Nondestructive Identification of Inhomogeneous Residual Stress State in Deformable Bodies on the Basis of the Acoustic Sounding Method

Analysis of inhomogeneous residual stress (RS) fields in bodies is one of the major problems of the mechanics of deformable solid bodies. In the present research the new techniques of identification of inhomogeneous RS in bodies are developed on the basis of surface displacement measurement in a set of points under vibrating sounding load. Corresponding nonlinear ill-posed inverse problems (IP) are formulated and solved numerically by means of iterative regularization. Based on computational experiments, the most advantageous sounding load types and frequency ranges providing the best reconstruction accuracy are revealed. The examples for a cantilever, a plate, a layer, and a cylindrical tube are presented.

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Process Signature for Laser Hardening

Metals ◽

10.3390/met11030465 ◽

2021 ◽

Vol 11 (3) ◽

pp. 465

Author(s):

Friedhelm Frerichs ◽

Yang Lu ◽

Thomas Lübben ◽

Tim Radel

Keyword(s):

Residual Stress ◽

Phase Transformation ◽

Heating Time ◽

Temperature Gradients ◽

Laser Hardening ◽

Thermal Loads ◽

Zero Crossing ◽

Residual Stress State ◽

Stress Curve ◽

Process Signature

During many manufacturing processes for surface treatment of steel components heat will be exchanged between the environment and the workpiece. The heat exchange commonly leads to temperature gradients within the surface near area of the workpiece, which involve mechanical strains inside the material. If the corresponding stresses exceed locally the yield strength of the material residual stresses can remain after the process. If the temperature increase is high enough additionally phase transformation to austenite occurs and may lead further on due to a fast cooling to the very hard phase martensite. This investigation focuses on the correlation between concrete thermal loads such as temperature and temperature gradients and resulting modifications such as changes of the residual stress, the microstructure, and the hardness respectively. Within this consideration the thermal loads are the causes of the modifications and will be called internal material loads. The correlations between the generated internal material loads and the material modifications will be called Process Signature. The idea is that Process Signatures provide the possibility to engineer the workpiece surface layer and its functional properties in a knowledge-based way. This contribution presents some Process Signature components for a thermally dominated process with phase transformation: laser hardening. The target quantities of the modifications are the change of the residual stress state at the surface and the position of the 1st zero-crossing of the residual stress curve. Based on Finite Element simulations the internal thermal loadings during laser hardening are considered. The investigations identify for the considered target quantities the maximal temperature, the maximal temperature gradient, and the heating time as important parameters of the thermal loads.

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Influence of Steel Grain Size on Residual Stress in Grinding Processing

Materials Science Forum ◽

10.4028/www.scientific.net/msf.638-642.2389 ◽

2010 ◽

Vol 638-642 ◽

pp. 2389-2394 ◽

Cited By ~ 3

Author(s):

Masahide Gotoh ◽

Katsuhiro Seki ◽

M. Shozu ◽

Hajime Hirose ◽

Toshihiko Sasaki

Keyword(s):

Mechanical Properties ◽

Residual Stress ◽

Grain Size ◽

Stress State ◽

Mechanical Grinding ◽

Fine Grained ◽

Residual Stress State ◽

Analysis Methods ◽

Average Grain Size ◽

Fine Grained Steels

The fine-grained rolling steels NFG600 and the conventional usual rolling steels SM490 were processed by sand paper polishing and mechanical grinding to compare the residual stress generated after processing. The average grain size of NFG600 and SM490 is 3 μm and 15μm respectively. Therefore improvement of mechanical properties for such fine-grained steels is expected, it is important to understand the residual stress state of new fine-grained materials with processing. In this study, multi axial stresses of two kinds of specimens after polishing and grinding were measured by three kinds of analysis methods including cos-ψ method. As a result, as for σ33, the stress of NFG was compression, though that of SM490 was tension.

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About Residual Stress State of Castings: The Case of HPDC Parts and Possible Advantages through Semi-Solid Processes

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.327.272 ◽

2022 ◽

Vol 327 ◽

pp. 272-278

Author(s):

Elisa Fracchia ◽

Federico Simone Gobber ◽

Claudio Mus ◽

Yuji Kobayashi ◽

Mario Rosso

Keyword(s):

Residual Stress ◽

Stress State ◽

Residual Stresses ◽

Casting Process ◽

Ray Method ◽

Premature Failure ◽

Thin Walls ◽

Residual Stress State ◽

Semi Solid ◽

Pressure Die Casting

Nowadays, one of the most crucial focus in the aluminium-foundry sector is the production of high-quality castings. Mainly, High-Pressure Die Casting (HPDC) is broadly adopted, since by this process is possible to realize aluminium castings with thin walls and high specific mechanical properties. On the other hand, this casting process may cause tensile states into the castings, namely residual stresses. Residual stresses may strongly affect the life of the product causing premature failure of the casting. Various methods can assess these tensile states, but the non-destructive X-Ray method is the most commonly adopted. Namely, in this work, the residual stress analysis has been performed through Sinto-Pulstec μ-X360s. Detailed measurements have been done on powertrain components realized in aluminium alloy EN AC 46000 through HPDC processes to understand and prevent dangerous residual stress state into the aluminium castings. Furthermore, a comparison with stresses induced by Rheocasting processes is underway. In fact, it is well known that Semi-Solid metal forming combines the advantages of casting and forging, solving safety and environmental problems and possibly even the residual stress state can be positively affected.

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Analysis of Residual Stress State in Thermal Barrier Coatings

Fracture Mechanics of Ceramics ◽

10.1007/978-1-4757-4019-6_13 ◽

2002 ◽

pp. 169-178 ◽

Cited By ~ 1

Author(s):

T.-J. Chuang ◽

E. R. Fuller

Keyword(s):

Residual Stress ◽

Stress State ◽

Thermal Barrier Coatings ◽

Thermal Barrier ◽

Barrier Coatings ◽

Residual Stress State

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Effects of deposition temperature and thermal cycling on residual stress state in zirconia-based thermal barrier coatings

Surface and Coatings Technology ◽

10.1016/s0257-8972(99)00341-2 ◽

1999 ◽

Vol 120-121 ◽

pp. 103-111 ◽

Cited By ~ 115

Author(s):

V. Teixeira ◽

M. Andritschky ◽

W. Fischer ◽

H.P. Buchkremer ◽

D. Stöver

Keyword(s):

Residual Stress ◽

Stress State ◽

Thermal Cycling ◽

Thermal Barrier Coatings ◽

Deposition Temperature ◽

Thermal Barrier ◽

Barrier Coatings ◽

Residual Stress State

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Analysis of the Influence of Surface Modifications on the Fatigue Behavior of Hot Work Tool Steel Components

Materials ◽

10.3390/ma14237324 ◽

2021 ◽

Vol 14 (23) ◽

pp. 7324

Author(s):

Thomas Wild ◽

Timo Platt ◽

Dirk Biermann ◽

Marion Merklein

Keyword(s):

Residual Stress ◽

Stress State ◽

Surface Integrity ◽

Fatigue Behavior ◽

Hot Forging ◽

Surface Modifications ◽

Bending Test ◽

Fatigue Properties ◽

Machining Processes ◽

Residual Stress State

Hot work tool steels (HWS) are widely used for high performance components as dies and molds in hot forging processes, where extreme process-related mechanical and thermal loads limit tool life. With the functionalizing and modification of tool surfaces with tailored surfaces, a promising approach is given to provide material flow control resulting in the efficient die filling of cavities while reducing the process forces. In terms of fatigue properties, the influence of surface modifications on surface integrity is insufficiently studied. Therefore, the potential of the machining processes of high-feed milling, micromilling and grinding with regard to the implications on the fatigue strength of components made of HWS (AISI H11) hardened to 50 ± 1 HRC was investigated. For this purpose, the machined surfaces were characterized in terms of surface topography and residual stress state to determine the surface integrity. In order to analyze the resulting fatigue behavior as a result of the machining processes, a rotating bending test was performed. The fracture surfaces were investigated using fractographic analysis to define the initiation area and to identify the source of failure. The investigations showed a significant influence of the machining-induced surface integrity and, in particular, the induced residual stress state on the fatigue properties of components made of HWS.

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