Transverse Vibration Technique to Identify Deteriorated Wood Floor Systems

Abstract

KEYWORDS: Floor System, Nondestructive Evaluation, . Currently, the use of stress wave techniques is limited to NDE . individual wood members. Evaluating each member of a . structural system is labor intensive and time consuming. For he Forest Products Laboratory, USDA Forest Ser-. in situ inspection of timber structures, a more efficient stratvice, has been developing nondestructive evaluation . egy would be to screen whole structural systems or subsys-(NDE) techniques to identify degradation of wood . tems in terms of their overall performance and serviceability. in structures and the performance characteristics . Examining the dynamic response of the structural system trasonic transmission NDE techniques for both laboratory any organisin reduces the strength and stiffness of the mathat remain in the structure. This work has focused on using . might provide an alternative way to gain insight into the dynamic testing techniques, particularly stress wave and ul-. ongoing performance of the system. Deterioration caused by and field investigations.. . terials and thus could affect the dynamic behavior of the . system. If, for example, one structural system or sections of Our initial efforts were aimed at using stress wave tech-. the system were found to respond to dynamic loads in a manniques to identify wood degradation. In a previous publica-. ner significantly different from that of other similar systems tion, 1 we reported on an inexpensive experimental technique . or the surrounding sections of the system, a more extensive that was developed to observe longitudinal stress wave be-. inspection of that system or section would be warranted. havior in small wood specimens. The technique utilized a .mechanical impactor to induce a wave in the specimen. Wave . Based on this conceptual strategy, we began to investigate propagation was observed by placing a piezo film sensor on . the possibility of using transverse vibration techniques to inspect full-size wood floor T the surface of the wood. Output of the sensor was recorded and displayed on a digital storage oscilloscope. This technique enabled us to examine fundamental wave propagation characteristics and the biological degradation of wood. Recently, we investigated the use of speed of sound transmission to locate degraded regions in wood materials. 2 The test setup we developed consisted of two 84-kHz rolling transducers coupled to an ultrasonic systems by evaluating component systems. This paper describes the experimental setup developed for our research and typical results obtained from its use. TRANSVERSE VIBRATIONTransverse vibration techniques have received considerable attention for NDT applications in the wood industry.3 To illustrate these methods, an analogy can be drawn between the behavior of a vibrating beam and the vibration of a mass that is attached to a weightless spring transmitting and receiving Fig. I : Mass-spring dashpot vibration model (left) and unit. A stress wave was introduced into a specimen in the transverse direction by transversely...

EDGE Glued Panels Grading through Transversal Vibration Testing

“…To illustrate these methods of transverse vibration (Fig. 1), an analogy can be drawn between the behavior of a vibrating beam and the vibration of a mass that is attached to a weightless spring and internal damping force [19,22]. According to [20], this natural vibration frequency of wood will depends on: the modulus of elasticity of wood, span between the two supports, wood density, and the type of support.…”

“…In the Figure 1, the mass M is supported from a rigid body by a weightless spring whose stiffness is denoted by K. Internal friction or damping is represented by the dashpot D. A forcing function equaling P 0 sin ωt or zero is applied for forced or free vibration, respectively. When M is set into vibration, its equation of motion can be expressed by the following [19,22]:…”

“…Mass-spring dashpot vibration (left) and transversely vibrating beam (right). Adapted from [19] and [22] According to these last aforementioned literatures, the equation 1 can be solved for either K or D, and a solution for K will lead to an expression for modulus of elasticity E or MOE for a beam simply supported at its ends:…”

“…In this equation 2, f r is natural frequency in Hertz, W is beam weight in kilograms, L is beam span in meters, I is beam moment of inertia in meter to fourth power, and g is the acceleration due to gravity, i.e., 9.8 m/s 2 [19,22]. The Figure 2 shows the scheme of a machine to determine MOE by transverse vibration.…”