scholarly journals Modelling of stiffness degradation due to cracking in laminates subjected to multi-axial loading

2016 ◽  
Vol 374 (2071) ◽  
pp. 20160017 ◽  
Author(s):  
M. Kashtalyan ◽  
C. Soutis
Keyword(s):  
Structural Integrity ◽  
Axial Loading ◽  
Mode Interaction ◽  
Damage Mode ◽  
Shear Lag ◽  
Full Account ◽  
Matrix Cracks ◽  
Stiffness Properties ◽  
Equivalent Constraint Model ◽  
Constraint Model

The paper presents an analytical approach to predicting the effect of intra- and interlaminar cracking on residual stiffness properties of the laminate, which can be used in the post-initial failure analysis, taking full account of damage mode interaction. The approach is based on a two-dimensional shear lag stress analysis and the equivalent constraint model of the laminate with multiple damaged plies. The application of the approach to predicting degraded stiffness properties of multidirectional laminates under multi-axial loading is demonstrated on cross-ply glass/epoxy and carbon/epoxy laminates with transverse and longitudinal matrix cracks and crack-induced transverse and longitudinal delaminations. This article is part of the themed issue ‘Multiscale modelling of the structural integrity of composite materials’.

scholarly journals Application of the Equivalent Constraint Model to Investigate Stiffness Properties of Transversally Cracked and Split Frp Laminates

1999 ◽  
Vol 8 (5) ◽  
pp. 096369359900800 ◽  
Author(s):  
M. Kashtalyan ◽  
C. Soutis
Keyword(s):  
Matrix Cracking ◽  
Shear Lag ◽  
Transverse Cracks ◽  
New Approach ◽  
Shear Lag Model ◽  
Transverse Cracking ◽  
Stiffness Properties ◽  
Lag Model ◽  
Equivalent Constraint Model ◽  
Constraint Model

A new approach based on the Equivalent Constraint Model (ECM) [ 1 ] of the damaged lamina is applied to investigate the stiffness degradation in [0m/90n]s laminates due to matrix cracking both in the 90° (transverse cracking) and 0° (splitting) plies. The advantage of the approach is that it avoids cumbersome consideration of a repeated laminate element defined by the intersecting pairs of transverse cracks and splits, intrinsic to the earlier developed models [ 2 – 6 ]. Instead, two coupled problems for ECM laminates are solved. The stress field in the damaged lamina is determined by means of an improved 2-D shear lag analysis, and the reduced stiffness properties are described with the help of Insitu Damage Effective Functions, for which closed form expressions are obtained. Comparison of the new ECM/2-D shear lag model with the earlier developed models shows a reasonable agreement.

Analysis of Fatigue Damage Mechanisms and Residual Properties of Polymer Matrix Composites

2000 ◽  
Author(s):  
Costas Soutis ◽  
Maria Kashtalyan
Keyword(s):  
Composite Laminates ◽  
Polymer Matrix Composites ◽  
Matrix Cracking ◽  
Matrix Composites ◽  
Residual Properties ◽  
Stiffness Properties ◽  
Observed Damage ◽  
Equivalent Constraint Model ◽  
Constraint Model ◽  
Longitudinal Cracks

Abstract Resin dominated damage modes such as matrix cracking in the off-axis plies and matrix crack-induced local and edge delaminations are common failure mechanisms in composite laminates under tensile or thermal fatigue. Accurate prediction of the laminate stiffness and strength must consider all the above-mentioned damage modes. In the present paper, an approach is developed for the analysis of cross-ply laminates damaged by transverse and longitudinal cracks and transverse and longitudinal delaminations that initiate and grow along these cracks. It is based on the Equivalent Constraint Model (ECM) of the damaged ply and employs an improved 2-D shear lag method to determine the stress field in the cracked and locally delaminated ply. The method is applied to predict residual stiffness properties of cross-ply graphite/epoxy laminates using experimentally observed damage patterns.

scholarly journals A Study of Matrix Crack Tip Delaminations and their Influence on Composite Laminate Stiffness

1999 ◽  
Vol 8 (4) ◽  
pp. 096369359900800 ◽  
Author(s):  
Maria Kashtalyan ◽  
Costas Soutis
Keyword(s):  
Transverse Crack ◽  
Crack Density ◽  
Crack Tip ◽  
Implicit Functions ◽  
Transverse Cracks ◽  
Transverse Cracking ◽  
Stiffness Properties ◽  
Equivalent Constraint Model ◽  
Constraint Model ◽  
Stiffness Loss

Reduction of the stiffness properties of cross-ply [0m/90n]s laminates due to delaminations, growing at the 0/90 interface from the tips of transverse cracks in the 90° plies and splits in the 0° plies, is analysed by means of a theoretical approach based on the Equivalent Constraint Model (ECM). Reduced stiffness properties of the damaged lamina are derived as explicit functions of the crack density and relative delamination area associated with that lamina and implicit functions of the two damage parameters associated with the neighbouring laminae. Transverse crack tip delaminations are found to cause significant reduction in the laminate shear modulus and Poisson's ratio. Contribution of each damage mode (transverse cracking, transverse crack tip delaminations, splitting and split tip delaminations) into stiffness loss is established.

scholarly journals Modelling Cracked Cross-Ply Laminates with Delamination Buckling

2018 ◽  
Vol 774 ◽  
pp. 60-65 ◽  
Author(s):  
A. Köllner ◽  
Maria Kashtalyan ◽  
Igor Guz ◽  
C. Völlmecke
Keyword(s):  
Structural Stability ◽  
Analytical Framework ◽  
Matrix Crack ◽  
Stability Behavior ◽  
Matrix Cracks ◽  
Stiffness Properties ◽  
Delamination Buckling ◽  
Plane Compression ◽  
Constrained Model ◽  
Modelling Approach

The mechanical behavior of cross-ply laminates loaded under in-plane compression containing matrix cracks and delaminations is investigated in order to study their influence on the structural stability behavior. This is done by employing a semi-analytical modelling approach which comprises an analytical framework for a structural stability analysis of damageable structures and the Equivalent Constrained Model for deriving reduced stiffness properties of the cracked layers. Cross-ply laminates with varying delamination depths as well as varying matrix crack densities are studied.

Numerical Study of an Impusively Loaded Vessel Containing Double Versus Single Closure Bolt Patterns

2017 ◽  
Author(s):  
Joseph E. D. Hess
Keyword(s):  
Finite Element ◽  
Structural Integrity ◽  
Numerical Study ◽  
Axial Loading ◽  
Element Model ◽  
Pressure Vessels ◽  
Bolted Joint ◽  
Single Row ◽  
Asme Code ◽  
Calculation Results

Impulsively loaded pressure vessels are often closed using a bolted joint configured in a double staggered row pattern. The bolted joint design must maintain the placement of the vessel opening covers to support the structural integrity of the shell and also provide the necessary preload of sealing surfaces for leak prevention. Good design practice suggests configuring tensile loaded bolted joints with a double rows pattern in order to minimize prying against the bolt head induced by localized moments. Double bolt row patterns allow moments induced by load offsets to be reacted through contact of the faying surfaces of the bolted members and if separation occurs by differential axial loading of the two bolt rows. This acts to reduce direct prying of the mated members against the bolt heads. Material cost and operational time savings could be realized if a single bolt row design with acceptable performance was implemented. In this paper a detailed finite element model is described and calculation results are presented for two vessel configurations subjected to an impulsive load; a double staggered 64 bolt pattern and a single row 32 bolt pattern. Finite element results are compared to each other and to the rules of ASME Code Case 2564 in Section VIII, Division 3. Special attention is given to the loading induced in the bolts and to the relative deflection of faying surfaces containing seals. It will be shown that reducing the bolt count per opening from 64 to 32 results in increased peak response of the bolts, seal opening gaps, and shell. Nonetheless a single row bolt pattern does appear feasible and within the bounds of the Code Case.

Modeling the Effective Elastic Behavior of a Transversely Cracked Laminated Composite

1998 ◽  
Vol 120 (1) ◽  
pp. 191-198
Author(s):  
D. J. Thomas ◽  
R. C. Wetherhold
Keyword(s):  
Laminated Composite ◽  
Point Of View ◽  
Crack Spacing ◽  
Elastic Behavior ◽  
Shear Lag ◽  
Underlying Assumption ◽  
Shear Lag Model ◽  
Matrix Cracks ◽  
State Present ◽  
Lag Model

The solution for the stress state present in the vicinity of transverse matrix cracks within a composite laminate is typically obtained by assuming a regular crack spacing geometry for the problem and applying a shear-lag analysis. In order to explore the validity of this underlying assumption, the probability density function for the location of the next transverse matrix crack within a crack bounded region is examined. The regular crack spacing assumption is shown to be reasonable from an engineering point of view. Continuing with this assumption, a generalized shear-lag model for multilayer, off-axis laminates subjected to full in-plane loads is developed. This model is used to quantitatively evaluate the effective elastic properties of the damaged material. The results are applicable to materials such as ceramic matrix or polymer matrix unidirectional fiber systems where damage in the form of transverse matrix cracks arises.

3-D Non-Linear Finite Element Analysis of a Non-Gasketed Flange Joint Under Combined Internal Pressure and Axial Loading

2007 ◽  
Author(s):  
Muhammad Abid ◽  
Abdul W. Awan
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Internal Pressure ◽  
Structural Integrity ◽  
Experimental Studies ◽  
Axial Loading ◽  
External Loading ◽  
Flange Joint ◽  
Element Analysis ◽  
Bolted Flange

A number of analytical and experimental studies have been conducted to study ‘strength’ and ‘sealing capability’ of bolted flange joint only under internal pressure loading. Due to the ignorance of the external i.e. axial loading, the optimized performance of the bolted flange joint can not be achieved. A very limited work is found in literature under combined internal pressure and axial loading. In addition, the present design codes do not address the effects of axial loading on the structural integrity and sealing ability of the flange joints. From previous studies, non-gasketed joint is claimed to have better performance as compared to conventional gasketed joint. To investigate non-gasketed joint’s performance i.e. joint strength and sealing capability under combined internal pressure and any applied external loading, an extensive 3D nonlinear finite element analysis is carried out and overall joint performance and behavior is discussed.

Evolution of Crack Density in Cross-Ply Laminates - Application of a Coupled Stress and Energy Criterion

2016 ◽  
Vol 713 ◽  
pp. 262-265
Author(s):  
Maria Kashtalyan ◽  
I.G. García ◽  
Vladislav Mantič
Keyword(s):  
Composite Laminates ◽  
Crack Density ◽  
Great Influence ◽  
Energy Criterion ◽  
Matrix Cracking ◽  
Transverse Cracks ◽  
Transverse Cracking ◽  
Finite Fracture Mechanics ◽  
Equivalent Constraint Model ◽  
Constraint Model

The first damage mode to appear in continuous fibre-reinforced composite laminates subjected to in-plane loading is usually transverse cracking, i.e. matrix cracking in the off-axis plies of the laminate. Since the density of transverse cracks has a great influence on the subsequent failure steps like delaminations, it is important to be able to predict it accurately. In this paper, the evolution of crack density with increasing external load is predicted using a combination of the Coupled Criterion of Finite Fracture Mechanics and the Equivalent Constraint Model.

scholarly journals Beyond the L-Strut: Redefining the Biomechanics of Rhinoplasty Using Topographic Optimization Modeling

2018 ◽  
Vol 39 (12) ◽  
pp. 1309-1318 ◽  
Author(s):  
Graeme Ewan Glass ◽  
Robert M T Staruch ◽  
Julia Ruston ◽  
Charles A East ◽  
P J Tan
Keyword(s):  
Structural Integrity ◽  
Axial Loading ◽  
Internal Stresses ◽  
Graft Material ◽  
Stress Concentrations ◽  
Fe Modelling ◽  
Minimum Width ◽  
Deformation And Failure ◽  
Inferior Portion ◽  
Structural Scale

AbstractRhinoplasty utilizes cartilage harvested from the nasal septum as autologous graft material. Traditional dogma espouses preservation of the “L-strut” of dorsal and caudal septum, which is less resistant to axial loading than virgin septum. Considering the 90° angle between dorsal and caudal limbs, the traditional L-strut also suffers from localized increases in internal stresses leading to premature septal “cracking,” structural-scale deformation, or both. Deformation and failure of the L-strut leads to nasal deviation, saddle deformity, loss of tip support, or restriction of the nasal valve. The balance between cartilage yield and structural integrity is a topographical optimization problem. Guided by finite element (FE) modelling, recent efforts have yielded important modifications including the chamfering of right-angled corners to reduce stress concentrations and the preservation of a minimum width along the inferior portion of the caudal strut. However, all existing FE studies offer simplified assumptions to make the construct easier to model. This review article highlights advances in our understanding of septal engineering and identifies areas that require more work to further refine the balance between the competing interests of graft acquisition and the maintenance of nasal structural integrity.

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