scholarly journals Fatigue crack growth in epoxy polymer nanocomposites

2021 ◽  
Vol 379 (2203) ◽  
pp. 20200436
Author(s):  
Anthony J. Kinloch ◽  
Rhys Jones ◽  
John G. Michopoulos
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Material Selection ◽  
Threshold Value ◽  
Fatigue Behaviour ◽  
Fatigue Threshold ◽  
Worst Case ◽  
Epoxy Nanocomposite

The present paper describes detailed analyses of experimental data for the cyclic-fatigue behaviour of epoxy nanocomposite polymers. It has been shown that the data may be interpreted using the Hartman–Schijve relationship to yield a unique, ‘master’, linear relationship for each epoxy nanocomposite polymer. By fitting the experimental data to the Hartman–Schijve relationship, two key materials parameters may be deduced: (i) the term A , which may be thought of as the fatigue equivalent to the quasi-static value of the fracture energy, G c , and (ii) the fatigue threshold value, Δ G thr , below which no significant fatigue crack growth (FCG) occurs. It has then been established that the values of these parameters, together with the slope, n , and intercept, D , of the Hartman–Schijve master relationship, may be used (i) to compute the experimental results measured for the fatigue behaviour of the epoxy nanocomposite polymers, (ii) to understand the observed fracture and fatigue behaviour of these materials with respect to the structure of the epoxy nanocomposite polymers, and (iii) to deduce the ‘upper-bound’, i.e. ‘worst-case’, FCG rate curve which may be used by industry as a material development, material selection, design and service-life prediction tool when these epoxy nanocomposite polymers are used in engineering applications such as structural adhesives and/or as matrices in fibre-reinforced composites. This article is part of a discussion meeting issue ‘A cracking approach to inventing new tough materials: fracture stranger than friction’.

A Method for the Analysis of the Growth of Short Fatigue Cracks

1995 ◽  
Vol 117 (4) ◽  
pp. 408-411 ◽  
Author(s):  
A. J. McEvily ◽  
Y.-S. Shin
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Material Constant ◽  
Plastic Zone Size ◽  
Surface Cracks ◽  
Zone Size ◽  
Short Cracks

A method for the analysis of the fatigue crack growth rate for short cracks has been developed and is applied to the case of fatigue crack growth of short surface cracks in a 1045 carbon steel. The method entails three modifications to standard LEFM procedures. These modifications include the use of a material constant to bridge between smooth and cracked specimen behavior, consideration of the plastic zone size to crack length ratio, and incorporation of the development of crack closure. Comparisons are made between calculations based upon this approach and experimental data.

Near-Threshold Fatigue Crack Growth Behavior of ECAPed Ultrafine-Grained Copper

2021 ◽  
Vol 1016 ◽  
pp. 1193-1198
Author(s):  
Shou Dao Qu ◽  
Ze Sheng You
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Threshold ◽  
Coarse Grained ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Resistance ◽  
Ultrafine Grained ◽  
Stress Ratios ◽  
Near Threshold

Fatigue crack growth resistance of ultrafine grained Cu processed by equal channel angular pressing (ECAP) was investigated. Particular emphasis was devoted to the effects of microstructure evolution on fatigue crack growth in the near-threshold regime. The ultrafine grained Cu exhibits a lower fatigue threshold than coarse-grained Cu at stress ratios of 0.1 and 0.7. Fatigue induced coarsening of the UFG structure near the fatigue crack and intergranular fatigue crack growth are observed.

scholarly journals Requirements and Variability Affecting the Durability of Bonded Joints

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1468 ◽  
Author(s):  
Rhys Jones ◽  
Daren Peng ◽  
John G. Michopoulos ◽  
Anthony J. Kinloch
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Upper Bound ◽  
The United States ◽  
Fatigue Threshold ◽  
Growth Equation ◽  
Bonded Joints ◽  
Cohesive Failure ◽  
Structural Adhesives

This paper firstly reveals that when assessing if a bonded joint meets the certification requirements inherent in MIL-STD-1530D and the US Joint Services Standard JSSG2006 it is necessary to ensure that: (a) There is no yielding at all in the adhesive layer at 115% of design limit load (DLL), and (b) that the joint must be able to withstand design ultimate load (DUL). Secondly, it is revealed that fatigue crack growth in both nano-reinforced epoxies, and structural adhesives can be captured using the Hartman–Schijve crack growth equation, and that the scatter in crack growth in adhesives can be modelled by allowing for variability in the fatigue threshold. Thirdly, a methodology was established for estimating a valid upper-bound curve, for cohesive failure in the adhesive, which encompasses all the experimental data and provides a conservative fatigue crack growth curve. Finally, it is shown that this upper-bound curve can be used to (a) compare and characterise structural adhesives, (b) determine/assess a “no growth” design (if required), (c) assess if a disbond in an in-service aircraft will grow and (d) to design and life in-service adhesively-bonded joints in accordance with the slow-growth approach contained in the United States Air Force (USAF) certification standard MIL-STD-1530D.

Remaining Lives of Fatigue Crack Growths for Pipes With Subsurface Flaws and Subsurface-to-Surface Flaw Proximity Rules

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Genshichiro Katsumata ◽  
Yinsheng Li ◽  
Kunio Hasegawa ◽  
Valery Lacroix
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Surface Flaw ◽  
Japan Society ◽  
Rule Based ◽  
Aspect Ratios ◽  
Inner Surface ◽  
American Society

If a subsurface flaw is located near a component surface, the subsurface flaw is transformed into a surface flaw in accordance with a subsurface-to-surface flaw proximity rule. The recharacterization process from subsurface to surface flaw is adopted in all fitness-for-service (FFS) codes. However, the specific criteria of the recharacterizations are different among the FFS codes. Recently, the authors have proposed a new subsurface-to-surface flaw proximity rule based on experimental data and equivalent fatigue crack growth rate calculations. In this study, fatigue crack growth calculations were carried out for pipes with subsurface flaws, using the proximity rule provided in the current ASME (American Society of Mechanical Engineers) Section XI and JSME (The Japan Society of Mechanical Engineers) codes and the proposed subsurface-to-surface flaw proximity rule. Different pipe sizes, flaw aspect ratios, and ligament distances from subsurface flaws to inner surface of pipes were taken into account. The results indicate the current proximity rule gives less conservative fatigue lives, when the aspect ratios of the subsurface flaws are small.

A Theory for Fatigue Failure under Multiaxial Stress-Strain Conditions

1973 ◽  
Vol 187 (1) ◽  
pp. 745-755 ◽  
Author(s):  
M. W. Brown ◽  
K. J. Miller
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Failure ◽  
Physical Interpretation ◽  
Tensile Strain ◽  
Multiaxial Fatigue ◽  
Fatigue Data ◽  
Principal Strains

A new theory for multiaxial fatigue is presented that is based on a physical interpretation of the mechanisms of fatigue crack growth. It may be represented graphically by contours of constant life, which are expressed mathematically by where ε1, ε2 and ε3 are the principal strains, •ε1 ≥ ε2 ≥ ε3. This equation underlines the importance of strain parameters in correlating fatigue data. It illustrates the effect of both the shear strain and the tensile strain normal to the plane of maximum shear. The theory is compared with several classical and recent theories, which are briefly reviewed. It is shown that classical theories of fatigue failure cannot correlate experimental data, and may be dangerous if used for design purposes.

Explicit and Implicit Lifetime Assessment Methods of 9Cr-1Mo Steel Under Combined Creep and Fatigue Loads Using a Strip Yield Model

2014 ◽  
Author(s):  
B. Andrews ◽  
G. P. Potirniche
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Constitutive Equations ◽  
Crack Extension ◽  
Cyclic Loads ◽  
Yield Model ◽  
Creep Crack ◽  
Strip Yield Model

Growing demand for clean, affordable energy has driven the power industry towards generation plants with higher thermal efficiency and higher operating temperatures. ASTM Grade 91 is a high chromium (9Cr-1Mo) creep resistant steel commonly used in high temperature pressure vessel and piping applications. These service conditions often involve a combination of stationary and cyclic loads at elevated temperatures. Lifecycle assessments of components under such conditions require modeling of both creep and fatigue behaviors. This paper develops two approaches to modeling mixed creep and fatigue crack growth for lifetime assessment of high service temperature components. Both approaches model fatigue crack growth using the Paris law integrated over the number of lifetime cyclic reversals to obtain crack extension. A strip yield model is used to characterize the crack tip stress-strain fields. The first approach employed an explicit method to approximate creep crack growth using C* as a crack tip parameter characterizing creep crack extension. The Norton power law was explicitly solved to model the primary and secondary stages of creep. The second approach used an implicit method to solve a set of constitutive equations based on properties of the material microstructure to model all creep stages. Constitutive equations were fit to experimental data collected at stresses 10–60% of yield and temperatures 550–650°C. These methods were compared to published experimental data under purely stationary loads, purely cyclic loads and mixed loading. Both models showed good agreement with experimental data in the stress and temperature conditions considered.

A Theory for Fatigue Failure under Multiaxial Stress-Strain Conditions

1973 ◽  
Vol 187 (1) ◽  
pp. 745-755 ◽  
Author(s):  
M. W. Brown ◽  
K. J. Miller
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Failure ◽  
Physical Interpretation ◽  
Tensile Strain ◽  
Multiaxial Fatigue ◽  
Fatigue Data ◽  
Principal Strains

A new theory for multiaxial fatigue is presented that is based on a physical interpretation of the mechanisms of fatigue crack growth. It may be represented graphically by contours of constant life, which are expressed mathematically by where ε1, ε2 and ε3 are the principal strains, •ε1 ≥ ε2 ≥ ε3. This equation underlines the importance of strain parameters in correlating fatigue data. It illustrates the effect of both the shear strain and the tensile strain normal to the plane of maximum shear. The theory is compared with several classical and recent theories, which are briefly reviewed. It is shown that classical theories of fatigue failure cannot correlate experimental data, and may be dangerous if used for design purposes.

Two-parameter mechanistic model for the fatigue crack growth of metals

2019 ◽  
Vol 12 (2) ◽  
Author(s):  
Tawqeer Zada
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Failure ◽  
Mechanistic Model ◽  
Model Development ◽  
Two Parameters ◽  
Crack Growth Model ◽  
Two Parameter

In this paper, a two-parameter mechanistic model for the fatigue crack growth has been developed. Fatigue failure is the major causes of mechanical structural failure. The fatigue failure progress in three stages crack initiation, crack growth and final failure. The fatigue crack growth has been modelled by different approaches, however these approaches are generally empirical. In this paper, a mechanistic fatigue crack growth model is proposed. The striation and its relation to the cyclic load is used for the model development. Scanning electronic microscope results are used to establish relation between striation and crack growth. The developed model is two-parameters. The model has been implemented and validated using experimental data from the literature. The model prediction is satisfactory in region II of the crack growth curve. However, in region I and region III the model deviates from experimental data. It is suggested to incorporate interaction of monotonic and cyclic loading in the mechanistic modelling for the fatigue growth.

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