1. Scope

1.1 This test method describes the experimental methods and procedures for the determination of the critical mode I interlaminar strain energy release rate of continuous fiber-reinforced ceramic matrix composite (CMC) materials in terms of the GIc. This property is also sometimes described as the mode I fracture toughness or the mode I fracture resistance.
1.2 This test method applies primarily to ceramic matrix composite materials with a 2-D laminate structure, consisting of lay-ups of continuous ceramic fibers, in unidirectional tape or 2-D woven fabric architectures, within a brittle ceramic matrix.
1.3 This test method determines the elastic strain energy released per unit of new surface area created as a delamination grows at the interlaminar interface between two lamina or plies. The term delamination is used in this standard to specifically refer to this type of growth, while the term crack is a more general term that can also refer to matrix cracking, intralaminar delamination growth, or fiber fracture.
1.4 This test method uses a double cantilever beam (DCB) specimen to determine the critical mode I interlaminar strain energy release rate. A DCB test method has been standardized for polymer matrix composites (PMCs) under ASTM D5528. This standard addresses has a similar procedure, but with modifications to account for the different physical properties, reinforcement architectures, stress-strain response, and failure mechanisms of CMCs compared to PMCs.
1.5 This test is written for ambient temperature and atmospheric test conditions. But the test method can also be used for elevated temperature or environmental exposure testing with the use of an appropriate environmental test chamber, measurement equipment for controlling and measuring the chamber temperature, humidity, and atmosphere, high temperature gripping fixtures, and modified equipment for measuring delamination growth.
1.6 Values expressed in this test method are in accordance with the International System of Units (SI) and IEEE/ASTM SI 10.
1.7 This standard does not purport to address all of the safety concerns, if any associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific hazard statements are given in Section 8.
1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision of Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

Keywords

ceramic matrix composite; interlaminar delamination; mode i; critical strain energy release rate; fracture toughness; fracture resistance; double cantilever beam

Rationale

The objective of this ASTM standard test method for the critical mode I strain energy release rate (GIc) of fiber reinforced ceramic matrix composites is to provide the advanced ceramics composite community a detailed and comprehensive test procedure for determining the critical mode I strain energy release rate for interlaminar delamination growth of fiber reinforced ceramic matrix composites. This test method is based on the ASTM D5528 interlaminar fracture toughness standard for polymer matrix composites and uses the double cantilever beam specimen geometry, adhesively-bonded loading block and hinges for force application, and the compliance calibration calculations for the GIC values. It considers the identification of initiation GIC values and the assessment of R-curve behavior in CMCs. It is modified for smaller CMC test specimens and includes additions and changes addressing CMC-specific testing issues, compared to polymer matrix composites. The modifications are based on test method research and development done at Southern Research Institute (SRI) and Materials Research and Design (MR&D) under a Navy NAVAIR project. The work is described in ITAR-restricted project reports and conference presentations.
The guide will benefit the ceramic composites community by providing a new standard test method which gives detailed direction and guidance on equipment requirements, test specimen geometry and preparation, test procedures, data calculation, and reporting for fiber-reinforced ceramic matrix composites.
This document was originally written by Steve Gonczy and balloted at the subcommittee level in the Spring of 2018, where it received numerous comments and 3 negative votes. After major revisions it was balloted again in the Fall of 2018, again receiving negatives and comments. The active work item was eventually closed.
Despite the challenges in reaching ballot approval, a mode I interlaminar fracture test method is still needed by the community, and so the document has once again received significant revisions and is submitted for this third ballot under a new work item.

The title and scope are in draft form and are under development within this ASTM Committee.