64 research outputs found
Strain measurement by contour analysis
Background: The determination of yield stress curves for ductile metals from
uniaxial material tests is complicated by the presence of tri-axial stress
states due to necking. A need exists for a straightforward solution to this
problem. Objective: This work presents a simple solution for this problem
specific to axis-symmetric specimens. Equivalent uniaxial true strain and true
stress, corrected for triaxiality effects, are calculated without resorting to
inverse analysis methods. Methods: A computer program is presented which takes
shadow images from tensile tests, obtained in a backlight configuration. A
single camera is sufficient as no stereoscopic effects need to be addressed.
The specimen's contours are digitally extracted, and strain is calculated from
the contour change. At the same time, stress triaxiality is computed using a
novel curvature fitting algorithm. Results: The method is accurate as
comparison with manufactured solutions obtained from Finite Element simulations
show. Application to 303 stainless steel specimens at different levels of
stress triaxiality show that equivalent uniaxial true stress -- true strain
relations are accurately recovered. Conclusions: The here presented computer
program solves a long-standing challenge in a straightforward manner. It is
expected to be a useful tool for experimental strain analysis
The effect of compression shock heating in collision welding
This work discusses the origin of temperature rise during the collision
welding process. The different physical irreversible and reversible mechanisms
which act as heat sources are described: isentropic compression work, shock
dissipation, plasticity, and phase transitions. The temperature increase due to
these effects is quantified in a continuum mechanics approach, and compared to
predictions of atomistic molecular dynamics simulations. Focusing on a single
impact scenario of 1100 aluminium at 700 m/s, our results indicate that shock
heating and plastic work only effect a temperature rise of 100 K, and that the
effects of phase change are not significant. This temperature rise cannot
explain welding. In consequence, the relevant mechanism which effects bonding
in collision welding must be due to the jet, which is only formed at oblique
impact angles
A Review of Computational Methods in Materials Science: Examples from Shock-Wave and Polymer Physics
This review discusses several computational methods used on different length and time scales for the simulation of material behavior. First, the importance of physical modeling and its relation to computer simulation on multiscales is discussed. Then, computational methods used on different scales are shortly reviewed, before we focus on the molecular dynamics (MD) method. Here we survey in a tutorial-like fashion some key issues including several MD optimization techniques. Thereafter, computational examples for the capabilities of numerical simulations in materials research are discussed. We focus on recent results of shock wave simulations of a solid which are based on two different modeling approaches and we discuss their respective assets and drawbacks with a view to their application on multiscales. Then, the prospects of computer simulations on the molecular length scale using coarse-grained MD methods are covered by means of examples pertaining to complex topological polymer structures including star-polymers, biomacromolecules such as polyelectrolytes and polymers with intrinsic stiffness. This review ends by highlighting new emerging interdisciplinary applications of computational methods in the field of medical engineering where the application of concepts of polymer physics and of shock waves to biological systems holds a lot of promise for improving medical applications such as extracorporeal shock wave lithotripsy or tumor treatment
Structures under crash and impact: continuum mechanics, discretization and experimental characterization
Required reading for those in the relevant areas of work, this book examines the testing and modeling of materials and structures under dynamic loading conditions.Readers get an in-depth analysis of the current mathematical modeling and simulation tools available for a variety of materials, alongside discussions of the benefits and limitations these tools pose in industrial design.The models discussed are also available in commercial codes such as LS-DYNA and AOTODYN.Following a logical and well organized structure, this volume uniquely combines experimental procedures with numerical simulati
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