João Telésforo Nóbrega de Medeiros

Micro and nanometric wear evaluation of metal discs used on determination of biodiesel fuel lubricity

The contact of diesel fuel with engine subsystems demands a good wear resistance. Lubricity is an important feature for integrity of injection system and the sulphur composites are primarily responsible for lubrication of the injector nozzle. Biodiesel is responsible for partially restoring the lubricity of diesel fuel that presents low levels of sulphur composites and, furthermore, it causes less pollution than diesel fuel. The lubricity is measured through the wear scar diameter following the ASTM D 975 standards. However, the friction and wear with light loads of micro/nanocomponents are highly dependent on surface interactions that can be evaluated by microscopy techniques. This study aimed to measure and to analyze the biodiesel lubricity and their blends (B5, B20) with diesel by observing the wear scars of discs using the scanning electronic microscopy (SEM), atomic force microscopy (AFM) and micro roughness techniques. The fuels performance was evaluated using HFRR tribometer. The tests conditions were based on standard ADTM D-6079-04. The coefficient of friction was measure during the test. After the test, the worn ball and disc were analyzed by SEM, AFM and profilometer. The results showed that the addition of biodiesel in diesel improve the tribological performance of fuel. Also, the just WSD value is not sufficient to evaluate the lubrication ability of a fuel. Analysis of the worn disc surfaces proved to be compatible with WSD number and also more sensitive to these kinds of fuels, showing mainly the form and intensity of the wear.

Composites of polyester + glass fiber residues vs. composites with mineral fillers

Polymer composites, such as those composed of a polyester, glass fibers (GFs), and mineral fillers (e.g. CaCO3), pose a threat to the environment because of the growing amount of residues and due to difficulties in their recycling. Therefore, we have studied effects of incorporation of (polyester + GFs) waste material as a filler into virgin composites. Two types of polyester + glass fiber composites were developed using hot compression molding, one of them with recycled (polyester + glass fiber) material obtained via knife or ball milling; the other, a control group, contained CaCO3, a traditional filler in this field. Dynamic friction and wear rate were determined using a pin-on-disk tribometer and a stylus profilometer, respectively. As expected, the presence of the residues significantly decreases dynamic friction and wear rate when compared to CaCO3, since the main constituent of the residues is a polymeric material. Thus, polyester + glass fiber composite residues are a candidate for a partial substitution of CaCO3. This should lower the environmental contamination caused by discarding the residues as well as provide composites with lower wear rates.

Tribological Study of the Damage Mechanics of Polymer-Metal Contacts Used in Implants

Polyurethane is a biocompatible material and its use is increasing as human or animal implants. However, problems due to wear debris and their interaction with the host require a better understanding of wear mechanisms and the genesis of the debris formation. Some effects of the contact pressure and geometry were experimentally investigated to identify the response, obtained by contact temperature, mass variation, Scanning Electron Microscopy and EDS microanalysis, of polyurethane samples from sliding against metallic surfaces.

A New Method for the Evaluation of Wear Damage in Dry Rolling Contact by Sound Intensity Level and Residual Stress Measurements

The contact fatigue wear of rolling surfaces is associated with the behavior of dislocations located at the specimen surface and subsurface. This behavior depends on the Hertzian Pressure and specimen shear strength, which affect the residual stress fields developed during cyclic loading. This work describes a new nondestructive method to evaluate changes on the residual stress fields and wear damage in dry rolling contact. A disc-disc testing machine was used into a semi-anechoic chamber to evaluate the audible sound signal (noise intensity level) continuously generated by the mechanical contact. Pairs of discs of heat treated DIN 100Cr6 (AISI 52100) steel were tested under Hertzian nominal pressures from P o = 1.5 GPa to P o = 2.5 GPa, at velocities of 40±0.5 m/s. The sound signals were later distributed into box-and-plot graphics which indicated four percentile groups (quartiles) and revealed the main tendency and dispersion of these signals. An XRD analysis, using the sin 2 ψ technique was applied to measure the residual stresses and to associate them with the noise intensity level quartiles at different stages of testing. Microstructural analyses of tested disc surfaces and resulting debris, using a Scanning Electron Microscope (SEM), showed a relation between the different noise levels and surface damage mechanisms, such as microspalling, micropitting, plastic deformation, delamination and brittle fracture.

Audible Noise, Contact Temperature, Life and Microfracture of Dry Rolling Surfaces Using DIN 100Cr6 Steel

Abstract. It was developed an approach to associate the load, life, temperature and audible acoustic emission to rolling contact fatigue wear of heat treated (OQT, Oil Quenching and Tempering, and SBQT, Salt Bath Quenching and Tempering) DIN 100Cr6 steel surfaces submitted to an hydrostatic stress field under dry rolling by friction at a disc-disc testing machine. A dynamic sensor was utilized as the stopping criteria. The material response to rolling contact fatigue was investigated and results of a canonical correlation analysis are presented.