Duration of load effects in lumber. Part III: Code considerations

1982 ◽  
Vol 9 (3) ◽  
pp. 526-536 ◽  
Author(s):  
Borg Madsen ◽  
Kenneth Johns
Keyword(s):  
Fracture Mechanics ◽  
Structural Design ◽  
Design Codes ◽  
Specific Design ◽  
Damage Models ◽  
Mechanics Model ◽  
Complicated Model ◽  
Load Effects ◽  
Elastic Fracture ◽  
Duration Of Load

The implications for practical structural design with wood of a visco-elastic fracture mechanics model, recently developed and verified experimentally by the authors, are presented. These are compared with those of the presently used Madison concept, and with those of the cumulative damage models. Following discussion of present practice and the consequences of the fracture mechanics model, specific design recommendations are made as to how this more complicated model might be incorporated into design codes.

Duration of load effects in lumber. Part I: A fracture mechanics approach

1982 ◽  
Vol 9 (3) ◽  
pp. 502-514 ◽  
Author(s):  
Kenneth Johns ◽  
Borg Madsen
Keyword(s):  
Fracture Mechanics ◽  
Stress Ratio ◽  
Failure Time ◽  
Creep Function ◽  
Load Effect ◽  
Mechanics Model ◽  
Current Design ◽  
Load Effects ◽  
Duration Of Load

In Part I of this paper, the deterioration of the strength of lumber with continued application of constant stress, called the duration-of-load effect, is treated using a viscoelastic, limited ductility fracture mechanics model. The model is explained and developed in a general way, then modified for use with commercial lumber. The problems of assigning correct creep function parameters and values of stress ratio for use in calculations involving the model are discussed. The evident weakening of boards surviving a long-term test can be used to project a failure time that is longer than the test period. Numerical results are shown and compared with the Madison curve, the basis for current design codes. Parts II and III of this paper demonstrate experimental verification and discuss design implications.

Duration of load effects in lumber. Part II: Experimental data

1982 ◽  
Vol 9 (3) ◽  
pp. 515-525 ◽  
Author(s):  
Borg Madsen ◽  
Kenneth Johns
Keyword(s):  
Experimental Data ◽  
Fracture Mechanics ◽  
Load Test ◽  
Design Practice ◽  
Coefficient Of Correlation ◽  
Similar Test ◽  
Mechanics Model ◽  
Viscoelastic Fracture ◽  
Load Effects ◽  
Duration Of Load

The viscoelastic fracture mechanics model developed in Part I is calibrated using a 70-day duration of load test on commerical lumber. The model is then verified using another similar test on a different population of boards, and on a unique 6-year test just terminated. All three test programs are described. The model is used to tentatively project results beyond the period of testing. The strength predictions of the model compare well with those obtained experimentally during the tests, the coefficient of correlation being 0.95. Implications for design practice are outlined in Part III of this paper.

Fracture mechanics in design and service: ‘living with defects’ - Fracture mechanics and the design of wood structures

1981 ◽  
Vol 299 (1446) ◽  
pp. 217-226 ◽  
Keyword(s):  
Fracture Mechanics ◽  
Wood Products ◽  
Design Codes ◽  
Wood Structures ◽  
Linear Elastic ◽  
Orthotropic Elasticity ◽  
Potential Benefits ◽  
Elastic Fracture ◽  
Mechanics Concepts ◽  
Timber Engineering

Applications of linear-elastic fracture mechanics concepts for treating brittle fracture of wood and wood products are discussed. The influence of orthotropic elasticity and heterogeneity of wood structure on the computational and experimental aspects of wood fracture are introduced. Several applications of fracture mechanics for the development of design criteria in timber engineering are discussed to illustrate the potential benefits of application of fracture mechanics in design codes.

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.

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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