Several studies on the fracture toughness of polytetrafluorethylene (PTFE) have focused on the plane strain condition using conventional fracture test specimens, such as compact tension and single-edge-notched bending specimens. On the other hand, there are few studies on this type of material using the double-edge-notched tension (DE(T)) specimen, which can offer an advantage in investigating constraint effects. DE(T) specimens can be used under plane strain and plane stress conditions. In this study, the effects of the crack depth on the fracture toughness are experimentally investigated on DE(T) specimens made of PTFE. As PTFE exhibits highly nonlinear behavior in the elastic–plastic regime and undergoes large deformations, the J-integral can be estimated by separating it into elastic and plastic portions. The elastic portion of the J-integral was obtained by a 2D domain approach using the digital image correlation (DIC) method together with a new strain-energy density function. The plastic portion of J was determined considering a factor calibration estimated from the load separation method. The crack-tip opening displacement (CTOD) and crack extension (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40430_2025_5651_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="26" /> </InlineMediaObject> <EquationSource Format="TEX">$\Delta a$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <mi>a</mi> </mrow> </math></EquationSource> </InlineEquation>) were estimated using a DIC virtual extensometer. Crack-tip constraint effects on fracture toughness were also presented using the plastic constraint factor based on the local maximum normal-stress-to-flow-stress ratio. Results showed that fracture toughness was quite sensitive to the strain hardening, while insignificant crack depth effects were observed on the fracture toughness when the crack-tip stress was lower than 20% of the flow stress. The influence of the relative crack depth is evident on the plastic portion of J. Our finding indicates that the combination of methods, including DIC, can be helpful to study the fracture toughness of highly nonlinear ductile polymers.

Effects of crack depth on fracture toughness of double edge cracked specimens of polytetrafluorethylene

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发表日期：

2025年5月27日

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P. R. Farias Junior,
J. C. A. D. Filho,
L. C. S. Nunes

摘要

Several studies on the fracture toughness of polytetrafluorethylene (PTFE) have focused on the plane strain condition using conventional fracture test specimens, such as compact tension and single-edge-notched bending specimens. On the other hand, there are few studies on this type of material using the double-edge-notched tension (DE(T)) specimen, which can offer an advantage in investigating constraint effects. DE(T) specimens can be used under plane strain and plane stress conditions. In this study, the effects of the crack depth on the fracture toughness are experimentally investigated on DE(T) specimens made of PTFE. As PTFE exhibits highly nonlinear behavior in the elastic–plastic regime and undergoes large deformations, the J-integral can be estimated by separating it into elastic and plastic portions. The elastic portion of the J-integral was obtained by a 2D domain approach using the digital image correlation (DIC) method together with a new strain-energy density function. The plastic portion of J was determined considering a factor calibration estimated from the load separation method. The crack-tip opening displacement (CTOD) and crack extension ( $\Delta a$ $Δ a$ ) were estimated using a DIC virtual extensometer. Crack-tip constraint effects on fracture toughness were also presented using the plastic constraint factor based on the local maximum normal-stress-to-flow-stress ratio. Results showed that fracture toughness was quite sensitive to the strain hardening, while insignificant crack depth effects were observed on the fracture toughness when the crack-tip stress was lower than 20% of the flow stress. The influence of the relative crack depth is evident on the plastic portion of J. Our finding indicates that the combination of methods, including DIC, can be helpful to study the fracture toughness of highly nonlinear ductile polymers.