Repeatable pre-cracking preparation for fracture testing of polymeric materials

Nithiananthan Kuppusamy,Rachel A Tomlinson

doi:10.1016/j.engfracmech.2015.12.007

Nithiananthan Kuppusamy, Rachel A Tomlinson

Open Access

https://doi.org/10.1016/j.engfracmech.2015.12.007

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Journal: Engineering Fracture Mechanics	Publication Date: Dec 17, 2015
Citations: 18	License type: cc-by

Affiliation: University of Sheffield

Abstract

Currently, in order to create a sharp pre-crack in a polymeric material for fracture toughness testing, a hand-held razor blade is used. This technique produces cracks of varying angle, length, and crack-front shape. Additionally, there are considerable safety concerns regarding the handling of sharp razor blades. A repeatable, safe method of producing a consistent, sharp pre-crack of a specified length, orientation and crack front is presented here, by use of a simple custom fixture. The specimen preparation procedure has wide applicability for fracture analysis of many brittle materials.

Highlights

Composite materials are substituting more conventional materials in load-bearing applications in many industries in order to reduce the weight of a component and provide bespoke material properties
The aim of this paper is to evaluate critically the methodologies for introduction of pre-cracks recommended in the fracture testing standards for polymeric materials, focusing on ease of use and repeatability
It is observed in BS ISO 13586:2000 [3] that it is vitally important to use specimens containing a sharp, pre-crack in order for the Linear Elastic Fracture Mechanics (LEFM) theories to be valid

Summary

Introduction

Composite materials are substituting more conventional materials in load-bearing applications in many industries in order to reduce the weight of a component and provide bespoke material properties. If it is not possible to create a precrack using the above methods, the standards warn not to apply pressure to the new razor blade on to the centre of the notch, since this could introduce residual stresses at the tip of the natural crack and effectively alter the measured KIc values [2,3]. It is suggested in the ASTM D6068 [4], that pre-cracking may be performed by induced fatigue cycles, this is. A more efficient, repeatable method to generate a pre-crack of specified length is developed

Development of methodology

Prototype pre-crack rig

Further development

Determination of optimum compressive load

Repeatability of the method

Discussion

Conclusion