Session: 12-04-02: Drucker Medal Symposium

Paper Number: 150297

150297 - Quasi-Static and Dynamic Crack Growth in Cellulose Nano Papers: An Experimental Study 

Cellulose Nano Papers (CNP) are green materials with a potential for many wide ranging applications including structural. They are renewable and biodegradable materials with superior mechanical properties. Understanding the fracture and failure characteristics CNP is crucial for optimizing their performance and advancing their application range. This study focuses on the influence of film thickness on the mechanical properties CNP made from nanofibers using sol-gel approach. By analyzing the tension and fracture behaviors under vastly different strain rates, this research aims to contribute to the understanding of failure mechanics CNP.

The work comprises of fabricating nano papers derived from commercially procured cellulose nano fibrils or CNF. The CNP fabrication process followed the modified hand sheet making procedure recommended by the Technical Association of the Pulp and Paper Industry (TAPPI). To investigate the effect of film thickness on the mechanical properties, the CNP of different thicknesses ranging from 50 to 200 micrometers were prepared. Tension tests were conducted to evaluate the elastic properties, yield and ultimate stress, and strain-at-failure of the cellulosic papers under quasi-static loading conditions. The 2D digital image correlation (DIC) method was employed to measure and analyze the full-field deformations during tension tests. The results suggest significant thickness effect in these fibrous sheets. An elastic modulus of ~10 GPA and ultimate stress of >100 MPa with >6% strain at failure at the high end have been measured. Microscopy on CNP samples was is used to understand the observed differences. Quasi-static fracture tests on single edge notched tension specimens were also performed to quantify the critical stress intensity factors and assess the crack growth resistance. A crack initiation toughness of  appox. 10 MPa(m)^1/2 with increasing stress intensity factor values during stable crack growth regime was observed. Subsequently, dynamic crack growth studies in CNP were also carried out at elevated rates to contrast the effect of strain rate on crack growth behavior by employing ultra high speed photography and DIC. A long-rod impactor was used to indirectly load an edge cracked CNP specimen glued to an edge-notched PMMA support structure to achieve rapid loading. The full field optical data analysis revealed rapid crack growth reaching approx. 600 m/sec in these fibrous films.  The crack initiation and growth behaviors are currently being analyzed to assess the strain rate effects.  Preliminary results suggest a drop in the crack initiation toughness at the higher strain rate, suggesting a rate dependent crack initiation and growth behavior.

Presenting Author: Azeez Adebayo Auburn University

Presenting Author Biography: Mr. Adebayo is a doctoral student of Dr. Hareesh Tippur at Auburn University, AL.

Authors:

Azeez Adebayo Auburn University
Hareesh Tippur Auburn University