scholarly journals Investigation of progressive damage and fracture in laminated composites using the smeared crack approach

2012 ◽  
Author(s):  
Christian Heinrich ◽  
Anthony Waas
Keyword(s):  
Laminated Composites ◽  
Progressive Damage ◽  
Damage And Fracture ◽  
Smeared Crack Approach ◽  
Smeared Crack

scholarly journals Fracture of Elastomeric Materials by Crosslink Failure

2018 ◽  
Vol 85 (8) ◽  
Author(s):  
Yunwei Mao ◽  
Lallit Anand
Keyword(s):  
Free Energy ◽  
Failure Mode ◽  
Chain Scission ◽  
Progressive Damage ◽  
Central Feature ◽  
Single Chain ◽  
Elastomeric Material ◽  
Damage And Fracture ◽  
Elastomeric Materials ◽  
Covalent Crosslinks

If an elastomeric material is subjected to sufficiently large deformations, it eventually fractures. There are two typical micromechanisms of failure in such materials: chain scission and crosslink failure. The chain scission failure mode is mainly observed in polymers with strong covalent crosslinks, while the crosslink failure mode is observed in polymers with weak crosslinks. In two recent papers, we have proposed a theory for progressive damage and rupture of polymers with strong covalent crosslinks. In this paper, we extend our previous framework and formulate a theory for modeling failure of elastomeric materials with weak crosslinks. We first introduce a model for the deformation of a single chain with weak crosslinks at each of its two ends using statistical mechanics arguments, and then upscale the model from a single chain to the continuum level for a polymer network. Finally, we introduce a damage variable to describe the progressive damage and failure of polymer networks. A central feature of our theory is the recognition that the free energy of elastomers is not entirely entropic in nature; there is also an energetic contribution from the deformation of the backbone bonds in a chain and/or the crosslinks. For polymers with weak crosslinks, this energetic contribution is mainly from the deformation of the crosslinks. It is this energetic part of the free energy which is the driving force for progressive damage and fracture of elastomeric materials. Moreover, we show that for elastomeric materials in which fracture occurs by crosslink stretching and scission, the classical Lake–Thomas scaling—that the toughness Gc of an elastomeric material is proportional to 1/G0, with G0=NkBϑ the ground-state shear modulus of the material—does not hold. A new scaling is proposed, and some important consequences of this scaling are remarked upon.

Progressive Fatigue Damage Simulation in Laminated Composites Based on Explicit Finite Element Formulation

2019 ◽  
Vol 64 (2) ◽  
pp. 1-12
Author(s):  
Yuri Nikishkov ◽  
Guillaume Seon ◽  
Andrew Makeev
Keyword(s):  
Finite Element ◽  
Laminated Composites ◽  
Test Methods ◽  
Remaining Useful Life ◽  
Image Correlation ◽  
Progressive Damage ◽  
Damage Analysis ◽  
Explicit Finite Element ◽  
Analysis Methods ◽  
Open Hole

Advanced polymeric composites are playing a major role in designing high-performance and lightweight vertical lift structures. However, uncertain residual strength and remaining useful life of the composite rotor and airframe structures due to complexity of failure mechanisms and susceptibility to manufacturing irregularities, which may be precursors to structural damage, impose risks that cannot be mitigated exclusively by time-consuming and costly experimental iterations. Validated analysis techniques accelerating design, certification, and qualification of composite structures are needed. Our team has been taking essential steps toward improving confidence in material qualification for laminated composites. The first step started with our reduced lamina test methods, short-beam shear, and small-plate twist based on digital image correlation measuring as a subset the standard material properties and, in addition, key properties that cannot be currently measured using any standard test methods. The lamina properties provide essential material input data for laminate analysis. The laminate analysis was the second step increasing confidence in material qualification. A known weakness of the existing progressive damage analysis methods is the lack of effective techniques to predict ultimate failure. The newly developed methodology relies on explicit finite element modeling and eliminates convergence issues in the ply-level progressive damage analysis methods due to severe nonlinear discontinuities after propagation of damage beyond detectable size. This work shows results of applying this methodology to nanosilica-toughened IM7/PMT-F3GHT open-hole tension strength/fatigue, open-hole compression strength/fatigue, and bearing strength multidirectional laminate configurations. The ability to predict progression of damage from initiation to ultimate strength and fatigue for advanced material systems including IM7/PMT-F3GHT carbon/epoxy reinforced by nanosilica has been demonstrated for the first time.

scholarly journals Effects of Nonuniform Fiber Geometries on the Microstructural Fracture Behavior of Ceramic Matrix Composites

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Hye-gyu Kim ◽  
Wooseok Ji ◽  
Nam Choon Cho ◽  
Jong Kyoo Park
Keyword(s):  
Optimization Algorithm ◽  
Fracture Behavior ◽  
Ceramic Matrix Composite ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Shear Loading ◽  
Matrix Composites ◽  
Specific Loading ◽  
Smeared Crack Approach ◽  
Smeared Crack

Microstructural fracture behavior of a ceramic matrix composite (CMC) with nonuniformly distributed fibers is studied in the presentation. A comprehensive numerical analysis package to study the effect of nonuniform fiber dimensions and locations on the microstructural fracture behavior is developed. The package starts with an optimization algorithm for generating representative volume element (RVE) models that are statistically equivalent to experimental measurements. Experimentally measured statistical data are used as constraints while the optimization algorithm is running. Virtual springs are utilized between any adjacent fibers to nonuniformly distribute the coated fibers in the RVE model. The virtual spring with the optimization algorithm can efficiently generate multiple RVEs that are statistically identical to each other. Smeared crack approach (SCA) is implemented to consider the fracture behavior of the CMC material in a mesh-objective manner. The RVEs are subjected to tension as well as the shear loading conditions. SCA is capable of predicting different fracture patterns, uniquely defined by not only the fiber arrangement but also the specific loading type. In addition, global stress-strain curves show that the microstructural fracture behavior of the RVEs is highly dependent on the fiber distributions.

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