scholarly journals Role of Anisotropic Strength and Stiffness in Governing the Initiation and Propagation of Yielding in Polycrystalline Solids

2019 ◽  
Vol 50 (3) ◽  
pp. 1185-1201 ◽  
Author(s):  
Andrew C. Poshadel ◽  
Paul R. Dawson
Keyword(s):  
Anisotropic Strength ◽  
Initiation And Propagation ◽  
Polycrystalline Solids ◽  
Strength And Stiffness

An Study of Influence of Imperfections on the Delamination of Diamond-Like Carbon Films

2002 ◽  
Vol 719 ◽  
Author(s):  
Myoung-Woon Moon ◽  
Kyang-Ryel Lee ◽  
Jin-Won Chung ◽  
Kyu Hwan Oh
Keyword(s):  
Cross Sections ◽  
Focused Ion Beam ◽  
Imaging System ◽  
Ion Beam ◽  
Carbon Films ◽  
Diamond Like Carbon ◽  
Glass Substrates ◽  
Atomic Force ◽  
Initiation And Propagation

AbstractThe role of imperfections on the initiation and propagation of interface delaminations in compressed thin films has been analyzed using experiments with diamond-like carbon (DLC) films deposited onto glass substrates. The surface topologies and interface separations have been characterized by using the Atomic Force Microscope (AFM) and the Focused Ion Beam (FIB) imaging system. The lengths and amplitudes of numerous imperfections have been measured by AFM and the interface separations characterized on cross sections made with the FIB. Chemical analysis of several sites, performed using Auger Electron Spectroscopy (AES), has revealed the origin of the imperfections. The incidence of buckles has been correlated with the imperfection length.

scholarly journals Biomimetic Composites with Enhanced Toughening Using Silk Inspired Triblock Proteins and Aligned Nanocellulose Reinforcements

2019 ◽  
Author(s):  
Pezhman Mohammadi ◽  
A. Sesilja Aranko ◽  
Christopher P. Landowski ◽  
Olli Ikkala ◽  
Kristaps Jaudzems ◽  
...  
Keyword(s):  
Spider Silk ◽  
Cellulose Nanofibrils ◽  
High Strength ◽  
Beta Sheets ◽  
Conformational Switching ◽  
Multiple Length Scales ◽  
The Matrix ◽  
Strength And Stiffness ◽  
Flow Alignment

Silk and cellulose are biopolymers that show a high potential as future sustainable materials.They also have complementary properties, suitable for combination in composite materials where cellulose would form the reinforcing component and silk the tough matrix. Therein, a major challenge concerns balancing structure and properties in the assembly process. We used recombinant proteins with triblock architecture combining structurally modified spider silk with terminal cellulose affinity modules. Flow-alignment of cellulose nanofibrils and triblock protein allowed a continuous fiber production.The protein assembly involved phase separation into concentrated coacervates, with subsequent conformational switching from disordered structures to beta sheets. This gave the matrix a tough adhesiveness, forming a new composite material with high strength and stiffness combined with increased toughness. We show that versatile design possibilities in protein engineering enable new fully biological materials, and emphasize the key role of controlled assembly at multiple length scales for realization.<br>

scholarly journals Processes and mechanisms governing the initiation and propagation of CMEs

2008 ◽  
Vol 26 (10) ◽  
pp. 3089-3101 ◽  
Author(s):  
B. Vršnak
Keyword(s):  
Magnetic Flux ◽  
External Disturbance ◽  
Source Region ◽  
Flux Rope ◽  
Impulsive Phase ◽  
3 Dimensional ◽  
Initiation And Propagation ◽  
Region Size ◽  
The Magnetic Field

Abstract. The most important observational characteristics of coronal mass ejections (CMEs) are summarized, emphasizing those aspects which are relevant for testing physical concepts employed to explain the CME take-off and propagation. In particular, the kinematics, scalings, and the CME-flare relationship are stressed. Special attention is paid to 3-dimensional (3-D) topology of the magnetic field structures, particularly to aspects related to the concept of semi-toroidal flux-rope anchored at both ends in the dense photosphere and embedded in the coronal magnetic arcade. Observations are compared with physical principles and concepts employed in explaining the CME phenomenon, and implications are discussed. A simple flux-rope model is used to explain various stages of the eruption. The model is able to reproduce all basic observational requirements: stable equilibrium and possible oscillations around equilibrium, metastable state and possible destabilization by an external disturbance, pre-eruptive gradual-rise until loss of equilibrium, possibility of fallback events and failed eruptions, relationship between impulsiveness of the CME acceleration and the source-region size, etc. However, it is shown that the purely ideal MHD process cannot account for highest observed accelerations which can attain values up to 10 km s−2. Such accelerations can be achieved if the process of reconnection beneath the erupting flux-rope is included into the model. Essentially, the role of reconnection is in changing the magnetic flux associated with the flux-rope current and supplying "fresh" poloidal magnetic flux to the rope. These effects help sustain the electric current flowing along the flux-rope, and consequently, reinforce and prolong the CME acceleration. The model straightforwardly explains the observed synchronization of the flare impulsive phase and the CME main-acceleration stage, as well as the correlations between various CME and flare parameters.

Mechanical Behavior and Failure Mechanisms of SCS-6/Ti3Al Composites

1990 ◽  
Vol 194 ◽  
Author(s):  
S. M. Jeng ◽  
C. J. Yang ◽  
J.-M. Yang ◽  
D. G. Rosenthal ◽  
J. Goebel
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Room Temperature ◽  
Failure Mechanisms ◽  
Crack Initiation And Propagation ◽  
Al Composite ◽  
Initiation And Propagation ◽  
Bend Tests ◽  
Scanning Electron

AbstractThe mechanical properties and failure mechanisms of the SCS-6/Ti3Al composite have been studied. Both tensile and notched bend tests were conducted at room temperature on the monolithic and fiber-reinforced Ti-25Al-10Nb-3V-1Mo. Optical and scanning electron microscopy were used to study the crack initiation and propagation mechanisms. The role of the fiber, matrix and interfacial properties on the composite behavior was also assessed.

scholarly journals Nanocomposite toughness, strength and stiffness: role of filler geometry

2014 ◽  
Vol 1 (1) ◽  
pp. 3-17 ◽  
Author(s):  
Israel Greenfeld ◽  
H. Daniel Wagner
Keyword(s):  
Strength And Stiffness

scholarly journals Deformation and fracture behavior of new strain-transformable titanium alloys: a multi-scale investigation

2020 ◽  
Vol 321 ◽  
pp. 11006
Author(s):  
Chloé VARENNE ◽  
Frédéric PRIMA ◽  
Cédrik BROZEK ◽  
Julie BOURGON ◽  
Jacques BESSON ◽  
...  
Keyword(s):  
Titanium Alloys ◽  
Coarse Grained ◽  
Multi Scale ◽  
Ti Alloys ◽  
Deformation And Fracture ◽  
Initiation And Propagation ◽  
Deformation Features ◽  
Deformation Work ◽  
Ductile Fracture Process

Titanium alloys possessing Twinning and Transformation Induced Plasticity effects show promising mechanical properties, particularly high ductility, hardenability, impact and fracture toughness. This work focuses on a strain-transformable, coarse-grained β-Ti-Cr-Sn alloy displaying TWIP effect. To account for the enhanced properties of this alloy, compared to more conventional β-Ti alloys, fracture and deformation features were correlated at different scales. Examinations evidenced a major role of twinning and, more generally, of plasticity-induced phenomena in the ductile fracture process. The resistance of this alloy to plastic deformation (work-hardening), and to crack initiation and propagation is interpreted in view of the progressive, multiscale twinning mechanisms that occur up to the very final stages of fracture.

Verification of Fracture and Fatigue Performance of Titanium Gr. 29 Welds in Tapered Stress Joints

2012 ◽  
Author(s):  
Jaime Buitrago ◽  
Nathan A. Nissley ◽  
Gabriel Rombado
Keyword(s):  
Abrupt Change ◽  
Bending Moment ◽  
Small Scale ◽  
High Pressure And Temperature ◽  
Steel Catenary Riser ◽  
Initiation And Propagation ◽  
Single Piece ◽  
Weld Inspection ◽  
Strength And Stiffness ◽  
Selection Of

Design of a Steel Catenary Riser (SCR) requires the use of connection hardware to accommodate the bending moment that arises from the abrupt change in stiffness at the floater hang-off. Reliability of this connection hardware is of paramount importance in ultra deepwater applications (up to 3000m), especially those involving high pressure and temperature fluids. One type of such connection hardware is a metallic tapered stress joint. Because of its inherent density, strength, and stiffness, steel is not well suited for these applications due to the length and weight constraints. Titanium Gr. 29 (Ti), which is as strong as steel but lighter and more flexible, has been identified as a good material candidate for a tapered stress joint. The required length (∼40ft) and thickness (∼3.5in.) of the Titanium Stress Joint (TSJ) cannot be fabricated as a single piece due to forging size limitations. Thus, an intermediate girth weld becomes necessary. The fracture and fatigue performances in the presence of the external seawater and cathodic protection (CP) and the internal sour production with galvanic effects between the Ti and steel must be assessed to verify the service life of the stress joint. ExxonMobil has developed and initiated a Joint Industry Project to fully address the fracture and fatigue qualification of titanium welds. In particular, the project plans to establish a robust methodology for the future qualification of TSJs that parallels, to the extent possible, the qualification process currently used for SCRs. This paper discusses the primary aspects of the titanium weld qualification: (1) selection of test specimens, (2) load frequency effects on initiation and propagation lives, (3) environmental assisted cracking due to hydride formation under cathodic and galvanic conditions, (4) full-thickness small-scale fatigue, (5) size effect on fatigue, and (6) weld inspection.

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