Surface Related Failure Research Articles

Influence of surface finishing on the outcome of a 3-point bending test in polymer-based dental composits assessed by qualitative and quantitative fractography

ObjectivesThe aim of the study was to evaluate the influence of surface finishing in three polymer-based composits (composits) on the result of a 3-point bending test using quantitative and qualitative fractography as well as microstructural characteristics. Materials and methods270 rectangular specimens (n = 30) of three composits were prepared, stored and tested according to NIST No. 4877. Prior testing, the samples were subjected to three surface treatments: 1) no treatment, to preserve the oxygen inhibition layer, 2) with FEPA P1200 (ANSI equivalent grit 600) SiC paper abraded surface, and 3) polished surface. A three-point bending testing was employed, followed by quantitative (assessment of reason for failure and fracture pattern) and qualitative (fracture mirror measurements) fractography, 3D and 2D surface imaging, surface roughness, reliability and Fe-SEM analysis. The mirror radius that runs in the direction of constant stress was used to calculate the mirror constant (A) using Orr's equation. Uni- and multifactorial ANOVA, Tukey's post hoc test, and Weibull analysis was performed for statistical analysis. ResultsSurface finishing has less influence on the fracture pattern, reliability and mechanical parameters and has no influence on the mirror constant. The amount of inorganic filler has a direct impact on flexural strength and modulus, while the ranking of materials was independent of surface treatment. Failures initiated by volume defects were the most common failure mode (77.0%) with surface defects accounting for 14.9% (edge) and 7.7% (corner). Polishing resulted in lower peak-to valley height compared to no treatment, both 3–4 times lower compared to the 600 grit treatment. The increase in roughness within the analyzed range did not lead to an increase in surface-related failures. ConclusionsThe clear dominance of volume defects in all examined materials as a cause of material fracture reduces the impact of roughness on the measured properties. This insight was only possible using qualitative and quantitative research fractography.

Analytical and Experimental Investigation to Resolve Surface Related Fatigue Failure in Helical Gears

With the improvement of metallurgical process and tools it became possible to modify the material property of the steel to a desired possible level where its torque transmission capability can be enhanced. Case hardening and surface grinding is one such method which is used to leverage the surface durability and core strength of gears. With the enhancement in the torque transmission capability the load per unit area of face width also increased causing huge surface pressure. They are subjected to various conditions of load, speed, temperature, and ambient conditions. Micropitting is one such surface related failure which starts on tooth flank in terms of surface texture change. This may further grow in magnitude and result in catastrophic failure. This research work is performed to compare the results of analytical and experimental investigation for the possible micropitting initiative zone. Analytical approach is carried out by using the KISSsys model and the experimental work is carried out by using a dynamometer test rig to apply the load on the gearbox shaft for a defined load cycle. It was clearly visible that the micropitting has initiated below the pitch line of pinion. Tooth profile is later modified with lead and crown modification. After the application of this modification the tooth profile related failure was not visible for similar load testing cycle.

Thermal stabilization of additively manufactured superalloys through defect engineering and precipitate interactions

Laser peening (LP) is a mechanical surface modification technique capable of enhancing a treated material's resistance to surface-related failures through the introduction of deep, high-magnitude compressive residual stresses. Conventional LP enables material improvement in systems operating in ambient or low temperature (<0.5Tm where Tm is the melting temperature) conditions. At high temperature (>0.5Tm), LP-induced property enhancements and microstructural modifications encounter thermal degradation through dislocation annihilation, stress relaxation, and grain coarsening. Motivated by the need to retain critical material enhancements, a novel, modified LP technique was introduced and employed in this work, coined laser peening plus thermal microstructure engineering (LP + TME). This approach incorporates cyclic LP events with the inclusion of intermittent, 600 °C (0.55Tm) heat treatment steps in order to impart highly thermally stable microstructural modifications in additively manufactured (AM) Inconel 718. Microstructural and mechanical property evolution was evaluated through instrumented indentation and transmission electron microscopy (TEM). Surface-level compressive residual stresses were discovered to increase by as much as 84% from 167.13 MPa to over 300 MPa following LP + TME and a 350-h, 600 °C exposure. Surface and near-surface microhardness of samples subjected to LP + TME was observed to increase by 33% (to 630 HV) compared to untreated, as-built specimens even after exposure to 600 °C. Hardened zones were characterized by the presence of highly dense dislocation networks and precipitated strengthening phases. Both property enhancement and thermal stability were determined to be the result of various mechanisms at work, stemming from the synergistic combination of cyclic strain and thermal input. These include the facilitated nucleation of γ’’ and δ phases which aid in stabilizing LP-induced microstructures and provide material enhancements at high temperatures; precipitate-dislocation interactions including Orowan bypassing, Friedel cutting; and dislocation pinning effects. The results from this work are of significant interest as they are in contrast with what is typically expected at temperatures exceeding 0.5Tm meaning the technique outlined herein could offer a viable solution to overcoming obstacles preventing the widespread use of LP in critical, high temperature applications.

Post-processing of Laser Additive Manufactured Inconel 718 Using Laser Shock Peening

The components built using new generation feature based design and manufacturing process, called laser additive manufacturing (LAM) is inherited with tensile residual stress due to rapid heating and cooling during material processing. Laser shock peening (LSP) is an advanced surface engineering process that imparts beneficial compressive residual stresses into materials yielding longer product life by increasing the resistance to many surface-related failures, such as wear. LSP is widely used by various industries including aerospace, power generation, chemical processing, etc. to increase the life of engineering components. This paper reports LSP of LAM built Inconel 718 and the parametric study is conducted by varying peak laser power and number of shots at three different levels. Optimum laser power and number of shots derived using grey relational analysis is found to be 170 mW and 7, respectively for maximum hardness and minimum depth of profile. The investigation show that LSP changed the surface morphology and mechanical properties of the LAM built structure. The surface investigation using optical profilometer and Vickers micro-hardness shows a maximum profile depth of 10 μm and hardness of 360 HV. Residual stress measurement indicates compressive residual stress of 214.9–307.9 MPa on the LAM sample surface after LSP. The wear studies show an improvement by a factor of 1.70 for LSP treated LAM samples as compared to that of as-built condition. This study unwrap avenues for using LSP as property enhancement post-processing technique LAM fabricated structures with geometrical complexities.

Studying the effect of Different wt % AL2O3 Nanoparticles of 2024Al Alloy / AL2O3 Composites on Mechanical Properties

&#x0D; The nanocompsite of alumina (Al2O3) produced a number of beneficial effects in alloys. There is increasing in resistance of materials to surface related failures , such as the mechanical properties , fatigue and stress corrosion cracking .The experimental results observed that the adding of reinforced nanomaterials type Al2O3 enhanced the HB hardness, UTS, 0.2 YS and ductility of 2014 Al/Al2O3 nano composites . the analysis of experiments, indicated that The maximum enhancement was observed at 0.4 wt.% Al2O3. The ultimate improvement percentage were 15.78% HB hardness, 18.1% (UTS), 12.86% (0.2 YS) and 25.71% ductility. These enhancements in the above properties maybe to high dislocation density resulting in good bounding between Al2O3 and metal matrix.&#x0D;

Effect of Confinement Layer on Laser Ablation and Cavitation Bubble during Laser Shock Peening

Laser shock peening (LSP) is one of surface treatments to induce residual compressive stresses near metal surface to improve the resistance of materials to surface-related failures, such as fatigue and stress corrosion cracking. In LSP process, short pulsed laser is focused and irradiated to the material covered by transparent overlay such as glass or water. This transparent overlay is also known as a confinement layer and has an important role to increase impact pressure during LSP process. When confinement layer is liquid, the characteristics of the layer such as temperature, viscosity, etc. affect the phenomena occurring during the peening process and undoubtedly influence the induced residual stress. In the present study, Acoustic Emission (AE) technique coupling with high speed camera was applied to study the effect of confinement layer on LSP process. The results were discussed using the impact force calculated by inverse analysis of detected AE waveforms and bubble parameters observed by high speed camera. The results showed that temperature, thickness and viscosity of confinement layer had strong influence on the generation and collapse of cavitation bubble. The optimization of process parameters could be obtained by AE technique.

Comparative study of RF MEMS micro-contact materials

A systematic comparison between several pairs of contact materials based on an innovative methodology early developed at NOVA MEMS is hereby presented. The technique exploits a commercial nanoindenter coupled with electrical measurements, and test vehicles specially designed to investigate the underlying physics driving the surface-related failure modes. The study provides a comprehensive understanding of micro-contact behavior with respect to the impact of low-to-medium levels of electrical current. The decrease of the contact resistance, when the contact force increases, is measured for contact pairs of soft material (Au/Au contact), harder materials (Ru/Ru and Rh/Rh contacts), and mixed configuration (Au/Ru and Au/Ni contacts). The contact temperatures have been calculated and compared with the theoretical values of softening temperature for each couple of contact materials. No softening behavior has been observed for mixed contact at the theoretical softening temperature of both materials. The enhanced resilience of the bimetallic contacts Au/Ru and Au/Ni is demonstrated.

Variation of structure with input energy during laser surface engineering of ceramic coatings on aluminum alloys

Surface modification of metal alloys using laser has become a unique tool to reduce surface related failure mechanisms such as wear, corrosion, erosion or high temperature oxidation. Laser surface engineered (LSE) ceramic coatings have been proved to enhance surface properties of Al alloys such as hardness and wear resistance. This technique has been shown to be capable of producing a wide variety of interesting metallurgical microstructure in the coating as well as in the adjoining substrate. These microstructures provide novel properties, which cannot be produced by any conventional processing technique. In addition, these coatings are metallurgically bonded, thus providing a sound and adherent interface between the coating and the substrate. In this present investigation, laser surface engineering technique has been employed to deposit ceramic (TiC) coating on aluminum alloy substrate. TiC coating was deposited on two types of aluminum substrates, alloy 2024 and 6061 using an Nd-YAG laser beam. The effect of laser processing parameters, such as power intensity and speed on the thickness, microstructure and morphology of both the coating and the heat-affected zone have been evaluated using a scanning electron microscope (SEM). Results of experiments in this study show that by controlling the process parameters it is possible to produce varied microstructures according to the surface requirement of the application.

Surface-related failure mechanisms in integrated circuit arrays : D. J. Fitzgerald and A. S. Grove, Proc. 1970 Ann. Symp. Reliab., Los Angeles, IEEE Cat. No. 70 C 2-R, 3–5 February (1970), p. 249

Surface-related failure mechanisms in integrated circuit arrays : D. J. Fitzgerald and A. S. Grove, Proc. 1970 Ann. Symp. Reliab., Los Angeles, IEEE Cat. No. 70 C 2-R, 3–5 February (1970), p. 249