Lengthscale effects in optical strain measurement for fracture characterization in simple shear

Optical strain measurement techniques have been extensively developed in recent years in order to cope in various environments. Power stations and wind turbine blades can provide challenging environments for the use of a measurement technique. There are, however, many installation problems to be overcome. For example, there is the need to have regard for the hostile environment in steam generating plant and the demanding conditions to which wind turbine blades are subjected. Ideally the outputs from individual sensors would be used for continuous remote monitoring. However, measurements can also be useful each time the plant is shut down during a plant outage; which would be used to complement data from existing proven rugged monitoring methods. This paper addresses the monitoring of pressurized steam pipes as to their micro-strain growth related to time in service. This paper presents the progress made in the developing of a ruggedised digital speckle ‘sensor’ and associated image capture system. The effect of subsurface defects in the strain distribution is examined.

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Comparative Study of As-Built Geometric and Mechanical Properties of Additively Manufactured Ceramics

Volume 1A: 38th Computers and Information in Engineering Conference ◽

10.1115/detc2018-86017 ◽

2018 ◽

Author(s):

John C. Steuben ◽

Athanasios P. Iliopoulos ◽

John G. Michopoulos

Keyword(s):

Mechanical Properties ◽

Strain Measurement ◽

High Performance ◽

Marked Decrease ◽

Measurement Techniques ◽

Direct Ink Writing ◽

Optical Strain Measurement ◽

Broad Variety ◽

Optical Strain ◽

Am Processes

Additive Manufacturing (AM) encompasses a broad variety of fabrication techniques characterized by successive additions of mass and/or energy to a build domain. AM processes have been developed for a wide variety of feedstock materials, including metals, polymers, and ceramics. In the present work we study the AM of ceramics using the Direct Ink Writing (DIW) technique. We performed comparative studies between additively manufactured and conventionally manufactured test articles, in order to quantify the variations in output geometry and mechanical properties induced by the DIW process. Uniaxial tests are conducted using high-performance optical strain measurement techniques. In particular, it is shown that the DIW-produced specimens exhibit anisotropic shrinkage when fired, as well as a marked decrease in stiffness and ultimate strength. We conclude with a discussion of potential mechanisms which may be responsible for these property degradations, and introduce potential adaptations to the DIW AM process that may be effective in combating them.

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Advanced measurement techniques for braided composite structures: A review of current and upcoming trends

Journal of Composite Materials ◽

10.1177/0021998320903105 ◽

2020 ◽

Vol 54 (25) ◽

pp. 3895-3917 ◽

Cited By ~ 1

Author(s):

Garrett W Melenka ◽

Cagri Ayranci

Keyword(s):

Computed Tomography ◽

Strain Measurement ◽

Composite Structures ◽

Measurement Methods ◽

Micro Computed Tomography ◽

Braided Composites ◽

Optical Strain Measurement ◽

In Situ Strain Measurement ◽

Optical Strain

Braiding is an advanced textile manufacturing method that is used to produce two-dimensional and three-dimensional components. Unlike laminated structures, braids have interlaced yarns that form a continuity between layers. This structure allows for improved impact resistance, damage tolerance, and improved through-thickness reinforcement. Despite the numerous advantages of braided composites, braids also have shortcomings. Their highly complex fiber architecture presents challenges in the availability and choice of the strain measuring and characterization techniques. Advanced measurement methods such as optical strain measurement, micro-computed tomography, and in situ strain measurement are required. Optical strain measurement methods such as digital image correlation and high-speed imaging are necessary to accurately measure the complex deformation and failure that braided composites exhibit. X-ray-based micro-computed tomography measurements can provide detailed geometric and morphologic information for braided structures, which is necessary for accurately predicting the mechanical properties of braided structures. Finally, in situ strain measurement methods will provide detailed information on the internal deformation and strain that exists within braided structures. In situ sensors will also allow for in-service health monitoring of braided structures. This paper provides a detailed review of the aforementioned sensing technologies and their relation to the measurement of braided composite structures.

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