The Journal of Strain Analysis for Engineering Design

The final stages of many forging processes involve the flow of material into corner cavities or other surface details within a die. The process at this stage is essentially a ‘coining’ operation, and is usually characterised by high forming forces and relatively little material flow. These forces can be particularly severe under closed-die cold forging conditions, as in, for example, the manufacture of specialised headed fasteners, and can lead to problems of premature tool failure or the production of faulty products. This paper presents an upper bound analysis of such a ‘coining’ stage during a cold forging process. The theoretical analysis is based on an upper-bound formulation derived previously by the author, but, as will be shown, can be extended with ease to investigate the deformation of a family of similar workpiece geometries. The upper bound predictions for mean forging pressure ratio were compared with experimental results and good agreement was obtained. In addition, the change in the workpiece geometry during forging was noted and is commented upon.

This paper presents a novel technique for direct determination of derivatives of the displacement recorded by holographic interferometry. In the recording of a double exposure hologram, a set of relatively high frequency carrier fringes is coherently superimposed upon the displacement fringes by slightly changing the object beam direction, in addition to deforming the object. The resultant fringe pattern is a perturbed carrier fringe pattern, and the local fringe spacing directly determines displacement derivatives. Fringe spacing is accurately determined by measuring the separation of a pair of diffracted orders produced by a laser beam diffracted by the local carrier fringes.

A well-known theoretical equation for the distribution of contact load along threads in standard nut-bolt connections is generalized to incorporate the case of axially variable Young's moduli of the threaded elements. The influence of the material selection for homogeneous bolt and nut on the thread load concentration factor is initially addressed. The theoretical possibility of equalising the thread load distribution over the whole engagement by a convenient axial variation of the nut Young's modulus is then examined.

This paper presents a numerical method of analysing the elastic stability of thin laminated and longitudinally stiffened shells of revolution. The anisotropic elastic properties of composite materials are taken into account. The discrete longitudinal stiffener is dealt with as a beam-column, and its eccentricity effect is also considered. The basic elastic and geometric stiffness properties of the stiffeners are synthesized into a stiffness matrix compatible with an axisymmetric shell element by a series of transformations, to be used in conjunction with a finite element representation of a thin axisymmetric shell, where the displacements are decomposed into Fourier harmonics. Thus, the effect of the stiffeners can be rigorously accounted for in stability analysis. Examples are given to show that the results agree well with existing solutions by other analytical methods and by experiments.

The magnitudes and positions of the principal stress indices at a series of isolated oblique holes in thick, wide plates subjected to uniaxial tension have been determined using the photoelastic frozen-stress technique. The model series covered nominal plate thickness to hole diameter ratios of 1.33, 2.0, and 3.0, hole obliquity angles of 0, 15, 30, 45, and 60 degrees, and applied load directions of 0, 30, 60, and 90 degrees relative to the major axis of the surface ellipse. The results are discussed in detail and compared with other independent values available in the literature.

An improved strain gauge method for measuring the dynamic stress intensity factor, K_ID, of a running crack is described. By orienting the gauge relative to the crack propagation path the gauge response is optimized for the analysis. Higher order terms in the dynamic strain field representation are demonstrated to be important in the analysis. An application of the method is illustrated in the measurement of K_ID for a very hard alloy steel, 4340, with a crack propagating at 656 m/s.

Steam turbines are a fundamental component in most electrical power generation systems around the world. Their efficiency and capital cost are dependent on the quality of the blade roots which secure the thermodynamic aerofoil sections to the high speed rotor. This paper outlines a design analysis for such a root system using classical stress analysis and the finite element method. Comparisons are made between the results of both and experimental pull tests. For reasons of simplicity, the analysis considers only the primary centrifugal load on the root and not secondary steam bending loads.