The Effect of Notches on the Failure of Two-Dimensional Nonwoven Fiber Networks

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Yinglong Chen ◽  
Thomas Siegmund
Keyword(s):  
Fiber Orientation ◽  
Shear Failure ◽  
Fiber Material ◽  
Failure Strength ◽  
Double Edge ◽  
Unnotched Specimen ◽  
Notch Geometry ◽  
Notch Length ◽  
Nonwoven Fiber ◽  
Tearing Strength

Abstract The tearing response of sheets of nonwoven fiber material is investigated. It addresses the question on how notch length and notch geometry is related to the tearing strength and tearing processes. The system considered consists of elastic-brittle fibers connected by strong interfiber bonds. Fiber fracture is the only failure mechanism. For a random fiber orientation case, deformation of the unnotched specimen occurs by long-range fiber chains connecting the load inducing boundaries, and failure is by tearing the cross section. The strength of the notched random fiber sheets is well described by a net section criterion, independent of the notch geometry. For a fiber orientation with symmetry relative to the loading direction, tensile loading is transferred by formation of the X-shaped fiber chains centered in the specimen. The subsequent failure occurs along the fiber chain by shear. Thus, the tearing strength is independent of the notch depth in double-edge notched and single-edge notched specimens, when the presence of shallow notch does not disrupt the force chains in the model. As the notch disturbs the fiber chains, alternative shear failure path forms near the notch tip, leading to a dependence of failure strength on the notch geometry. Then, the failure strength of notched nonwoven networks is described by a shear strength and a notch geometry term.

Multi-Phase Finite Element Modeling of Machining Unidirectional Fiber Reinforced Composites

2007 ◽  
Author(s):  
Chinmaya R. Dandekar ◽  
Yung C. Shin
Keyword(s):  
Finite Element ◽  
Temperature Distribution ◽  
Fiber Orientation ◽  
Cohesive Zone ◽  
Interfacial Layer ◽  
Shear Failure ◽  
Cohesive Zone Modeling ◽  
Fiber Reinforced ◽  
Phase Approach ◽  
Multi Phase

A multi-phase and a continuum based finite element model using the commercial finite element package ABAQUS is developed for simulating the orthogonal machining of composite materials. The materials considered for this study are a glass fiber reinforced epoxy composite and a ceramic matrix composite. The effect of varying the fiber orientation and tool rake angle on the cutting force, temperature distribution and damage during machining are considered. In the multi-phase approach the fiber and matrix are modeled as continuum elements with isotropic properties separated by an interfacial layer while the tool is modeled as a rigid body. The cohesive zone modeling approach is used for the interfacial layer. Bulk deformation and shear failure is considered in the fiber and matrix while the traction separation in the cohesive zone is used to ascertain the extent of delamination below the work surface. For validation purposes simulation results of the multi-phase approach are compared with experimental measurements. Parametric studies are conducted utilizing the equivalent homogenous (EHM) material model. The EHM simplifies the composite material into an anisotropic but locally homogenous material. External heating effect on the workpiece is considered in the EHM model to include preliminary results on Laser Assisted Machining. The model is successful in predicting cutting forces, temperature distribution entry and exit damage with respect to the fiber orientation.

The effect of fiber orientation on matrix plasticity and fracture behavior of SiC fiber-reinforced titanium matrix composites

1994 ◽  
Vol 9 (7) ◽  
pp. 1767-1779 ◽  
Author(s):  
Hsing-Pang Chiu ◽  
S.M. Jeng ◽  
J-M. Yang
Keyword(s):  
Plastic Deformation ◽  
Crack Initiation ◽  
Fiber Orientation ◽  
Fracture Behavior ◽  
Critical Energy ◽  
Plastic Deformation Zone ◽  
Initiation Energy ◽  
Critical Energy Release Rate ◽  
The Matrix ◽  
Notch Length

The effect of fiber orientation on the matrix plasticity and fracture behavior of SCS-6 fiber-reinforced Ti-15V-3Al-3Cr-3Sn composites was studied. The laminates used in this study were [0]6, [0/±45]s, and [90/±45]s. Three-point bending tests were conducted on chevron-notched specimens to determine the crack initiation energy, fracture toughness, and fracture strength as a function of notch length. The critical energy release rate was determined from the slope of the crack initiation energy versus notch length curve. The damage evolution and development of the matrix plastic deformation zone at the notch tip during the crack initiation and propagation as a function of fiber orientation were also determined. The relationships among the crack-tip matrix plastic deformation zone size, the critical energy release rate, and notch strength of the composites were discussed.

Thermal Damage, Cracking and Rapid Erosion of Cannon Bore Coatings

2003 ◽  
Vol 125 (3) ◽  
pp. 299-304 ◽  
Author(s):  
John H. Underwood ◽  
Anthony P. Parker ◽  
Gregory N. Vigilante ◽  
Paul J. Cote
Keyword(s):  
Thermal Damage ◽  
Shear Failure ◽  
Low Cycle Fatigue ◽  
Steel Substrate ◽  
Zone Model ◽  
Open Crack ◽  
Failure Strength ◽  
Closed Crack ◽  
Cyclic Shear ◽  
Coating Failure

Thermal damage observed at the bore of fired cannons has increased noticeably in the past decade, due to the use of higher combustion gas temperatures for improved cannon performance. Current authors and coworkers recently have described cannon firing damage and proposed new thermo-mechanical models to gain understanding of its causes, with emphasis on the severe damage that occurs in the steel beneath the chromium plating used to protect the cannon bore. Recent refinements in the models will be used here to characterize some additional damage observations in the area beneath the protective coating of fired cannons. Model results validated by microstructural observations give predictions of near-bore temperature and stress distributions and good agreement with observed depths of hydrogen cracking in the high strength steel substrate. Interest in damage and failure within a coating is also of concern for cannons, since coating failure leads to extremely rapid erosion of coating and substrate. The slip zone model of Evans and Hutchinson is adapted here to predict failure strength of cannon coatings based on observed crack spacing and microhardness of thermally damaged areas. Results are described for electroplated chromium coatings from fired cannons and for sputtered chromium and tantalum coatings with laser-heating damage to simulate firing. Coating mechanics analysis of fired and laser-heated samples provides an insitu measurement of coating failure strength, showing that sputtered chromium has more than twice the failure strength of electroplated chromium. An analysis of cyclic shear failure of a coating interface at an open crack shows a six-fold decrease in low cycle fatigue life compared to the life of a closed crack. Recommendations are given for preventing rapid coating failure and catastrophic erosion of fired cannon, with emphasis on methods to prevent deep, open cracks in coating and substrate.

scholarly journals Validating the Classical Failure Criteria for Applicability to the Notched Woven-Roving Composite Materials

2014 ◽  
Vol 2014 ◽  
pp. 1-12
Author(s):  
Mohamed Mostafa Yousef Bassyouny Elshabasy
Keyword(s):  
Composite Materials ◽  
Failure Mechanism ◽  
Fiber Orientation ◽  
Shear Failure ◽  
Failure Criteria ◽  
Interfacial Shear ◽  
Current Investigation ◽  
Experimental Part ◽  
Failure Theories ◽  
Bending Loading

The classical failure criteria are phenomenological theories as they ignore the actual failure mechanism and do not concentrate on the microscopic events of failure. The main objective of the current investigation is to modify the classical failure theories to comprise the essential failure mechanism (interfacial shear failure) in the thin-layered woven-roving composite materials. An interfacial shear correction factor (MH6) is introduced into the nondimensional shear terms in the studied classical failure criteria. Thus the validity of applying these theories to the investigated material will be augmented. The experimental part of the current study is conducted on thin-layered circular specimens. The specimens are fabricated from two plies of fiber E-glass woven-roving fabric reinforced with polyester. The fabrics are laid to have [±45°] or [0°, 90°] fiber orientation. The specimens used are plain, where no macroscopic sources of stress concentration exist or having circular notches of five, seven, or nine mm radii. The specimens are subjected to low cycle completely reversed fatigue bending loading where the S-N and the R.D.-N curves are plotted for each group of specimens.

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