Microhardness of Thin SIO2 Films On Silicon.

1991 ◽  
Vol 226 ◽  
Author(s):  
B. Yost ◽  
Che-Yu Li ◽  
Bette Bergman-Reuter ◽  
Tim Sullivan
Keyword(s):  
Residual Stress ◽  
Silicon Substrates ◽  
Sio2 Films ◽  
Stress Levels ◽  
Thermal Histories

AbstractHardness properties of CVD SiO2, films deposited on silicon substrates are investigated by microindentation techniques. It is found that the hardness of these films is sensitive to the thermal histories and doping and is less influenced by the residual stress levels.

An Analytical Model for the Generation of Residual Stresses in Sprayed Coatings Deposited Progressively onto Planar Substrates

1997 ◽  
Author(s):  
Y.C. Tsui ◽  
T.W. Clyne
Keyword(s):  
Residual Stress ◽  
Analytical Model ◽  
Finite Thickness ◽  
Misfit Strain ◽  
Substrate Thickness ◽  
Layer By Layer ◽  
Spreadsheet Program ◽  
Spray Coatings ◽  
Stress Levels ◽  
Planar Substrates

Abstract An analytical model has been developed to predict the residual stress distributions in thermal spray coatings on substrates of finite thickness. This is based on the concept of a misfit strain, caused by either the quenching of splats or by differential thermal contraction during cooling. During spraying, the coatings are asssumed to deposit on the substrate in a progressive (layer-by-layer) manner. Although the misfit strain ("the quenching strain") is the same for each successive incremental layer of deposit, this is imposed each time on a "substrate" of changing thickness. The final stress distribution will in general differ from that which would result if the coating were imposed on the substrate (with the same misfit strain) in a single operation. The model is straightforward to apply: for example, it can be implemented using a standard spreadsheet program. The required input data are the quenching strain (or stress), the spraying temperature, material properties and specimen dimensions. Comparisons have been made between the predictions from this model and from a numerical model for two plasma sprayed systems. Good agreement is observed. The effects of varying certain parameters, such as coating thickness, substrate thickness, coating stiffness, etc, are readily explored, so that the model provides a useful tool for controlling residual stress levels. Application of the model to determine the quenching stress, in conjunction with the use of a curvature monitoring technique, is briefly outlined. In addition, an analysis is made of the errors introduced by using Stoney's equation to deduce stress levels from curvature measurements.

Residual stress in piezoelectric poly(vinylidene-fluoride-co-trifluoroethylene) thin films deposited on silicon substrates

2010 ◽  
Vol 519 (4) ◽  
pp. 1441-1444 ◽  
Author(s):  
Sharon Roslyn Oh ◽  
Kui Yao ◽  
Choi Lan Chow ◽  
Francis Eng Hock Tay
Keyword(s):  
Thin Films ◽  
Residual Stress ◽  
Vinylidene Fluoride ◽  
Silicon Substrates ◽  
Poly Vinylidene Fluoride

Static and Dynamic Techniques for Residual Stress Measurements in Microelectromechanical Systems

2006 ◽  
Author(s):  
Mary Vechery ◽  
Andrew Dick ◽  
Luke Currano ◽  
Madan Dubey ◽  
B. Balachandran
Keyword(s):  
Residual Stress ◽  
Lead Zirconate Titanate ◽  
Microelectromechanical Systems ◽  
Measurement Techniques ◽  
Single Layer ◽  
Lead Zirconate ◽  
Nonlinear Frequency ◽  
Stress Measurements ◽  
Stress Levels ◽  
Dynamic Techniques

A major concern in the development of microelectromechanical systems (MEMS) is the presence of residual stress. Residual stress, which is produced during the fabrication of multi-layer thin-film structures, can significantly affect the performance of microscale devices. Though experimental measurement techniques are accurate, actual stress measurements can vary dramatically from run to run and wafer to wafer. For this reason, modeling of this stress is a challenging task. Past work has focused on experimental, static techniques for determining residual stress levels in single-layer and bi-layer structures. In this effort, two different experimental techniques are used for determining residual stress levels in four-layer piezoelectrically driven cantilever and clamped-clamped structures. One of the techniques is based on wafer bow measurements, and the other technique is a dynamic technique that is based on parameter identification from nonlinear frequency-response data. The devices studied, which consist of a piezoelectric layer or lead zirconate titanate (PZT) layer, are fabricated with varying lengths, widths, and material layer thickness. The results obtained from the static and dynamic techniques are compared and discussed.

Comprehensive Solutions for the Response of Freestanding Beams With Tensile Residual Stress Subject to Point-Loading

2013 ◽  
Vol 81 (3) ◽  
Author(s):  
John Gaskins ◽  
N. Scott Barker ◽  
Matthew R. Begley
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Explicit Form ◽  
Critical Loads ◽  
Entire Range ◽  
Elastic Beam ◽  
Materials Characterization ◽  
Tensile Residual Stress ◽  
Stress Levels ◽  
Nonlinear Membrane

This paper provides comprehensive solutions for the load-deflection response of an elastic beam with tensile residual stresses subjected to point-loading. A highly accurate explicit approximation is derived from the exact implicit solution for moderate rotations, which greatly facilitates property extraction and the design of devices for materials characterization, actuation, and sensing. The approximation has less than 6% error across the entire range of loads, displacements, geometry, and residual stress levels. An illustration of the application of the theory is provided for microfabricated nickel beams. The explicit form provides straightforward estimates for the critical loads and deflection defining the limits where classical asymptotic limits (e.g., pretensioned membrane, plate, and nonlinear membrane) will be accurate. Regimes maps are presented that identify critical loads, displacements, and properties correspond to these behaviors. Finally, the explicit form also enables straightforward estimations of bending strains relative to stretching, which is useful in the design of materials experiments that can be approximated as uniform straining of the beams.

scholarly journals Measurement of Residual Stress and Young’s Modulus on Micromachined Monocrystalline 3C-SiC Layers Grown on and Silicon

Micromachines ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1072
Author(s):  
Sergio Sapienza ◽  
Matteo Ferri ◽  
Luca Belsito ◽  
Diego Marini ◽  
Marcin Zielinski ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Residual Stress ◽  
Young’S Modulus ◽  
Defect Density ◽  
Young's Modulus ◽  
Complete Characterization ◽  
Thin Layers ◽  
Silicon Substrates ◽  
Mems Fabrication ◽  
Clamped Beams

3C-SiC is an emerging material for MEMS systems thanks to its outstanding mechanical properties (high Young’s modulus and low density) that allow the device to be operated for a given geometry at higher frequency. The mechanical properties of this material depend strongly on the material quality, the defect density, and the stress. For this reason, the use of SiC in Si-based microelectromechanical system (MEMS) fabrication techniques has been very limited. In this work, the complete characterization of Young’s modulus and residual stress of monocrystalline 3C-SiC layers with different doping types grown on <100> and <111> oriented silicon substrates is reported, using a combination of resonance frequency of double clamped beams and strain gauge. In this way, both the residual stress and the residual strain can be measured independently, and Young’s modulus can be obtained by Hooke’s law. From these measurements, it has been observed that Young’s modulus depends on the thickness of the layer, the orientation, the doping, and the stress. Very good values of Young’s modulus were obtained in this work, even for very thin layers (thinner than 1 mm), and this can give the opportunity to realize very sensitive strain sensors.

Estimation of Residual Stress Levels in Fitness for Service Evaluations of Linepipe

2018 ◽  
Author(s):  
Robert Andrews ◽  
Simon Slater
Keyword(s):  
Residual Stress ◽  
Carbon Steel ◽  
Residual Stresses ◽  
Parent Material ◽  
Plastic Strains ◽  
Stress Distributions ◽  
Butt Welding ◽  
Stress Levels ◽  
High Level ◽  
Welding Processes

Codified fitness for service methods such as API 579 or BS 7910 require consideration of residual stresses in fracture assessments, and guidance is given for upper bound residual stress distributions in common weld geometries. However, these distributions are not appropriate for some welding processes currently or historically used in the manufacture of linepipe, such as high frequency induction welding or flash butt welding. In addition, some linepipe manufacturing routes generate large plastic strains which result in high residual forming stresses, or mechanically relax residual stresses generated in earlier stages of production. This paper first reviews the code recommendations for the effects of plastic strains and stresses from high level pressure testing on residuals stresses. The paper then briefly describes the major methods of producing carbon steel linepipe and provides recommended residual stress levels for the seam weld and parent material of linepipe using the code recommendations. These are based on assumed uniform residual stresses combined with mechanical stress relaxation due to manufacturing steps such as cold expansion and hydrostatic testing. The recommendations are compared with measured residual stress levels from the open literature. Proposals are given for reduced residual stress levels when assessing axial cracks in carbon steel linepipe.

Re-cold expansion process simulation to impart the residual stresses around fastener holes in 6061 A-T6 aluminium alloy

2008 ◽  
Vol 222 (11) ◽  
pp. 1325-1332 ◽  
Author(s):  
J S Jang ◽  
D W Kim
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Process Simulation ◽  
Fatigue Cracks ◽  
External Loading ◽  
Process Conditions ◽  
Expansion Process ◽  
Fatigue Crack Nucleation ◽  
Cold Expansion ◽  
Stress Levels

Cold expansion processes are widely used in aerospace structures to eliminate or delay fatigue crack nucleation and to improve fatigue life. Fastener holes, in which the fatigue cracks initiate from stress concentrations, are plastically expanded using a mandrel pulled through the hole. Cold expansion technology has been applied to enhance low-cycle fatigue performance in repair as well as production applications. Repair of aircraft structures is a key component to extend aircraft service life. Re-cold expansion process conditions such as the degree of cold expansion should be determined to impart the beneficial compressive residual stresses around the holes under tensile loadings. In this paper, a process simulation using three-dimensional finite element analysis is conducted to determine the residual stress imparted by re-cold expansion in the fastener holes under the external loading conditions. Three levels of re-cold expansion under three external loading levels are performed in this numerical investigation. It is shown that the re-cold expansion process with at least 6 per cent of the degree of cold expansion imparts deep residual stresses around the hole so that the resulting stress levels on the hole entry side remain compressive under applied external stress levels between 100 and 200 MPa. In addition, residual stress redistribution under various applied external stresses is discussed.

scholarly journals Electron Backscattered Diffraction to Estimate Residual Stress Levels of a Superalloy Produced by Laser Powder Bed Fusion and Subsequent Heat Treatments

Materials ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 4643
Author(s):  
Mathieu Terner ◽  
Jiwon Lee ◽  
Giulio Marchese ◽  
Sara Biamino ◽  
Hyun-Uk Hong
Keyword(s):  
Residual Stress ◽  
Elevated Temperatures ◽  
Heat Treatments ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Electron Backscattered Diffraction ◽  
Significant Drop ◽  
Powder Bed ◽  
Stress Relieving ◽  
Stress Levels

Metal Additive Manufacturing and Laser Powder Bed Fusion (LPBF), in particular, have come forth in recent years as an outstanding innovative manufacturing approach. The LPBF process is notably characterized by very high solidification and cooling rates, as well as repeated abrupt heating and cooling cycles, which generate the build-up of anisotropic microstructure and residual stresses. Post-processing stress-relieving heat treatments at elevated temperatures are often required in order to release some of these stresses. The effects of 1 h–hold heat treatments at different specific temperatures (solutionizing, annealing, stress-relieve and low-temperature stress-relieve) on residual stress levels together with microstructure characterization were therefore investigated for the popular Alloy 625 produced by LPBF. The build-up of residual stress is accommodated by the formation of dislocations that produce local crystallographic misorientation within grains. Electron backscattered diffraction (EBSD) was used to investigate local misorientation by means of orientation imaging, thereby assessing misorientation or strain levels, in turn representing residual stress levels within the material. The heavily constrained as-built material was found to experience full recrystallization of equiaxed grains after solutionizing at 1150 °C, accompanied by significant drop of residual stress levels due to this grains reconfiguration. Heat treatments at lower temperatures however, even as high as the annealing temperature of 980 °C, were found to be insufficient to promote recrystallization though effective to some extent to release residual stress through apparently dislocations recovery. Average misorientation data obtained by EBSD were found valuable to evaluate qualitatively residual stress levels. The effects of the different heat treatments are discussed and suggest that the peculiar microstructure of alloys produced by LPBF can possibly be transformed to suit specific applications.

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