presented in graphical form as a function of patch parameters, namely stiffness, location and length. An empirical equation connecting reduction in stress intensity factor and these patch parameters is presented.

Trehalose Toxicity in Cuscuta reflexa

a,a-Trehalose induced a rapid blackening of the terminal 2.5-centimeter region of excised Cuscuta relexa Roxb. vine. The incorporation of radioactivity from [I'C]glucose into alkali-insoluble fraction of shoot tip was markedly inhibited by 12 hours of trehalose feeding to an excised vine. This inhibition was confied to the apical segment of the vine in which cell elongation occurred. The rate of blackening of shoot tip explants was hastened by the addition of gibberellic acid A3, which promoted elongation growth of isolated Cuscuta shoot tips. The symptom of trehalose toxicity was duplicated by 2-deoxygucose, which has been shown to be a potent inhibitor of ceD wall synthesis in yeast. The observations suggest that trehalose interferes with the synthesis of ceDl wail polysaccharides, the chief component of which was presumed to be cellulose.

On an analytical-numerical procedure for the analysis of cylindrical shells with arbitrarily oriented cracks

An analytical-numerical procedure for obtaining stress intensity factor solutions for an arbitrarily oriented crack in a long, thin circular cylindrical shell is presented. The method of analysis involves obtaining a series solution to the governing shell equation in terms of Mathieu and modified Mathieu functions by the method of separation of variables and satisfying the crack surface boundary conditions numerically using collocation. The solution is then transformed from elliptic coordinates to polar coordinates with crack tip as the origin through a Taylor series expansion and membrane and bending stress intensity factors are computed. Numerical results are presented and discussed for the pressure loading case.

Development of special fastener elements

A special finite element (FASNEL) is developed for the analysis of a neat or misfit fastener in a two-dimensional metallic/composite (orthotropic) plate subjected to biaxial loading. The misfit fasteners could be of interference or clearance type. These fasteners, which are common in engineering structures, cause stress concentrations and are potential sources of failure. Such cases of stress concentration present considerable numerical problems for analysis with conventional finite elements. In FASNEL the shape functions for displacements are derived from series stress function solutions satisfying the governing difffferential equation of the plate and some of the boundary conditions on the hole boundary. The region of the plate outside FASNEL is filled with CST or quadrilateral elements. When a plate with a fastener is gradually loaded the fastener-plate interface exhibits a state of partial contact/separation above a certain load level. In misfit fastener, the extent of contact/separation changes with applied load, leading to a nonlinear moving boundary problem and this is handled by FASNEL using an inverse formulation. The analysis is developed at present for a filled hole in a finite elastic plate providing two axes of symmetry. Numerical studies are conducted on a smooth rigid fastener in a finite elastic plate subjected to uniaxial loading to demonstrate the capability of FASNEL.

An absolute method for the determination of surface tension of liquids using pendent drop profiles

Drop formation at conical tips which is of relevance to metallurgists is investigated based on the principle of minimization of free energy using the variational approach. The dimensionless governing equations for drop profiles are computer solved using the fourth order Runge-Kutta method. For different cone angles, the theoretical plots of XT and ZT vs their ratio, are statistically analyzed, where XT and ZT are the dimensionless x and z coordinates of the drop profile at a plane at the conical tip, perpendicular to the axis of symmetry. Based on the mathematical description of these curves, an absolute method has been proposed for the determination of surface tension of liquids, which is shown to be preferable in comparison with the earlier pendent-drop profile methods.

Estimation of gear tooth deflection by the finite element method

The finite element method (FEM) is used to determine for pitch-point, mid-point and tip loading, the deflection curve of a Image 1 diamentral pitch (DP) standard spur gear tooth corresponding to number of teeth of 14, 21, 26 and 34. In all these cases the deflection of the gear tooth at the point of loading obtained by FEM is in good agreement with the experimental value. The contraflexure in the deflection curve at the point of loading observed experimentally in the cases of pitch-point and mid-point loading, is predicted correctly by the FEM analysis.

The apical control of lateral bud development in excised shoot tips of Cuscuta reflexa cultured in vitro

Excised shoot tips of Cuscuta reflexa Roxb. (dodder), a rootless and leafless angiospermic plant parasite, were cultured in vitro for the study of the control of lateral bud development by the apex. In a chemically defined medium lacking hormones, the basal bud alone developed into a shoot. The addition of coconut milk to the growth medium induced the activation of multiple lateral buds, but only a single bud developed further into a shoot. The decapitation of this shoot induced the development of another shoot and the process could be repeated. This showed the controlling effect of the apex in correlative control of bud development. Application of indole-3-acetic acid to the shoot tip explant delayed the development of the lateral bud. Gibberellic acid A3 induced a marked elongation growth of the explant and reinforced apical dominance. The direct application of cytokinin to an inhibited bud relieved it from apical dominance. A basipetally decreasing concentration gradient of auxin may prevail at the nodes. Bud outgrowth is probably stimulated by cytokinin produced locally in the bud.

Trehalose Toxicity in Cuscuta reflexa - Sucrose Content Decreases In Shoot Tips Upon Trehalose Feeding

Trehalose, an alpha,alpha-diglucoside, induced a rapid blackening and death of shoot tips of Cuscuta reflexa (dodder) cultured in vitro. The onset of toxic symptom was delayed if any of the several sugars which support the in vitro growth of Cuscuta was supplied with trehalose. The rate of trehalose uptake or its accumulation in the tissue was not affected by sugar cofeeding. The levels of total and reducing sugars declined appreciably in the trehalose-fed shoot tip explants compared to control tissue cultured in absence of a carbon source. This was not due to an increased rate of respiration of the trehalose-treated tissue. In shoot tips cultured in presence of both trehalose and sucrose, the decline in total and reducing sugars was curtailed. There was a marked fall in the level of sucrose; and invertase activity was higher in trehalose-fed shoot tips. The incorporation of label from [14C]glucose into sucrose in the shoot tip explant was reduced as early as 12 h of trehalose feeding. The results suggest that increased utilization of sucrose as well as an inhibition of its synthesis contribute to the drastic fall in the sucrose content upon trehalose feeding.

Load Transfer from a Smooth Elastic Pin to a Large Sheet

The plane problem of load transfer from an elastic interference or clearance fit pin to a large elastic sheet with a perfectly smooth interface is solved. As the load on the pin is monotonically increased, the pin-hole interface is in partial contact above certain critical load in interference fit and throughout the loading range in clearance fit.Such situations result in mixed boundary-value problems with moving boundaries and the arc of contact varies nonlinearly with applied load. These problems are analyzed by an inverse technique in which the arcs of contact/separation are prescribed and the causative loads are evaluated. A direct method of analysis is adopted using biharmonic polar trigonometric stress functions and a simple collocation method for satisfying the boundary conditions. A unified analytical formulation is achieved for interference and clearance fits. The solutions for the linear problem of push fits are inherent in the unified analysis. Numerical results highlighting the effects of pin and sheet elasticity parameters are presented.

Performance of graphic aluminium particulate composite materials

Friction characteristics of journal bearings made from cast graphic aluminum particulate composite alloy were determined under mixed lubrication and compared with those of the base alloy (without graphite) and leaded phosphor bronze. All three materials ran without seizure while the performance of the particulate composite and leaded phosphor bronze improved with running. Temperature rise in the journal bearing under mixed/boundary lubrication was also measured. It was found that with 0.3D/1000 to 1.5D/1000 clearance and a low lubrication rate (typical value for a bearing of diameter 35 mm × length 35 mm is 80 mm3/min) and at a PV value of 73 × 106 Nm m−2 min−1 graphitic aluminium alloy journal bearings operate satisfactorily without seizure and excessive temperature rise. In comparison, the bronze bearings, with all the other parameters remaining the same, could not run without excessive temperature rise at clearances below D/1000 at lubrication rates lower than 200 mm3/min

On factors influencing the ductile-to-brittle transition in a bulk metallic glass

An experimental study to ascertain the ductile-to-brittle transition (DBT) in a bulk metallic glass (BMG) was conducted. Results of the impact toughness tests conducted at various temperatures on as-cast and structurally relaxed Zr-based BMG show a sharp DBT. The DBT temperature was found to be sensitive to the free-volume content in the alloy. Possible factors that result in the DBT were critically examined. It was found that the postulate of a critical free volume required for the amorphous alloy to exhibit good toughness cannot rationalize the experimental trends. Likewise, the Poisson's ratio-toughness correlations, which suggest a critical Poisson's ratio above which all glasses are tough, were found not to hold good. Viscoplasticity theories, developed using the concept of shear transformation zones and which describe the temperature and strain rate dependence of the crack-tip plasticity in BMGs, appear to be capable of capturing the essence of the experiments. Our results highlight the need for a more generalized theory to understand the origins of toughness in BMGs.

Flow over a cylinder with a hinged-splitter plate

Previous work on rigid splitter plates in the wake of a bluff body has shown that the primary vortex shedding can be suppressed for sufficiently long splitter plates. In the present work, we study the problem of a hinged-splitter plate in the wake of a circular cylinder. The splitter plate can rotate about the hinge at the base of the cylinder due to the unsteady fluid forces acting on it, and hence the communication between the two sides of the wake is not totally disrupted as in the rigid splitter plate case. In our study, we investigate this problem in the limit where the stiffness and internal damping associated with the hinge are negligible, and the mass ratio of the splitter plate is small. The experiments show that the splitter plate oscillations increase with Reynolds numbers at low values of Re, and are found to reach a saturation amplitude level at higher Re, Re>4000. This type of saturation amplitude level that appears to continue indefinitely with Re, appears to be related to the fact that there is no structural restoring force, and has been observed previously for transversely oscillating cylinders with no restorin force. In the present case, the saturation tip amplitude level can be tip to 0.45D, where D is the cylinder diameter. For this hinged-rigid splitter plate case, it is found that the splitter plate length to cylinder diameter ratio (L/D) is crucial in determining the character and magnitude of the oscillations. For small splitter plate length (L/D <= 3.0), the oscillations appear to be nearly periodic with tip amplitudes of about 0.45D nearly independent of L/D. The nondiinensional oscillation frequencies (fD/U) on the other hand are found to continuously vary with L/D from fD/U approximate to 0.2 at L/D = 1 to fD/U approximate to 0.1 at L/D = 3. As the splitter plate length is further increased beyond L/D >= 4.0, the character of the splitter plate oscillations suddenly changes. The oscillations become aperiodic with much smaller amplitudes. In this long splitter plate regime, the spectra of the oscillations become broadband, and are reminiscent of the change in character of the wake oscillations seen in the earlier fixed-rigid splitter plate case for L/D >= 5.0. In the present case of the hinged-splitter plate, the sudden transition seen as the splitter plate length (L/D) is increased from 3 to 4 may be attributed to the fact that the wake vortices are no longer able to synchronize with the plate motions for larger splitter plate lengths. Hence, as observed in other vortex-induced vibration problems, the oscillations becomeaperiodic and the amplitude reduces dramatically.

Analytical estimation of stress intensity factors in patched cracked plates

The fatigue and fracture performance of a cracked plate can be substantially improved by providing patches as reinforcements. The effectiveness of the patches is related to the reduction they cause in the stress intensity factor (SIF) of the crack. So, for reliable design, one needs an accurate evaluation of the SIF in terms of the crack, patch and adhesive parameters. In this investigation, a centrally cracked large plate with a pair of symmetric bonded narrow patches, oriented normally to the crack line, is analysed by a continuum approach. The narrow patches are treated as transversely flexible line members. The formulation leads to an integral equation which is solved numerically using point collocation. The convergence is rapid. It is found that substantial reductions in SIF are possible with practicable patch dimensions and locations. The patch is more effective when placed on the crack than ahead of the crack. The present analysis indicates that a little distance inwards of the crack tip, not the crack tip itself, is the ideal location, for the patch.

Observation of kink shear bands in an aluminium single crystal fracture specimen

The near-tip deformation field in a high-constraint three-point bend specimen of pure aluminium single crystal is studied using in situ electron back-scattered diffraction and optical metallography. The orientation considered has the notch lying on the (0 1 0) plane and the notch front along direction. Results clearly show the occurrence of a kink shear sector boundary at 90° to the notch line on the specimen free surface as predicted by the analytical model of Rice [J.R. Rice, Mech. Mater. 6 (1987) 317].