A method and apparatus for digital image correlation. A camera system is used to obtain larger scale images of a larger scale dot pattern on a surface of a workpiece and smaller scale images of a smaller scale dot pattern on the surface of the same workpiece. The smaller scale dot pattern forms a larger dot in the larger scale dot pattern in the larger scale images. The larger scale images and the smaller scale images may be used to determine a measurement of the workpiece.

This disclosure relates to a real-time video extensometer. Typically, the apparatus of the disclosure combines the image source, data processing and electrical output on to a single processing board in order to achieve high frequency images and low latency times on data flow. Further, the video processing engine processes the image on a pixel basis and updating the output the intermediate extension/strain result so that after receipt of the final image pixel, a final extension/strain value is achieved and immediately output for evaluation.

A process for analyzing a fracture or crack surface of a TiAl turbomachine part is provided. The process includes: marking on the surface the position and the orientation of cleavage facets, so as to identify a region of fracture or crack initiation and to determine the direction of propagation of this fracture or crack; examining the surface and detecting the regions with the presence of equiaxed grains and/or lamellar grains, so as to evaluate the temperature at which the fracture or crack has taken place, and comparing the heat tintings of the surface with those of samples from a heat tinting color chart so as to evaluate the speed of propagation of the fracture or crack.

A method for determining material parameters includes applying a character grid over a planar sample, clamping the planar sample in a frame in accordance with directions of orthotropy of the planar sample; collecting a first set of data that describes a first position of the character grid; applying predetermined normal and shear stresses to the planar sample thereby bringing the planar sample into a deformed state and changing the position of the character grid; collecting a second set of data that describes a second position of the character grid, determining a relative position change of the character grid by correlating the collected first set of data and the second set of data; determining a relative displacement and a current distortion state of the planar sample; determining a deformation equilibrium of the deformed state of the planar sample; and calculating the material parameters from the deformation equilibrium.

A true stress testing system broadly comprising a force input machine, an imaging system, and a computer. The imaging system includes a light source for projecting a light beam at the specimen in a first direction and a camera positioned on an opposite side of the specimen for receiving portions of the light beam not blocked by the specimen such that a shadow image of the specimen is created via the camera. The computer may determine a minimum dimension of the specimen perpendicular to the first direction at a point in time over a plurality of points along the force axis via the shadow image of the specimen such that the processor accounts for changes in position of the minimum dimension along the specimen. A true stress of the specimen may then be determined according to the minimum dimension of the specimen perpendicular to the first direction at the point in time.

The disclosed method includes, from a topographic map showing, for a set of points {x} located in a midplane of the fracture surface, a height of the fracture surface h relative to the midplane: a step of determining, for each point x on the topographic map, a quantity ω.sub.∈ representative of an average difference in height).sub.IδxI≦∈ between the height h of the fracture surface at point x in question and the height h of the fracture surface at one or more points {x+δx} located inside a circle of radius ∈ centered on point x in question, a step of determining, according to a test distance δr, a spatial correlation function C∈ representing a spatial correlation between points {x} and points {x+δx} such as IδxI=δr, and a step of determining a correlation length ξ from the spatial correlation function C∈.

To provide a fracture-visualization sensor capable of visualizing the fracture behavior of a composite material and a composite-material fracture-visualization system using the fracture-visualization sensor.

A first luminescent film including a mechanoluminescent material is provided on one surface of a composite material. The first luminescent film has a maximum stress per unit of cross-sectional area within the range of 19-43 N/mm.sup.2.

A hypergravity model test device for simulating a progressive failure of a shield tunnel face, including a model box, a shield tunnel model, a servo loading control system and a data acquisition system. The servo loading control system includes a servo motor, a planetary roller screw electric cylinder and a loading rod. The data acquisition system includes a displacement transducer, an axial force meter, a pore pressure transducer, an earth pressure transducer and an industrial camera. The servo loading control system is connected to an excavation plate through the loading rod to control the excavation plate to move back and forth along an axial direction of the shield tunnel model at a set speed to simulate failure of the shield tunnel face. A method for simulating a progressive failure of a shield tunnel face is also provided.

The present disclosure describes systems and methods to correct for perspective calibration variations of a variable thickness specimen with a single camera extensometer in a video extensometer system. In some examples, the systems and methods compensate for a change between a reference characteristic, such as a calibration plane, and an actual physical characteristic, such as a testing plane associated with a surface of a test specimen, during a testing operation. In some examples, a correction value is applied to an output (e.g., measured dimensions of the imaged test specimen) to compensate for the difference between the reference characteristic and the physical characteristic.

Coal rock three-dimensional strain field visual system and method are provided under a complex geological structure. The system includes a stress condition simulation system and a strain monitoring system. The stress condition simulation system includes a similar simulation experiment rack, a loading system and a circular slideway. The method includes preparing a 3D printing wire, printing a strain visual similar model, simulating a stratum dip angle and a gas-containing condition, applying stress fields, recording a cracking and dyeing condition of microcapsules inside the model, and the like. The system can realize tracing the generation and development of internal cracks in simulation models with complex geological conditions, and tracing the three-dimensional movement of internal ink dots to draw four-dimensional images of displacement fields.