Theoretical and experimental analysis of circular saw tensioning

Summary Tensioning is the saw prestressing procedure most commonly used in the forest products industry to increase the stability of thin circular saws. This procedure stiffens the saw blade by introducing favorable in-plane residual stresses either by local plastic deformation or by local heating. In industry today, rolling is the standard procedure for introducing such stresses.The first part of this paper is concerned with a method of tension evaluation. The method examined consists of measuring saw blade modal stiffness, and it correlates the elastic stiffness of the saw, which approximates the vibration modes, and the natural frequencies associated with these modes. The predictions of the saw frequency shift due to stiffness variations were found to agree closely with experimentally determined frequencies. The method thus offers a practical procedure for tension evaluation and could replace the currently used technique of measuring the light gap under a straightedge placed along the saw diameter.The second part of this paper theoretically analyzes the relationship between the rolling load and the resulting tensioning stresses. The procedure followed in the theoretical model determines the identation load by equating the external power of loading with the power of storing in the elastic zones and of internal dissipation in the plastic zone.The residual stresses obtained by superpositioning the stresses due to unloading were generally in good agreement with the experimentally determined tensioning stresses outside the rolled region. The theory developed can be very useful in predicting tensioning stresses for a given rolling load and roller geometry.List of Symbols a, b Inside and outside saw disc radii - A, B Arbitrary constants - c Saw disc tensioning radius - c_i, c₀ Inside and outside rolling/indentation radii - c_n Neutral radius - d Track width - E Modulus of elasticity or strain energy - E_ext External power of the loading - E_p Power dissipation due to plastic deformation - E_d Power dissipation due to velocity discontinuity - E_e Power stored in elastic zones - f_n Resonant frequency of a saw disc n — nodal diameters - f _n ^TM Measured resonant frequency - f _n ^TC Resonant frequency calculated from the variation in the saw disc stiffness - F Rolling load - H Half saw disc thickness - K_n Modal stiffness, n=number of nodal diameters - K _n ^* Conventional or bending stiffness - K _n ^** Geometric or tensioning stress stiffness - K _n ^T Modal stiffness of a tensioned saw disc - M_n Modal mass, n=number of nodal diameters - M, N Integration constants - P_ave Average indentation pressure - p, p, p' Radial pressures at elastic-plastic boundaries; loading, unloading and residual - p_i, p_O Radial pressures inside and outside the elastic-plastic boundaries The Authors would like to express their gratiude to C. H. Zierdt and J. Rhemrev for assistance in the experimental investigations. The authors are also grateful to Hanchett Co. and California Saw Knife and Grinding, Inc. for supplying stretcher rolls and experimental saw discs, respectively. They are also grateful for the financial support of the project from the U.C. Forest Products Laboratory, California Cedar Products Co., California Saw Knife and Grinding, Inc., Hudson Lumber Co., MacMillan Bloedel Research Ltd., Potlatch Corp., Simpson Timber Co., Sun Studs, Inc. and Weyerhaeuser Co. Finally, the authors thank the National Science Foundation for its generous support of the research     

Quantum theory of chemical reaction dynamics

It is now possible to use rigorous quantum scattering theory to perform accurate calculations on the detailed state-to-state dynamics of chemical reactions in the gas phase. Calculations on simple reactions, such as H + D2 --> HD + D and F + H2 --> HF + H, compete with experiment in their accuracy. Recent advances in theory promise to extend such accurate predictions to more complicated reactions, such as OH + H2 --> H2O + H, and even to reactions of molecules on solid surfaces. New experimental techniques for probing reaction transition states, such as negative-ion photodetachment spectroscopy and pump-probe femtosecond spectroscopy, are stimulating the development of new theories.     

Performance of rice (Oryza sativa (L.)) under AWD irrigation practice—A brief review

Paddy and Water Environment - Alternate wetting and drying (AWD) is an irrigation technique where water is applied to the field a number of days after disappearance of ponded water. This is in...     

A review of residual stresses and tensioning in circular saws

Summary The origin and measurement of residual stresses and their effect on the transverse stability of circular saws are discussed, with emphasis placed on nondestructive stress analyses, their limits of application, and their possible adaptation to the measurement of residual stresses in circular saws. Saw stability variations can be computed once the stress distribution is known. Evaluation of the X-ray diffraction technique and the ultrasonic and magnetic methods were considered for this purpose.Alternatively, saw stability can be related to resonance and bending stiffness measurements in specific modes. However, the state of stress cannot be inferred from these tests. For saw stability prediction, measurement of the state of stress is more essential than are direct stiffness measurements.The authors would like to express their gratitude to Professor R. M. Bragg, Department of Material Science and Engineering, U. C. Berkeley, and to Dr. R. L. Gause and Mr. W. N. Clotfelter, Marshall Space Flight Center, Huntsville, Alabama, for valuable suggestions and permission to use X-ray and ultrasonic equipment. The authors are also grateful for the financial support of the project from the University of California Forest Products Laboratory; the California Cedar Products Company, Stockton; the California Saw, Knife and Grinding Company, San Francisco; Sun Studs, Roseburg, Oregon; Weyerhaeuser Company, Tacoma, Washington; and McIntire-Stennis Funds.     

Vibration control of band saws: Theory and experiment

Summary Active vibration control is a key to the improvement of the cutting performance and productivity of band saws. In this paper a new method is presented for active control of band saw vibration. The transfer function of a closed-loop system consisting of the band saw, a feedback control law and the dynamics of the sensing and force actuation devices is derived. Analysis of the root loci of the closed-loop system gives two stability criteria. Stabilizing controller design is carried out for both collocation and dislocation of the sensors and actuators. It is found that vibration in all the modes can be damped through use of only one sensor and one actuator and that the control algorithms presented are realizable in practice. The theory presented is experimentally verified.This work is supported by the National Science Foundation, the University of California Forest Products Laboratory, and the authors' group of industrial sponsors     

An evaluation of four candidate genes for use in selection programmes aimed at increased intramuscular fat in Duroc swine

Summary A sufficient level of intramuscular fat (IMF) is needed to enhance consumer acceptance of pork products, and is currently receiving greater attention within swine genetic improvement programmes. An examination of previously described and novel genetic variants within candidate genes for IMF deposition was performed to evaluate potential use of genetic markers in marker-assisted selection (MAS). Biological candidate genes implicated to play a role in adipogenesis were investigated within two different lines of purebred Duroc pigs. These included MC4R , FABP3 , DLK1 , and TCF7L2 . Significant variation in IMF within the control line was described by the MC4R genotype and a novel Bsr fI single nucleotide polymorphism within the FABP3 gene. Genetic markers for DLK1 and TCF7L2 evaluated in this population are not currently recommended for selection in Duroc swine. Existence of MC4R and FABP3 mutations may be useful markers in MAS aimed at IMF improvement, provided that gene effects are segregating and the presence of an association is detected within the population. However, additional work to confirm the use of the investigated genetic markers in selection programmes is needed.     

Principles and Practice of Therapeutic Exercise for Horses

Physical therapists are an integral component of the medical team in human health care. They are backed by a solid foundation of basic science and clinical research. Veterinarians have only recently begun to incorporate physical therapy into clinical practice, but without formal research that validates therapeutic interventions specific to equine patients. The purpose of this article is to present a series of therapeutic exercises adapted for horses based on knowledge and experience of human physical therapy, equine biomechanics, and the types of movement dysfunction commonly seen in the performance horse. Injuries, lameness and musculoskeletal pain syndromes, frequently encountered in equine practice, are disorders that may be successfully addressed with physical therapy. Incorporating standard therapeutic interventions based on clinical success in humans, basic science research, or expert opinion is possible with the understanding that these techniques will ultimately be accepted or refuted when their success or failure is formally documented. This review is designed to stimulate discussion and encourage research that will add to the knowledge base and lead to effective therapeutic protocols in the equine patient.