JP2005214698A - Method for measuring internal stress of composite structure material due to radioactive diffraction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein there is nothing in an example for measuring the residual stress state related to a high strength material such as a nano composite material like high strength SIC or a bonding material thereof because an experiment is difficult or an experimental technique is not established. <P>SOLUTION: An X-ray stress measuring method capable of measuring the stress of the surface of a sample (-about 20 mm) and a neutron stress measuring method capable of measuring the stress in the sample (about several 10 mm) are combined by noticing a neutron diffraction method capable of fractionating the lattice diffraction pattern at every name phase of the deep layer of the material or high intensity X-rays to measure the three-dimensional stress distribution in the material in each of fine structural phases to clear the effect of the residial stress exerted on the material strength or destruction mechanism of high strength reaction sintered SiC. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of simultaneously measuring internal stresses of a composite structure material such as a nanocomposite material such as high-strength SiC or a bonding material thereof by radiation diffraction. The present invention is a method for simultaneously measuring the internal stress of a nanocomposite material such as SiC used in general industrial fields, nuclear power, space / aviation, and the like, and a composite structure material such as a bonding material thereof. In the present invention, the X-ray can measure the strain due to the residual stress in the sample surface and the neutron beam due to the residual stress in the crystal lattice inside the sample. By simultaneously measuring these, it is possible to obtain the stress information of the whole substance. It is.

  Diffraction structure analysis and residual stress evaluation of various materials using neutron rays and synchrotron radiation X-rays have been performed, but composite structures such as nano-composite materials such as high-strength SiC and their bonding materials are simultaneously and three-dimensional. There was no method that could be analyzed analytically.

  More than 2.5 times the conventional product strength (bending strength: 1200MPa) by using a silicon carbide material that has recently been manufactured by vacuum reaction sintering method in which molten SiC is poured into carbon powder and aggregate SiC particles (αSiC) without pressure High-strength SiC ceramics have emerged, and the prospect of joint technology development using the same reactive sintering method for the same material is also emerging.

  The reason for the development of high-strength in this material is due to the nano-fine structure composed of silicon carbide (βSiC) produced by the reaction of molten silicon and carbon powder and unreacted free silicon (Si). Conceivable. That is, as shown in FIG. 1, high-strength SiC is a composite material composed of three phases of αSiC, βSiC, and Si. Each of the high-strength SiC is generated by interphase residual stress and external force generated due to the difference in thermal expansion coefficient between phases. The complex stress state of the phase is expected to affect the crack propagation behavior and fracture mechanism, which is considered to be a factor that has a unique material strength.

  Therefore, it is expected that the material strength of this material can be further improved by clarifying the relationship between these interfacial stress analysis and fracture mechanism and adding a new nanostructure that can relieve these stresses. In a nanocomposite material such as SiC and its bonding material, the inside of the material is in a complex triaxial stress state (three-dimensional stress generated inside the object received from the outside), and these generated stresses are expressed in each phase (αSiC, Although it is assumed that βSiC and Si phase) each share high strength, the surface of the sample is changed from a triaxial stress state to a plane stress state (a plane acting inside the object that receives external force). The stress component state is very complex in the material, and it affects the specific material strength and fracture mechanism of the material. It is considered that you are.

  For this reason, there are no examples in which the residual stress state relating to such a high-strength material has been measured so far because the difficulty of the experiment and the experimental method have not been established.

  On the other hand, in the present invention, neutron diffraction using a neutron diffraction apparatus (FIG. 2) that can separate the lattice diffraction patterns for each nanophase (for example, αSiC phase, βSiC phase, and further Si phase) of these material deep layers. X-ray stress measurement method capable of measuring the stress on the sample electrode surface (about 20 μm) by paying attention to the high-intensity X-ray (radiation light X-ray) of the method and synchrotron radiation stress measurement device (FIG. 3), Combined with the neutron stress measurement method that can measure the stress inside the sample (several tens of millimeters), the three-dimensional stress distribution inside the sample is measured in each microstructure phase, and the material strength and fracture mechanism of high-strength reactive sintered SiC Confirmation data was obtained that could clarify the effect of residual stress on.

  According to the present invention, the microstructure of the composite structure material and the stress distribution at the time of stress loading can be measured three-dimensionally, and the structure can be prevented from being broken in advance, and it is useful for increasing the strength of the material.

  The specific method of the present invention is as follows. (1) First, a neutron type high-resolution powder diffractometer (HRPD) and a synchrotron radiation stress measuring device (RESA) installed in the experimental nuclear reactor JRR-3M of the Japan Atomic Energy Research Institute are used. . Using HRPD, a powder diffraction pattern of a powdered high-strength ceramic material as shown in FIG. 3 is measured. From this measurement result, the constituent phases of the high-strength ceramic material are clarified and the lattice plane spacing of each phase in an unstrained state is grasped. In addition, the elastic constant and Poisson's ratio for each diffraction surface of the high-strength ceramic material are measured using RESA. These basic data are used for the following residual stress evaluation.

  (2) Next, the three-dimensional residual stress distribution of the high-strength ceramic material, the general reaction sintered ceramic material, and the powder sintered ceramic material is measured using a neutron stress measurement method. First, the residual stress generation mechanism of such a material is clarified by comparing the residual stress state of each phase of the high-strength ceramic material. Next, the influence of the residual stress on the material strength of the high-strength ceramic material is examined from the relationship between the stress state and the material strength of three kinds of materials having greatly different material strengths.

  (3) Finally, the stress change of each phase of the high strength ceramic material subjected to uniaxial tensile load (when external force works only from one direction) is measured, and the stress share of each phase with respect to the mechanical load stress is calculated. To grasp.

  In other words, a plurality of bending test pieces of high-strength ceramic material are prepared, and the three-dimensional residual stress distribution for all the test pieces (the stress that remains in the object three-dimensionally even if this external force is removed once the external force is applied) ). For all specimens, the bending strength is measured by a four-point bending load test to identify the starting point of fracture. From the relationship between the residual stress state near the starting point of fracture and the bending strength of each specimen, the residual stress on the material strength is measured. Clarify the impact.

And, from the relationship between the stress burden of each phase, the general bending strength of each phase, and the bending strength of high-strength ceramic materials, it is possible to identify the phase that is the starting point of fracture and clarify the cause of high strength development. .
As described above, by measuring the three-dimensional interphase stress distribution of high-strength ceramics using neutrons, it is possible to grasp the residual stress state generated in each phase and the stress burden of each phase accompanying external load, and based on these information By clarifying the effects of residual stress on the material strength and fracture mechanism of high-strength ceramics, we can expect further enhancement of the strength of this material and expansion of the neutron application range.

  Acquisition of diffraction patterns from each phase required for stress sharing analysis of nanocomposite materials such as high-strength SiC and the nanocomposite structure (αSiC, βSiC, and Si phase) of the joint material, which is the key to the research of the present invention Has already been completed in a preliminary test by the neutron diffraction method, revealing that diffraction patterns of SiC and Si phases and their individual recognition are possible (FIG. 4). That is, as shown in FIG. 4, the difference in diffraction pattern from αSiC, βSiC, and free Si in the microstructure of high-strength reaction-sintered SiC can be distinguished. Since the tissue lattice is distorted, the position of each diffraction pattern changes. Based on the information, it is possible to analyze the ratio of stress sharing of each tissue.

  On the other hand, because αSiC and βSiC diffraction lines initially overlap, stress evaluation is possible for αSiC because there are independent diffraction lines, but stress evaluation is difficult because there is no independent peak in βSiC. Met. Therefore, the peak positions of each diffraction line were examined using αSiC and βSiC lattice constants in the JCPDS (standard specification) powder diffraction database. As a result, the difference is about 0.1 ° to 0.3 °, but in neutron stress measurement, since the Gaussian approximation method is used as the peak position determination method, if the peaks overlap even if the peaks overlap, It was found that the diffraction angle can be determined.

It is a figure which shows that the microstructure of high intensity | strength reaction sintered SiC is comprised from the nanocomposite structure of (alpha) SiC, (beta) SiC, and free Si. It is a figure which shows that the lattice distortion information inside a structure can be measured with a neutron diffraction apparatus. It is a figure which shows that the lattice distortion information on the surface of a structure can be measured with a synchrotron radiation stress measuring device. It is a figure which shows the difference of each diffraction pattern from (alpha) SiC, (beta) SiC, and free Si of the microstructure of high intensity | strength reaction sintering SiC.

Claims (7)

  A method of simultaneously measuring the distortion of the structural lattice of a composite structural material by diffractometry of neutron rays and synchrotron radiation X-rays.   The method according to claim 1, wherein the internal stress of a composite structural material composed of high-strength microstructure ceramics composed of SiCα particles, free Si and SiCβ particles is measured.   The method according to claim 1, wherein the residual stress is evaluated by three-dimensionally measuring the structural distortion of the inside and the surface of the composite structural material with neutron rays and synchrotron radiation X-rays.   The method according to claim 2, wherein the residual stress at the joint between the high-strength microstructure ceramics composed of SiCα particles, free Si and SiGβ particles is measured.   Combining the synchrotron radiation X-ray stress measurement method capable of measuring the stress on the extreme surface of a composite structural material with the neutron stress measurement method capable of measuring the material or internal stress, the three-dimensional stress distribution inside the material can be determined for each microstructure phase. A method of measuring residual stress exerted on the strength and fracture mechanism of the material.   The method according to claim 5, wherein the composite structural material comprises high-strength microstructure ceramics composed of SiCα particles, free Si and SiCβ particles. (1) Measure the powder diffraction pattern of the high-strength ceramic material powdered using a neutron diffractometer, clarify the constituent phases of the high-strength ceramic material from the measurement results, and the lattice plane spacing of each phase in the unstrained state Measure the elastic constant and Poisson's ratio for each diffraction surface of the high-strength ceramic material using a synchrotron radiation stress measurement device, and obtain these measurement results as basic data.
(2) Three-dimensional residual stress distribution of high-strength ceramic materials, general reaction sintered ceramic materials, and powder sintered ceramic materials is measured using neutron stress measurement method. Considering the effect of residual stress on the material strength of high-strength ceramic materials from the relationship of material strength,
(3) Finally, the stress change of each phase of the high-strength ceramic material subjected to uniaxial tensile load is measured, the stress share of each phase with respect to the mechanical load stress is measured, and the relationship between the bending strength of the high-strength ceramic material It is possible to identify the phase that is the starting point of fracture and clarify the cause of high strength, and to develop a material with higher strength by changing the material composition and the structure to remove the cause. A method of measuring the residual stress on the strength and fracture mechanism of ceramic materials.

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