Experimental investigation of cyclic plasticity continuum damage evolution in an engineering component subjected to thermal loading

1993 ◽  
Vol 28 (4) ◽  
pp. 263-272 ◽  
Author(s):  
F P E Dunne ◽  
D B Puttergill ◽  
D R Hayhurst ◽  
Q J Mabbutt
Keyword(s):  
Grain Boundaries ◽  
Thermal Loading ◽  
Cyclic Plasticity ◽  
Test Facility ◽  
Thermal Shock Test ◽  
Continuum Damage ◽  
Loading Test ◽  
Cyclic Thermal Loading ◽  
Slip Bands ◽  
Persistent Slip Bands

A thermal shock test facility is designed and built to enable to enable a copper model slag tap component to be tested under cyclic thermal loading conditions. Infra-red line heaters and pumped cooling water are used to impose temperature loading cycles on to the specimen. Accurate focussing of the line heaters using a two degree of freedom adjustment mechanism, enables a heating area of width 3 mm to be applied to the specimen. Both the heating and the cooling processes are controlled by a proportional, integral, and derivative feedback micro-processor controller. Specimen temperature fields are obtained using thermocouples, and specimen displacements and strains are measured using linear voltage displacement transducers and strain gauges. A cyclic thermal loading test is carried out for approximately 7150 cycles on a model slag tap component. The variations of specimen strains and displacements are recorded and compared with results obtained from a finite element viscoplastic damage analysis. Good agreement between the predicted and experimental results is obtained. Microstructural examination of the specimen reveals the development of persistent slip bands and micro-cracking at grain boundaries. This occurs at the regions of the specimen undergoing cyclic plasticity due to the imposed cyclic thermal loading. The experimental observations of cyclic plasticity damage formation in copper undergoing cyclic thermal loading indicates the suitability of the Continuum Damage Mechanics (CDM) theory to model the evolution of cyclic plasticity damage. The damage is characterized by the development of fields of micro-cracked grain boundaries due to the formation and interaction of persistent slip bands within the grains.

Approximate method for the analysis of components undergoing ratchetting and failure

1998 ◽  
Vol 33 (1) ◽  
pp. 55-65 ◽  
Author(s):  
J Lin ◽  
F P E Dunne ◽  
D R Hayhurst
Keyword(s):  
Approximate Method ◽  
Mechanical Loading ◽  
Thermal Loading ◽  
Cyclic Plasticity ◽  
Processing Unit ◽  
Computationally Efficient ◽  
Element Analysis ◽  
Cyclic Thermal Loading ◽  
Central Processing ◽  
Practical Design

An approximate method has been presented for the design analysis of engineering components subjected to combined cyclic thermal and mechanical loading. The method is based on the discretization of components using multibar modelling which enables the effects of stress redistribution to be included as creep and cyclic plasticity damage evolves. Cycle jumping methods have also been presented which extend previous methods to handle problems in which incremental plastic straining (ratchetting) occurs. Cycle jumping leads to considerable reductions in computer CPU (central processing unit) resources, and this has been shown for a range of loading conditions. The cycle jumping technique has been utilized to analyse the ratchetting behaviour of a multibar structure selected to model geometrical and thermomechanical effects typically encountered in practical design situations. The method has been used to predict the behaviour of a component when subjected to cyclic thermal loading, and the results compared with those obtained from detailed finite element analysis. The method is also used to analyse the same component when subjected to constant mechanical loading, in addition to cyclic thermal loading leading to ratchetting. The important features of the two analyses are then compared. In this way, the multibar modelling is shown to enable the computationally efficient analysis of engineering components.

What types of grain boundaries can be passed through by persistent slip bands?

2003 ◽  
Vol 18 (5) ◽  
pp. 1031-1034 ◽  
Author(s):  
Z. F. Zhang ◽  
Z. G. Wang ◽  
J. Eckert
Keyword(s):  
Grain Boundaries ◽  
Large Angle ◽  
Fatigue Cracking ◽  
Stress Axis ◽  
Slip Systems ◽  
Slip Bands ◽  
Persistent Slip Bands ◽  
Different Types ◽  
The Difference ◽  
Intergranular Fatigue Cracking

Three typical interactions of persistent slip bands (PSBs) with different types of grain boundaries (GBs) were investigated and analyzed in fatigued copper crystals. The results show that PSBs cannot transfer through all types of large-angle GBs, regardless of their orientation with respect to the stress axis. Secondary slip was often observed near the GBs, leading to strain incompatibility. When the slip systems of the two adjacent crystals are coplanar, the transmission of a PSB across a GB strongly depends on the slip directions of the two adjacent crystals. It was found that only the low-angle GBs can be passed through by PSBs, and accordingly they are insensitive to intergranular fatigue cracking. For a special copper bicrystal with coplanar slip systems, the ladderlike dislocation arrangements within the adjacent PSBs become discontinuous and a dislocation-affected-zone appears near the GB due to the difference in the slip direction of the two adjacent crystals. Therefore, the necessary conditions for the transmission of a PSB across a GB are that the neighboring grains have a coplanar slip system and identical slip directions.

Continuum damage based constitutive equations for copper under high temperature creep and cyclic plasticity

1992 ◽  
Vol 437 (1901) ◽  
pp. 545-566 ◽  
Keyword(s):  
Constitutive Equations ◽  
Damage Evolution ◽  
Thermal Loading ◽  
Evolution Equations ◽  
Experimental Results ◽  
Cyclic Plasticity ◽  
Nominal Composition ◽  
Cyclic Thermal Loading ◽  
Temperature Range ◽  
Good Agreement

Viscoplastic constitutive equations without damage for cast copper have been developed for cyclic mechanical and cyclic thermal loading over the temperature range 20-500 °C (nominal composition: 99.99 % Cu, 0.005 % O 2 , B.S. 10355-1037). Model predictions have been compared with experimental cyclic plasticity tests. Good agreement has been achieved. Creep and cyclic plasticity damage evolution equations have been developed. The effect of cyclic hardening on creep damage evolution has been modelled by introducing an internal variable to represent the state of material hardening. A creep cyclic plasticity interaction law has been proposed, and with the creep and cyclic plasticity damage evolution equations, has been combined with the viscoplastic constitutive equations to establish a unified material model for copper over the temperature range 20-500 °C. Predictions of lifetime and deformation history have been made for uni-axial test specimens subject to strain-controlled cyclic plasticity and ratchetting. Good agreement has been obtained with experimental results. The model has been validated for mechanical loading by predicting the response of uni-axial test specimens to strain-controlled cyclic plasticity with strain hold periods, and to combined strain-controlled cyclic plasticity tests with strain holds and ratchetting. The predictions compare well with experimental results. The model has been validated for cyclic thermal loading by predicting the response of uni-axial test specimens subjected to thermal loading cycles. Good comparisons have been achieved with experimental results.

Ex and in situ investigations on the role of persistent slip bands and grain boundaries in fatigue crack initiation

2017 ◽  
Vol 32 (23) ◽  
pp. 4276-4286 ◽  
Author(s):  
Heinz Werner Höppel ◽  
Philip Goik ◽  
Christian Krechel ◽  
Mathias Göken
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Grain Boundaries ◽  
Fatigue Crack Initiation ◽  
Slip Bands ◽  
Persistent Slip Bands ◽  
Image Position

Abstract

The initial fatigue crack

1957 ◽  
Vol 242 (1229) ◽  
pp. 189-197 ◽  
Keyword(s):  
Fatigue Crack ◽  
Grain Boundaries ◽  
Low Temperatures ◽  
Room Temperature ◽  
Fatigue Cracks ◽  
Slip Bands ◽  
Persistent Slip Bands

A discussion is given of the formation of persistent slip bands during cyclic stressing and their development into fatigue cracks. In copper and in aluminium at low temperatures fatigue cracks appear to be formed in this way; at room temperature in aluminium they may form also along grain boundaries.

Modelling of combined high-temperature creep and cyclic plasticity in components using continuum damage mechanics

1992 ◽  
Vol 437 (1901) ◽  
pp. 567-589 ◽  
Keyword(s):  
Finite Element ◽  
High Temperature ◽  
Damage Mechanics ◽  
Thermal Loading ◽  
Continuum Damage Mechanics ◽  
Stress Redistribution ◽  
Cyclic Plasticity ◽  
Solution Technique ◽  
Continuum Damage ◽  
Final State

A computer-based finite-element viscoplastic damage solver has been developed for the analysis of structural components subject to combined cyclic thermal and mechanical loading. The solver, which is based on continuum damage mechanics, is able to predict the combined evolution of creep and cyclic plasticity damage by solution of the combined boundary-initial value problem. The computational difficulties which arise due to the different timescales, associated with material behaviour at the different temperatures within a thermal field, have been overcome by the use of a normalization technique. The high computer demands associated with the detailed numerical solution of combined thermo-mechanical problems, which have prevented their use in design, have been overcome by the development of a novel ‘cycle jumping’ method which avoids repetitive calculations over those cycles in which the damage fields change insignificantly. Between the ‘jumps’ in the solution technique, the damage and the strain rate fields are coupled and hence allow stress redistribution. The finite-element solver has been used to successfully predict the high temperature behaviour of a slag tap component subjected to cyclic thermal loading generated by infrared heaters and water cooling ducts. The initiation of damage and micro-cracking has been found to occur early in the lifetime at approximately 3000 cycles adjacent to the cooling duct; and the propagation of failure zones has been found to stabilize at 60 000 cycles after which no further damage evolution occurs. A further development of the technique, which requires even less computer resource, is the ‘cycle leaping’ method which neglects the effect of stress redistribution over large numbers of cycles, by leaping from the first few cycles to the final state. With this method good predictions have been made of the fields of damaged and micro-cracked material in the final state of the slag tap component. The technique has potential for use at the early or conceptual stages of design.

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