Bernd Eigenmann

Determination of residual stresses in ceramics and ceramic-metal composites by x-ray diffraction methods

Abstract A survey is given of the research done in the field of X-ray residual stress determinations on ceramics and ceramic-metal composites. The principles of X-ray residual stress determinations are described and helpful hints are given for X-ray stress determinations in ceramic materials. X-ray elastic constants of common ceramics are included. A number of interesting examples of X-ray residual stress determinations on ceramics and ceramic-metal composites are presented.

Determination of inhomogeneous residual stress states in surface layers of machined engineering ceramics by synchrotron x-rays

Abstract Ceramic components for engineering applications must in most cases be ground after sintering in order to achieve a sufficient precision of the final dimensions as well as a sufficient surface quality. Since the surface layers influenced by grinding are very shallow, the determination of near-surface grinding residual stresses and their gradients within the penetration depth of the X-rays is difficult. In this paper, a procedure is applied which allows the investigation of residual stress states in ground ceramic surfaces by X-ray diffraction using synchrotron radiation and parallel beam optics. Three different ceramics were examined. In all cases, compressive residual stresses were found in the surface layers of the materials investigated. The magnitudes and gradients of the grinding residual stresses markedly depend on the grinding parameters and on the resulting mechanism of materials removal.

Experimental and theoretical investigation of the residual stress distribution in brazed ceramic-steel components

Abstract The residual stress state of brazed ceramic-steel components was investigated by neutron diffraction experiments. In addition, X-ray residual stress measurements were performed at the surface of the specimens. The neutron data show clear evidence of plastic deformation in the steel during cooling from the brazing temperature. Finite element calculations modelling the temperature dependent elastic-plastic behavior of the materials correspond very well to the observed residual stress distributions.

Fracture mechanical evaluation of the effects of grinding residual stresses on bending strength of ceramics

Abstract In order to evaluate the effects of grinding residual stresses on bending strengths, the near-surface distributions of grinding residual stresses of differently ground Al 2 O 3 samples were determined non-destructively by means of depth-resolved X-ray residual stress analyses. It was found that the compressive surface residual stresses increase with increasing single grain cutting depth. In parallel, an increase of the four-point bending strength of the samples was observed. Its magnitude was compatible with the increase of bending strengths expected from the residual stress intensity of the grinding residual stresses acting on the failure critical defects.

Residual Stresses in Brazed Joints of Cemented Carbide and Steel with Complex Geometry

Joining of cemented carbide cutting edges and tool bodies of steel by brazing creates residual stresses in the joints due to the thermal mismatch of the components during cooling from brazing temperature. Such residual stress states can cause early failure of the tools by cracking of the cutting edge under quasi-static or cyclic loading conditions. In order to characterize the residual stress states occurring in brazed cutting tools of steel and cemented carbide, cemented carbide cutting edges were brazed into steel bodies of different types of steel. A combination of numerical and experimental methods was applied for the analysis of the resulting residual stress states. The influence of the phase transformation behavior of the steel body on the residual stress development was demonstrated. The failure behavior of the joints was explained by superposition of residual and loading stresses.

X-Ray Stress Determination in Ceramics and Ceramic-Metal Composites

Ceramics belong to the oldest materials used by mankind. Since about two decades, however, worldwide considerable efforts are made to tailor advanced types of ceramics to fulfill special chemical, thermal, mechanical, and/or electrical requirements. In this context, the residual stress states of ceramics and ceramic-metal-composites become of increasing interest. It has been demonstrated for instance that compressive surface residual stresses can improve the strength of ceramic components under certain loading conditions [1 - 8]. Consequently, reliable procedures are necessary to measure the residual stress states of advanced ceramics. Today, for this purpose, the sin2 Ψ -method of X-ray stress analysis [9] is the most appropriate method. In this article, special features of X-ray stress determinations on ceramics and ceramic-metal-composites are summarized, and selected examples are presented to characterize the actual knowledge in this research field.

Brazing residual stresses in components of different metallic materials

Abstract Brazing residual stresses are a consequence of differences between the thermal expansion coefficients of the brazed partners and the solder. In this study, components of copperr, austenitic steel and a nickel-base alloy brazed on ferritic steel are investigated. Using simplifying assumptions, the resulting stress states are estimated and compared with experimental X-ray stress analyses and curvature measurements. This gives clear evidence of complicated inhomogeneous plastic deformations in the compounds, which occur during cooling down from the brazing temperature. In addition, X-ray residual stress determinations allow a quantitative description to be given of edge effects in the compounds examined.

Röntgenographische Bestimmung elastischer Spannungen

Die rontgenographische Spannungsmessung (RSM) gewann im Laufe ihrer Entwicklung fur die verschiedensten materialwissenschaftlichen und materialtechnischen Gebiete erhebliche Bedeutung. Sie fand bei naturwissenschaftlichen Fragestellungen ebenso Anwendung wie bei ingenieurwissenschaftlichen. Nachfolgend wird deshalb auf eine fachspezifische Unterteilung verzichtet und die chronologische Entwicklung dieser Disziplin unter Herausstellung wichtiger Untersuchungen und Forschungsergebnisse fur 5 abgrenzungswurdig erscheinende Zeitabschnitte beschrieben. Das Gebiet der RSM ist durch die bibliographischen Arbeiten von Isenburger (1949, 1953) und besonders J. Hauk (1976, 1982, 1987, 1990, 1992, 1993, 1994) nahezu vollstandig erfast.

Residual Stresses in Brazed Ceramic-Metal Compounds

The residual stresses in metal-ceramic compounds were investigated by X-ray and neutron diffraction. The neutron data show clear evidence for plastic flow in the steel so that elastic models cannot be expected to give a satisfactory explanation of the residual stress state. Finite-element calculations taking into account the temperature dependent elastic-plastic behavior of the materials reproduce the experimental results very well.