Stiffness Of Sheets Research Articles

Automated knot detection with visual post-processing of Douglas-fir veneer images

Knots on digital images of 51 full veneer sheets, obtained from nine peeler blocks crosscut from two 35-foot (10.7 m) long logs and one 18-foot (5.5 m) log from a single Douglas-fir tree, were detected using a two-phase algorithm. The algorithm was developed using one image, the Development Sheet, refined on five other images, the Training Sheets, and then applied to all remaining sheets. In phase one, global thresholding was used to segment the image through a series of morphological operations to isolate regions likely to contain knots. In phase two, adaptive thresholding was applied to grey scale and red component segmented images to improve the accuracy of the segmented knot. Overall performance, judged in terms of confusion matrix performance metrics, was better for the red component images. Red component recall (true positive) rate was 1.00, 0.99, and 0.96 for the Development, Training, and complete sets, respectively. For the grey scale images, recall rates were 0.96 for all sets. Red component accuracy was 0.76, 0.92, 0.73 (Development, Training, and complete) and those for the grey scale images were 0.71, 0.85, and 0.69, respectively. Red component precision also exceeded that of the grey scale (0.75, 0.93, 0.73 compared to 0.72, 0.88, 0.70). A greater percentage of knots (78%) segmented from red component images were correctly sized, while 16% had more pixels than required and 6% had fewer pixels. Comparative figures for the grey scale images were 57% correctly sized, 2% with more pixels, and 42% with less pixels. Based on our results, we will adopt the red component image for continuing work with digital veneer images from a sample of Douglas-fir trees selected on the basis of acoustic velocity measures. Together with acoustic measurements of the veneer sheets, we are investigating the extent that the number, size, and spatial arrangement of knots influences the average stiffness of veneer sheets, with a view to determining if a relationship exists between the average stiffness of veneer sheets in a peeler block, stiffness of the log, and stiffness of the parent tree from a range of silvicultural treatments.

Abaca as a reinforcement fiber for softwood pulp

We investigated the affect on paper strength properties of adding a neutral sulfite abaca pulp to a softwood kraft pulp. Standard isotropic laboratory handsheets were made, and sheets were also made in a dynamic sheet former. The pure abaca pulp had higher tear and tensile indices for a given refining energy than the softwood pulp. The addition of abaca to the softwood pulp increased the tear strength, fracture toughness, and folding endurance for the isotropic sheets. The tensile stiffness of isotropic sheets was independent of the abaca content, but the tensile strength decreased slightly with increasing abaca content, perhaps because the addition of abaca led to a decrease in density. The anisotropic sheets showed the same trends as the isotropic sheets. Tearing resistance and fracture toughness increased with the addition of abaca. Tensile strength and tensile stiffness were only slightly affected by the addition of abaca, but the geometric mean values for the pure abaca sheets were slightly higher than those of the pure softwood sheets.

Bonding Characteristics of Fiber-Reinforced Polymer Sheet-Concrete Interfaces under Dowel Load

Based on a series of experimental tests on notched concrete beams externally bonded with unidirectional fiber-reinforced polymer (FRP) sheets, this paper investigates the bond characteristics of FRP sheet-concrete interfaces under dowel load, which acts vertically on the FRP sheet and leads to a mix-mode interface peeling. The peeling properties of FRP sheet-concrete interfaces under the dowel load are evaluated in terms of their interface dowel load-carrying capacity, critical interface peeling angle, and interface peeling fracture energy. Experimental parameters include strength of concrete substrate, tension stiffness of FRP sheets, properties of bonding adhesives, concrete surface treatment methods, and length of precrack set between the FRP sheet and concrete substrate. Analytical models clarifying the relationships among the interface dowel load-carrying capacity, the interface peeling angle, and the interface peeling fracture energy are built up and also verified by test results. Further, this paper shows how to use the interface peeling fracture energy calibrated from the present dowel tests for the practical design of spalling prevention, which is now becoming a popular application of FRP sheets for the maintenance and repair of existing concrete structures in Japan.

Peeling Behavior and Spalling Resistance of Bonded Bidirectional Fiber Reinforced Polymer Sheets

This paper presents the peeling behavior and spalling resistant effect of bidirectional fiber reinforced polymer (FRP) sheets externally bonded to concrete surfaces. Experimental investigations are carried out through a series of newly designed punching-peeling tests. A wide range of variables, such as FRP sheet layers and fiber direction, plate constraint, concrete strength, adhesives, bond length of FRP sheets, diameter of indenter, and types of fibers, are considered in the experimental investigation. Theoretical study is also conducted for the specimens. Interfacial fracture energy is calculated analytically using a membrane-peeling method. It is realized that only two material parameters, i.e., the interfacial fracture energy of the FRP-concrete interface and the tensile stiffness of FRP sheets, are necessary to represent the interfacial spalling resistant behavior. Finally, the theoretical results are validated by comparing with experimental results. Comparison of theoretical to experimental results shows that the proposed theoretical model is satisfactory in reasonably and accurately predicting the peeling behavior and spalling resistant capacity of bidirectional FRP sheets bonded to concrete surface.

Finite crystal elasticity of carbon nanotubes based on the exponential Cauchy-Born rule

A finite deformation continuum theory is derived from interatomic potentials for the analysis of the mechanics of carbon nanotubes. This nonlinear elastic theory is based on an extension of the Cauchy-Born rule called the exponential Cauchy-Born rule. The continuum object replacing the graphene sheet is a surface without thickness. The method systematically addresses both the characterization of the small strain elasticity of nanotubes and the simulation at large strains. Elastic moduli are explicitly expressed in terms of the functional form of the interatomic potential. The expression for the flexural stiffness of graphene sheets, which cannot be obtained from standard crystal elasticity, is derived. We also show that simulations with the continuum model combined with the finite element method agree very well with zero temperature atomistic calculations involving severe deformations.

Imaging anisotropic elastic properties of an orthotropic paper sheet using photorefractive dynamic holography

An important material property in the paper industry is the anisotropic stiffness distribution due to the fibrous microstructure of paper and to processing procedures. Ultrasonic methods offer a means of determining the stiffness of sheets of paper from the anisotropic propagation characteristics of elastic Lamb waves along the machine direction and the cross direction. That is, along and perpendicular to the direction of paper production. Currently, piezoelectric ultrasonic methods are employed in the industry to measure the elastic polar diagram of paper through multiple contacting measurements made in all directions. This paper describes a new approach utilizing the INEEL Laser Ultrasonic Camera to provide a complete image of the elastic waves traveling in all directions in the plane of the paper sheet. This approach is based on optical dynamic holographic methods that record the out of plane ultrasonic motion over the entire paper surface simultaneously without scanning. The full-field imaging technique offers great potential for increasing the speed of the measurement and it ultimately provides a substantial amount of information concerning local property variations and flaws in the paper. This report shows the success of the method and the manner in which it yields the elastic polar diagram for the paper from the dispersive flexural or antisymmetric Lamb wave.

The safety and efficacy of chronically implanted subdural electrodes: A prospective study

The popularity of subdural electrodes for the presurgical evaluation of patients with intractable seizures is increasing. However, few reports have prospectively dealt with their efficacy and safety. We conducted a 5-year prospective study of patients evaluated by the California Comprehensive Epilepsy Program, who subsequently underwent subdural electrode implantation at one of two institutions. Efficacy was examined by ultimate outcome with regards to postsurgery resection seizure frequency. Fifty-five patients underwent 58 implant procedures and postresection outcomes were available in 47 patients. Safety was defined by the incidence of expected and unexpected complications, and neuropathologic examination of tissue specimens. The most common expected adverse effects during implant were fever < or = 102 degrees (41%), cerebrospinal fluid leakage (19%), headache (15%), and nausea (4%). There were no infections. Unexpected adverse events included fever > 102 degrees F (5%), migraine (5%), iatrogenic electrode dysfunction (5%), and temporalis muscle fibrosis (5%). The incidence of pathologic findings suggestive of foreign body reaction was 10%. There were no permanent sequelae. Surgical outcomes were excellent in all (> or = 75% seizure reduction) with 50% seizure free regardless of the focus. Subdural electrodes are a safe, easy, and efficacious tool for evaluating seizure foci prior to resective surgery. They should no longer be considered investigational devices.

Materials evaluation : Ultrasonic procedures for predicting adhesive bond strength Rose, J.L, Meyer, P.A. 31 (June 1973) 109–114

An important material property in the paper industry is the anisotropic stiffness distribution due to the fibrous microstructure of paper and to processing procedures. Ultrasonic methods offer a means of determining the stiffness of sheets of paper from the anisotropic propagation characteristics of elastic Lamb waves along the machine direction and the cross direction. That is, along and perpendicular to the direction of paper production. Currently, piezoelectric ultrasonic methods are employed in the industry to measure the elastic polar diagram of paper through multiple contacting measurements made in all directions. This paper describes a new approach utilizing the INEEL Laser Ultrasonic Camera to provide a complete image of the elastic waves traveling in all directions in the plane of the paper sheet. This approach is based on optical dynamic holographic methods that record the out of plane ultrasonic motion over the entire paper surface simultaneously without scanning. The full-field imaging technique offers great potential for increasing the speed of the measurement and it ultimately provides a substantial amount of information concerning local property variations and flaws in the paper. This report shows the success of the method and the manner in which it yields the elastic polar diagram for the paper from the dispersive flexural or antisymmetric Lamb wave.

X.Additional experiments on moving-coil reproducers and on flexible disks

Abstract In this paper various details of moving-coil reproducers are discussed. The modulus of elasticity of paper is determined and used to compare the stiffness of conical sheets and disks of the same radius. A series of experiments is outlined, showing the influence of reinforcing certain portions of the diaphragm. The combination modes of a reed-driven paper disk are treated, and by comparison with theory, heterogeneity of the paper is disclosed. The exact solution of a lossless reed-driven disk vibrating in vacuo is given, due allowance being made for variation in the apparent mass of the reed itself. The case of a coil-driven circular aluminium disk is examined experimentally, and the frequency band occupied by the first symmetrical mode is shown to be only 5 cycles. With constant current in the coil, the output at resonance is some 2000 times greater than at non-resonant frequencies. The influence of the magnetic field upon the output and upon the coil impedance of a reproducer is analysed. The output criterion of the magnet is stipulated in terms of total gap area, air-gap flux density, and the coil space factor. It is shown that the oscillation of a coil driven by an alternating current in a non-uniform magnetic field is accompanied by a motion of translation. This is akin to the process of rectification.