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.

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.

Magnitude and Distribution of Retained Residual Stresses in Laboratory Fracture Mechanics Specimens Extracted From Welded Components

2012 ◽  
Author(s):  
R. G. Hurlston ◽  
J. K. Sharples ◽  
A. H. Sherry
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
Structural Integrity ◽  
Specimen Size ◽  
Finite Element Analyses ◽  
Structural Components ◽  
Stress Partitioning ◽  
Material Fracture

Quantifying material fracture toughness properties is an important step in ensuring structural integrity of industrial components. Welding of structural components can cause large magnitudes of residual stress to be generated, which can be defined as a stress that exists in a material when it is under no primary loading. These stresses can be retained in laboratory fracture mechanics testing specimens removed from non-stress relieved welds, making the quantification of valid material fracture toughness difficult. The aim of this paper is to investigate, analytically, the levels and distributions of residual stresses retained in fracture mechanics specimens taken from welded components. This was achieved using parametric finite element analyses. Furthermore, in order to ensure the validity of fracture toughness measurements derived from components that contain residual stress, a robust method for the design of stress-free fracture mechanics specimens is proposed. Significant weld residual stresses have been shown to be retained in certain laboratory specimens post extraction from non stress-relieved welds. The magnitude and distribution of retained residual stress has been shown to be dependant on material properties, specimen size, specimen type and removal location. In addition, the stress partitioning method has been shown to provide a useful approach for estimating the levels and distributions of residual stresses retained in fracture mechanics specimens extracted in certain orientations.

scholarly journals Experimental fracture and mechanical properties of Antarctic ice: preliminary results

1996 ◽  
Vol 23 ◽  
pp. 284-292 ◽  
Author(s):  
M. A. Rist ◽  
P. R. Sammonds ◽  
S. A. F. Murrell ◽  
P. G. Meredith ◽  
H. Oerter ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Nucleation ◽  
Ice Core ◽  
Critical Stress Intensity Factor ◽  
Ice Shelf ◽  
Small Surface ◽  
Preliminary Results ◽  
Mechanics Model ◽  
Apparent Fracture Toughness

An experimental study of the fracture mechanics and rheology of ice from the Ronne Ice Shelf, Antarctica, is currently being undertaken. The apparent critical stress-intensity factor (or apparent fracture toughness,KQ) for crack propagation has been measured using a three-point bend method for inducing crack growth perpendicular to the axis of cylindrical ice-core specimens. Tensile crack nucleation under applied uniaxial compressive stress has also been evaluated. Both methods have allowed a profile of ice elastic and fracture properties with depth through the ice shelf to be constructed. Preliminary results indicate that the measured elastic modulus increases with depth through the firn and upper meteoric ice before reaching a constant value in the deeper, dense meteoric and basal marine ice. The resistance to fracture, as measured by changes in apparent fracture toughness and crack-nucleation stress, increases with depth right through the firn and meteoric ice layers. A simple fracture mechanics model applied to the Ronne Ice Shelf indicates that crevasses form from small surface cracks, less than 40 cm deep, which quickly grow to depths of 40–60m and then remain stable.

scholarly journals Experimental fracture and mechanical properties of Antarctic ice: preliminary results

1996 ◽  
Vol 23 ◽  
pp. 284-292 ◽  
Author(s):  
M. A. Rist ◽  
P. R. Sammonds ◽  
S. A. F. Murrell ◽  
P. G. Meredith ◽  
H. Oerter ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Nucleation ◽  
Ice Core ◽  
Critical Stress Intensity Factor ◽  
Ice Shelf ◽  
Small Surface ◽  
Preliminary Results ◽  
Mechanics Model ◽  
Apparent Fracture Toughness

An experimental study of the fracture mechanics and rheology of ice from the Ronne Ice Shelf, Antarctica, is currently being undertaken. The apparent critical stress-intensity factor (or apparent fracture toughness, K Q) for crack propagation has been measured using a three-point bend method for inducing crack growth perpendicular to the axis of cylindrical ice-core specimens. Tensile crack nucleation under applied uniaxial compressive stress has also been evaluated. Both methods have allowed a profile of ice elastic and fracture properties with depth through the ice shelf to be constructed. Preliminary results indicate that the measured elastic modulus increases with depth through the firn and upper meteoric ice before reaching a constant value in the deeper, dense meteoric and basal marine ice. The resistance to fracture, as measured by changes in apparent fracture toughness and crack-nucleation stress, increases with depth right through the firn and meteoric ice layers. A simple fracture mechanics model applied to the Ronne Ice Shelf indicates that crevasses form from small surface cracks, less than 40 cm deep, which quickly grow to depths of 40–60m and then remain stable.

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.

FEA Welding Residual Stress and Fracture Mechanics Model for Nozzles With J-Groove Attachment Welds: Methodology and Application

2004 ◽  
Author(s):  
John E. Broussard ◽  
E. Stephen Hunt ◽  
Glenn A. White
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
Model Development ◽  
Welding Residual Stress ◽  
Element Analysis ◽  
Mechanics Model ◽  
Modeling Techniques ◽  
Reactor Pressure

Residual stresses due to welding in reactor pressure vessel (RPV) top head nozzle penetrations have been predicted using finite element analysis since the early 1990s. While the analyses were originally targeted at calculating nozzle stresses, the finite element methods have been extended to model a number of different aspects of RPV head penetrations. Both top and bottom head penetrations have been modeled, and the effects of J-groove butter weld deposition and subsequent thermal stress relief of the top head are now included in the analytical model. Development work has recently been completed to integrate a fracture mechanics model into the welding residual stress model. This has allowed for the prediction of crack tip stress intensity factors in the presence of welding residual stresses that include the effects of stress redistribution due to the presence of the crack. This paper presents some of the modeling techniques used in these recent analyses, and some key results obtained.

Investigation Into the Effect of Residual Stress on Crack-Tip Constraint and Brittle Fracture

2011 ◽  
Author(s):  
R. G. Hurlston ◽  
J. K. Sharples ◽  
A. H. Sherry
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Fracture Mechanics ◽  
Brittle Fracture ◽  
Plastic Strain ◽  
Residual Stresses ◽  
Crack Tip ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Unique Material

It is well known that the level of constraint of material at a crack-tip during loading can affect the apparent fracture toughness of components and structures. The effects of geometry and loading on the development of constraint are well defined. Recent research has shown that residual stresses, defined as stresses existing in a material when it is under no primary load, present in the crack-tip region can also affect constraint. However, the effects of this on fracture toughness are not, currently, well understood. The aim of this paper is to investigate the use of constraint based fracture mechanics to quantify unique material fracture toughness curves in two-parameter fracture mechanics type analyses. A novel method for generating residual stresses in single edge notch bend specimens, with minimal associated crack-tip plastic strain, has been devised analytically. Experimental validation has been undertaken to investigate the applicability of constraint based fracture mechanics to characterise the effect of residual stress on brittle fracture of a pressure vessel steel. The results suggest that the use of a unique material toughness curve is possible, certainly when there is a negligible effect of prior plastic strain in the crack-tip region.

Characterisation of Residual Stress Levels Retained in Fracture Mechanics Specimens Machined From Non-Stress Relieved Welds

2013 ◽  
Author(s):  
Robert J. A. McCluskey ◽  
Gang Zheng ◽  
Andrew H. Sherry ◽  
David J. Smith
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
Hole Drilling ◽  
Deep Hole ◽  
Deep Hole Drilling ◽  
Integrity Assessment ◽  
Weld Residual Stress ◽  
Stress Levels

The structural integrity assessment of weldments in engineering components, including piping, is dependent upon the acquisition of valid fracture toughness data. Test standards provide guidance for the preparation of fracture mechanics specimens machined from welds, recognising that under some circumstances retained weld residual stress in the specimens may influence the test, for example, by impairing the ability to establish a valid fatigue pre-crack. To date, however, there are little experimental data quantifying the level and distribution of retained residual stress in fracture mechanics specimens. This paper describes an experimental study characterising the residual stresses retained in single-edge notched bend specimens machined from a non stress-relieved, narrow-gap Tungsten Inert Gas welded pipe, manufactured from 304L stainless steel. The original weld residual stress field was characterised using neutron diffraction and deep hole drilling. The residual stress levels retained in the test specimens were subsequently quantified using deep hole drilling. The results indicated that reasonable levels of residual stress are retained within specimens, although for high toughness, ductile steel, this is insufficient to influence the fracture toughness measurement. The results, however, have implications for testing non stress-relieved welds manufactured from low toughness materials, where retained residual stresses could unduly influence fracture toughness measurements.

Characterization of interfaces in CVD-coated nicalon fiber-reinforced SiC

1989 ◽  
Vol 47 ◽  
pp. 556-557
Author(s):  
K.L. More ◽  
R.A. Lowden
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Chemical Vapor ◽  
Chemical Vapor Infiltration ◽  
Frictional Stress ◽  
Fiber Reinforced ◽  
Pull Out ◽  
Carbon Coated ◽  
Fiber Matrix

The mechanical properties of fiber-reinforced composites are directly related to the nature of the fiber-matrix bond. Fracture toughness is improved when debonding, crack deflection, and fiber pull-out occur which in turn depend on a weak interfacial bond. The interfacial characteristics of fiber-reinforced ceramics can be altered by applying thin coatings to the fibers prior to composite fabrication. In a previous study, Lowden and co-workers coated Nicalon fibers (Nippon Carbon Company) with silicon and carbon prior to chemical vapor infiltration with SiC and determined the influence of interfacial frictional stress on fracture phenomena. They found that the silicon-coated Nicalon fiber-reinforced SiC had low flexure strengths and brittle fracture whereas the composites containing carbon coated fibers exhibited improved strength and fracture toughness. In this study, coatings of boron or BN were applied to Nicalon fibers via chemical vapor deposition (CVD) and the fibers were subsequently incorporated in a SiC matrix. The fiber-matrix interfaces were characterized using transmission and scanning electron microscopy (TEM and SEM). Mechanical properties were determined and compared to those obtained for uncoated Nicalon fiber-reinforced SiC.

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