A gear is a rotating machine part having cut teeth, which mesh with another toothed part in order to transmit torque. Gears may be spur, helical, bevel or worm in which Helical Gear is most common type of gear used in engineering applications. The increased in performance requirement such as high load carrying capacity, high speed, high reliability and long life leads to new design of gear. So as to fulfill above demand here we used a concept of asymmetric gear profile in which two different pressure angles are assign to two faces of gear tooth. In literature it shows that increased in drive side pressure angle shows improve in strength of spur gear. In this paper we find the effect of coefficient of asymmetry on strength and contact ratio of different helical gear pairs having gear ratio equal to one and transmit same power. All the gear pair are design in Cre-O parametric 2.0 and the analysis is carried out in ANSYS workbench 16.0. Results from numerical analysis shows that as coefficient of asymmetry and helix angle increases Von-Mises stress and total deformation decreases. To validate the results from numerical analysis experiment stress measurement is done using digital strain indicator in which a strain gauge (UFLA-1-350-23) is mounted at the root of the gear and strain is calculate for different loads. In further study we find the effect of coefficient of asymmetry on contact ratio of helical gear pairs, here it shows that decreased in coefficient of asymmetry leads to increased contact ratio.
Raghuwanshi and Parey  used the photo elasticity technique to measure spur gear mesh stiffness. The variations in the stress intensity factor (SIF) and mesh stiffness have been quantiﬁed with angular displacements of the gears. M. Divandari et al.  developed a six degree-of-freedom nonlinear dynamic model including different gear errors and defects for investigation of effects of tooth localized defect and profile modifications on overall gear dynamics. Lin and Parker  analytically investigated the parametric instabilities from mesh stiffness variation in multi mesh, two stage gear trains. They also, examined the effects of mesh stiffness parameters on instabilities systematically. In this paper, spur gear mesh stiffness is calculated using mathematical and numerical method with matlab and MS Excel spread sheet. For calculating the mesh stiffness, bending stiffness, axial compression stiffness, Hertzian contact stiffness, shear stiffness and effect of fillet- foundation deflection on mesh stiffness are considered. Also, the load sharing ratio is considered for two teeth pairs in contact and three teeth pairs in contact and the calculation of mesh stiffness for high contact ratio spur gear pair is explained. The same numerical simulation can be performed for low contact ratio which is much simpler than that simulation for high contact ratio spur gear pair. The mathematical equations from literatures  –  are modelled in matlab and the single pair tooth mesh stiffness of pinion and gear is calculated along pinion roll angle.
16 Read more
Abstract The gear smoothness in the transmission of power mainly depends on the contact ratio. When the contact ratio is higher, the load shared by the pair of teeth in mesh will be lower. In the helical gear, the additional contact ratio is created due to face advance which is called face contact ratio and it provides the higher contact ratio than that of spur gear. The face contact ratio can improve by changing the few parameters such as helical lead and face width. In the present work, the face contact ratio is improved by altering those parameters and their effects on the load sharing based fillet stress are also determined for one mesh cycle in the asymmetric helical gear designed through direct design procedure using finite element method.
In Fig.2 and Fig 3, the points are located along the line of action within the interval of the length of action. Considering contact ratio 1.4 and above, the initial contact point for pinion tooth with the gear tooth is point ‘g’, and simultaneously for the second tooth of the same pinion, which is already in mesh will be at point ’c’. Therefore, the load will be shared between these two points similarly points ‘f’ and ‘b’, also ‘e’ and ‘a’ will have simultaneous action. Then point ‘a’ will goes out of contact, therefore the full load will be applied starting from point ’e’,
Deng et al.(2003) estimated the LSR based on bending stiffness for different standard pressure angle. Muni et al.(2007) optimized the fillet strength for direct design asymmetric Normal Contact Ratio (NCR) spur gear. Li (2008) investigated that the effect of addendum on contact and bending strength by using three dimensional (3D) finite element method and stated that increase in addendum influences to reduce load sharing at tip. Senthil Kumar et al.(2008) developed a non-standard asymmetric rack cutter to generate asymmetric gear and optimized the fillet strength with optimum profile shift. Thirumurugan and Muthuveerappan (2010,2011) developed a finite element model to accurately estimate the fillet stress based on load sharing for symmetric NCR spur gears. Furthermore, suggested that MPCM yields reasonably accurate than single point load model and found critical loading points for symmetric NCR and High Contact Ratio (HCR) gears based on load sharing.
In 2005, Wang and Howard  presented the methods and results of the use of FEA high contact ratio gears in mesh. The numerical models were developed with gears in mesh under quasi-static conditions. The details of transmission error, combined torsional mesh stiffness, load-sharing ratio, contact stress and tooth root stress against various input loads over a complete mesh cycle are also taking into account. Thus, various tooth profile modifications are presented and comparisons between the results show evidence for the optimal profile modification expected to gain the maximum benefit of high contact ratio gears. Also, the optimal relief length is normally dependent on the gears’ geometrical properties. The results of optimal relief length vs. the tooth addendum variations have shown that the relief length can be very small, and it suggests that the contact ratio or the module be increased in order to retain the natural benefits of high contact ratio gears.
13 Read more
ABSTRACT: In this paper, comparison of high contact ratio gears and low contact ratio gears has been done for the same load. we have considered the bending strength, shearing at contact region, normal stress and some contact parameters like contact pressure, penetration and contact stiffness to compare HCR gears and LCR gears. in the results we have found that HCR gears r deforming less when compared to the later type for the same load transmitted. bending strength in HCR gear set less when compared to the later one because of the load distribution among the teeth.
12 Read more
In Japanese seismic designs of nuclear power plants, the uplift of the basemat of structures is a very important factor. In current design methods, the seismic behavior of structures is analyzed using lumped mass SR models, and the ground contact ratio is also calculated using these models. However, the shapes of some actual buildings are so complicated that it is more effective to use detailed 3-dimensiional models in order to evaluate the accurate seismic behavior of the structures. In this paper, uplift behavior of a PWR reactor building is analyzed using a 3-dimensional model. The result of the analysis is compared with that obtained using a SR model. It is shown that the uplift behavior estimated using the SR model is greater than that using the 3-dimensional FEM model and that the difference becomes greater with the increase in the input ground motion level.
Figure 6 shows that the contact stress of gear varied very slowly with different modules and large module could improve the bending fatigue stress. Figure 7 presents that the contact ratio decrease with increasing module, and small module would result in high contact ratio, which was good to the stability of transmission of motion. In addition, the teeth number of high speed and heavy load gear need to be larger than 28, so the module should smaller than 3.4 mm.
The contact area between the cable and electrode is of primary interest. To calculate the deformation of the cable subject to the specific clamp force in our system, a simulation model was developed using COMSOL Multiphysics. This enables the evaluation of the contact area of cable. In addition, the maximum mechanical stress within the cable insulation was also calculated. This stress could lead to induction of a non- homogeneous radial mechanical stress in the cable insulation across which the space charge measurement is conducted. In addition, there is a fundamental limit for the clamping force to prevent the onset of mechanical damage to the insulation of the cable (e.g. when plastic deformation starts).
Abstract: An effort was made to find a relationship between the ratio of average asperities height and lubricant thickness at the point of contact of rolling element ball bearings, and empirical equations to predict the life for bearings under constant motion. Two independent failure mechanisms were considered, fatigue failure and lubricant failure resulting in seizing of the roller bearing. A theoretical formula for both of these methods was established for the combined probability of failure using both of these failure mechanisms. Fatigue failure was modeled with the empirical equations of Lundberg and Palmgren and standardized in DIN/ISO281. The seizure failure, which this effort sought to investigate, was predicted using Greenwood and Williamson’s theories on surface roughness and asperities during lubricated contact. These two mechanisms were combined, and compared to predicted cycle lives of commercial roller bearing, and a clear correlation was demonstrated. This effort demonstrated that the Greenwood-Williams theories on the relative height of asperities versus lubricant film thickness can be used to predict the probability of a lubricant failure resulting in a roller bearing seizing during use.
12 Read more
The effect of fibers and their hybrid effect on the tensile strength and percentage elongation are shown in the fig.4b. The improvement in the tensile strength was seemed to be a function of the fiber reinforcement. The tensile strength of PA66/PTFE blend is 66.5 N/mm2 (Table 3). But the effect of 10wt. % SGF improved the strength of the blend to 76.81N/mm2which is 15.5% increase [5, 6]. This promotion of strength is greatly attributed to the silane coated SGF. The silane will act as coupling agent in developing the interfacial bond between the matrix blend and the SGF. The slenderness ratio (l/d) of the SGF also promotes the strength by increasing the surface area of contact with the matrix. The interfacial bond between the surface of SGF and the matrix blend has greatly compatibilized for the effective development of strength of the filled composite. The good elastic modulus of SGF supported the blend matrix in resisting the external load. Further, addition of SCF into the blend improved the strength by almost 25% than that of neat blend [7, 8]. But 8% improvement over the SGF. Short carbon fibers are good in specific modulus and specific strength. This made the composites to possess high strength than that of SGF. The interfacial bond developed between the blend and SCF is superior. SCF are rigid and very tough. The results revealed that the incorporation of SCF improves both rigidity and the toughness of the polymer blend. The degree of compatibility between SCF and blend were good for the effective development of the materials. The hybrid effect of fibers on the tensile strength of composite is most appreciable. It is 97.22 N/mm2 which is almost 46% increase over the neat blend. This shows that the effective interfacial bond and the network between thermoplastic and the fibers were established during the process of polymer blending. The load carrying capacity of the fibers through matrix is very good. Further, the synergistic effect of fillers and the fibers has contributed a lot to the development of strength of the composites. Furthermore, SCF as a nucleating agent can increase the crystallization rate and decreases the crystal size of the blend . Therefore, due to this effect, a substantial improvement in tensile strength due to hybrid effect of fibers was exhibited by PA66/PTFE blend. Among the studied composites, hybrid effect of fibers is most appreciable.
14 Read more
The results of these tests are presented in Fig. 6. Although the friction coefficient was slightly lower in the first test, from the second run onward, the results show a nearly constant friction coefficient. Based on these results, because the effect of wear on the friction coefficient was relatively small, the difference in values between the first and second runs can be attributed to the effects of initial conditioning (contact alignment) on the first run. After performing the running-in operation to exclude the effects of initial conditioning, factors related to the sliding velocity and reciprocation count were investigated.
10 Read more
Abstract: The objective of this work was finding out the most advisable testing conditions for an effective and robust charac- terization of the tensile strength (TS) of concrete disks. The independent variables were the loading geometry, the angle subtended by the contact area, disk diameter and thickness, maximum aggregate size, and the sample compression strength (CS). The effect of the independent variables was studied in a three groups of experiments using a factorial design with two levels and four factors. The likeliest location where failure beginning was calculated using the equations that account for the stress–strain field developed within the disk. The theoretical outcome shows that for failure beginning at the geometric center of the sample, it is necessary for the contact angle in the loading setup to be larger than or equal to a threshold value. Nevertheless, the measured indirect tensile strength must be adjusted to get a close estimate of the uniaxial TS of the material. The correction depends on the loading geometry, and we got their mathematical expression and cross-validated them with the reported in the literature. The experimental results show that a loading geometry with a curved contact area, uniform load distribution over the contact area, loads projected parallel to one another within the disk, and a contact angle bigger of 12 ° is the most advisable and robust setup for implementation of BT on concrete disks. This work provides a description of the BT carries on concrete disks and put forward a characterization technique to study costly samples of cement based material that have been enabled to display new and improved properties with nanomaterials.
21 Read more
The next two size bands (photographs (b) and (c) in Figure 9) show an interesting phenomenon. The wear track shows two distinct regions, a central region where mostly dents are present, and outer regions where the surface is grooved. The particles appear to be tumbling through the central region and plough at the sides. The reason for this becomes clear when one considers the nature of the lubricant film. The film consists of a central plateau and a surrounding ÔhorseshoeÕ of lower thickness. Thus the particles at the outer edges of the track are rolled over in a region of thin film; more of their bulk is embedded in the contacting surfaces and the particles tolerate relative sliding motion by ploughing through the ball surface. In the central region less of the material is embedded and the particles tend to tumble through the contact. Figure 10 schematically
24 Read more
Besides the alloys mentioned in the above paragraphs, Au-Ni has materials characteristics showing it to be a potentially promising alternative to gold. It has been reported that Au-Ni alloy contacts yield much lower adhesion than pure gold contacts . Low force (as low as 0.6 mN) stable contact and reliable re-opening were also achieved in the previous research report. However, in the previous study, only samples with one composition (5 % Ni) were investigated, using bulky samples (rivets) as test components instead of a MEMS test structure. Therefore we have undertaken a study of a wider range of alloy compositions, tested under a configuration typical of MEMS switches. The Au-Ni phase diagram is shown in Fig. 1 . Note that both metals are FCC structures, and exist as a two phase mixture at relatively low temperature under equilibrium conditions. However, a metastable single phase alloy may also be produced under the low processing temperatures utilized for the film deposition. Thus, a comparison of the metastable solid-solutions and the two-phase mixtures of the same overall composition can be undertaken, so that both microstructure effects and composition effects can be examined.
196 Read more
symplectic diffeomorphisms; (vi) Diffn, the group of conformal volume preserving diffeomorphisms. Strictly speaking, this is the classification in the complex case ; in the real case these is a further minor refinement (see  ) . While classes (i)-(iii) are widely studied in the context of dynamical systems and class (v) has recently been utilized by McLachlan and Perlmutter  , the contact group (iv) has not been extensively studied in this setting. This thesis is about contact structures, which are one of the Lie pseudogroup structures.
178 Read more
tube, doubly-connected source area , thermal constriction resistance between smooth-sphere and rough flats in contact , a general solution for the thermal constriction resistance due to flux applied over circular portion of a compound disk , a transient thermal response of two semi-infinite bodies through a small circular contact area, spreading resistance of an isoflux rectangular flux channel  and a strip contact spot on a layer of material source for the heat-flux specified boundary conditions on the contact zone. Recently a number of new solutions and application of thermal spreading resistance theory have been addressed in [14-15]. A review of thermal spreading resistance in compound and orthotropic systems is presented in . Some correlation equations and important aspects of thermal spreading resistance theory are summarized in . The other contributed work is a comparison of planar, axis-symmetric and 3-D spreading resistance , calculation of spreading resistance in heat sinks , thermal spreading resistance of rectangular sources and plates with non-unity aspect ratio , the spreading resistance between two parallel contacts  and a numerical modeling to understand the effects of thermal spreading resistance on the total resistance from junction to ambient for square and rectangular entities .
Orthotropic annular fins with least axial Biot number and large contact Biot number are reported to be most effective for heat transfer. This is because of larger area available with longer fin for heat transfer. Although, in such cases, fin efficiency is lower with larger aspect ratio, it can be opted under conditions demanding larger amount of heat transfer.
In recent years, synthesis of nanoparticles (Nps) has special attention because of increased surface area to volume ratio, increased activity, and modified structure compared to macromolecules . Nps are added to polymers to obtain unique physical and chemical properties, which cannot be achieved, by adding particles with micronized, silver nanoparticles (AgNps) are reported to exhibit the strong biocidal effect on more species of bacteria including Pseudomonas aeruginosa bacteria . Hence increasing their contact with bacteria, vastly improve their bactericidal effectiveness. They bind to microbial DNA, preventing bacterial replication, and to sulfhydryl groups in the metabolic enzymes of the bacterial electron transport chain, causing their inactivation [3, 4]. PCs are an important thermoplastic polymer because of low-cost, inexpensive, non-toxic, and temperature resistant and exhibits low water absorption properties . Therefore, PCs are very attractive material using in a wide range of applications includes medical devices, bulletproof windows, food packaging, mineral water bottles, packaging and self-cleaning .