Thermo-Elastic Model of Epicenter Displacement by Laser Pulse Irradiated on Metallic Surfaces

2017 ◽  
Vol 1 (2) ◽  
Author(s):  
Thanh Chung Truong ◽  
Ayalsew Dagnew Abetew ◽  
Jung-Ryul Lee ◽  
Jeong-Beom Ihn
Keyword(s):  
Pulse Laser ◽  
Rise Time ◽  
Degrees Of Freedom ◽  
Surface Displacement ◽  
Laser Ultrasonics ◽  
Elastic Model ◽  
Beam Size ◽  
Metallic Surfaces ◽  
Penetration Effect ◽  
Pulse Echo

In recent years, there is a much interest in developing of nondestructive testing (NDT) systems using the pulse-echo laser ultrasonics. The key idea is to combine a low-power and short-pulsewidth laser excitation with a continuous sensing laser; and use a scanning mechanism, such as five degrees-of-freedom (5DOF)-axis robot, laser mirror scanner, or motorized linear translation or rotation scanner stage, to scan the combined beam on the structure. In order to optimize the parameters of the excitation laser, a realistic theoretical model of the epicenter displacement in thermo-elastic regime is needed. This paper revisits and revises the study of Spicer and Hurley (1996, “Epicentral and Near Epicenter Surface Displacements on Pulsed Laser Irradiated Metallic Surfaces,” Appl. Phys. Lett., 68(25), pp. 3561–3563) on thermo-elastic model of epicenter displacement with two new contributions: first, we revised Spicer’s model to take into account the optical penetration effect, which was neglected in Spicer’s model; and second, the revised model was used to investigate the effect of laser rise time and beam size to the epicenter displacement. We showed that a pulse laser with short rise time generates an equivalent surface displacement with a pulse laser with long rise time, except a “spike” at the beginning of the epicenter waveform; also when the laser beam size increases, the epicenter displacement decreases. These two conclusions were then validated by experiments.

A Two-Dimensional Linear Assumed Strain Triangular Element for Finite Deformation Analysis

2005 ◽  
Vol 73 (6) ◽  
pp. 970-976 ◽  
Author(s):  
Fernando G. Flores
Keyword(s):  
Finite Deformation ◽  
Degrees Of Freedom ◽  
Yield Function ◽  
Triangular Element ◽  
Deformation Analysis ◽  
Elastic Model ◽  
Stress Strain ◽  
Metric Tensor ◽  
Assumed Strain ◽  
Non Linear

An assumed strain approach for a linear triangular element able to handle finite deformation problems is presented in this paper. The element is based on a total Lagrangian formulation and its geometry is defined by three nodes with only translational degrees of freedom. The strains are computed from the metric tensor, which is interpolated linearly from the values obtained at the mid-side points of the element. The evaluation of the gradient at each side of the triangle is made resorting to the geometry of the adjacent elements, leading to a four element patch. The approach is then nonconforming, nevertheless the element passes the patch test. To deal with plasticity at finite deformations a logarithmic stress-strain pair is used where an additive decomposition of elastic and plastic strains is adopted. A hyper-elastic model for the elastic linear stress-strain relation and an isotropic quadratic yield function (Mises) for the plastic part are considered. The element has been implemented in two finite element codes: an implicit static/dynamic program for moderately non-linear problems and an explicit dynamic code for problems with strong nonlinearities. Several examples are shown to assess the behavior of the present element in linear plane stress states and non-linear plane strain states as well as in axi-symmetric problems.

scholarly journals Flexible Model for Miro-launcher Dynamics

2019 ◽  
Vol 304 ◽  
pp. 07013
Author(s):  
Teodor-Viorel Chelaru ◽  
Valentin Pana ◽  
Alexandru Iulian Onel ◽  
Tudorel-Petronel Afilipoae ◽  
Andrei Filip Cojocaru ◽  
...  
Keyword(s):  
Rigid Body ◽  
Degrees Of Freedom ◽  
Elastic Model ◽  
Six Degrees Of Freedom ◽  
Body Model ◽  
Rigid Body Model ◽  
Three Stages ◽  
Flight Parameters ◽  
Elastic Modes ◽  
Flexible Model

The paper presents aspects regarding flexible model used for describing the dynamics of the three stages micro-launcher. This work analyses transverse flexible oscillations. By the hypotheses adopted, the flexibility problem will be reduced to a group of equations that will be attached to the rigid body model with six degrees of freedom, thus obtaining an elastic model for the launcher. The results analysed will be the flight parameters the launcher, with the influence of the elastic modes considered. The novelty of the paper consists in highlighting the influence of elasticity on the launcher control problem.

On the rise time of ultrafast surface displacement of laser-irradiated surface

Ultrasonics ◽  
2000 ◽  
Vol 38 (1-8) ◽  
pp. 475-480 ◽  
Author(s):  
Vitalyi Gusev ◽  
Jean-Marc Breteau ◽  
Pascal Picart
Keyword(s):  
Rise Time ◽  
Surface Displacement

Effect of Sensor Failure on Dynamometry Calibration

2020 ◽  
Author(s):  
Nicholas Vlajic ◽  
Michael Jonson ◽  
Manton Guers
Keyword(s):  
Degrees Of Freedom ◽  
Fluid Dynamic ◽  
Least Square ◽  
Elastic Model ◽  
Sensor Failure ◽  
Static Loads ◽  
Six Degrees Of Freedom ◽  
In Situ Calibration ◽  
Calibration Matrix

Abstract Dynamometers are used to measure integrated fluid dynamic loads such as thrust, torque or side forces. To resolve all of three force and three moment components, multiple embedded force gages are often used. Due to arrangement, static loads, and redundancy, the number of sensor channels can exceed the six degrees of freedom needed to resolve the generalized rigid body forces. This paper considers modeling of the force gages as simple springs to develop an elastic model of the dynamometer. The method was applied to a dynamometer consisting of six three-component force gages arranged in an axisymmetric ring. A calibration matrix based on the elastic model with individual force gage sensitivities was shown to match a full calibration matrix where properly summed force gage voltages were obtained under global load application. The elastic model was then extended to consider calibration matrices where sensors were assumed to fail. In this scenario, several virtual loads were applied to the dynamometer and the calibration matrix was obtained by minimizing the least square error. It was found that nearly half of the sensors could be lost and still a virtual calibration could be applied to the measurements. Extending the least square idea, an actual in-situ calibration matrix was formed by striking the dynamometer with a diverse set of instrumented hammer strikes. This calibration matrix also agreed with the other calibrations at frequencies below where system dynamics become important.

Flexible control over optical reflection property of metallic surfaces via pulse laser

2019 ◽  
Vol 31 (2) ◽  
pp. 022502
Author(s):  
Xiao Luo ◽  
Mingyong Cai ◽  
Weijian Liu ◽  
Changhao Chen ◽  
Rui Pan ◽  
...  
Keyword(s):  
Pulse Laser ◽  
Metallic Surfaces ◽  
Flexible Control ◽  
Optical Reflection ◽  
Reflection Property

scholarly journals The exchange of energy between organic molecules in a molecular beam and metallic surfaces

1931 ◽  
Vol 132 (819) ◽  
pp. 50-66 ◽  
Keyword(s):  
Kinetic Energy ◽  
Small Molecules ◽  
Internal Energy ◽  
Degrees Of Freedom ◽  
Molecular Beam ◽  
Organic Molecules ◽  
Solid Surfaces ◽  
Metallic Surfaces ◽  
Large Molecules ◽  
Internal Degrees Of Freedom

When a molecular beam of a substance is directed against a heated target, the molecules rebound and, together with any fragments resulting from decomposition, can be caught on a liquid air-cooled surface. Since the fragments are in a molecular beam they cannot react before reaching the liquid air surface and we may expect, therefore, that work of this kind will yield considerable information about the nature of the primary change in chemical reactions. Furthermore, we may expect to obtain information about the exchange of energy between solid surfaces and gaseous molecules. Experiments on the heat conductivity of gases at low pressure have yielded considerable information on this exchange of energy and there has been a number of papers dealing with the theoretical aspects of the problem. We must here emphasise the important point that in practically all previous work, both theoretical and experimental, only small molecules have been considered; in these cases the internal energy has been completely neglected and only the kinetic energy of the molecules has been considered. It is obvious that when we are dealing with the chemical decomposition of large molecules, any changes in kinetic energy after collision with the wall must be relatively unimportant compared with changes of internal energy; therefore, we shall consider only the transfer of energy from the wall to the internal degrees of freedom.

Multibody Models for Tower Vibrations With an Unbalanced Rotor

2021 ◽  
Author(s):  
Simon S. Pedersen ◽  
Niclas B. Madsen ◽  
José L. Escalona ◽  
Ole Balling
Keyword(s):  
Degrees Of Freedom ◽  
Simulation Models ◽  
Experimental Results ◽  
Elastic Model ◽  
Valuable Insight ◽  
Multibody Model ◽  
Unbalanced Rotor ◽  
Resonance Frequencies ◽  
Low Degrees ◽  
Elliptical Motion

Abstract This paper compares different models that can be used to analyze the vibrations of an unbalanced rotor with horizontal axis over a flexible tower. Model results are compared with experimental results. The modeled system is equivalent to a wind turbine with perfectly rigid blades. The selected models are the linear elastic model that is obtained using the linear theory of vibrations and two multibody models. The first multibody model uses Component Mode Synthesis for the description of the tower flexibility while the second multibody model used a lumped properties approach. Experimental results validate with reasonable agreement the resonance speeds of an unbalanced rotor. Furthermore, the models, while low degrees of freedom, give valuable insight of inertial loads on drivetrain components based on tower top dynamic motion. The work presented in this paper showed the use of 3 low-degrees of freedom models to predict resonance and tower top displacements. All simulation models did exhibit slightly higher resonance frequencies than the experimental results. The results showed that the tower top motion for the rectangular tower resembles a figure eight type motion, while the square tower top shows an elliptical motion.

Nondestructive Characterization of Plasma Sprayed Coatings by Laser Ultrasonics

1996 ◽  
Author(s):  
M. Viens ◽  
D. Drolet ◽  
A. Blouin ◽  
J.-P. Monchalin ◽  
C. Moreau
Keyword(s):  
Pulse Laser ◽  
Coating Thickness ◽  
Deposition Process ◽  
Laser Ultrasonics ◽  
Scanning System ◽  
Laser Ultrasonic ◽  
Ultrasonic Scanning ◽  
Plasma Sprayed Coatings ◽  
Plasma Sprayed ◽  
Sprayed Coatings

Abstract Nondestructive methods previously developed for the detection of flaws, such as delaminations, or for the evaluation of the elastic properties of materials, could be judiciously adapted in order to get a better assessment of plasma-sprayed coatings. Laser ultrasonics is a nondestructive evaluation method which relies on both optics and ultrasonics. A short-pulse laser generates an ultrasonic wave into the material to be inspected, and a long-pulse laser, coupled to an interferometer, detects the resulting ultrasonic displacement. Laser ultrasonics is a remote sensing method and therefore could be used for the monitoring of hot plasma-sprayed coatings during the deposition process. In this work, experiments were performed on samples composed of ZrO2 sprayed under different conditions onto thick copper substrates. The samples were first probed by conventional ultrasonic transducers and then by a non contact laser-ultrasonic scanning system. The two series of measurements agreed well. These experiments showed that, after calibration, the coating thickness could be measured during the deposition process, with a relatively good accuracy, by laser ultrasonics. The laser-ultrasonic scanning system also revealed non uniformity of more than 10% in the coating thickness of the tested samples. This thickness variation is possibly caused by a temperature gradient induced in the coatings during spraying.

scholarly journals ON STOCHASTICITY IN NEARLY-ELASTIC SYSTEMS

2012 ◽  
Vol 12 (03) ◽  
pp. 1150020 ◽  
Author(s):  
MARK FREIDLIN ◽  
WENQING HU
Keyword(s):  
Degrees Of Freedom ◽  
Intrinsic Property ◽  
Model Systems ◽  
Elastic Model ◽  
Deterministic System ◽  
Time Behavior ◽  
Long Time Behavior ◽  
Deterministic Systems ◽  
Elastic Systems ◽  
Long Time

Nearly-elastic model systems with one or two degrees of freedom are considered: the system is undergoing a small loss of energy in each collision with the "wall". We show that instabilities in this purely deterministic system lead to stochasticity of its long-time behavior. Various ways to give a rigorous meaning to the last statement are considered. All of them, if applicable, lead to the same stochasticity which is described explicitly. So that the stochasticity of the long-time behavior is an intrinsic property of the deterministic systems.

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