Dynamic crack initiation and growth in cellulose nanopaper

Chengyun Miao,Hareesh V Tippur,Haishun Du,Xinyu Zhang

doi:10.1007/s10570-021-04310-x

Abstract

Cellulose nanopaper (CNP) made of cellulose nanofibrils has gained extensive attention in recent years for its lightweight and superior mechanical properties alongside sustainable and green attributes. The mechanical characterization studies on CNP at the moment have generally been limited to tension tests. In fact, thus far there has not been any report on crack initiation and growth behavior, especially under dynamic loading conditions. In this work, crack initiation and growth in self-assembled CNP, made from filtration of CNF suspension, are studied using a full-field optical method. Dynamic crack initiation and growth behaviors and time-resolved fracture parameters are quantified using Digital Image Correlation technique. The challenge associated with dynamic loading of a thin strip of CNP has been overcome by an acrylic holder with a wide pre-cut slot bridged by edge-cracked CNP. The ultrahigh-speed digital photography is implemented to map in-plane deformations during pre- and post-crack initiation regimes including dynamic crack growth. Under stress wave loading conditions, macroscale crack growth occurs at surprisingly high-speed (600–700 m/s) in this microscopically fibrous material. The measured displacement fields from dynamic loading conditions are analyzed to extract stress intensity factors (SIF) and energy release rate (G) histories. The results show that the SIF at crack initiation is in the range of 6–7 MPa m1/2, far superior to many engineering plastics. Furthermore, the measured values increase during crack propagation under both low- and high-strain rates, demonstrating superior fracture resistance of CNP valuable for many structural applications.Graphical abstract

Highlights

Cellulose nanofibrils (CNF), an advanced bio-nano-material produced from lignocellulosic biomass, offers outstanding properties such as high elastic modulus, high specific surface area, high thermal stability, as well as biocompatibility, biodegradability and lightweight characteristics (Du et al, 2020; Xie et al, 2018)
The challenge associated with dynamic loading of a thin strip of Cellulose nanopaper (CNP) has been overcome by an acrylic holder with a wide pre-cut slot bridged by edge-cracked CNP
Miao et al (Chengyun Miao et al, 2020) comparatively evaluated crack initiation and growth behaviors of CNP made by two methods namely casting and filtration, and observed increasing crack growth resistance during the entire fracture process starting from crack initiation to significant growth

Summary

Introduction

Cellulose nanofibrils (CNF), an advanced bio-nano-material produced from lignocellulosic biomass, offers outstanding properties such as high elastic modulus, high specific surface area, high thermal stability, as well as biocompatibility, biodegradability and lightweight characteristics (Du et al, 2020; Xie et al, 2018). Miao et al (Chengyun Miao et al, 2020) comparatively evaluated crack initiation and growth behaviors of CNP made by two methods namely casting and filtration, and observed increasing crack growth resistance during the entire fracture process starting from crack initiation to significant growth Their results showed that the CNP made by the filtration method outperformed the cast counterpart in terms of mechanical properties. DIC to measure thermal expansion of cellulose nanocrystal (CNC) films (Diaz et al, 2013), the in-plane strain fields on CNP under tension (Zhao et al, 2018), and fracture strength of CNF hydrogel composite subjected to cyclic loading (Wyss et al, 2018). The details about the experiments pertaining to mapping crack tip fields in single edge notched CNP specimens subjected to dynamic loadings by DIC are discussed This is followed by calculating fracture mechanics parameters (crack velocity, stress intensity factors and energy release rates) from the DIC measurements. Fracture mechanics parameters are qualitatively correlated with fractographic features and summarized

Preparation of CNP

Dynamic Fracture

Comparison with quasi-static fracture behavior

Findings

Concluding Remarks