Nondestructive Measurement of Emissivity of Damaged Parts of Coatings

Low Infrared emissivity coating (LIREC) is prone to generating some problems such as bulges, degumming, and abrasion. In order to study whether the performance of LIREC under different damages can meet the work needs, it is essential to timely measure and evaluate the performance state of LIREC in the application process. The existing methods for measuring the damage of LIREC have some disadvantages such as expensive equipment, complex operation, and inaccurate measurement results. In this paper, a measurement method of LIREC damage capability based on thermal imager is proposed. The radiation temperature is measured by thermal imager, the real temperature and ambient temperature of coating surface are measured by thermocouple, and the emittance of coating surface is calculated. Non-contact and continuous large-area emissivity measurements are carried out on the damaged parts of the coating and verified by experiments. The measurement results show that the different damage types and damage degrees directly affect the measurement results of LIREC. Wear damage increases the emissivity of the coating while debonding damage basically does not change the coating emissivity. Shedding damage of small diameter forms voids, which causes the increase of the damage parts of emittance. In addition, bulge damage impedes temperature transfer and reduces emissivity. This method can timely and accurately measure and evaluate the performance state of LIREC and can provide a new idea for the accurate measurement of damage emissivity of LIREC.

Failures of Sliding Bearings

A mechanical part, which supports the moving part, is termed a mechanical bearing and can be classified into rolling (ball or roller) bearings and sliding bearings. This article discusses the failures of sliding bearings. It first describes the geometry of sliding bearings, next provides an overview of bearing materials, and then presents the various lubrication mechanisms: hydrostatic, hydrodynamic, boundary lubrication, elastohydrodynamic, and squeeze-film lubrication. The article describes the effect of debris and contaminant particles in bearings. The steps involved in failure analysis of sliding bearings are also covered. Finally, the article discusses wear-damage mechanisms from the standpoint of bearing design.

Effects of Bearing Steps on Probable Wear Damage of Main Bearings of an IC Engine

When two bearing shells are assembled in the bearing housing, it is possible that the edges of the two shells do not fit in the radial direction completely and have an offset relative to each other. This assembly error, which can have different causes, is called the bearing step in this paper. The bearing step can lead to wear damage in bearings. The effects of bearing step on the lubrication performance of main bearings and the probable wear damage have been investigated. To calculate the bearing lubrication characteristics such as maximum oil film pressure and minimum oil film thickness, elasto-hydrodynamic model, which includes the mass conservation algorithm, has been applied. The objective of this work is to investigate the effects of bearing steps on the lubrication performance of the main bearings and assess the probable wear damage of main bearings due to bearing step. The prediction of elasto-hydrodynamic model is very proximate to what really happened. The results show that for the under-study 12-cyl engine, main bearing No. 2 involved with medium wear damage. Wear damage in this main bearing No. 3 is not a concern, while main bearing No.4, 5 and 6 do not predict the probability of wear damage. For main bearing No.7, it is concluded that considering step and bore relief in simulation has high importance so that the solution without step and bore relief does not predict the wear, but with step and bore relief predicts medium wear damage.

Tribotesting

This chapter discusses the processes and procedures involved in tribotesting, the significance of test parameters and conditions, and practical considerations including test metrics and measurements and the interpretation of wear damage. It also describes the different types of erosion tests in use and common approaches for adhesive wear and abrasion testing.