The Prediction of Notch and Crack Effects

1966 ◽  
Vol 3 (03) ◽  
pp. 364-368
Author(s):  
Paul Kuhn
Keyword(s):  
Static Loading ◽  
Aircraft Design ◽  
Fatigue Loading ◽  
Engineering Structures ◽  
Service Experience ◽  
Small Load ◽  
Automobile Engines ◽  
Quantitative Understanding ◽  
The One ◽  
Reliable Methods

Historically, engineering structures have been designed for static strength, that is, for the one-time application of a large load. However, service loads, as a rule, are repeated loads, and a rather small load can break a structure if it is repeated very often; this phenomenon is known as the fatigue problem. Fatigue was for a while a serious problem in the design of automobiles. But automobile engines, for instance, are built by hundreds of thousands to one design. Service experience thus furnishes highly reliable information as to which parts are underdesigned, and the design methods can be improved by adding experience factors. In aircraft design, this avenue of approach can be used only to a very limited extent, largely because any failure in the air is likely to be catastrophic. Thus, strong efforts must be made to provide reliable methods of design by research rather than by developing factors derived from service experience. This paper briefly discusses two separate but related phases of aircraft fatigue research: The effect of notches under fatigue loading, and the effect of cracks under static loading. Quantitative understanding of notches under fatigue loading enables the designer to minimize the appearance of cracks. Quantitative understanding of cracks under static loading enables the designer to produce a structure which is safe when cracks do occur.

Crack Growth in Stainless Steel 304 under Creep-Fatigue Loading

2007 ◽  
Vol 353-358 ◽  
pp. 485-490 ◽  
Author(s):  
Y.M. Baik ◽  
K.S. Kim
Keyword(s):  
Stress Intensity Factor ◽  
Stainless Steel ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Rates ◽  
Static Loading ◽  
Fatigue Loading ◽  
Creep Fatigue ◽  
Crack Growth Rates

Crack growth in compact specimens of type 304 stainless steel is studied at 538oC. Loading conditions include pure fatigue loading, static loading and fatigue loading with hold time. Crack growth rates are correlated with the stress intensity factor. A finite element analysis is performed to understand the crack tip field under creep-fatigue loading. It is found that fatigue loading interrupts stress relaxation around the crack tip and cause stress reinstatement, thereby accelerating crack growth compared with pure static loading. An effort is made to model crack growth rates under combined influence of creep and fatigue loading. The correlation with the stress intensity factor is found better when da/dt is used instead of da/dN. Both the linear summation rule and the dominant damage rule overestimate crack growth rates under creep-fatigue loading. A model is proposed to better correlate crack growth rates under creep-fatigue loading: 1 c f da da da dt dt dt Ψ −Ψ     =         , where Ψ is an exponent determined from damage under pure fatigue loading and pure creep loading. This model correlates crack growth rates for relatively small loads and low stress intensity factors. However, correlation becomes poor as the crack growth rate becomes large under a high level of load.

The calculation of required fire resistance limits for engineering structures of technological pipe racks at oil and gas processing plants on the basis of an evaluation of the time needed for personnel evacuation and rescue in case of fire

2021 ◽  
Vol 30 (5) ◽  
pp. 58-65
Author(s):  
A. Yu. Shebeko ◽  
Yu. N. Shebeko ◽  
A. V. Zuban
Keyword(s):  
Fire Resistance ◽  
Oil And Gas ◽  
Probabilistic Method ◽  
Processing Plant ◽  
Engineering Structures ◽  
Gas Processing ◽  
Processing Plants ◽  
The One ◽  
In Fire ◽  
Rescue Time

Introduction. GOST R 12.3.047-2012 standard offers a methodology for determination of required fire resistance limits of engineering structures. This methodology is based on a comparison of values of the fire resistance limit and the equivalent fire duration. However, in practice incidents occur when, in absence of regulatory fire resistance requirements, a facility owner, who has relaxed the fire resistance requirements prescribed by GOST R 12.3.047–2012, is ready to accept its potential loss in fire for economic reasons. In this case, one can apply the probability of safe evacuation and rescue to compare distributions of fire resistance limits, on the one hand, and evacuation and rescue time, on the other hand.A methodology for the identification of required fire resistance limits. The probabilistic method for the identification of required fire resistance limits, published in work [1], was tested in this study. This method differs from the one specified in GOST R 12.3.047-2012. The method is based on a comparison of distributions of such random values, as the estimated time of evacuation or rescue in case of fire at a production facility and fire resistance limits for engineering structures.Calculations of required fire resistance limits. This article presents a case of application of the proposed method to the rescue of people using the results of full-scale experiments, involving a real pipe rack at a gas processing plant [2].Conclusions. The required fire resistance limits for pipe rack structures of a gas processing plant were identified. The calculations took account of the time needed to evacuate and rescue the personnel, as well as the pre-set reliability of structures, given that the personnel evacuation and rescue time in case of fire is identified in an experiment.

Static Loading Tests of New Type of Bolt Assembly Connection Developed for Perspective Temporary Steel Railway Bridges

2014 ◽  
Vol 590 ◽  
pp. 331-335 ◽  
Author(s):  
Marcela Karmazínová ◽  
Michal Štrba
Keyword(s):  
Numerical Modelling ◽  
Failure Mechanism ◽  
Static Loading ◽  
Fatigue Loading ◽  
Preliminary Evaluation ◽  
Problem Solution ◽  
Static Tests ◽  
Actual Behaviour ◽  
Loading Tests ◽  
Plate Connections

The paper deals with the problems of the actual behaviour, failure mechanism and load-carrying capacity of the special bolt connection developed and intended for the assembly joints of the truss main girders chords of perspective railway steel temporary bridges. Within the framework of this problem solution, several types of structural details of assembly joints have been considered as the conceptual structural design. Based on the preliminary evaluation of advantages or disadvantages of these ones, in principle two basic structural configurations – so-called “tooth” and “splice plate” connections have been selected for the subsequent detailed investigation. This investigation is mainly based on the experimental verification of the actual behaviour, strain and failure mechanism and corresponding strength of the connection, and on its numerical modelling using FEM. This paper is focused only on the static loading tests results of the splice plate connections and their evaluation, which have already been finished. Simultaneously with the static tests, the fatigue loading tests are being realized, too, but they have not been finished so far, as well as the FEM numerical modelling.

A Master S-N Curve Representation of Subsea Umbilical Tube Weld Fatigue Data

2010 ◽  
Author(s):  
Pingsha Dong ◽  
Xinhua Yang
Keyword(s):  
Stress Ratio ◽  
Correction Term ◽  
Fatigue Loading ◽  
Nominal Stress ◽  
Stress Range ◽  
Fatigue Data ◽  
Range Parameter ◽  
Weld Fatigue ◽  
Curve Representation ◽  
The One

In this paper, some of the available duplex and super-duplex stainless steel umbilical tube fatigue data are analyzed using an equivalent nominal stress range parameter, which shares a great deal of similarity to the one used in the 2007 ASME Div 2 Code. The proposed fatigue parameter consists of nominal stress range, a size correction term RTt with RT being the tube radius and t being tube wall thickness, and a stress ratio term (1 − R) with R being applied stress ratio. With it, the available girth weld fatigue test data are shown to collapse into a narrow band. The equivalent nominal stress range parameter is also shown to be effective in correlating seam weld data collected from seam-welded umbilicals, but with a different slope in log-log based S-N plot. Coiling/uncoiling low-cycle effects can be addressed by introducing a pseudo elastic nominal stress definition. Miner’s rule can be used to combine both coiling/uncoiling effects with subsequent high-cycle fatigue loading.

scholarly journals Experimental and numerical analysis of heat convection in cylindrical composite structures with internal defects

2019 ◽  
Vol 28 ◽  
pp. 096369351987969
Author(s):  
Aleksander Muc ◽  
Małgorzata Chwał ◽  
Adam Stawiarski
Keyword(s):  
Heat Transfer ◽  
Finite Element Method ◽  
Static Loading ◽  
Composite Structures ◽  
Fatigue Loading ◽  
Cooling Process ◽  
Various Boundary Conditions ◽  
Laminated Panels ◽  
Numerical Finite Element ◽  
External Loads

The present article discusses the influence of delamination and external loads on the heat transfer in flat and curved laminated panels. Three cases are considered in details: (1) the unloaded structure (length is a constant), (2) the static loading, and (3) the fatigue loading. Here, the comparison between experimental and numerical (finite element method) results is presented. The numerical model allows us to adopt implementations of various boundary conditions as well as the size of delamination. The influence of the shallowness parameter and the thermal resistance is demonstrated. The experimental detection of temperature contours during the cooling process has been conducted at different points in the area surrounding the delamination.

Healing Ligaments Have Shorter Lifetime and Greater Strain Rate During Fatigue Than Creep at Functional Stresses

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Gail M. Thornton ◽  
Soraya J. Bailey
Keyword(s):  
Cyclic Loading ◽  
Strain Rate ◽  
Static Loading ◽  
Fatigue Loading ◽  
Cyclic Fatigue ◽  
Time Dependent ◽  
Daily Activities ◽  
Ligament Injury ◽  
Fatigue Lifetime ◽  
Creep Loading

Healing ligaments have compromised strength, which makes them susceptible to damage during daily activities at normal functional stresses. Daily activities expose ligaments to cyclic (fatigue) and static (creep) loading. A gap injury was created in the midsubstance of both hindlimb medial collateral ligaments of 40 female 1-year-old New Zealand White rabbits. After a 14-week healing interval, medial collateral ligament gap scars were exposed to long-term fatigue and creep loading over a range of functional force/stress levels. Lifetime and strain behavior were compared during fatigue and creep. The contribution of time-dependent mechanisms to fatigue lifetime was modeled using creep data. Fatigue-loaded healing ligaments had shorter lifetime, greater steady-state strain rate and greater increase in strain at 0.8 h than creep-loaded healing ligaments. The actual fatigue lifetime was less than the predicted fatigue lifetime which was derived from time-dependent damage alone, indicating an important role for cycle-dependent damage mechanisms in healing ligaments during fatigue loading. Cyclic loading decreased lifetime and increased strain rate and strain prior to rupture compared to static loading in healing ligaments. These findings suggest that, after a ligament injury, more care should be taken when exercises result in cyclic loading rather than static loading of the healing ligament even at functional stresses.

scholarly journals High cycle (fatigue) resistance of reinforced concrete beams with lap splices

1993 ◽  
Vol 20 (4) ◽  
pp. 642-649 ◽  
Author(s):  
Telvin Rezansoff ◽  
James A. Zacaruk ◽  
Jeffrey G. Afseth
Keyword(s):  
Static Loading ◽  
Fatigue Loading ◽  
Reinforced Concrete Beams ◽  
Bond Failure ◽  
Lap Splices ◽  
Lap Splice ◽  
Major Variable ◽  
Effective Depth ◽  
High Degree ◽  
Tension Loading

Full-scale specimens were tested so that lap spliced bottom bars were subjected to cyclic tension loading. The major variable was the degree of transverse confining reinforcement (stirrups) provided along the lap. Lap splices were confined either with the maximum transverse reinforcement deemed to be effective for static loading, permitting the use of shorter lap splice lengths, or with stirrups spaced at approximately one half the effective depth of the beam, requiring the use of a longer lap length. Failure in all specimens with heavier stirrups (shorter laps) occurred with fatiguing of the reinforcing steel, showing fatigue resistances that were comparable with the results for continuous bars tested in flexure. With the lighter (nominal) stirrups, fatigue loading usually produced a splice failure, where the confining concrete split away from the lap in a typical bond failure after fewer load cycles. For comparable bond resistance under static loading, the beams with the heavier stirrup confinement along a shorter lap length were superior under fatigue loading. As previously shown with low cycle, high intensity reversal (seismic) loading, the current study shows that it is prudent to provide a high degree of transverse reinforcing confinement to lap splices that are subjected to fatigue loading. Key words: concrete, reinforcement, lap splices, fatigue, bond, beams, confinement, stirrups, tension.

Bond Strength and Damage of Long Rebar Anchored in HPC under Static and Fatigue Loading

2006 ◽  
Vol 324-325 ◽  
pp. 867-870 ◽  
Author(s):  
Jian Zhuang Xiao ◽  
Chuan Zeng Zhang ◽  
Horst Falkner
Keyword(s):  
Static Loading ◽  
High Strength Steel ◽  
High Performance ◽  
High Performance Concrete ◽  
High Strength ◽  
Fatigue Loading ◽  
Element Analysis ◽  
Bond Behaviour ◽  
Steel Bar ◽  
Reinforcement Bar

This paper presents an experimental study on the anchorage behaviour of long high-strength steel rebars embedded in high-performance concrete (HPC) under both static loading and fatigue loading. The HPC was designed as C60 with its cube compressive strength larger than 60 MPa, and the high-strength steel bar was adopted as HRB500 with its characteristic yield strength equals 500 MPa. Under 3×106 fatigue loading cycles and then followed by a monotonous static loading, the strain and the stress state of the reinforcement bar, and the bond stress between the concrete and the 700 mm-long bar were investigated. Based on the test results and the ANSYS finite element analysis, the bond behaviour between HPC and long high-strength steel bars is discussed.

Crack Growth Behavior of Aluminum Alloys Tested in Liquid Mercury

1986 ◽  
Vol 108 (1) ◽  
pp. 37-43 ◽  
Author(s):  
J. A. Kapp ◽  
D. Duquette ◽  
M. H. Kamdar
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Intensity Factor ◽  
Crack Growth ◽  
Static Loading ◽  
Fatigue Loading ◽  
Loading Conditions ◽  
Fixed Load

Crack growth rate measurements have been made in three mercury embrittled aluminum alloys each under three loading conditions. The alloys were 1100-0, 6061-T651, and 7075-T651. The loading conditions were fixed displacement static loading, fixed load static loading, and fatigue loading at two frequencies. The results showed that mercury cracking of aluminum was not unlike other types of embrittlement (i.e. hydrogen cracking of steels). Under fixed load static conditions no crack growth was observed below a threshold stress intensity factor (KILME). At K levels greater than KILME cracks grew on the order of cm/s, while under fixed displacement loading, the crack growth rate was strongly dependent upon the strength of the alloy tested. This was attributed to crack closure. In the fatigue tests, no enhanced crack growth occurred until a critical range of stress intensity factor (ΔKth) was achieved. The ΔKth agreed well with the KILME obtained from the static tests, but the magnitude of the fatigue growth rate was substantially less than was expected based on the static loading results. Observations of the fracture surfaces in the SEM suggested a brittle intergranular fracture mode for the 6061-T651 and the 7075-T651 alloys under all loading conditions. The fractographic features of the 1100-0 alloy under fixed load and fatigue loading conditions were also brittle intergranular. Under fixed displacement loading the cracks grew via a ductile intergranular mode.

scholarly journals The role of thermal activation in motion and force generation by molecular motors

2000 ◽  
Vol 355 (1396) ◽  
pp. 511-522 ◽  
Author(s):  
R. Dean Astumian
Keyword(s):  
Molecular Motors ◽  
Atp Hydrolysis ◽  
Force Production ◽  
Hand Model ◽  
Small Load ◽  
Wide Range ◽  
One Step ◽  
The One ◽  
Kinesin Molecule ◽  
Stochastic Properties

The currently accepted mechanism for ATP–driven motion of kinesin is called the hand–over–hand model, where some chemical transition during the ATP hydrolysis cycle stretches a spring, and motion and force production result from the subsequent relaxation. It is essential in this mechanism for the moving head of kinesin to dissociate, while the other head remains firmly attached to the microtubule. Here we propose an alternative Brownian motor model where the action of ATP modulates the interaction potential between kinesin and the microtubule rather than a spring internal to the kinesin molecule alone. In this model neither head need dissociate (which predicts that under some circumstances a single–headed kinesin can display processive motion) and the transitions by which the motor moves are best described as thermally activated steps. This model is consistent with a wide range of experimental data on the force–velocity curves, the one ATP to one–step stoichiometry observed at small load, and the stochastic properties of the stepping.

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