The two most widely used techniques for experimental stress analysis and transducer design are foil strain gages and Photoelastic methods.
Photoelasticity is a visual full field technique for stress analysis determining quantitative measurements of strain direction and magnitude. It enables stress analysis on actual parts and structures of any size, shape and material operating under actual service load conditions.
When photoelastic materials are strained and viewed under polarized light, colored fringe patterns are seen. Interpretation of these patterns leads to an understanding of the overall stress field and permits the measurement of strain magnitude and direction at any point. A coating of photoelastic material can be applied directly to the surface of a test specimen or a 2-D model can be made with the photoelastic material.
Photoelastics is a tremendous aid for choosing strain gage locations for continual stress reporting. It assists in determining gage size and optimal gage geometry. Visualization of the photoelastic response to applied loads aids in identifying areas of excess material, while revealing stress concentrations on the manufactured part.
Photoelastic Analysis Provides:
Instant identification of stress concentrations, gradients and zero-stressed areas on metals, concrete, composites and more
A quantitative measurement of stress and strain identified at any point on a structure
How Photoelastics is Applied
Photoelastic material is applied as a flat sheet to an existing flat part or molded to the contours of the part
Photoelastic material can be used to form 2-D scaled models.
A 2-D model made from a .25” thick sheet of photoelastic material is shown in tension. A classic strain pattern is visualized with maximum tensile stresses on the top and bottom inside edges of the central hole confirmed by the many color bands. The strain gradient is high in these locations as shown by the tightly spaced color bands. There is very low compressive stresses on the left and right of the central hole visualized by few colors bands and a large white area – an indication of very low stresses. The loading pins at the left and right of the model show tightly banded colors, an indication of high contact stresses which is expected.
The strain gage is the most frequently used device in stress analysis work throughout the world today. Precise results of surface strains can be obtained quickly using relatively inexpensive methods and instrumentation. Stress information can be read in real time or collected and analyzed over extended periods of time.
We offer comprehensive strain gage services and provide a wide array of strain gages to meet project demands. We bond gages for experimental stress analysis and load cell design elements in a wide variety of transducers. We assess sensitivity, cost, operating conditions and Wheatstone bridge configurations for each application. Provide expertise and resources for R&D, custom bonding, and high volume applications. Partnered with the worlds largest strain gage manufacturers and maintain inventories of strain gages and installation materials for expediting services. We have a 30-year history of applying strain gages in many complex environments and surfaces.
Complete Stress Analysis Services
Stress-Tek uses Photoelasticity and strain gages coupled with FEA providing a complete array of stress analysis services:
- Validating stress assumptions
- Prototype testing
- Post design evaluation
- Product reliability and design adequacy
- Failure analysis
- Material property evaluation
Photoelastic Stress Analysis of Feed Through Holes in a Beam Subjected to Bending Load.
A flat sheet of Photoelastic material is bonded to the surface of this perforated beam section. The stress field of patterned feed through holes is visualized as the beam section is subjected to bending loads. There are high stresses around the two rows of multi hole patterns but there is no stress on each side of the large central hole as visualized by the two black dots surrounded by white areas on either side of the central hole.
Photoelastic Stress Analysis of a Weld Joint in Bending
Photoelastic material is bonded to the contours of a welded component. This welded beam is in pure bending and exhibiting a complex stress pattern around the top and bottom surfaces of the centrally located weld. These are areas where the bending stress is at a maximum. The weld area in the beam center shows a constant stress field as a solid yellow color. The neutral axis is clearly defined by the horizontal black areas on either side of the weld. These black areas disappear in the beam center due to the increased complexity of the weld stresses.