Stato dell'arte della Simulazione di Materiali Compositi

Composites Structures: Civil Airplanes Applications

Boeing 787 Airbus A350

In black the composite parts

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Composites Structures: Automotive & Marine

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Composites Structures: Manufacturing & Civil

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• More than 10 000 customers• More than 1000 employees • More than 48 years experience• More than 200 Business Partner • Partnered with the industry majors to

deliver software which fits with customer processes

MSC Software: A Global Team

• The attractiveness of composites lies in their mechanical properties; such as weight, strength, stiffness, corrosion resistance, fatigue life. That is why the analysis of composite structures is imperative for the industries. The main advantage of composites is their flexibility in design. Mechanical properties of the laminate can be altered simply by changing the stacking sequence, fibre lay-up and thickness of each ply which leads to optimization in a design process.

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Introduction to Composites: Technologies

• Laminate effective material properties are tailored to meet performance requirements through the use of lamination theory integrated in the MSC.Software products.

• Used to accurately predict laminate properties. These analysis methods address:

• Stress-strain relationship for membrane and bending response

• Thermal and moisture effects

• Inelastic behavior

• Strength and failure

• Interlaminar stresses

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θ= 0º, t=0.0125

θ= 45º, t=0.01

θ= 90º, t=0.01

θ= -45º, t=0.01

θ=0º, t=0.01

θ= -45º, t=0.0125

θ= 90º, t=0.0125

θ= 45º, t=0.0125

Classical Lamination Theory (CLT)

• First-Ply Failure (FPF)– Linear analysis based on failure theory– Compute failure index or strength ratio

for the ply material– Optimization of ply angle/thickness

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Critical Margin of Safety

First-Ply-Failure Analysis

• Evaluate the load redistribution in a composite structure as the plies fail progressively

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CZM

DelaminationPFA

• Simulate delamination growth from initial flaw

• Study crack propagation to design for fail-safe structures

VCCT

Going Beyond First-Ply-Failure

• The progressive failure analysis is a method developed for predicting the nonlinear response and failure of laminated composite structures from initial loading to final failure.

• Failure is indicated by the failure criteria used.

• When failure occurs, the FEM element stiffness is degraded.

• The material will not heal; the damaged elements keep the degraded properties after unloading.

• Investigations of effect of overloads on composite structures

Progressive Failure Analysis

• Once the strains and stresses are known throughout the composite laminate, a failure theory is used to detect failures for each lamina at a given load level, when failure index is larger than one, degrade material stiffnesses

• Available for existing criteria:HillTsai-WuHoffman

• Available for NEW criteria:These failure theory are able to predict the failure load and also the mode of failure such as fiber failure and/or matrix failure.PuckHashinHashin-tapeHashin-fabric

Progressive Failure Analysis

• How does failure affect the different material moduli ?

• Assume – 1-direction is fiber direction– 2-direction is matrix direction in the plane of the ply– 3-direction is through the ply thickness

• Fiber failure– Reduce E1 and E3

• Matrix failure– Reduce E2, G12, G23 and G31

Progressive Failure Analysis

Rigid elliptical cylinder hitting composite shell

5-layered compositePuck criterion,

PFA with element deactivation to simulate crack propagation

Progressive Failure Analysis

• Integrated structural analysis software suite to predict strength, reliability and durability of structural composite components

• Based on constituent properties, Fiber and Matrix, evaluates the structural and material response including degradation of material properties due to initiation and growth of damage.

• Over 20 Micro Mechanical Failure Criteria Failure Criteria available with Nastran Adv. PFA analysis

Micromechanical Composite Material Definition

• Longitudinal tension

• Longitudinal compression

• Transverse tension

• Transverse compression

• Normal tension

• Normal compression

• In-plane shear

• Transverse normal shear

• Longitudinal normal shear

• Modified distortion energy

• Inter-ply relative rotation

Honeycomb failure modes recognized

• Fiber micro-buckling

• Tsai-Wu theory

• Hill theory

• Hoffman theory

• Maximum stresses theory

• Maximum strain theory

• First strain invariant failure

theory

• Inter-ply relative rotation

• Fiber crashing

Wrinkling Crimping Dimpling

Advanced Progressive Failure Analysis:Failure Theories

Fusolage Stiffened Panel Adv. Progressive Failure A nalysis with Micromecanical material definition (Fi ber / Matrix)

Glued Contact between frames and panel

Micromechanical Damage IndexStress Strain

Modeling composite materials at constituent Level

Continuum Elements are required for Composites Modelling:

• When detailed out-of plane stress recovery are needed

• When transverse shear effect are predominant

• When accurate interlaminate stresses such near localized region of complex loading or geometry

• When better contact condition are needed

3D composites

Detailed out-of plane stress recovery

3D composites

• Delamination is one of the main failure mechanisms in laminated composites• Possible reasons for delamination are:• Manufacturing defects and stress• Gradients near geometric discontinuities (like stiffener terminations and

bolted joints)• Delamination may result in local failure or even a significant loss of the

structural integrity • Three different approach available:

– VCCT– CZM– Breaking glued contact

Delamination Introduction

(Virtual Crack Closure Tecnique)

• The VCCT is the fracture mechanics approach for studying delamination and crack initiation and growth.

• It is used for calculating the energy release rate of single or multiple cracks.

Fracture Mechanics with VCCT

• In linear fracture mechanics, a crack starts to grow when– Total G > Gc

– G is the energy release rate– Gc is the fracture toughness

• VCCT is a methods used to compute the energy release rate.• Energy release rate:

G = Fu/2a

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(Virtual Crack Closure Tecnique)Fracture Mechanics with VCCT

Mode I: Opening

Mode II: Sliding

Mode III: Tearing

(Virtual Crack Closure Tecnique)Fracture Mechanics with VCCT

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VCCT with Remeshing VCCT without Remeshing

VCCT Examples:

• The so-called interface elements can be used to simulate the onset and progress of delamination. The constitutive behavior of these elements is expressed in terms of tractions versus relative displacements between the top and bottom edge/surface of the elements.

• Considering a 3-D interface element, the relative displacement components with respect to the local element system:

Cohesive Zone Modeling (CZM)Delamination:

• The interface elements can be modeled between 2D and 3D structural finite elements:

• The effective traction is introduced as a function of the effective opening displacement, and is characterized by an initial reversible response followed by an irreversible response as soon as a critical vc effective opening displacement has been reached. Three standard functions are currently available

Cohesive Zone Modeling (CZM)Delamination:

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Cohesive Zone Modeling: examples

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• Release glued contact when stress criteria is satisfied:

• Use contact normal and tangential stress

• After break, do regular contact with friction and separation

Breaking glued contactDelamination:

• Coating debonding

• Load with rigid body

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Breaking glued contact: examples

• Thermosets used as matrices in fibrous composites

• Cure is the reaction that transforms the matrix from a liquid oligomer to a cross linked glassy polymer

• Cure is initiated by increased temperature

• Cure leads to chemical shrinkage

• The progress of the reaction is characterised by the degree of cure (α)

• Prediction is critical for predicting final shape

• Four Cure Kinetics models implemented in MSC.Software technology:

Cure kinetics model 1 : by Lee, Loos and Springer

Cure kinetics model 2 : by Scott

Cure kinetics model 3 : by Lee, Chiu, and Lin

Cure kinetics model 4 : by Johnston and Hubert

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Curing Simulation

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Curing Simulation

Springing in Crowning and Twisting

• MSC.Software expertise is proven by the collaboration with all main global players in the composites material market

• MSC.Software solutions are already succefully applied in any stage of composites products development:– Conceptual Design– Optimization– Manufacturing

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• MSC.Software local team is highlyexperienced in delivering and implementing our solutions to customers

Conclusions:

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Armando MeteAccount Manager Aerospace Industry - Italy+39 06 42272249+39 3357851319armando.mete@mscsoftware.com

http://www.mscsoftware.com/

Largest Autoclave in the World Statistics:Inside working diameter: 30ft. (9.26M)Ouside diameter: 32ft. (9.88M)Inside working length: 76 ft. (23.5M)Overall length: 112 ft. (34.5M)Vessel volume: 82,000 cu.ft.Max temperature: 450FMax pressure: 150 psigVought Aircraft in Charleston, SC