Strain-controlled applications

Strain-controlled applications. In these applications, a definite strain is applied. The failure mode for the part may be fracture from exceeding the maximum elongation for the material, permanent deformation from exceeding the yield point, or fracture over time from strain close to the maximum elongation and subsequent creep rupture. 

The main concern regarding the utilization of Monascus pigments relates to the production of the citrinin mycotoxin in Monascus cultures. Several methods for controlling the mycotoxin production were proposed, including selection of non-toxinogenic strains, control of citrinin biosynthesis, and modifications of culture conditions. Despite their wide and traditional food applications in Asian countries, Monascus pigments have not been approved for use in the United States or European Union. 

Loading can be either load (or stress) controlled, displacement (or strain) controlled, or something in between. Examples include aerodynamic loads on an aircraft (see Aerospace applications), which tend to be load controlled, and the displacement of a sealant between relatively stiff adherends, which is displacement controlled. Because average adhesive strain, in its simplest form, is defined as displacement divided by bond thickness, strains and resulting stresses are higher in thin bondlines subjected to displacement-controlled loading scenarios. Joints loaded in such a manner often perform better with thicker bondlines. Displacement-controlled situations include thermal expansion/shrinkage of adherends, mismatched adherend expansion, and attachments bonded to pressure vessels or other adherends that are stressed. 

A 3D positioning actuator with a stacked structure as pictured in Figure 4.1.21 was proposed by a German company, where shear strain was utilized to generate thex andy displacements [38]. Polymer-packed PZT bimorphs have been commercialized by ACX for vibration reduction/control applications in smart structures [39]. 

Udd E, Schulz W L and Seim J M, Multi-axis fiber grating strain sensor applications for structural monitoring and process control . In Proc. SPIE -Process Monitoring Applications of Fiber Optic Sensors, 1999, 3538, 206-14. 

Altman, G. H., H. H. Lu et al. 2002. Advanced bioreactor with controlled application of multi-dimensional strain for tissue engineering. /Biomech Eng-Trans ASME 124(6) 742-49. 

The stress-strain behavior of a material provides important information relevant to its range of applicability. Load bearing applications may require certain stiffness or strength properties, the latter of which has been addressed in (see Chap. 19). For strain-controlled loading modes experienced by sealants, the modulus must be sufflciently low and the strain capabilities sufficiently high to provide adequate flexibility to meet the mechanical or thermally driven deformations. Due in part to the popularity of screw-driven test frames, most stress-strain characterization experiments have traditionally been carried out at a constant crosshead displacement rate, effectively straining the specimen at the desired rate. Results obtained are often quite rate and temperature dependent, so care is needed in reporting these details. 

The Institute has many-year experience of investigations and developments in the field of NDT. These are, mainly, developments which allowed creation of a series of eddy current flaw detectors for various applications. The Institute has traditionally studied the physico-mechanical properties of materials, their stressed-strained state, fracture mechanics and developed on this basis the procedures and instruments which measure the properties and predict the behaviour of materials. Quite important are also developments of technologies and equipment for control of thickness and adhesion of thin protective coatings on various bases, corrosion control of underground pipelines by indirect method, acoustic emission control of hydrogen and corrosion cracking in structural materials, etc. 

If the acceleration is variable, as in sinusoidal movement, piezoelectric systems are ideal. In case of a constant acceleration, and hence a force that is also constant, strain gages may be employed. For petroleum applications in boreholes, however, it is better to use servo-controlled accelerometers. Reverse pendular accelerometers and single-axis accelerometers are available. 

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