A Fracture Mechanics Model for the Repair of Microcantilevers by Laser Induced Stress Waves

2005 ◽  
Author(s):  
Zayd C. Leseman ◽  
Sai Koppaka ◽  
Thomas J. Mackin
Keyword(s):  
Fracture Mechanics ◽  
Strain Energy ◽  
Full Range ◽  
Laser Pulses ◽  
Stress Waves ◽  
Laser Fluences ◽  
Mechanics Model ◽  
Induced Stress ◽  
Model Predictions ◽  
Good Agreement

A fracture mechanics model was developed, and experimentally verified, to model stress wave repair of stiction-failed microcantilevers. This model allows us to predict accurately the number of laser pulses, at a specific fluence and wavelength, required to fully repair stiction-failed microcantilevers. The proposed fracture mechanics model includes the strain energy stored in a stiction-failed microcantilever and the strain energy supplied by laser induced stress-waves propagating in the material. The ‘unstuck’ portion of the microcantilever is modeled as a crack so that crack growth reduces the stiction-failed length of the microcantilever. A full range of experiments have been performed to validate the model. Experiments using laser fluences ranging from 0.5 kJ/m2 – 45 kJ/m2 at two different wavelengths have been performed. The experiments are in good agreement with the model predictions. Additionally we have identified practical ranges for irradiation, including a lower bound fluence below which repair is impractical, and an upper bound above which damage to the substrate and microcantilevers occurs.

A Thermomechanical Model for Adhesion Reduction of MEMS Microcantilevers

2001 ◽  
Author(s):  
James W. Rogers ◽  
Thomas J. Mackin ◽  
Leslie M. Phinney
Keyword(s):  
Fracture Mechanics ◽  
Laser Irradiation ◽  
Release Rate ◽  
Laser Heating ◽  
Strain Energy ◽  
Thermal Strain ◽  
Critical Value ◽  
Thermomechanical Model ◽  
Mechanics Model ◽  
Adhesion Reduction

Abstract We present a model for reducing adhesion in MEMS structures using laser heating and compare the model to experimental results. Using a fracture mechanics model, the interface between the stiction-failed microcantilever and the substrate is treated as a crack, and the energy release rate is calculated using elastic theory. In order to include the effect of laser irradiation of the microcantilevers, an associated thermal strain energy is included in the fracture model. As the beam peels, the free length reaches a critical value where the beam buckles, decreasing the energy of the system. The results of the model predict a temperature difference of 100 K is able to repair microcantilevers as long as 600 μm. Experiments are performed that demonstrate the peeling of stiction-failed beams from the substrate after laser irradiation as predicted by the thermomechanical model.

Reliability of Carbon Coated Optical Fibers

2005 ◽  
Author(s):  
Srinath S. Chakravarthy ◽  
Wilson K. S. Chiu
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Fracture Mechanics ◽  
Optical Fibers ◽  
Critical Role ◽  
Carbon Film ◽  
Mechanics Model ◽  
Carbon Coated ◽  
Good Agreement ◽  
Deposition Conditions

The inert strength of carbon coated optical fibers has been observed to be less than that standard optical fibers. The fracture toughness of the carbon film and the residual stress in the film play a critical role in determining the strength of the carbon coated optical fibers. The fracture toughness and the residual stress in the film were measured for a variety of deposition conditions. A recently developed fracture mechanics model was used to predict the failure of carbon coated optical fibers. Model based strength predictions were compared to experimentally measured values. The prediction was found to be in good agreement with the measured values.

scholarly journals Explosion-Induced Stress Wave Propagation in Interacting Fault System: Numerical Modeling and Implications for Chaoyang Coal Mine

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Xiaojun Feng ◽  
Qiming Zhang ◽  
Muhammad Ali
Keyword(s):  
Energy Density ◽  
Stress Wave ◽  
Coal Mine ◽  
Strain Energy Density ◽  
Strain Energy ◽  
Stress Waves ◽  
Fault System ◽  
Propagation Process ◽  
Geological Engineering ◽  
Induced Stress

Exploring the propagation of stress waves in rocks with preexisting discontinuities is of great importance to reveal rock and geological engineering problems, particularly dynamic disasters like earthquakes and rockbursts in underground coal mining. In this paper, six 3D models established with COMSOL Multiphysics are employed to explore the influence of two preexisting faults with different orientations on the propagation process of explosion-induced stress waves and the reflection effect. Considering the propagation process of stress waves, the interactive effect between two different size faults is discussed. The results show that the dip angles of the preexisting fault and the differences of the elastic modulus, density, and Poisson’s ratio between faults and rocks have great influence on the distribution of stresses and strain-energy density. Immediately after the stress wave induced by blasting arrived at preexisting fault A, a relatively high concentration of the strain-energy density was observed at the last wave before passing through fault A. The presence of faults leads to the reflection of most of the blast energy. When the stress wave propagates across fault A, the strain energy stored in the stress wave becomes attenuated; thus, most strain energy was absorbed by the fault’s domain. Finally, the modeling results were implicated in Chaoyang Coal Mine to account for the distribution of the observed seismic events. This study has guiding significance for the attenuation law of stress waves passing through joint/fissure zones in geological engineering, earthquake engineering, and underground mining engineering.

A novel model of Z-pin insertion in prepreg based on fracture mechanics

2021 ◽  
pp. 095440542110144
Author(s):  
Guobiao Ji ◽  
Liang Cheng ◽  
Shaohua Fei ◽  
Jiangxiong Li ◽  
Yinglin Ke
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Analytical Model ◽  
Model Parameters ◽  
Force Model ◽  
Fe Model ◽  
Cohesive Elements ◽  
Fe Method ◽  
Insertion Force ◽  
Mechanics Model

Through-thickness reinforcement is a promising solution to the problem of delamination susceptibility in laminated composites. Modeling Z-pin–prepreg interaction is essential for accurate robotics-assisted Z-pin insertion. In this paper, a novel Z-pin insertion force model combining the classical cohesive finite element (FE) method with a dynamic analytical fracture mechanics model is proposed. The velocity-dependent cohesive elements, in which the fracture toughness is provided by the analytical model, are implemented in Z-pin insertion FE model to predict the crack initiation and propagation. Then Z-pin insertion experiments are performed on prepreg sample with metallic Z-pins at different velocities to identify the analytical model parameters and validate the simulation predictions offered by the model. Dynamics of Z-pin interaction with inhomogeneous prepreg is described and the effects of insertion velocity on prepreg contact force are studied. Results show that the force model agrees well with experiments and the fracture toughness rises with the increasing Z-pin insertion velocity.

Fracture mechanics in design and service: ‘living with defects’ - Application of fracture mechanics to rubber articles, including tyres

1981 ◽  
Vol 299 (1446) ◽  
pp. 189-202 ◽  
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Strain Energy ◽  
Tensile Failure ◽  
Practical Application ◽  
Complicated Fracture ◽  
Fracture Work

The use of a fracture mechanics approach, based on the rate of release of strain energy, to account for various features of the failure of vulcanized rubbers is outlined. The properties considered include those to which fracture mechanics is often applied — tear, tensile failure, crack growth and fatigue — and others to which its application is less usual — abrasion, ozone attack and cutting by sharp objects. The relation of macroscopically observed properties to the basic molecular strength of the material is also discussed. An example of a quantitative practical application of the rubber fracture work, to groove cracking in tyres, is then considered. Finally, the rather more complicated fracture that can occur in rubber—cord laminates is discussed and it is shown that the energetics approach can be applied to some features, at least, of this.

The Behaviour of Multiple Loops in Torsion

1988 ◽  
Vol 15 (3) ◽  
pp. 149-156 ◽  
Author(s):  
R. A. Cavina ◽  
N. E. Waters
Keyword(s):  
Energy Method ◽  
Strain Energy ◽  
Vertical Axis ◽  
Experimental Measurements ◽  
Complementary Strain ◽  
Radial Axis ◽  
Strain Energy Method ◽  
Good Agreement

The angular stiffness of a multiple looped span, subject to rotation about a vertical axis (torsion) and also to rotation about a horizontal or radial axis (mesio-distal tilt), have been derived using the complementary (strain) energy method. Experimental measurements on enlarged models were in good agreement with the values calculated from the theoretical relationships obtained. The variations in angular stiffness resulting from changes in the loop height, width, and position of clinical sized loops are discussed.

Effective Modeling of Fatigue Crack Growth in Pipelines

2012 ◽  
Author(s):  
Steven J. Polasik ◽  
Carl E. Jaske
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Growth Models ◽  
Critical Parameters ◽  
Operating Pressure ◽  
Mechanics Model ◽  
Key Variables

Pipeline operators must rely on fatigue crack growth models to evaluate the effects of operating pressure acting on flaws within the longitudinal seam to set re-assessment intervals. In most cases, many of the critical parameters in these models are unknown and must be assumed. As such, estimated remaining lives can be overly conservative, potentially leading to unrealistic and short reassessment intervals. This paper describes the fatigue crack growth methodology utilized by Det Norske Veritas (USA), Inc. (DNV), which is based on established fracture mechanics principles. DNV uses the fracture mechanics model in CorLAS™ to calculate stress intensity factors using the elastic portion of the J-integral for either an elliptically or rectangularly shaped surface crack profile. Various correction factors are used to account for key variables, such as strain hardening rate and bulging. The validity of the stress intensity factor calculations utilized and the effect of modifying some key parameters are discussed and demonstrated against available data from the published literature.

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