Zella Kahn-Jetter

Optimal image correlation in experimental mechanics

The integration of optimization techniques for use in digital image correlation problems in experimental mechanics is discussed. Stereo sets of images of a speckle pattern on a loaded body are correlated using four types of optimization routines. The results obtained using the gradient-based first-order method and nongradient-based pattern search, simplex, and Powells methods compare extremely well with the original experimental results. The effectiveness and accuracy of these different optimal image processing techniques have also been analyzed and found suitable for this example

Using spreadsheets for studying machine design problems involving optimization

Advanced machine design problems involving optimization concepts may be analyzed using spreadsheets. In this article, linear and nonlinear examples were modeled on current versions of Microsoft Excel, QuattroPro for Windows, and Lotus 1‐2‐3. A comparison of data entering and presentation of solutions is discussed. It is shown that although all three software packages solve the problems successfully, Excel appears to be best suited for these types of problems.

Compressive/Tensile Stresses and Lignified Cells as Resistance Components in Joints between Stem Segments of Opuntia fulgida and Opuntia versicolor (Cactaceae)

Many species of Cactaceae, a diverse group of plants with a wide variety of morphologies and reproductive strategies, have segmented stems in which terminal stem segments may be separated from main stem segments with varying amounts of resistance. Terminal stem segments that are removed with little resistance may easily form adventitious roots to produce new plants asexually, whereas other species with high resistances to stem segment removal may predominately reproduce sexually. The purposes of this study were (1) to quantitatively determine the stresses at joints between stem segments of two species of Opuntia (Opuntia fulgida [jumping cholla] and Opuntia versicolor), (2) to determine whether lignified cells of the xylem cells in joints provide the major source of resistance to these stresses, and (3) to determine whether the resistances are related to whether species reproduction is correlated with resistance stresses. The overall concept of this study is that lignified xylem tissues are the main tissue of resistance to mechanical stresses (especially tensile stress) at stem segment joints since all other tissues have relatively thin‐walled cells. This condition is analogous to reinforcing rods in concrete. The computer‐aided design package, coupled with a geometric evaluation of relative positions of stem segments, provides adequate estimates of joint‐stress parameters among stem segments. Bending stresses at joints were more than 10 times greater than any other stresses. Expressing joint stress as a function of area of lignified xylem cells is a valid way of expressing the mechanics of joint integrity. Areas of lignified xylem cells were about two times greater for tensile tissues than they were for compressive tissues, and tensile joint portions exhibited a greater percentage of lignified xylem tissues closer to the external surface. Stresses at joints as a function of area of lignified xylem cells were about four times greater for O. fulgida than for O. versicolor, and the relatively high bending stress values ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Compressive/Tensile Stresses and Lignified Cells as Resistance Components in Joints between Cladodes of Opuntia laevis (Cactaceae)

\mathrm{mean}\,=2955

Compressive/tensile stresses and lignified cells as resistance components in joints between cladodes of Opuntia laevis (Cactaceae): responses to applied stresses.

\end{document} kPa) at joints of O. fulgida coincide with its ability to have terminal stem segments removed easily and its ability to reproduce asexually by rooted stem segments. In contrast, lower bending stress values ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Stresses on joints of Opuntia laevis: forces necessary for mechanical failure and role of lignified xylem cells as resistance components

\mathrm{mean}\,=1021