Mechanism Of Surface Deformation Research Articles

Lithospheric rheology in southern Italy inferred from postseismic viscoelastic relaxation following the 1980 Irpinia earthquake

Postseismic relaxation is modeled for the Irpinia earthquake, which struck southern Italy in 1980. Our goal is to understand the mechanism of surface deformation due to stress relaxation in the deep portion of the crust‐lithosphere system for a shallow normal fault source and to infer the rheological properties of the lithosphere in the extensional environment of peninsular Italy. The modeling is carried out within the framework of our normal mode viscoelastic theory at high spatial resolution in order to accurately resolve the vertical surface displacements for a seismic source. The slip distribution over the faults is first inverted from coseismic leveling data, the misfit between observed and modeled vertical displacements being minimized by means of the L2 norm. Slip distribution is then used within the viscoelastic model to invert for the viscosities of the lower crust and generally of the lithosphere. Inversion is based on leveling data sampled along three lines crossing the epicentral area. Postseismic deformation in the Irpinia area is characterized by a broad region of crust upwarping in the footwall of the major fault and downwarping in the hanging wall that is responsible for the long‐wavelength features of the vertical displacement pattern. The χ2 analysis indicates that the Irpinia earthquake cannot constrain the rheology of the upper mantle but only of the crust; a full search in the viscosity spaces makes it possible to constrain the crustal viscosity to values of the order of 1019 Pa s, in agreement with previous studies carried out in different tectonic environments.

One-Step Multilevel Microfabrication by Reaction−Diffusion

A new experimental technique is described that uses reaction--diffusion phenomena as a means of one-step microfabrication of complex, multilevel surface reliefs. Thin films of dry gelatin doped with potassium hexacyanoferrate are chemically micropatterned with a solution of silver nitrate delivered from an agarose stamp. Precipitation reaction between the two salts causes the surface to deform. The mechanism of surface deformation is shown to involve a sequence of reactions, diffusion, and gel swelling/contraction. This mechanism is established experimentally and provides a basis of a theoretical lattice-gas model that allows prediction surface topographies emerging from arbitrary geometries of the stamped features. The usefulness of the technique is demonstrated by using it to rapidly prepare two types of mold for passive microfluidic mixers.

Effects of surface deformation on corrosive wear of stainless steel in sulfuric acid solution

Corrosive wear behaviors of austenitic, ferritic and duplex stainless steel in sulfuric acid solution were investigated. Transmission electron microscopy with energy dispersive X-ray, scanning electron microscopy, microhardness tester, etc. were used to study the mechanism of surface deformation of stainless steel after corrosive wear tests. The result indicated that the corrosive wear rate of austenitic stainless steel (ASS) was the highest and that of duplex stainless steel (DSS) was the lowest if the applied loads were higher than 25 N. Because martensitic transformation induced brittleness and increased corrosion rate of ASS surface, the corrosive wear rate of ASS increased largely though the surface microhardness of ASS was largely increased during corrosive wear under high loads. The corrosive wear rate of ferritic stainless steel (FSS) also increased largely under high loads though FSS had the best corrosive wear resistance under low loads. The corrosive wear rate of DSS had a linear relationship with loads. The abilities of surface deformation strengthening of two phases were very different. The investigation indicated that surface deformation strengthening of DSS with proper ratio of γ phase was one of the important methods to improve corrosive wear resistance of stainless steel.

Influence of thin coatings deposited by a dynamic ion mixing technique on the fatigue life of TITANIUM ALLOYS

The technique of dynamic ion mixing involving a physical vapour deposition method and a simultaneous ion implantation has been used in order to improve the fatigue resistance of two titanium alloys. This process allows the deposition of adherent NiTi and SiC amorphous coatings of the order of 1 μm thick. Both treated substrates have been tested at room temperature in the low cycle fatigue range, revealing significant fatigue life improvement. NiTi and SiC films modify the surface deformation mechanisms of fatigued materials and largely suppress or delay crack initiation. These effects depend, however, on the nature of the film, the microstructure of the substrate and the stress amplitude applied during the fatigue tests. To explain the fatigue results, the mechanical properties of these thin films have been characterized by different techniques: scratch-tests, micro-Vickers indentations, Young's modulus measurements by a resonant frequency method and “fracture stress” determination by in situ tensile tests. The results have shown that their mechanical properties are very different to those of the corresponding classically deposited solid materials and are influenced by the film thickness. The results are discussed according to the mechanical properties of the coatings and the substrate deformation and damage modes associated with their microstructure.

Understanding and quantification of elastic and plastic deformation during a scratch test

An understanding of abrasion resistance and the associated surface deformation mechanisms is of primary importance in the materials engineering and design of many important industrial components undergoing wear and abrasion. Instrumented scratch testing has been shown to be a useful tool for characterization of the abrasion resistance of materials. Although most studies on scratch resistance have been limited to the theoretical case of purely plastic materials, experiments on metals and polymers have shown that the contact mechanics and indentation behavior are strongly influenced by the elastic behavior. In this work, the normal and tangential scratch forces, the penetration depth relative to the initial surface and the three-dimensional topographic relief of the scratched surface are measured. These parameters have allowed us to accurately calculate the actual contact area between the indenter and the material, taking into account both elastic deformation and pile-up phenomena. This contact surface was used to estimate the real mean contact pressure during scratch testing. This pressure was compared to the static hardness of the studied materials, as well as to the classical definitions of the scratch hardness. The ratio between the plastic and elastic deformation during a scratch test with a Berkovich indenter was then related to the ratio of the Elastic modulus to the hardness for the tested bulk materials. This scratch experiments were performed on a wide range of materials from polymers to metals and demonstrate the importance of taking both elastic deformation and pile-up into account in order to accurately understand and characterize the scratch resistance of materials.

Surface deformation and electrical properties of HfN thin films deposited by reactive sputtering

The electrical and mechanical properties of HfN films deposited on silicon by a reactive r.f. sputtering method are examined and discussed in terms of the films' structure and deposition conditions. The structural information has been obtained by employing a thin film X-ray diffraction method, Auger electron spectroscopy and electron microscopy. The recently developed energy principle of indentation has been applied in discussing the results of thin films' indentation by means of a depth-sensing technique. The theory allows the assessment of the details of surface deformation of nitrides, including the delamination process. The electrical properties of the studied films (i.e. resistivity and Hall coefficient) and their structure are found to be related to the deposition conditions. Moreover, the variation of the resistivity (electrical properties) appears to be accompanied by differences in the residual stress level as measured by the deflection method, and by differences in the mechanism of surface deformation (mechanical properties) of the HfN films.

The unlubricated reciprocating sliding wear of a martensitic stainless steel in air and CO 2 between 20 and 300 °C

A limited programme of work has been undertaken to investigate the self-wear behaviour of a high strength martensitic stainless steel. This material is used as boiler tube supports in advanced gas-cooled reactors. Some tests were carried out in air at room temperature to permit comparison with data sets for other materials but most of the tests were in CO 2 in the temperature range 20–300 °C. Wear rates were measured by specimen weight loss and by continuous collection and intermittent weighing of wear debris. At room temperature, both in air and CO 2, specific wear rates were initially high, i.e. of the order of 10 −12 m 3 N −1 m −1. The severe wear rate however decreased with increasing temperature in CO 2 reaching a value of about 1 × 10 −13 m 3 N −1 m −1 at 300°C. Wear transitions were observed at all temperatures except 200 °C and resulted in a decrease in wear rate by between a factor of two and two orders of magnitude. The extent of the decrease in rate, however, showed no consistent trend with either temperature or load. Associated with the wear transition was a change in friction behaviour from widely fluctuating during the severe wear stage to smoother sliding in the post-transition stage. The duration of the severe wear stage at 20°C in CO 2 appeared to be proportional to load. A correlation was found between the initial wear kinetics and the mode of wear surface deformation. The highest wear rates occurred when the surface contact interactions resulted in gall formation; galling being defined as the displacement of material from one part of a surface to another region by a ploughing mechanism. The severe wear rate progressively decreased as the surface deformation mechanism changed to one of transfer from one surface to the other with the subsequent formation of features called prows. There was clear metallographic evidence that wear debris was generated by breakdown of these surface features.

Deformations of stacks of thin layers under normal compressive loads

Stacks, each consisting of 40 thin metallic layers, were compressed under loads of up to 5000 kg. Measurements of the electrical resistance of the stacks (i.e. for the 39 metal-to-metal contacts in series) revealed four distinct regions of deformation. The extent of these regions was marked by sharp changes in the slope of the curves obtained when load was plotted against electrical conductance. The first change occured at a load of approximately 200 kg, irrespective of layer size, roughness, or hardness. Two further transitions occurred at pressures equal to 2·5 and 22·5 per cent approximately of the surface hardness. Above the upper transition point the bulk properties play a large part in the mechanism of surface deformation.