ORIGINAL ARTICLE Non-destructive estimation of modulus of elasticity of wood polymer composite Amey Kale 1 • Shakti Chauhan 1 Received: 11 November 2016 / Accepted: 20 December 2016 Ó Indian Academy of Wood Science 2017 Abstract Dynamic modulus of elasticity (DMoE) of wood polymer composites, prepared with varying proportion of wood content, was determined using flexural vibration and ultrasonic pulse transit time methods. The DMoE was compared with the flexural modulus as measured by stan- dard three point bending test. The elastic modulus of the composite increased with the increasing fiber content. Both vibration methods exhibited a strong linear association with static modulus. DMoE by ultrasonic pulse method was higher compared to flexural vibration method at low wood content and the difference diminished at 50% wood in composites. Both the dynamic modulus were higher as compared to the static modulus at all fiber loadings, how- ever the difference between dynamic and static modulus reduced non-linearly with increasing wood content. Keywords Elastic modulus Á Flexural vibration Á Non- destructive testing Á Ultrasonic Á WPC Introduction Non-destructive vibration methods are extensively used to determine elastic constants, damping and attenuation characteristics, fatigue behaviour, presence of flaws and other defects in the materials (Kolsky 1963; Bucur 1996; Tanasoiu et al. 2002; Hearmon 1966). Vibration methods require a very small force for a very short duration resulting in very small displacements. Thus such methods becomes more relevant in studying properties of visco- elastic polymeric materials where prolonged elongation, stresses and fatigue are may result changes in the structure of polymeric material and, consequently, in the properties of materials during static tests (Perepechko 1975). These changes are the results of orientation and other effects due to the high value of the mechanical stresses appearing in the material and the relatively large strains. Polymers like polypropylene, polyethylene (HDPE and LDPE), elastomers, etc., are highly visco-elastic in nature and exhibit non-linearity in the stress–strain curves at a very small load. This non-linearity at small loads itself leads to ambiguity in determination of elastic modulus by static methods in such polymers (Tucker et al. 1998). Aggarwal (2008) observed significant variation in elastic modulus of HDPE, which is highly visco-elastic polymer, with change in the upper value of stress for determination of slope of stress–stain curve, whereas this variation was negligible in case of polystyrene which is a stiff polymer. In addition, the process parameters and formulations like fiber content, coupling agent and other additives strongly influences the properties of wood polymer composites (WPC). Since WPCs are now increasingly being used for semi-structural applications, they become prone to mois- ture absorption and fungal degradation particularly at high wood content. This may change their strength and stiffness over a period of time. Therefore, fast and reliable methods to assess such changes are necessary. Vibration methods provide scope for quick assessment of important properties like Young’s modulus and shear modulus, and such methods are relatively immune to the deficiencies associated with the static tests. Localizing resonance frequency of different vibration modes in a specimen of a specific shape and, measuring the speed and attenuation of a stress wave in the material are the two fundamental vibration methods. Tucker et al. (1998) used & Shakti Chauhan shakti@icfre.org; shakti32@gmail.com 1 Institute of Wood Science and Technology, Bengaluru, India 123 J Indian Acad Wood Sci DOI 10.1007/s13196-016-0183-5