scholarly journals Fundamental Mechanism of Slow Crack Growth in Semi-Crystalline Polymers under a Constant Load

2019 ◽  
Vol 10 (11) ◽  
pp. 721-731
Author(s):  
Norman Brown
Keyword(s):  
Crack Growth ◽  
Slow Crack Growth ◽  
Constant Load ◽  
Crystalline Polymers ◽  
Fundamental Mechanism

Fracture Morphologies of Carbon-Black-Loaded SBR Subjected to Low-Cycle, High-Stress Fatigue

1989 ◽  
Vol 62 (2) ◽  
pp. 272-287 ◽  
Author(s):  
Alfred Goldberg ◽  
Donald R. Lesuer ◽  
Jacob Patt
Keyword(s):  
Carbon Black ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
High Stress ◽  
Strength Loss ◽  
Tensile Tests ◽  
Constant Load ◽  
Low Carbon ◽  
Definition Of ◽  
Cyclic Damage

Abstract In the absence of a mechanical defect at the surface, failure is almost always initiated in the bulk of a sample at a material flaw. A variety of flaw morphologies are observed; however, the extent of cyclic damage could not be related to either flaw size or flaw type. Energy dispersive spectographic analysis did not reveal any differences in chemistry between a flaw site and regions remote from a flaw. The size and definition of a flaw increase with an increase in carbon-black loading. Initiation flaw sites are enveloped by fan-shaped or penny-shaped regions which develop during cycling. With the highly loaded carbon-black samples, these regions consist of concentric bands which increase in number and become more prominent with an increase in test temperature. This is attributed to the presence of knotty tearing. With low carbon-black loadings, the absence of any significant disorientations in the tearing paths during either a cycle or a series of cyclic events results in the absence of individual resolvable bands within the fatigue-tear regions. The size and morphology of a fatigue-tear region appears to be independent of the fatigue load or the extent of the damage (strength loss). By contrast, either an increase in cycling load or an increase in damage at constant load increases the definition of the fatigue-region morphology for all formulations of carbon black. The morphologies in regions leading to failure during the final cycle are identical to the morphologies of fractured surfaces obtained in conventional tensile tests—tear steps or ridges at low magnifications and slow crack-growth with coarse tear paths and fast crack-growth with fine tear paths at high magnifications. Morphologies typical of slow crack-growth are also seen within the banded (fatigue) regions. On the finest scale, the morphology can be described in terms of tearing of individual groups of rubber strands, collapsing to form a cell-like structure.

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

scholarly journals Unique Slow Crack Growth Behavior of Isotactic Polypropylene: The Role of Shear Layer-Spherulites Layer Alternated Structure

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2746
Author(s):  
Mingjin Liu ◽  
Jiaxu Luo ◽  
Jin Chen ◽  
Xueqin Gao ◽  
Qiang Fu ◽  
...  
Keyword(s):  
Shear Layer ◽  
Crack Growth ◽  
Isotactic Polypropylene ◽  
Slow Crack Growth ◽  
Crack Growth Behavior ◽  
Polymer Science ◽  
The Past ◽  
Propagation Behavior ◽  
Crack Propagation Behavior

With the development of polymer science, more attention is being paid to the longevity of polymer products. Slow crack growth (SCG), one of the most important factors that reveal the service life of the products, has been investigated widely in the past decades. Here, we manufactured an isotactic polypropylene (iPP) sample with a novel shear layer–spherulites layer alternated structure using multiflow vibration injection molding (MFVIM). However, the effect of the alternated structure on the SCG behavior has never been reported before. Surprisingly, the results showed that the resistivity of polymer to SCG can be enhanced remarkably due to the special alternated structure. Moreover, this sample shows unique slow crack propagation behavior in contrast to the sample with the same thickness of shear layer, presenting multiple microcracks in the spherulites layer, which can explain the reason of the resistivity improvement of polymer to SCG.

Slow crack growth in polyethylene - a review

1991 ◽  
Vol 41 (1) ◽  
pp. 55-67 ◽  
Author(s):  
Norman Brown ◽  
Xici Lu ◽  
Yan-Ling Huang ◽  
Ruzheng Qian
Keyword(s):  
Crack Growth ◽  
Slow Crack Growth

The Fracture Toughness of Hardened Tool Steels

1987 ◽  
Vol 109 (4) ◽  
pp. 314-318 ◽  
Author(s):  
D. F. Watt ◽  
Pamela Nadin ◽  
S. B. Biner
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Crack Opening ◽  
Compact Tension ◽  
Testing Procedure ◽  
Tool Steels ◽  
Opening Displacement ◽  
Tempering Temperature ◽  
Toughness Testing

This report details the development of a three-stage fracture toughness testing procedure used to study the effect of tempering temperature on toughness in 01 tool steel. Modified compact tension specimens were used in which the fatigue precracking stage in the ASTM E-399 Procedure was replaced by stable precracking, followed by a slow crack growth. The specimen geometry has been designed to provide a region where slow crack growth can be achieved in brittle materials. Three parameters, load, crack opening displacement, and time have been monitored during the testing procedure and a combination of heat tinting and a compliance equation have been used to identify the position of the crack front. Significant KIC results have been obtained using a modified ASTM fracture toughness equation. An inverse relationship between KIC and hardness has been measured.

Sign in / Sign up

Export Citation Format

Share Document