Ulric S. Lindholm

Bio: Ulric S. Lindholm is an academic researcher from Southwest Research Institute. The author has contributed to research in topics: Constitutive equation & Deformation (engineering). The author has an hindex of 21, co-authored 38 publications receiving 2419 citations.

Some experiments with the split hopkinson pressure bar

Abstract: A n application of the split Hopkinson pressure bar to the dynamic testing of materials is given whereby continuous records of the strain vs time, strain rate vs time, stress vs time, and stress vs strain may be simultaneously recorded For many materials a nearly constant true plastic strain rate can be maintained for loading durations on the order of 100 μsec The assumptions made in applying the method are checked experimentally Three annealed face centred cubic metals—lead, aluminium, and copper, are tested both dynamically and at lower strain rates to determine their rate sensitivity The results indicate that a single thermally activated mechanism is predominant A possible mechanism of this type is the intersection of glide and forest dislocations In aluminium, the previous strain rate history of loading is shown to affect the material's dynamic response only A rapid annealing effect is also evidenced Finally, the method is shown to be applicable to some non-metallic materials

High strain-rate testing: Tension and compression

Abstract: Details of the split Hopkinson pressure-bar method for obtaining complete stress-strain curves at strain rates on the order of 1000 sec−1 in either tension or compression are presented. In compression, a gage for measuring radial strain and, therefore, Poisson's ratio is also described. Some typical results are presented for aluminum, and various factors pertaining to the accuracy of the results are discussed.

Elastic Vibration Characteristics of Cantilever Plates in Water

Abstract: : The presence of the liquid free surface has a significant effect upon the dynamic plate characteristics (frequencies) only when the surface is less than about one-half span length from the plate. The effect of the liquid free surface on the resonant frequency of a vertical surface peircing plate is highly dependent upon the relationship between the depth of immersion of the plate and the mode of vibration. The overall damping of cantilever plate vibration is increased significantly in water as compared with air. The results of this study would indicate that for those problem areas in the field of Naval dynamics wherein elastic plate vibrations are involved, and for which predictions of resonant frequencies and damping factors are derived, knowledge is either inadequate or unavailable. For cantilever plates, the present results should enable one to predict resonant frequencies in practical applications with some degree of confidence; but damping factors have been obtained only to within order-of-magnitude and to show trends. Clearly, similar information is very much needed for other plate geometries (i.e., skewed) and support conditions.

Response of Various Metals to Large Torsional Strains Over a Large Range of Strain Rates—Part 1: Ductile Metals

Abstract: This paper presents torsional test results for six metals subjected to large shear strains and high strain rates. Included are 2024-T351 aluminum, 7039 aluminum, low alloy steel, S-7 tool steel, tungsten alloy and DU-.75Ti (Depleted Uranium). The specimens are strained to fracture at strain rates from quasi-static to over 100 s−1 . All of the materials exhibit strain hardening and strain rate hardening. At the higher strain rates some of the materials develop shear instabilities and localizations. Constitutive relationships are derived from the test data and finite element computations of the tests are performed.

Phenomenological Modeling of Hardening and Thermal Recovery in Metals

Abstract: Modeling of hardening and thermal recovery in metals is considered within the context of unified elastic-viscoplastic theories. Specifically, the choices of internal variables and hardening measures, and the resulting hardening response obtained by incorporating saturation-type evolution equations into two general forms of the flow law are examined. Based on the analytical considerations, a procedure for delineating directional and isotropic hardening from uniaxial hardening data has been developed for the Bodner-Partom model and applied to a nickel-base superalloy, B1900 + Hf. Predictions based on the directional hardening properties deduced from the monotonic loading data are shown to be in good agreement with results of cyclic tests.

Microtubule nucleation by γ-tubulin complexes

Abstract: Microtubule nucleation is regulated by the γ-tubulin ring complex (γTuRC) and related γ-tubulin complexes, providing spatial and temporal control over the initiation of microtubule growth. Recent structural work has shed light on the mechanism of γTuRC-based microtubule nucleation, confirming the long-standing hypothesis that the γTuRC functions as a microtubule template. The first crystallographic analysis of a non-γ-tubulin γTuRC component (γ-tubulin complex protein 4 (GCP4)) has resulted in a new appreciation of the relationships among all γTuRC proteins, leading to a refined model of their organization and function. The structures have also suggested an unexpected mechanism for regulating γTuRC activity via conformational modulation of the complex component GCP3. New experiments on γTuRC localization extend these insights, suggesting a direct link between its attachment at specific cellular sites and its activation.