Method and apparatus for estimating life expectancy of mechanical structures

An apparatus for estimating a life expectancy of a mechanical structure to which a number of repeated loads is applied, said mechanical structure being made of a material and having a surface, comprising:

• means for detecting a length dimension of cracks formed in the surface of the structure within a zone area of the surface of the structure, said means for detecting including means for detecting and producing data indicating a length dimension of cracks in each of a plurality of sampling area located within said zone area;
• means receiving said crack length dimension data for determining and producing data representative of a length of a greatest length crack from within each of said sampling areas;
• means receiving said greatest length crack data from within each of said sampling areas for statistically processing said greatest length crack data to form a distribution of lengths of said greatest length crack data for said zone area, and further for statistically estimating and producing a signal indicating a statistically estimated length of a greatest length crack within said zone area;
• means receiving said statistically estimated greatest length crack signal for estimating and producing a life expectancy value of the structure from a relationship between a length of a greatest length crack formed in the surface of the structure and a life ratio of the structure, wherein a life ratio represents a number of repeated loads applied to the structure to an average number of loads needed to be applied to the structure for rupture to occur;
• and
• means responsive to said life expectancy value for displaying the estimated life expectancy value of the structure.

An apparatus for estimating a life expectancy of a mechanical structure to which a number of repeated loads is applied, said apparatus comprising:

• determining and estimating means for experimentally determining a relationship between a maximum crack length of micro cracks formed in the surface of the structure and a life ratio of the structure, wherein a life ratio represents the number of repeated loads applied to the structure to the number of loads needed to be applied to the structure in order for rupture to occur, and for estimating a life expectancy value of the structure by calculating a current life ratio from the maximum crack length of the micro cracks based on said relationship;
• detecting means for detecting a maximum crack length and providing a signal indicating said maximum crack length to said determining and estimating means;
• and
• displaying means for receiving and displaying the estimated life expectancy value of the structure.

A method of estimating a life expectancy of a mechanical structure to which a number of repeated loads are applied, said structure being made of a metallic material and having a surface, comprising the steps of;

• experimentally determining a relationship between lengths of greatest length miniscule cracks formed in the surface of the material and a life ratio of the material with a specimen of the material, said minuscule cracks having a range in length of 50 microns to 10 millimeters, wherein said life ratio represents a number of repeated loads applied to the specimen to a number of repeated loads applied to the specimen when rupture occurs;
• determining a zone area of the structure that is subjected to a higher stress concentration than the remainder of the structure, and measuring a length of a greatest length minuscule crack formed in the surface within said zone;
• and
• estimating the life expectancy of the structure by calculating a current life ratio from said measured length based on said relationship.

A method of estimating a life expectancy of a mechanical structure to which a number of repeated loads are applied, said structure being made of a metallic material having a crystal structure and having a surface, comprising the steps of:

• experimentally determining a relationship between lengths of greatest length minuscule cracks formed in the surface of the material and a life ratio of the material, each of said minuscule cracks having an initial length of a diameter of a grain of crystal structure, wherein said life ratio represents a number of repeated loads applied to a specimen of the material to an average number of repeated loads applied to the specimen of the material in order for rupture to occur;
• statistically estimating a length of a greatest length miniscule crack formed in the surface of the structure by conducting an extreme value statistical process on lengths of greatest length minuscule cracks formed in the surface of the structure within each one of several surface sampling areas of the structure;
• and
• estimating the life expectancy of the structure by calculating a current life ratio from the statistically estimated length based on said relationship.

A method of estimating a life expectancy of a mechanical structure to which a number of repeated loads are applied, said structure being made of a metallic material having a crystal structure and having a surface, comprising the steps of:

• experimentally determining a relationship between lengths of greatest length minuscule cracks formed in the surface of the material and a life ratio of the material, said minuscule cracks having an initial length of a diameter of a grain of the crystal structure, and wherein said life ratio represents the number of repeated loads applied to the material to the number of repeated loads applied to the material when rupture occurs;
• calculating an estimated length of a greatest length minuscule crack formed in the surface of the structure by conducting an extreme value statistical process on lengths of greatest length minuscule cracks each formed within one of several surface sampling areas of the structure;
• and
• estimating the life expectancy of the structure by calculating a current life ratio from the estimated length of the greatest length minuscule crack based on said relationship.

A method of estimating a life expectancy of a mechanical structure to which a number of repeated loads are applied, said structure being made of a metallic material having a crystal structure and having a surface, comprising steps of:

• experimentally determining a relationship between a length of greatest length minuscule cracks having a length of no less than a diameter of a grain of the crystal structure formed in the surface of the material and a life ratio of the material, wherein said life ratio represents a number of repeated loads applied to the material to an average number of repeated loads applied to the material when a rupture occurs;
• calculating a length of a greatest length miniscule crack by conducting an extreme value statistical process on measured lengths of greatest length minuscule cracks formed in each of several surface sampling areas of the structure, the measured lengths being detected by using video magnifying means for forming a magnified image of the respective surface sampling areas, and image analyzing processor means for converting the image thus formed into signals representing the measured lengths within the imaged area;
• and
• estimating the life expectancy of the structure by calculating a current life ratio from the calculated length of the greatest length minuscule crack based on said relationship.

A method of determining a degree of damage to a mechanical structure subjected to repeated loading, said mechanical structure having a material, and said material having a crystal structure and a surface, comprising the steps of:

• experimentally determining a relationship between lengths of greatest length minuscule cracks formed in the surface of the material and having a range in size of between no less than a diameter dimension of a grain of the crystal structure and 10 millimeters and a life ratio of the structure, wherein said life ration represents a number of repeated loads applied to the material to a number of repeated loads applied to the material when rupture occurs;
• estimating a length of a greatest length minuscule crack of all minuscule cracks formed in the surface of the material of the structure including conducting an extreme value statistical process calculating step on respective lengths of greatest length minuscule cracks formed in each of several sampling areas on the surface of the structure, and further locating said sampling areas to correspond with areas of high stress concentration;
• and
• estimating a life expectancy of the structure by calculating a current life ratio from the estimated length of the greatest length minuscule crack based on said relationship.