William N. Sharpe

Bio: William N. Sharpe is an academic researcher. The author has contributed to research in topics: Solid mechanics. The author has an hindex of 1, co-authored 1 publications receiving 559 citations.

Springer Handbook of Experimental Solid Mechanics

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A Review of Dynamic Experimental Techniques and Mechanical Behaviour of Rock Materials

Abstract: The purpose of this review is to discuss the development and the state of the art in dynamic testing techniques and dynamic mechanical behaviour of rock materials. The review begins by briefly introducing the history of rock dynamics and explaining the significance of studying these issues. Loading techniques commonly used for both intermediate and high strain rate tests and measurement techniques for dynamic stress and deformation are critically assessed in Sects. 2 and 3. In Sect. 4, methods of dynamic testing and estimation to obtain stress–strain curves at high strain rate are summarized, followed by an in-depth description of various dynamic mechanical properties (e.g. uniaxial and triaxial compressive strength, tensile strength, shear strength and fracture toughness) and corresponding fracture behaviour. Some influencing rock structural features (i.e. microstructure, size and shape) and testing conditions (i.e. confining pressure, temperature and water saturation) are considered, ending with some popular semi-empirical rate-dependent equations for the enhancement of dynamic mechanical properties. Section 5 discusses physical mechanisms of strain rate effects. Section 6 describes phenomenological and mechanically based rate-dependent constitutive models established from the knowledge of the stress–strain behaviour and physical mechanisms. Section 7 presents dynamic fracture criteria for quasi-brittle materials. Finally, a brief summary and some aspects of prospective research are presented.

Assessment of digital image correlation measurement errors: methodology and results

Abstract: Optical full-field measurement methods such as Digital Image Correlation (DIC) are increasingly used in the field of experimental mechanics, but they still suffer from a lack of information about their metrological performances. To assess the performance of DIC techniques and give some practical rules for users, a collaborative work has been carried out by the Workgroup "Metrology" of the French CNRS research network 2519 "MCIMS (Mesures de Champs et Identification en Mecanique des Solides / Full-field measurement and identification in solid mechanics, http://www.ifma.fr/lami/gdr2519)". A methodology is proposed to assess the metrological performances of the image processing algorithms that constitute their main component, the knowledge of which being required for a global assessment of the whole measurement system. The study is based on displacement error assessment from synthetic speckle images. Series of synthetic reference and deformed images with random patterns have been generated, assuming a sinusoidal displacement field with various frequencies and amplitudes. Displacements are evaluated by several DIC packages based on various formulations and used in the French community. Evaluated displacements are compared with the exact imposed values and errors are statistically analyzed. Results show general trends rather independent of the implementations but strongly correlated with the assumptions of the underlying algorithms. Various error regimes are identified, for which the dependence of the uncertainty with the parameters of the algorithms, such as subset size, gray level interpolation or shape functions, is discussed.

Experimental characterization of the mechanical properties of 3D-printed ABS and polycarbonate parts

Abstract: Additive manufacturing (AM), more commonly referred to as 3D printing, has become increasingly popular for rapid prototyping (RP) purposes by hobbyists and academics alike. In recent years AM has transitioned from a purely RP technology to one for final product manufacturing. As the transition from RP to manufacturing becomes an increasingly accepted practice it is imperative to fully understand the properties and characteristics of the materials used in 3D printers. This paper presents the methodology and results of the mechanical characterization of acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) 3D printed parts to determine the extent of anisotropy present in 3D printed materials. Specimens were printed with varying raster ([+45/−45], [+30/−60], [+15/−75], and [0/90]) and build orientations (flat, on-edge, and up-right) to determine the directional properties of the materials. Reduced gage section tensile and Isopescu shear specimens were printed and loaded in a universal testing machine utilizing 2D digital image correlation (DIC) to measure strain. Results indicated that raster and build orientation had a negligible effect on the Young’s modulus or Poisson’s ratio in ABS tensile specimens. Shear modulus and shear yield strength varied by up to 33 % in ABS specimens signifying that tensile properties are not indicative of shear properties. Raster orientation in the flat build samples reveal anisotropic behavior in PC specimens as the moduli and strengths varied by up to 20 %. Similar variations were also observed in shear for PC. Changing the build orientation of PC specimens appeared to reveal a similar magnitude of variation in material properties.

Strengthening mechanisms in an Al–Mg alloy

Abstract: Recent improvements in strength and ductility of 5083 aluminum alloys have been obtained through the development of complex microstructures containing either reduced grain sizes (ultra-fine and nano-grained materials), grain size distributions (bimodal microstructures), particle reinforcements, or combinations of the above. Optimization of such microstructures requires an understanding of the conventional, coarse-grained basis alloy. We present here a complete experimental data set for conventional Al-5083 H-131, with primary alloying element Mg (4.77 wt%) and secondary element Mn (0.68 wt%) in compression over a range of strain rates (10−4–6000 s−1) at room temperature. The various strengthening mechanisms in Al-5083 are explored, including solute strengthening, precipitate hardening, strain hardening, strain rate hardening, and strengthening due to dislocation sub-structures. Previous experiments found in the literature on Al–Mg binary alloys allow us to calculate the solute strengthening due to Mg in solid solution, and TEM analysis provides information about precipitate hardening and dislocation cell structures. A basic strength model including these strengthening mechanisms is suggested.