Sudipto Ray and S.K. Roy Chowdhury
The paper's aim is to predict numerically the contact temperatures between two rough sliding bodies and to compare with the experimental results.
Abstract
Purpose
The paper's aim is to predict numerically the contact temperatures between two rough sliding bodies and to compare with the experimental results.
Design/methodology/approach
An elastic contact algorithm is used to analyze the normal contact between two nominally smooth surfaces. The algorithm evaluates real contact area using digitized roughness data and the corresponding contact pressure distribution. Using finite element method a steady state 3D temperature distribution at the interface between the sliding bodies is obtained. Using infrared (IR) imaging technique, experiments were carried out to measure the contact temperature distribution between rough rubbing bodies with a systematic variation of surface roughness and operating variables.
Findings
Contact temperature distributions over a wide range of normal load, sliding velocity and surface roughness have been obtained. It was seen that the maximum contact temperature expectedly increases with surface roughness (Sa values), normal load and sliding velocity. The results also indicate that the “hot spots” are located exactly at the positions where the contact pressures are extremely high. Temperatures can be seen to fall drastically at areas where no asperity contacts were established. The temperature contours at different depths were also plotted and it was observed that the temperatures fall away from the actual contact zone and relatively high temperatures persist at the “hot spot” zones much below the contact surface. Finally it is encouraging to find a good correlation between the numerical and experimental results and this indicates the strength of the present analysis.
Research limitations/implications
Experimental accuracy can be improved by using a thermal imaging camera that measures emissivity in situ and uses it to find the contact temperature. The spatial resolution and the response time of the camera also need to be improved. This can improve the correlation between numerical and experimental results.
Practical implications
One of the major factors attributed to the failure of sliding components is the frictional heating and the resulting flash temperatures at the sliding interface. However, it is not easy to measure such temperatures owing to the inherent difficulties in accessing the contact zone. Besides, thermal imaging techniques can be applied only with such tribo‐pairs where at least one of the contacting materials is transparent to IR radiation. In practice, such cases are a rarity. However, the good correlation observed between the numerical and experimental results in this work would give the practicing engineer a confidence to apply the numerical model directly and calculate contact temperatures for any tribo‐material pairs that are generally seen around.
Originality/value
A good correlation between the numerical and experimental results gives credence to the fact that the numerical model can be used to predict contact temperatures between any sliding tribo‐pairs.
Details
Keywords
Sudipto Ray and S.K. Roy Chowdhury
Although dependence of contact surface temperatures between rough sliding bodies on surface topography is more explicitly described in terms of three‐dimensional (3D) topographic…
Abstract
Purpose
Although dependence of contact surface temperatures between rough sliding bodies on surface topography is more explicitly described in terms of three‐dimensional (3D) topographic parameters, no work has yet been reported on this aspect. The paper seeks to carry out experiments to systematically correlate the 3D surface parameters to the contact temperature rise.
Design/methodology/approach
The surface temperatures at the contact between a relatively smooth zinc sulphide pin held against a rotating mild steel disc of varying surface topography were measured using an infrared thermal imaging system under different load and sliding velocity conditions. The main objective was to study the effect of 3D surface roughness parameters on the contact temperature rise.
Findings
The results indicate a rise in maximum contact temperature with the increase in a number of 3D parameters, such as, average surface roughness Sa, ten‐point height parameter Sz, skewness of the surface height distribution Ssk, mean summit curvature Ssc, and developed interfacial area ratio parameter Sdr while temperature was found to decrease with increasing values of another set of parameters, such as, kurtosis of the 3D surface texture Sku, summit density of the surface Sds, surface bearing index Sbi, core fluid retention index Sci, valley fluid retention index Svi, and root mean square slope of the surface Sdq.
Practical implications
In any sliding system, with mixed or boundary lubricated conditions, it can be attempted to find the optimum value of the roughness parameters so that on suitable processing of the surfaces a lower contact temperature rise can be achieved.
Originality/value
No work has yet been reported on the effect of 3D roughness parameters on contact temperature.
Details
Keywords
Sonal Sisodia and Nimit Chowdhary
Marketing strategy, product positioning, brand building, and economies of scope.
Abstract
Subject area
Marketing strategy, product positioning, brand building, and economies of scope.
Study level/applicability
MBA groups, marketing consultants and business management students of undergraduate and postgraduate level.
Case overview
Abhishek Industries Limited (ABIL) is an entrepreneurial venture of Mr Abhishek Batra that came into being in 1993. ABIL is the leading supplier of Terry Towels to some of world's leading retailers including Wal-Mart, JC Penney and Sears. In spite of some business fluctuations, ABIL has an impressive performance record that is reflected in its financial data. The concern, however, is that of product commoditisation, since established foreign importers and distributors prefer to sell the products under their own brand name. Consequently, even though the export margins may be lucrative; the lack of a brand presence is what bothers the senior management of the company. Given an optimistic domestic business scenario, the senior management is once again evaluating the odds to enter the domestic market using its own brand name. While some of the younger managers are optimistic and want ABIL to emerge as a brand, some senior colleagues are unsure.
Expected learning outcomes
The student's skills will be sharpened in working through a problem; it will help the students take an active role of a thinker, analyser, evaluator, decider and implementer; it will assist the students in learning to reason with the given quantitative as well as qualitative data; it will help the students think critically and reason effectively; it will make the students realize that the emphasis is not on solution. Rather, the process of arriving at a solution is more important.
Supplementary materials
Teaching note.
Details
Keywords
Manisha Chakrabarty and Partha Ray
World over, change of base year in the gross domestic product (GDP) is a standard practice of GDP estimation. However, unless a consistent series of GDP is released with respect…
Abstract
Purpose
World over, change of base year in the gross domestic product (GDP) is a standard practice of GDP estimation. However, unless a consistent series of GDP is released with respect to the new base for the earlier period, the existence of multiple growth rates creates problems for applied researchers, policymakers and the general public alike. Faced with such a menu of GDP series researchers often try to interpolate a consistent series of GDP. The main purpose of this paper is to analyses the nature of the data generating process of such multiple interpolated series of quarterly growth rates and tries to discern the consistency of such processes.
Design/methodology/approach
The present paper tries to look into the statistical implications and complications of such interpolated quarterly GDP/growth series in India in terms of three series of GDP, namely, with 1999–2000, 2004–2005 and 2011–2012 as its bases.
Findings
The analysis reveals that as a result of a change of base year, the nature of the data generating process of the old and new GDP series could undergo changes and experience different breakpoints. While all these conclusions seem to be valid for GDP growth at quarterly intervals, taking the data at annual frequency is less problematic.
Practical implications
The observation suggests that in most applied work, researchers may not have the luxury of only working with annual data and certain consistency checks will be necessary to check the veracity of the results based on quarterly data with those based on annual data. Second, moving forward it may be useful for the Authorities to make a transition to a chain-based linking method rather than fixed time-period-based bases as is currently done.
Originality/value
The analysis of Indian GDP in this paper is, perhaps, indicative of the fact that usage of quarterly GDP data is to be handled with caution and it is preferable that any serious empirical analysis uses annual GDP data whenever it is available/feasible. The comparison of GDP growth rates at different frequencies and examining the true nature of the process are quite unique in their contribution towards empirical macroeconomic research.