A review and evaluation of the advantages and limitations of laboratory equipment for measuring the shear strength of soils are presented. Equipment evaluated include direct shear, torsional shear, simple shear, triaxial, multiaxial (true triaxial), plane strain, hollow cylinder triaxial, and directional shear devices. The evaluation indicates that the impetus to obtain parameters for constitutive equations and modeling has resulted in the development of improved equipment and testing techniques; specifically, the development of multiaxial (true triaxial) and hollow cylinder triaxial test equipment. Although these devices are more versatile, the conventional solid cylinder triaxial test is still the most popular. The evaluation suggests that direct shear and simple shear devices are best utilized by designers who have gained experience applying the results from such tests to structures that have behaved satisfactorily.
Proper consideration must be given to the effects of membrane penetration, end restrain saturation and consolidation procedures, and rates of loading in any testing program.
An extended model for determining critical frequencies for tooth loading on spur and helical gear planetary trains is proposed. Torsional, flexural and axial generalized displacements of all the components are considered and a finite element procedure is used for generality.In order to avoid modulations between meshing pulsations and the carrier angular velocity, equations are written relative to rotating frames fixed to planet centers. Depending on their architectures, complex drives are broken down in basic 12 degree of freedom elements, namely:-external gear element (sun gear-planet element) -internal gear element (ring gear-planet element) -pin-carrier element -classical elements for shafts, bearings, couplings, etc. Details are given for elementary stiffness matrices. Due to contact conditions between mating teeth, these matrices are full and torsional, bending and traction effects are coupled.State equations point to parametrically excited differential systems with gyroscopic contributions. A first application of the model is conducted on a 3 planet epicyclic drive whose gyroscopic terms are neglected. Potentially dangerous frequencies for sun gear-planet arid planet-ring gear contacts are determined and contributions of some components of the planetary train are discussed.
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