Stress analysis testing

It would be desirable to make sample prototype tooling and analyze the flow effects on a product that is likely to present a flow problem. In addition to the usual physical testing of the product, the use of photo-stress analysis techniques plus the exposure to selected solvents to check for stress crack characteristics would lead to changes in the product to minimize the effects of the molding on the product performance. As an example there have been cases in the past where piano keys with frozen-in stresses have been released from perspiration, leaving open flow lines (Chapter 5, STRESS ANALYSIS). 

This photoelastic stress analysis is a technique for the nondestructive determination of stress and strain components at any point in a stressed product by viewing a transparent plastic product. If not transparent, a plastic coating is used such as certain epoxy, polycarbonate, or acrylic plastics. This test method measures residual strains using an automated electro-optical system. 

There is the microtoming optical analysis test. In this procedure thin slices (under 30 tixri) of the plastics are cut from the product at any level and microscopically examined under polarized light transmitted through the sample. Rapid quality and failure analysis examination occurs by this technique. This technique has been used for many years in biological studies and by metallurgists to determine flaws, physical and mechanical properties. Examination can be related to stress patterns, mechanical properties, etc. 

The codes and standards are drawn up by committees of engineers experienced in vessel design and manufacturing techniques, and are a blend of theory, experiment and experience. They are periodically reviewed, and revisions issued to keep abreast of developments in design, stress analysis, fabrication and testing. The latest version of the appropriate national code or standard should always be consulted before undertaking the design of any pressure vessel. 

Truss Stress Analysis The computation of member forces in an arbitrary plane truss is now examined. There exist some simple counting tests that may determine if a given truss is unstable. Failing that, one must attempt to compute the equilibrium state given some external forces in the process, one obtains values for all member forces. In this example, all truss members are identical in terms of material and area, grown in a developmental space where units are measured in meters EA is set to 1.57 x 104 N, corresponding to a modulus of elasticity for steel and a cylindrical member of diameter 1 cm. Consider a general truss with n joints and m beams external forces are applied at joints and the member forces are computed. Let the structure forces be... 

Dynamic properties are more relevant than the more usual quasi-static stress-strain tests for any application where the dynamic response is important. For example, the dynamic modulus at low strain may not undergo the same proportionate change as the quasi-static tensile modulus. Dynamic properties are not measured as frequently as they should be simply because of high apparatus costs. However, the introduction of dynamic thermomechanical analysis (DMTA) has greatly widened the availability of dynamic property measurement. 

Constant strain for stress relaxation tests and constant load creep tests may be conducted in simple devices. Temperature control is critical since the results are usually applied as a spectral representation for structural analysis or research purposes. Figure 8 illustrates a multistation creep tester with automated data recorders. Strain and load endurance tests are conducted in similar devices, but the conditions existing at failure and time to failure are normally the only data required. The endurance tests are used frequently to supplement the constant displacement rate tests for routine evaluation. 

The thin-wall bellows element should be designed for membrane stresses to conform to code-allowable stresses. The sum of membrane and secondary bending stresses should not exceed 1.5 times the yield stress in order to prevent the collapse of the corrugations caused by pressure. Bellows subjected to external pressure can be analyzed in a manner similar to a cylinder, utilizing an equivalent moment of inertia. The fatigue life can be estimated based on the sum of deflections and pressure stresses as compared to S/N curves based on bellows test data or using the curves in B31.3 Appendix X, Metal Bellows Expansion Joints. Formulas for the stress analysis of bellows are available in the Expansion Joints Manufacturing Association (EJMA) Standards (37). 

L. Chuck, E. R. Fuller, and S. W. Freiman, Chevron-Notch Bend Testing in Glass Some Experimental Problems, in Chevron-Notched Specimens Testing and Stress Analysis, eds. J. H. Underwood, S. W. Freiman, and F. R. Baratta, ASTM STP 855, ASTM, Philadelphia, PA, 1984, pp. 167-175. 

ANALYSIS - SCALING LAWS COMPUTER CODES - BLAST SUPPRESSION DYNAMIC STRESS ANALYSIS - STRUCTURES FABRICATION AND TESTING COST EFFECTIVENESS ANALYSIS ENGINEERING SUPPORT... 

S. Okikawa, M. Sakimoto, M. Tanaka, T. Sato, T. Toya, and Y. Kara, Stress Analysis of Passivation Film Crack for Plastic Molded LSI Caused by Thermal Stress, Proc. Internet ional Society for Testing and Failure Analysis, Oct. 1983, Los Angeles, CA. 

The stress relaxation test can be used for characterizing solid foods after taking precautions to minimize friction at the platen-food interface (Rao et al., 1995). For deformations in the nonlinear range, the empirical data analysis technique of Peleg (1980) has been used in several studies (e.g., Nussinovitch et al., 1990) ... 

O Brien, T.K., and S.J. Hooper. 1991. l.ocal delamination in laminates with angle ply matrix cracks Part I Tension tests and stress analysis , NASA Technical Memorandum 104055. 

Thermal residual stresses are inherent to fibre reinforced composites due to the heterogeneity of the thermo-mechanical properties of their two constituents. Such stresses build up when composite structures are cooled down from the processing temperature to the test temperature. Residual stresses will be present on both a fibre-matrix scale (micro-scale), and on a ply-to-ply scale (macro-scale) in laminates built up from layers with different orientations. It is recognised that these stresses should be taken into account in any stress analysis. 

Despite the common assumption of fault sealing in hydrocarbon fields, very few faults have been characterised in the detail needed which allows identification of the sealing mechanism or controls. Without the construction of a robust set of case histories from such analysis, future seal evaluation will remain a high risk venture. These case histories are also needed to integrate seal behaviour with pressure test, production and in situ stress analysis. The paper has highlighted the importance of an integrated approach from micro to macro and stressed the value of core-based studies to quantify fault rock properties, sub-seismic fault populations and sealing mechanisms. 

V.Hauk, Structural and Residual Stress Analysis by Nondestructive Testing Evaluation, Application, Assessment, Elsevier Publ., 1997. 

The critical values are generally obtained from a standard tensile test. Once the critical values are obtained the application of any (or all) of these criteria in conjunction with a dependable stress analysis is straightforward. Here we demonstrate the method by a simple example. Let us assume that it is desired to determine the torque required to cause failure of a 25 mm in diameter shaft constructed of an homogeneous isotropic plastic with a failure stress in tension, o, of 7 x 10 N/m. Assume further tlmt the modulus of elasticity, E, for this plastic is given by 3 x 10° N/m, and that is has a Poisson ratio of 0.3. We will explore the prediction of the three criteria just discussed. 

---