Abstract: For measuring the stress history in a simple form, which is widely applicable to various types of structural materials which the elastic modulus is different from each other, a large number of calcite particles is embedded as a stress sensor in a cement-based composite material that can be elastically deformed after receiving an external. A twin-crystal density of the calcite particles is measured after an external force is applied to the composite material, to convert the twin-crystal density to a strain by an approximate formula set in terms of a strain ? (%) generated in the composite material and a twin-crystal density Dtw (lines/mm) of the calcite particles, and further to convert this strain to a stress by the elastic modulus of the composite material, whereby to estimate the history of stress and strain. The approximate formula between strain and twin-crystal density is independent of the modulus of the composite material and is used in a common form.

Abstract: It is an object to provide a stress history measurement method and a stress sensor by which the stress history of an object being measured can be measured easily with high accuracy over a wide stress measurement range. In the stress history measurement method, the stress history to which the object being measured has been subjected is measured on the basis of the ratio of twinned calcite particles after the object to be measured has been subjected to an external force, the object having a stress sensor embedded therein and capable of being deformed elastically when being subjected to the external force, the sensor including a number of calcite particles. The stress sensor is configured such that a number of calcite particles are hardened by a resin with adjacent particles kept in contact with each other.

Abstract: It is an object to provide a stress history measurement method and a stress sensor by which the stress history of an object being measured can be measured easily with high accuracy over a vide stress measurement range. In the stress history measurement method, the stress history to which the object being measured has been subjected is measured on the basis of the ratio of twinned calcite particles after the object to be measured has been subjected to an external force, the object having a stress sensor embedded therein and capable of being deformed elastically when being subjected to the external, force, the sensor including a number of calcite particles. The stress sensor is configured such that a number of calcite particles are hardened by a resin with adjacent particles kept in contact with each other.

Abstract: There are provided a method by which a stress history of an object can be measured with high reliability if the object, which has temporarily been elastically deformed upon receiving an external force, recovers from the elastic deformation, and a composite material containing cement as a main component, of which a stress history can be measured with high reliability without reducing the strength of the material itself and without breaking the structure. To achieve the above-mentioned advantages, the method includes the steps of: acquiring an initial value of a twin density for calcite particles contained in an object to be measured that is elastically deformable upon receiving an external force; and measuring a history of stresses received by the object to be measured on the basis of a difference from the initial value in respect of the twin density for the calcite particles after the object to be measured receives the external force.

Abstract: The objective of the present invention is to provide a method for producing a calcite single crystal which is appropriately fine in a large scale with no difficulty. The method for producing a calcite single crystal according to the present invention is characterized in comprising the steps of mixing raw material calcium carbonate with an ammonium nitrate aqueous solution to obtain a raw material mixed liquid, wherein pH of the ammonium nitrate aqueous solution is not less than 7.0 and not more than 8.0, a concentration of the ammonium nitrate aqueous solution is not less than 2 M, and a concentration of calcium carbonate in the raw material mixed liquid is not less than 4 g/L and not more than 16 g/L; heating the raw material mixed liquid at not less than 125° C.; and then gradually cooling the raw material mixed liquid.

Abstract: There are provided a method by which a stress history of an object can be measured with high reliability if the object, which has temporarily been elastically deformed upon receiving an external force, recovers from the elastic deformation, and a composite material containing cement as a main component, of which a stress history can be measured with high reliability without reducing the strength of the material itself and without breaking the structure. To achieve the above-mentioned advantages, the method includes the steps of: acquiring an initial value of a twin density for calcite particles contained in an object to be measured that is elastically deformable upon receiving an external force; and measuring a history of stresses received by the object to be measured on the basis of a difference from the initial value in respect of the twin density for the calcite particles after the object to be measured receives the external force.