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2 edition of Effects of knots on stress waves in lumber found in the catalog.

Effects of knots on stress waves in lumber

C. C Gerhards

Effects of knots on stress waves in lumber

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  • 27 Currently reading

Published by U.S. Dept. of Agriculture, Forest Service, Forest Products Laboratory in [Madison, Wis.] .
Written in English

    Subjects:
  • Stress waves,
  • Lumber

  • Edition Notes

    SeriesResearch paper FPL -- 384
    ContributionsForest Products Laboratory (U.S.)
    The Physical Object
    Pagination28 p. :
    Number of Pages28
    ID Numbers
    Open LibraryOL14841284M

    Abstract: Method and apparatus are described for using stress wave measurements in the estimation of quality of finger joints in wood and quality of lumber, where quality is typically defined as strength. Application and measurement of stress waves in the transverse direction of the material allows localized measurements to be made, and features developed from this information are used in the.   Relative travel time values were used to identify decay since stress waves travel slower through decayed wood than through sound wood. RESULTS OF PILE CAP INSPECTION Ultrasonic wave travel times transverse to the grain of the timber pile cap were incorporated into contour and color gradient plots along the pile cap profile using SigmaPlot software. Longitudinal stress wave and transverse vibration are the most widely used NDT techniques toward structural lumber evaluation. Predicting MOE of lumber with longitudinal stress wave has received considerable research efforts in recent years in terms of lumber grading or presorting (Jayne , Kaiserlik and Pellerin , Gerhards


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Effects of knots on stress waves in lumber by C. C Gerhards Download PDF EPUB FB2

Effect of Knots on Stress Waves September in Lumber By C. GERHARDS, Engineer Introduction Although Stress waves have been proposed as a means for rapid machine stress rating of lumber, the concept has seen only limited commercial application.

A better understanding of how stress waves propagate and in-Cited by: 9. grain in lumber (,2,3,4).-his report is concerned with microsecond counter as the stress wave advances past propagation of stress waves in lumber containing knots each accelerometer.

Thus, the microsecond counter and how the propagation characteristics may be used times the stress wave as it travels the distance be. Gerhards () studied the effects of knots on stress waves in lumber and found that wave speed was slowed through knots and the curved grain around knots.

effects of knots on stress waves in lumber Download effects of knots on stress waves in lumber or read online books in PDF, EPUB, Tuebl, and Mobi Format. Click Download or Read Online button to get effects of knots on stress waves in lumber book now.

This site is like a library, Use search box in the widget to get ebook that you want. Knots lower lumber stiffness because they cause deviations from optimal grain orientation and concentrate stress (i.e., at the knot) (Megraw ;Kabir et al.

Gerhards () studied the effects of knots on stress waves in lumber and found that wave speed was slowed through knots and the curved grain around knots. Gerhards also suggested that, in lumber with cross grain and knots, the stress wave does not propagate with a normal.

Wood with small knots ( mm2) presents stiffness and strength statistically equal to wood free of defects. Eucalyptus wood stiffness is more sensitive to the presence of knots than the strength.

longitudinal compression stress waves in Douglas-fir 2 by 8 lumber. Cross grain causes the stress wave to advance with a front or contour skewed in the direction of the grain angle, rather than to advance with a front normal to the long axis of lumber. Thus, the timing of the stress wave in lumber with cross grain is complicated.

Based on the. The effect on strength depends approximately on the proportion of the cross section of the piece of lumber occupied by the knot, knot location, and distribution of stress in the piece. Limits on knot sizes are therefore made in relation to the width of the face and loca.

Many researchers have also studied the effect of knots on wave propagation. It has been found that a decrease in velocity is associated with a decrease in the stiffness, mainly because of the deviation in fibers around knots (Puccini ; Bucur ). However, these studies focused on the longitudinal direction.

Wood degradation and defects, such as voids and knots, affect the quality and processing time of lumber. The ability to detect internal defects in the log can save mills time and processing costs. In this study, we investigated three nonde-structive evaluation techniques for detecting internal wood defects.

Sound wave transmission, x-ray. revenue to MSR producers. Therefore, an experimental study was initiated to study the effect of large VQL (edge knots) on the strength properties of Spruce-Pine-Fir (SPF) MSR lumber.

Two groups of material were studied that had been graded by a Continuous Lumber Tester (CLT) to receive a EFb MSR grade designation. Longitudinal stress waves for lumber stress grading: Factors affecting applications: state of the art [Gerhards, C.

C] on *FREE* shipping on qualifying offers. Longitudinal stress waves for lumber stress grading: Factors affecting applications: state of the artAuthor: C.

C Gerhards. School of Forestry and Wood Products Michigan Technological University Townsend Drive Houghton, MI and Roy F. Pellerin† Emeritus Professor Department of Civil & Environmental Engineering Washington State University J Place Ocean Park, WA † Member of SWST.

(Received February ) qxd 6/15/04 PM Page Unsound knots (or loose knots) are knots which fall out of the lumber when pushed or have already fallen out. They are caused by a dead branch that was not fully integrated into the tree before it. When the moisture content was the same, the stress wave velocity increased with increasing the basic density of wood, and the increase rate for beech wood was %% while that of larch wood.

The knot depth ratio (KDR) evaluation method was designed to quantitatively evaluate the amount of knot in dimension lumber by a single-pass X-ray radiation. To verify the proposed method, KDR values for mm-thick specimens were predicted, and they were compared with the actual measured KDR values.

The knot is surrounded by the transition zone, and the density of the knot and the transition. Effect of cross grain on stress waves in lumber. Madison, Wis.: Forest Products Laboratory, (OCoLC) Material Type: Government publication, National government publication: Document Type: Book: All Authors / Contributors: C C Gerhards; Forest Products Laboratory (U.S.).

Annual book of ASTM. Vol Monitoring the adhesive curing process for parallel wood laminates () Effect of knots on stress waves in lumber. Research Paper FPL Forest Service. The wood samples were tested by the technique of stress wave, and the testing results were analyzed by using the statistic software of SPSS.

The results. The primary objective of Foundations of Stress Waves is to give the reader an understanding of stress wave behaviour while taking into account the dynamic constitutive equations of elastic-plastic solids.

The author has combined a 'materials characteristics' approach with a 'singularity surface' approach in this work, which readers will find to be a novel and unique route to solving their.

entation, opening faces, knots, and ran- don1 variability. Recent technology has allowed for nondestructive scanning of internal fea- tures of the log (Qa et al. Nonde- structive tools include gamma rays. x- rays, nuclear magnetic resonance, mi- crowaves, ultrasound blbration and lon- gitudinal stress waves.

These tools vary. strength (MOR) of lumber or veneer. He also summarized the effect various wood factors have on stress wave velocity (c), which ranges f to 20, ft/ sec parallel to the grain in defect-free wood at 9 to 15% moisture content (MC). Wave velocity 1) decreases as grain angle, wood temperature or moisture content.

(): The Effect of Moisture Content on the stress wave parameters; Proc. of the First European Symposium on Nondestructive Evaluation of Wood, pp:at all (): Non-contact Method to Determine Ultrasonic Velocity of wood based Panels; Proc. of the 10 th International Symposium on Nondestructive Testing of Wood, pp: Gerhards CC () Effect of knots on stress waves in lumber.

Research Paper FPL U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, WI. 28 pp. Gil-Moreno D, Dan RE () Comparing usefulness of acoustic measurements on. Effects of Moisture Content and Fiber Proportion on Stress Wave Velocity in Cathay Poplar (Populus cathayana) Wood Hao Liu, Jianmin Gao,* Yao Chen, and Yi Liu Changes in longitudinal stress wave velocity measured during the drying process of Cathay poplar (Populus cathayana) wood at different moisture contents were investigated.

lower grades of lumber that are prone to warp. Gerhards () studied the effects of knots on stress waves in lumber and found that wave speed was slowed through knots and the curved grain around knots. Gerhards also concluded that, in lumber with cross grain and knots, the stress wave does not propagate with a normal wave front as supposed by.

Where: E oe = Modulus of elasticity by stress waves (Pa). v oe = Speed of the stress waves (m/s). P H = Wood density with H moisture content (kg/m 3). Experimental design.

The experience was designed following the recommendations of Gutierrez-Pulido and de la Vara-Salazar (), which consisted in comparing the means of the parameters: modulus of elasticity using ultrasound (E us) and. Material properties and NDE measurements such as static MOE, impact stress wave and transverse vibration MOEs were collected for the lumber.

Before proceeding with final ultrasonic testing, pilot studies were done to study the effect of the strength reducing factors, such as grain angle and edge knots, on ultrasonic wave velocity.

Full 3D anisotropic model is based on the visible knot geometries on the surfaces. • Stress concentration factors represent the stress effects of multiple knots. • Virtual dynamic modulus of elasticity is determined for a range of wood qualities.

• Wood surface image and average density are sufficient as input parameters. The presence and dimension of knots is a fundamental characteristic to take into account in the prediction of the mechanical performance of softwood lumber, but the same is not true for hardwoods: low correlations between several parameters describing knots and bending strength have been reported for Eucalyptus (Piter et al.

a, b), oak (Riesco Muñoz and Remacha Gete ), and chestnut (Nocetti et al. Rock joints are prone to open and fail when subject to severe dynamic extension, which might result in spalling of surrounding rock and collapse of un.

for a stress wave to travel a specified distance. If the material dimensions are known, stress wave timing can be used to locate decay in timber members.

Since stress waves travel slower through decayed wood than sound wood, the localized condition of a member can be determined by measuring stress wave time at incremental locations along the. 1.) Stress Wave Method The stress wave method is based on that the speed of sound with the rate of attenuation or combination of these with other factors depend on the same fundamental quantities, that determine the strength and stiffness of wood.

In practice a compression wave is generated in the material by tapping it with a hammer (Figure 1). Knots attenuate more ionizing radiation than clear wood areas, because of the higher density. The differing density also affects elastic properties of knots and clear wood.

Effects of knots on waves propagation can be differently evaluated, according to the acoustic techniques used. Abstract. Based on the effects of stress wave propagation in larch (Larix gmelinii) wood, the propagation mechanism of stress wave was explored, and a theoretical model of the propagation velocity of stress waves in the three-dimensional space of wood was cross and longitudinal propagation velocities of stress wave were measured in larch wood under different.

Standard methods of testing small clear specimens of lumber. Annual book of ASTM standards Part ANSI/ASTM D (78). American Society for Testing and Materials, Philadelphia, Penn. 58– Effects of knots on stress waves in lumber. USDA For. Serv. Res. Pap. FPL p In the present paper, a model for the prediction of the local strength and stiffness properties is developed.

Compared to existing models, here the local material properties are described according to their morphological characteristics; i.e. the timber boards are subdivided into sections containing knots (knot sections) and sections without knots (clear wood sections).

And as electric meters lose accuracy in some moisture ranges, in this work a Stress Wave Timer was used to try and assess the possibility of estimating wood moisture based on variation in the propagation velocity of stress waves in two Eucalyptus species.

Effects of knot area and board basic density on the propagation of stress waves were also. The propagation of stress waves in wood is affected by tree species, moisture content, and environmental temperature (Chauhan and Walker ; Chan et al.

; Liu et al. ; Yang et al. Xu et al. () studied the effects of moisture content and temperature on the propagation velocity of stress waves in Korean pine wood. Books at Amazon. The Books homepage helps you explore Earth's Biggest Bookstore without ever leaving the comfort of your couch.

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the most numerous and severe defect in southern pine lumber (Divos and Tanaka ). The reduction in strength and stiffness associated with knots is often magnified by the grain deviation in the wood immediately surrounding knots (Karsulovic et al.

). The grain deviation.Since moisture content affects density and therefore the speed of propagation of a stress-wave in wood, acoustic measurements were taken on the sample trees around m from ground level with the probes inserted into the stem at two different depths, namely cm and 3 cm, which conform to previously published data on sapwood and heartwood.