Laser induced Zero-Group Velocity resonances in Transversely Isotropic cylinder

The transient response of an elastic cylinder to a laser impact is studied. When the laser source is a line perpendicular to the cylinder axis, modes guided along the cylinder are generated. For a millimetric steel cylinder up to ten narrow resonances can be locally detected by laser interferometry below 8 MHz. Most of these resonances correspond to Zero-Group Velocity guided modes while a few others can be ascribed to thickness modes. We observe that the theory describing the propagation of elastic waves in an isotropic cylinder is not sufficient to precisely predict the resonance spectrum. In fact, the texture of such elongated structure manifest as elastic anisotropy. Thus, a transverse isotropic (TI) model is used to calculate the dispersion curves and compare them with the measured one, obtained by moving the source along the cylinder. The five elastic constants of a TI cylinder are adjusted leading to a good agreement between measured and theoretical dispersion curves. Then, all the resonance frequencies are satisfactorily identified.Comment: 23 pages, 7 figures, submitted to the JAS

Comparison of impact results for several polymeric composites over a wide range of low impact velocities

Static indentation, falling weight, and ballistic impact tests were conducted in clamped plates made of AS4/3501-6 and IM7/8551-7 prepreg tape. The transversely isotropic plates were nominally 7-mm thick. Pendulum and ballistic tests were also conducted on simply supported plates braided with Celion 12000 fibers and 3501-6 epoxy. The 20 degree braided plates were about 5-mm thick. The impactors had spherical or hemispherical shapes with a 12.7 mm diameter. Residual compression strength and damage size were measured. For a given kinetic energy, damage size was least for IM7/8551-7 and greatest for the braided material. Strengths varied inversely with damage size. For a given damage size, strength loss as a fraction of original strength was least for the braided material and greatest for AS4/3501-6 and IM7/8551-7. Strength loss for IM7/8551-7 and AS4/3501-6 was nearly equal. No significant differences were noticed between damage sizes and residual compression strengths for the static indentation, falling weight, and ballistic tests of AS4/3501-6 and IM7/8551-7. For the braided material, sizes of damage were significantly less and compression strengths were significantly more for the falling weight tests than for the ballistic tests

Webs for cold formed steel flexural members structural behavior of transversely reinforced beam webs

Since 1973, a research project on webs for cold-formed steel flexural members has been conducted at the University of Missouri-Rolla under the sponsorship of American Iron and Steel Institute. This study deals with the structural behavior of beam webs subjected to bending stress, shear stress, combined bending and shear, web crippling and the effect of bending on web crippling load. In addition, it includes a study of beam webs reinforced by either transverse or longitudinal stiffeners. This report presents the research findings on transversely reinforced cold-formed steel beam webs. The results obtained from the study of beam webs subjected to other types of stress and the combinatiors thereof are presented in some other reports of the University of MissouriRolla referred to in the bibliography

Wave propagation in fiber composite laminates, part 2

An experimental investigation was conducted to determine the wave propagation characteristics, transient strains and residual properties in unidirectional and angle-ply boron/epoxy and graphite/epoxy laminates impacted with silicone rubber projectiles at velocities up to 250 MS-1. The predominant wave is flexural, propagating at different velocities in different directions. In general, measured wave velocities were higher than theoretically predicted values. The amplitude of the in-plane wave is less than ten percent of that of the flexural wave. Peak strains and strain rates in the transverse to the (outer) fiber direction are much higher than those in the direction of the fibers. The dynamics of impact were also studied with high speed photography

Limit states of composite steel-concrete bridges

Imperial Users onl

On the Mass Impact Loading of Ductile Plates

This paper examines the response of circular and square plates stluck by a rigid mass at the plate centre with a sufficient initial kinetic energy to produce large inelastic deformations. A simpliiicd analysis, which retains finite-deflection effects and assumes that the plates are made of a rigid, perfectly plastic material, provides a relatively simple theoretical solution for the maximum permanent Inusvet displacement and the response duration. It transpires that the theoretical predictions give reasonable agreement with the maximum v e n ttr ansverse displacements recorded in several experimental studies on fully clamped, circular and square ductile metal plates. The final theoretical expressions for the behaviour are easy to use and ideal for preliminary design purposes and would be sufficiently accurate for final designs in some applications

The consequences of wood cellular structure and rolling-shear in crossbanded veneer composites

A hierarchical modelling path of wood and wood composites' properties is presented. First the calculation model (WOOD123) is developed for elastic and shrinkage behaviour based on the complex ultra-, micro- and macro-structure of wood, based on the properties of wood main constituents and their orientation. Then the results and the understanding obtained are utilised in the development of the calculation program for the analysis and design of transversely loaded layered wood composite plates (OptiPly). The model (WOOD123) predicts the elastic and shrinkage properties of wood at the cell wall level and at the macro-level, where wood substances consist of earlywood, latewood and ray cells. The modelling of the cell wall properties and behaviour is based on the properties of cellulose, hemicellulose and lignin. At the cellular level wood substances consist of individual softwood cell types (earlywood, latewood and ray cells). Finally at the highest level of the cellular modelling, earlywood, latewood and ray cells are combined together to predict anisotropic elastic properties of wood, the effects of moisture content on the elastic properties and the nonlinear shrinkage in different directions. WOOD123 model, developed by this author, has been the first model capable of building the full path from the ultra- and micro-scale material properties, polymer orientation and arrangement to the orthotropic behaviour of wood. Earlier models are limited only to the prediction of cell wall properties or the layered structure of cell wall is neglected and the behaviour of cellular wood substance is modelled using homogenous cell walls. Due to the lack of suitable micro-scale testing devices and inadequate microscopy facilities and due to the large number of structural and material property parameters required in the model as input data, the development and verification of the model have been done mainly based on the material and structural parameters obtained from the literature. The elastic properties, the dependence of the elastic properties on the moisture content of wood and the complex shrinkage behaviour calculated by the model agreed well with the elastic constants and material behaviour presented in the literature. Next step was the modelling of the behaviour of layered wood composites. For the development and verification of OptiPly-program large experimental work has been carried out. Tests contain plywood and LVL manufactured using birch and spruce veneers, different veneer thicknesses and special lay-ups, short- and long-term tests were performed and test methods varied from standard tests to more complex beam-type and point-loaded plate tests. The tests showed that the shear deformations in cross veneers have a strong effect on the deflections and the strength of wood composite plates. However, the conventional theory based on Love-Kirchoff hypothesis does not take into account pronounced shear deformations of cross layers. The accuracy of the classical theory and the generalised Bernoulli's hypothesis is compared. The calculation based on the exact solution of the generalised Bernoulli's hypothesis by Heinisuo correlates well with the test results. The accuracy of prediction of the mid span deflection obtained using the generalised Bernoulli's hypothesis is −16% … +10%, and by the classical lamination theory is −26% … +13%, respectively. OptiPly-program was found to be reliable, slightly conservative and suitable for the practical design of plywood plates. At this moment Finnish plywood and LVL industry uses OptiPly-program in practice.reviewe

Expanding the Applicability of Press-Brake-Formed Tub Girders Through the Extension of the Maximum Span Length and the Evaluation of Pier Continuity

The Short Span Steel Bridge Alliance (SSSBA) is a group of bridge and buried soil steel structure industry leaders who provide educational information on the design and construction of short-span steel bridges in installations up to 140 feet in length. Within the SSSBA technical working group, a modular, shallow press-brake-formed tub girder (PBFTG) was developed to address the demand in the short-span steel bridge market for rapid infrastructure replacement solutions. PBFTGs consist of modular, shallow, trapezoidal boxes fabricated from cold-bent structural steel plate. A concrete deck, or other deck option, may be placed on the girder, and the modular unit can be shipped by truck to the bridge site. PBFTGs perform exceptionally well in simply supported, right, straight bridges utilizing current American Association of State and Highway Transportation Officials Load Resistance and Factor Design Bridge Design Specifications’ (AASHTO LRFD BDS) Live Load Distribution Factors (LLDFs). The specifications limit the use of PBFTGs outside of these scenarios, despite the expectation they would perform well in a variety of other situations. More research and data are necessary to validate the current limitations in the AASHTO LRFD BDS and increase the applicability of PBFTGs into continuous spans and skewed bridges. The scope of this project was to expand the applicability and usability of the PBFTG system. This was performed in several stages. First, a complete understanding and background of PBFTGs, LLDFs, box-girder capacity determinations, link slabs, and the AASHTO LRFD BDS was provided. This understanding and background of the restrictions placed on PBFTGs provided insight when developing the methodologies to overcome these restrictions. Next, analytical modeling techniques were developed and refined utilizing complicated geometry and nonlinear finite element methods. These modeling techniques were benchmarked against numerous historical laboratory tests and live load field tests of in-service PBFTG bridges. Then, the analytical tools were employed in sensitivity and parametric studies on PBFTG bridge models, resulting in proposed simplified empirical LLDFs, which better predict live load distribution than those equations present in the AASHTO LRFD BDS. These tools were also used to assess the effect of bearing line skew on the capacity of PBFTGs. Finally, life cycle laboratory fatigue testing was performed on two PBFTGs joined by a full-scale link slab to assess the applicability of the joint in continuous PBFTG bridges. Results of this project demonstrate the use of PBFTGs can be expanded into continuous spans using link slabs and more accurate LLDFs may be used to increase the economic viability of the system in the short-span bridge market. In addition, the analytical tools developed during this study relating to the capacity of skewed PBFTGs will serve as the basis for future research in this field