Visualization of Particle-Toughening Mechanism in Transparent Polyurethanes

2014 ◽  
Author(s):  
Mohammad H. Malakooti ◽  
Patrick L. Anderson ◽  
Henry A. Sodano
Keyword(s):  
Brittle Fracture ◽  
Maximum Load ◽  
Compact Tension ◽  
Image Correlation ◽  
Toughening Mechanism ◽  
Two Phase ◽  
Practical Applications ◽  
Reduced Modulus ◽  
Drastic Increase ◽  
Ductile Behavior

Highly cross-linked polyurethanes have a high elastic modulus and creep resistance, but they undergo a brittle fracture below the glass transition temperature. Unfortunately, a large number of glassy polyurethanes are prone to brittle fracture without undergoing large elastic deformations; in particular, brittle failure is common under conditions such as low temperature and high strain rates. While the rigidity in polymers is required for practical applications, the lack of resistance against crack propagation is essential to avoid catastrophic failures. The toughening of polymers is a crucial aspect of improving the strength and ductility at specific temperatures and deformation rates. One method that has shown promise in recent years is the creation of local regions of reduced modulus that absorb strain energy and toughen the polymer. For instance, rubbers are typically added to epoxy which phase separate upon polymerization and create local elastic regions that significantly toughen the polymer. In this study, a variety of two-phase transparent polyurethanes in the form of single inclusions is designed to study the toughening mechanism of the local regions of reduced modulus with an embedded crack. Synthesized heterogeneous polyurethanes show a transition from brittle to ductile behavior in addition to a drastic increase in the maximum load that the polymer can withstand. Compact tension experiments demonstrate that a small reduction in the inclusion’s Young’s modulus (∼10%) leads to an increase in the toughness by factor of 7 (∼700%). Moreover, digital image correlation is performed to map the strain distribution around the crack in order to visualize possible toughening mechanism. Comparison between the induced strain field in samples with inclusion and samples without inclusion reveals an efficient toughening mechanism of the polymers.

Random Forces Resulting From Internal Two-Phase Flow on Bends and Tees

2006 ◽  
Author(s):  
E. de Langre ◽  
J. L. Riverin ◽  
M. J. Pettigrew
Keyword(s):  
Two Phase Flow ◽  
Experimental Results ◽  
Time Dependent ◽  
Phase Flow ◽  
Water Mixture ◽  
Dimensionless Form ◽  
Two Phase ◽  
Practical Applications ◽  
Random Forces

The time dependent forces resulting from a two-phase air-water mixture flowing in an elbow and a tee are measured. Their magnitudes as well as their spectral contents are analyzed. Comparison is made with previous experimental results on similar systems. For practical applications a dimensionless form is proposed to relate the characteristics of these forces to the parameters defining the flow and the geometry of the piping.

The Stress Intensity Factor of Opening Mode Determined by Digital Image Correlation

2011 ◽  
Vol 83 ◽  
pp. 54-59 ◽  
Author(s):  
Rui Zhang ◽  
Ling Feng He ◽  
Chang Rong Li
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Digital Image Correlation ◽  
Intensity Factor ◽  
Digital Image ◽  
Correlation Method ◽  
Compact Tension ◽  
Image Correlation ◽  
Full Field ◽  
Opening Mode

Applications of the digital image correlation method (DIC) for the determination of the opening mode stress intensity factor (SIF) is investigated using an edge cracked aluminum plate in this paper. Standard compact tension test specimen was tested under tensile loading and the full-field displacement fields of the test sample were recorded using DIC. The SIF associated with unavoidable rigid-body displacement translation were calculated simultaneously from the experimental data by fitting the theoretical displacement field using the method of least-squares. Selection of displacement and convergence values is discussed. For validation, the SIF thus determined is compared with theoretical results, confirming the effectiveness and accuracy of the proposed technique. Therefore it reveals that the DIC is a practical and effective tool for full-field deformation and SIF measurement.

CREDIBILITY-BASED FUZZY MATHEMATICAL PROGRAMMING MODEL FOR PORTFOLIO SELECTION UNDER UNCERTAINTY

2014 ◽  
Vol 13 (01) ◽  
pp. 101-135 ◽  
Author(s):  
MUKESH KUMAR MEHLAWAT ◽  
PANKAJ GUPTA
Keyword(s):  
Mathematical Programming ◽  
Portfolio Selection ◽  
Programming Model ◽  
Fuzzy Optimization ◽  
Chance Constrained Programming ◽  
Fuzzy Mathematical Programming ◽  
Mathematical Programming Model ◽  
Two Phase ◽  
Solution Approach ◽  
Practical Applications

In this paper, we develop a hybrid bi-objective credibility-based fuzzy mathematical programming model for portfolio selection under fuzzy environment. To deal with imprecise parameters, we use a hybrid credibility-based approach that combines the expected value and chance constrained programming techniques. The model simultaneously maximizes the portfolio return and minimizes the portfolio risk. We also consider an additional important criterion, namely, portfolio liquidity as a constraint in the model to make it better suited for practical applications. The proposed fuzzy optimization model is solved using a two-phase approach. An empirical study is included to demonstrate applicability of the proposed model and the solution approach in real-world applications of portfolio selection.

Compact tension fracture specimen: Experimental and computational implementations on stress intensity factor

2018 ◽  
Vol 53 (8) ◽  
pp. 630-647 ◽  
Author(s):  
Behzad V Farahani ◽  
Paulo J Tavares ◽  
Jorge Belinha ◽  
PMGP Moreira
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Interpolation Method ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Image Correlation ◽  
The Finite Element Method ◽  
Point Interpolation Method ◽  
Point Interpolation

This work concentrates on the characterization of the stress intensity factor range for a compact tension specimen tested under a uniaxial tensile fatigue loading condition. The experimental solution is obtained using a three-dimensional full-field optical technique, digital image correlation. The deformation field is measured and documented for distinct crack lengths. As a relevant fracture parameter, stress intensity factor is thus experimentally measured combined with a computational overdeterministic algorithm for different crack lengths. Moreover, to verify the performance of the proposed fracture model, the cracked compact tension specimen is elasto-statically resolved using advanced discretization techniques, such as the finite element method, the meshless radial point interpolation method and the meshless natural neighbour radial point interpolation method. The finite element method model is thereby analysed with ABAQUS© to enable computation of mode I stress intensity factor results based on strain energy release rate criterion for different crack measurements in addition to strain contours. Likewise, the resolution pattern is repeated for meshless methods, and analogous numerical solutions are thus obtained. Overall, the experimental and numerical stress intensity factor results are compared with an available solution (ASTM E647) exhibiting a reasonable agreement. The novelty of this investigation is the amalgamation of an experimental digital image correlation procedure with a computational overdeterministic algorithm and, most importantly, the meshless formulation performance in the linear elastic fracture mechanics.

Characterization of elastic-plastic corner deformation and stress fields

2019 ◽  
Vol 10 (5) ◽  
pp. 660-677
Author(s):  
Norwahida Yusoff ◽  
Feizal Yusof
Keyword(s):  
Three Dimensional ◽  
Correlation Method ◽  
Finite Geometry ◽  
Compact Tension ◽  
Image Correlation ◽  
Stress Fields ◽  
Element Analysis ◽  
Content Type ◽  
Elastic Plastic ◽  
Corner Vertex

Purpose The purpose of this paper is to present the characteristics of elastic-plastic deformation and stress fields at the intersection of a crack front and the free surface of a three-dimensional body, referred to as corner fields. Design/methodology/approach The structures of elastic-plastic corner deformation field were assessed experimentally by looking at the corner border displacement and strain fields on the surface of a compact tension (CT) specimen using digital image correlation method. For assessment and verification purposes, the results were compared with the fields predicted through finite element analysis. The latter method was used further to assess the corner stress field. Findings The characteristics of displacement, strain and stress fields in the vicinity of a corner vertex in a finite geometry CT specimen in a strain hardening condition are independent of load and geometry. One of the distinctive features that becomes evident in this study is that the stress state at the corner vertex at θ=0° is a simple uniaxial tension. Originality/value This paper provides some insights on the structure of elastic-plastic corner fields that could optimistically be served as a fundamental framework towards the development of analytical solutions for elastic-plastic corner fields.

Diffusion and its Application in NiMnGa Alloys

2018 ◽  
Vol 19 ◽  
pp. 80-95 ◽  
Author(s):  
Le Zhou ◽  
Yong Ho Sohn
Keyword(s):  
Crystal Structure ◽  
Martensitic Transformation ◽  
Phase Diagrams ◽  
Diffusion Coefficients ◽  
Diffusion Couples ◽  
Arrhenius Behavior ◽  
Ferromagnetic Shape Memory Alloys ◽  
Two Phase ◽  
Austenitic Phase ◽  
Practical Applications

Heusler NiMnGa alloys are often categorized as ferromagnetic shape memory alloys or magnetocaloric materials, which are important for both practical applications and fundamental research. The NiMnGa alloys undergo a series of diffusion and diffusionless transformation from high temperature to low temperature. Among these transformation, martensitic transformation from austenitic phase to martensitic phase is critical in determining the properties of the alloys. Although martensitic transformation is considered diffusionless, diffusion also has important applications in the research of NiMnGa alloysDiffusion couples along with equilibrium alloys have been used to determine the ternary phase diagrams in NiMnGa alloys. Phase diagrams are important in selecting NiMnGa alloys, in particular two-phase NiMnGa alloys for practical applications. Furthermore, the diffusion couples effectively assist in the determination of compositions that exhibit martensitic transformation temperature near room temperature. Diffusion coefficients have been assessed for NiMnGa alloys. Tracer diffusivity of Ni, Mn and Ga was reported in a wide temperature range and followed Arrhenius behavior. Two different activation energies were obtained, corresponding to B2 and L21 crystal structure, respectively. Interdiffusion coefficients for NiMnGa alloys with B2 crystal structure are measured, which showed that Ni diffuses the fastest, followed by Mn then Ga. The diffusion coefficients provide useful information for fabricating NiMnGa alloys through diffusional process.A combinatorial approach involving diffusion couples and advance characterization has been developed to investigate the mechanical properties, microstructure and crystallography of NiMnGa alloys rapidly and systematically over a large compositional range. The composition-dependent modulus and hardness for NiMnGa alloys was extracted from the diffusion couples with the help of nanoindentation. Martensitic phases with non-modulated and various modulated crystal structures, and austenitic phase were identified in the interdiffusion zones by transmission electron microscopy. The results demonstrate the capability of using diffusion couples to speed up the discovery of new NiMnGa alloys or other similar alloys showing martensitic transformation.

Microstructures and High-temperature Strength of Silicide-reinforced Nb Alloys

2000 ◽  
Vol 646 ◽  
Author(s):  
C.L. Ma ◽  
Y. Tan ◽  
H. Tanaka ◽  
A. Kasama ◽  
R. Tanaka ◽  
...  
Keyword(s):  
High Temperature ◽  
Quaternary System ◽  
Eutectic Reaction ◽  
High Temperature Strength ◽  
Quaternary Alloys ◽  
Two Phase ◽  
Practical Applications ◽  
Arc Melting ◽  
Heat Treated ◽  
Very High

ABSTRACTThis article describes the phase stability, microstructures and mechanical properties of silicide-reinforced Nb alloys in Nb-Mo-W-Si quaternary system prepared by arc melting and heat treatment. There exists an equilibrium two-phase field of Nb solid solution (Nbss) and α(Nb,Mo,W)5Si3 in a Nb-rich region of this quaternary system. Alloys in this region have a eutectic reaction of L → Nbss+β(Nb,Mo,W)5Si3 during solidification. The β(Nb,Mo,W)5Si3 transforms to the stable α(Nb,Mo,W)5Si3 at very high temperature. The cast and heat treated hypoeutectic alloys consist of dendritic Nbss, network-shaped Nbss matrix and α(Nb,Mo,W)5Si3. These quaternary alloys exhibit excellent high-temperature strength, although the fracture toughness is still unacceptable for practical applications.

Experimental Study on Bedding Plane Interfacial Slip

2012 ◽  
Vol 256-259 ◽  
pp. 298-301
Author(s):  
Shu Hong Dai ◽  
Ying Sun ◽  
Zi Xian Dong
Keyword(s):  
Rock Fracture ◽  
Correlation Method ◽  
Bedding Plane ◽  
Image Correlation ◽  
Interfacial Slip ◽  
Practical Applications ◽  
Three Point Bending ◽  
Natural Interface ◽  
Extension Direction ◽  
Rock Specimens

Interfacial slip in rock was studied utilizing digital image correlation method (DICM). Notched rock specimens consisting of a natural interface under three point bending were employed for researching the characters and mechanisms of the interfacial slip. The displacement and strain fields on the surface of specimen were measured accurately by DICM. The experimental results show that the interfacial slip can change the crack extension direction and mode. The results are helpful in researching the mechanism of interfacial slip and practical applications in rock fracture problems.

scholarly journals Axisymmetric simulation of viscoelastic filament thinning with the Oldroyd-B model

2018 ◽  
Vol 851 ◽  
Author(s):  
Emre Turkoz ◽  
Jose M. Lopez-Herrera ◽  
Jens Eggers ◽  
Craig B. Arnold ◽  
Luc Deike
Keyword(s):  
Stress Component ◽  
Fluid Flows ◽  
Theoretical Description ◽  
Slender Body ◽  
Complex Materials ◽  
Two Phase ◽  
Practical Applications ◽  
Numerical Studies ◽  
Fundamental Understanding ◽  
The One

A fundamental understanding of the filament thinning of viscoelastic fluids is important in practical applications such as spraying and printing of complex materials. Here, we present direct numerical simulations of the two-phase axisymmetric momentum equations using the volume-of-fluid technique for interface tracking and the log-conformation transformation to solve the viscoelastic constitutive equation. The numerical results for the filament thinning are in excellent agreement with the theoretical description developed with a slender body approximation. We show that the off-diagonal stress component of the polymeric stress tensor is important and should not be neglected when investigating the later stages of filament thinning. This demonstrates that such numerical methods can be used to study details not captured by the one-dimensional slender body approximation, and pave the way for numerical studies of viscoelastic fluid flows.

Effect of Laser Parameters on Microstructure and Fracture Properties of Repaired Cracks with Micro/Nano Material Addition

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Wei Jiang ◽  
Yinyin Li ◽  
Guanglei Fang ◽  
FengLei Guo
Keyword(s):  
Compact Tension ◽  
Heating Time ◽  
Image Correlation ◽  
J Integral ◽  
Nano Materials ◽  
Power Laser ◽  
Fracture Properties ◽  
Laser Parameters ◽  
Equiaxed Grains ◽  
Selection Of

Abstract Compact tension specimens with prefabricated cracks are repaired by laser with micro/nano materials added at the crack tip. Different combinations of laser parameters, i.e., laser power, laser spot diameter and heating time, were applied to investigate their effects on the microstructures and fracture properties of repaired specimens. J-integrals were calculated according to the digital image correlation (DIC) measurements, and microstructures were examined using scanning electron microscopy (SEM). When suitable laser parameters were used, homogeneous and compact equiaxed grains with no cracks, pores, and agglomeration are observed in the repaired layer, and the J-integral of repaired specimens is approximately 20% less than that of unrepaired specimen. The paper reveals relations among laser parameters, J-integrals, and microstructures, and provides a guideline for the selection of laser repair parameters.

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