Thermo‐mechanical fatigue life assessment of hot forging die steel

Berti, Guido; Monti, Manuel

doi:10.1111/j.1460-2695.2005.00940.x

Cited by 33 publications

(19 citation statements)

References 8 publications

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“…Design of experiment (DoE) techniques were used in designing and analysing the experimental programme. A TMF life assessment model, based on the experimental data and using response surface methodology, has been discussed by the authors in previous papers 6,10 …”

Section: Methodsmentioning

confidence: 99%

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Improvement of life prediction in AISI H11 tool steel by integration of thermo‐mechanical fatigue and creep damage models

Berti

Monti

2009

Fatigue Fract Eng Mat Struct

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A B S T R A C T In hot forging operations, the die surfaces and the nearest surface layers of the die undergo mechanical and thermal cycles which significantly influence their service life. The real thermal and mechanical cycles have been previously investigated in forging plants by measurements and numerical simulation, and a reasonable variation window of process parameters has been determined. A new simulative test applied to AISI H11 hot working die steel has been used to generate failure data in conditions similar to those of the forging dies, but under a more controlled and economical method. Fracture surfaces of specimens for different tests observed by scanning electron microscopy (SEM) indicate that both thermo-mechanical fatigue (TMF) and creep phenomena can be considered to be main damage mechanisms and their contribution to the failure differs as testing conditions vary. As a result of the experiments, the failure is affected by both thermo-mechanical cycle and resting time at high temperature. Therefore, the authors developed a new lifetime prediction model obtained by combining the damage evolution laws, at each cycle, for pure creep and pure TMF. This combination was based on the linear accumulation rule. The damage evolution law for pure creep is obtained by modifying Rabotnov's law in order to suit the case of actual hot forging cycles, where temperature and stress vary widely. The damage evolution law for pure TMF is based on a generalization of the Wöhler-Miner law. This law is modified in order to take into account the presence of thermal cycle and thermal gradient. Comparison between the experimental cycles to failure and the predicted ones was performed using tests excluded in the determination of the coefficients. The conclusion was that the accuracy of prediction appears to be quite good and that the linear accumulation and interaction of TMF and creep is confirmed.Keywords creep damage; creep and thermo-mechanical fatigue interaction; forging die; life prediction; thermo-mechanical fatigue damage. N O M E N C L A T U R EA 0 , r = creep damage coefficients for the material b = mean stress coefficient D C = creep damage at time t D F = fatigue damage k = coefficient relevant to the damage rate M 0 = coefficient that depends on the cumulative damage effects N C = predicted number of cycles to fracture in pure creep N F = predicted number of cycles to fracture in pure thermo-mechanical fatigue N RE = experimental number of cycles to failure N RP = predicted number of cycles to failure (creep + TMF) R = stress ratio

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Section: Methodsmentioning

confidence: 99%

“…For these reasons the authors developed a new testing procedure and equipment able to apply the processing conditions of industrial forging to specimens representing a small part of the die 5,6 …”

Section: Introductionmentioning

confidence: 99%

Improvement of life prediction in AISI H11 tool steel by integration of thermo‐mechanical fatigue and creep damage models

Berti

Monti

2009

Fatigue Fract Eng Mat Struct

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“…Analysis of this chart makes it possible to state consistency of measurement results pertaining to the forging and die insert (material accretion on forging 220 mm 3 , loss on insert 236 mm 3 ). Based on the shape of the curve, a visible trend in the form of a stable wear process up to approx.…”

Section: Resultsmentioning

confidence: 99%

Wear Analysis of Die Inserts in the Hot Forging Process of a Forked Type Forging Using Reverse Scanning Techniques

Dworzak¹,

Hawryluk²,

Ziemba³

2017

Adv. Sci. Technol. Res. J.

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This article presents a wear analysis of die inserts used in the hot forging process of a forked forging (yoke), an element applied in steering systems of passenger vehicles. Studies involved the application of an original reverse scanning method intended for rapid and reliable wear analysis of forging tools (with complicated shape) affording easy assessment without the need to dismount tools from the forging unit. The developed method involves analysis of progressive wear of forging tools based on measurements (scanning) of forgings periodically collected from the process and constitutes a useful tool for measurement and testing. As the authors' earlier works have demonstrated, the proposed new approach to analysis of tool wear with the application of reverse 3D scanning has proven successful in multiple instances in the case of axially symmetrical objects. The presented results of studies indicate that it is possible to utilize the expanded method to analyze the lifetime of forging tools, including tools with complex geometry. Application of the reverse scanning method allows for continuous and practical monitoring of the condition of forging tools over the course of the forging process and should have a positive impact on improving production output and reducing production costs.

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“…Oudin and Rezai-Aria [7,8] carried out strain-controlled fatigue testes with the hot work steel X38CrMoV5, while the specimens were simultaneously loaded thermally and mechanically. Stress-controlled fatigue tests on the same steel grade were carried out by Berti and Monti [9] in order to characterise its thermomechanical fatigue behaviour. Within the framework of this experimental investigation the specimens were cyclically heated and cooled at a high speed, whereas plastic strains, as they appear in low cycle fatigue, were not considered.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigations on the fatigue failure of forging tools due to thermo-mechanical cyclic loading

et al. 2010

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During service hot forging dies are exposed to a combination of cyclic thermo-mechanical, tribological and chemical loads. Besides abrasive and adhesive wear on the die surface, fatigue crack initiation with subsequent fracture is one of the most frequent cause of failure. Fatigue cracks in forging dies are caused by local elasto-plastic strains due to cyclic mechanical and thermal loads. Aiming at a reduction of tool and production costs of forgings, tool life extension is necessary. In order to reach this goal, process design and process optimisation are currently done with the help of the finite element analysis (FEA). An integral part of this procedure is the tool design based upon fatigue life maximisation of forging dies in the Low-Cycle-Fatigue (LCF) region. Within the framework of this research the material fatigue damage of a forging die due to cyclic thermo-mechanical loads is analysed based on FEA process simulations. Besides this a material model which considers cyclic elasto-plastic material behaviour was used to describe the constitutive behaviour of the forging dies. The results of a fatigue life damage analysis applied to an industrial forging process in which the lower die shows a clear fatigue crack initiation. The crack initiation sites predicted with the FEA process simulations agree with the ones observed on the real die component.

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Thermo‐mechanical fatigue life assessment of hot forging die steel

Cited by 33 publications

References 8 publications

Improvement of life prediction in AISI H11 tool steel by integration of thermo‐mechanical fatigue and creep damage models

Improvement of life prediction in AISI H11 tool steel by integration of thermo‐mechanical fatigue and creep damage models

Wear Analysis of Die Inserts in the Hot Forging Process of a Forked Type Forging Using Reverse Scanning Techniques

Numerical investigations on the fatigue failure of forging tools due to thermo-mechanical cyclic loading

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