: An overview of the virtual crack closure technique is presented. The approach used is discussed, the history summarized, and insight into its applications provided. Equations for two-dimensional quadrilateral elements with linear and quadratic shape functions are given. Formula for applying the technique in conjuction with three-dimensional solid elements as well as plate/shell elements are also provided. Necessary modifications for the use of the method with geometrically nonlinear finite element analysis and corrections required for elements at the crack tip with different lengths and widths are discussed. The problems associated with cracks or delaminations propagating between different materials are mentioned briefly, as well as a strategy to minimize these problems. Due to an increased interest in using a fracture mechanics based approach to assess the damage tolerance of composite structures in the design phase and during certification, the engineering problems selected as examples and given as references focus on the application of the technique to components made of composite materials.

/pdf/virtual-crack-closure-technique-history-approach-and-53akn4ewzt.pdf

Virtual crack closure technique: History, approach, and applications

A Review on the Application of Nonlocal Elastic Models in Modeling of Carbon Nanotubes and Graphenes

Preface 1 Introduction: 1.1 Background 1.2 Fire reaction and fire resistive properties of composites 1.3 Composites and fire 1.4 Case studies of composites in fire 1.5 Concluding remarks References 2Thermal Decomposition of Composites in Fire: 2.1 Introduction2.2. Thermal decomposition mechanisms of organic polymers 2/3 Rate processes and characterisation of decomposition 2.4 Polymers and their decomposition processes 2.5 Fire damage to composites 2.6 Concluding remarks References 3 Fire Reaction Properties of Composites: 3.1 Introduction 3.2 Time-to-ignition 3.3 Heat release rate 3.4 Extinction flammability index & thermal stability index 3.5 Mass loss 3.6 Smoke 3.7 Smoke toxicity 3.8 Limiting oxygen index 3.9 Surface spread of flame 3.10 Fire resistance References 4. Fire Modelling of Composites: 4.1 Introduction 4.2 Thermal exposure 4.3 Modelling material fire dynamics 4.4 Structural modelling of fire response References 5 Modelling the Thermal Response of Composites in Fire: 5.1 Introduction 5.2 Response of composites to fire 5.3 Modelling heat conduction in composites 5.4 Modelling the fire response of composites 5.5 Modelling the thermal properties of composites 5.6 Concluding remarks References 6. Structural Properties of Composites in Fire: 6.1 Introduction 6.2 Laminate properties 6.3 Measurement of elastic constants 6.4 Mechanical properties as a function of temperature 6.5 Modelling of properties 6.6 Fire resistance of laminates under load 6.7 Modelling of fire resistance of laminates under load 6.8 Concluding remarks References 7. Post-Fire Properties of Composites: 7.1 Introduction 7.2 Post-fire properties of laminates 7.3 Modelling the post-fire properties of laminates 7.4 Post-fire properties of sandwich composites 7.5 Post-fire properties of fire protected composites 7.6 Concluding remarks References 8 Flame Retardant Composites: 8.1 Introduction 8.2 The combustion cycle 8.3 Flame retardants for composites 8.4 Flame retardant fillers for composite 8.5 Flame retardant organic polymers for composites 8.6 Flame retardant inorganic polymers for composites 8.7 Flame retardant fibres for composites 8.8 Fire protective surface coatings References 9 Fire Properties of Polymer Nanocomposites: 9.1 Introduction 9.2 Characterization of nanocomposite formation 9.3 Evaluation of fire retardancy 9.4 Clay modifications 9.5 Examples of fire retardancy of polymer nanocomposites 9.6 Mechanisms of fire retardancy in nanocomposites 9.7 Future trends in fire retardancy of nanocomposites References 10 Fire Safety Regulations: 10.1 Introduction 10.2 Fire safety regulations for rail 10.3 Fire safety regulations for automobiles, buses and trucks 10.4 Fire safety regulations for civil infrastructure 10.5 Fire safety regulations for civilian aircraft 10.6 Fire safety regulations for ships and submarines References 11 Fire Tests for Composites: 11.1 Introduction 11.2 Scale of fire reaction tests 11.3 Cone calorimeter 11.4 Atmosphere controlled cone calorimeter 11.5 Intermediate-scale cone calorimeter 11.6 Ohio State University calorimeter 11.7 Limiting oxygen index test 11.8 Flame spread tests 11.9 Smoke density tests 11.10 Furnace tests 11.11 Burn-through & jet-fire tests 11.12 Single burning item test 11.13 Room fire tests 11.14 Structural integrity in fire tests 11.15 Aircraft fire tests 11.16 Concluding remarks References 12 Health Hazards of Composites in Fire: 12.1 Introduction 12.2 Smoke toxicity test methods 12.3 Health hazards of combustion gases 12.4 N-gas model for smoke toxic potency 12.5 Health hazards of fibres 12.6 Personal protective wear against burning composite materials 12.7 Concluding remarks References Subject Index

Fire Properties of Polymer Composite Materials

Brittle failure of components weakened by cracks or sharp and blunt V-notches is a topic of active and continuous research. It is attractive for all researchers who face the problem of fracture of materials under different loading conditions and deals with a large number of applications in different engineering fields, not only with the mechanical one. This topic is significant in all the cases where intrinsic defects of the material or geometrical discontinuities give rise to localized stress concentration which, in brittle materials, may generate a crack leading to catastrophic failure or to a shortening of the assessed structural life. Whereas cracks are viewed as unpleasant entities in most engineering materials, U- and V-notches of different acuities are sometimes deliberately introduced in design and manufacturing of structural components. Dealing with brittle failure of notched components and summarizing some recent experimental results reported in the literature, the main aim of the present contribution is to present a review of some local approaches applicable near stress raisers both sharp and blunt. The reviewed criteria allowed the present authors to develop a new approach based on the volume strain energy density (SED), which has been recently applied to assess the brittle failure of a large number of materials. The main features of the SED approach are outlined in the paper and its peculiarities and advantages accurately underlined. Some examples of applications are reported, as well. The present review is based on the authors’ experience over more than 15 years and the contents of their personal library. It is not a dispassionate literature survey.

Recent developments in brittle and quasi-brittle failure assessment of engineering materials by means of local approaches

The review outlines modern trends in theoretical developments, novel designs and modern applications of sandwich structures. The most recent work published at the time of writing of this review is considered, older sources are listed only on as-needed basis. The review begins with the discussion on the analytical models and methods of analysis of sandwich structures as well as representative problems utilizing or comparing these models. Novel designs of sandwich structures is further elucidated concentrating on miscellaneous cores, introduction of nanotubes and smart materials in the elements of a sandwich structure as well as using functionally graded designs. Examples of problems experienced by developers and designers of sandwich structures, including typical damage, response under miscellaneous loads, environmental effects and fire are considered. Sample applications of sandwich structures included in the review concentrate on aerospace, civil and marine engineering, electronics and biomedical areas. Finally, the authors suggest a list of areas where they envision a pressing need in further research.

Review of current trends in research and applications of sandwich structures

Structural and Failure Mechanics of Sandwich Composites

The deformation of delaminated composites under axial compression is analyzed by a one-dimensional beam-plate model. In this model, a formulation that accounts for the transverse shear effects is also presented. With the perturbation technique, analytical solutions for the critical instability load and the postbuckling deflections are obtained. All possible instability modes, namely, local delamination buckling, global plate buckling, and coupled global and local (mixed) buckling, are considered. Specific emphasis is placed on studying the transverse shear effects on both the critical load and the postcritical characteristics, as well as the influence of the geometry such as that of the location of the delamination across the thickness. The postbuckling solution is used in conjunction with a /-integral formulation to study the postcritical characteristics with respect to possible quasistatic extension of the delamination and the energy absorption capacity of a beam.

Buckling and Postbuckling of Delaminated Composites Under Compressive Loads Including Transverse Shear Effects

A new one-dimensional high-order theory for orthotropic elastic sandwich beams is formulated. This new theory is an extension of the high-order sandwich panel theory (HSAPT) and includes the in-plane rigidity of the core. In this theory, in which the compressibility of the soft core in the transverse direction is also considered, the displacement field of the core has the same functional structure as in the high-order sandwich panel theory. Hence, the transverse displacement in the core is of second order in the transverse coordinate and the in-plane displacements are of third order in the transverse coordinate. The novelty of this theory is that it allows for three generalized coordinates in the core (the axial and transverse displacements at the centroid of the core and the rotation at the centroid of the core) instead of just one (midpoint transverse displacement) commonly adopted in other available theories. It is proven, by comparison to the elasticity solution, that this approach results in superior accuracy, especially for the cases of stiffer cores, for which cases the other available sandwich computational models cannot predict correctly the stress fields involved. Thus, this theory, referred to as the “extended high-order sandwich panel theory” (EHSAPT), can be used with any combinations of core and face sheets and not only the very “soft” cores that the other theories demand. The theory is derived so that all core=face sheet displacement continuity conditions are fulfilled. The governing equations as well as the boundary conditions are derived via a variational principle. The solution procedure is outlined and numerical results for the simply supported case of transverse distributed loading are produced for several typical sandwich configurations. These results are compared with the corresponding ones from the elasticity solution. Furthermore, the results using the classical sandwich model without shear, the first-order shear, and the earlier HSAPT are also presented for completeness. The comparison among these numerical results shows that the solution from the current theory is very close to that of the elasticity in terms of both the displacements and stress or strains, especially the shear stress distributions in the core for a wide range of cores. Finally, it should be noted that the theory is formulated for sandwich panels with a generally asymmetric geometric layout. [DOI: 10.1115/1.4005550]

/pdf/analysis-of-sandwich-beams-with-a-compliant-core-and-with-in-4gxgaz2b5k.pdf

George A. Kardomateas

Papers

Review of current trends in research and applications of sandwich structures

Structural and Failure Mechanics of Sandwich Composites

Buckling and Postbuckling of Delaminated Composites Under Compressive Loads Including Transverse Shear Effects

Analysis of Sandwich Beams With a Compliant Core and With In-Plane Rigidity—Extended High-Order Sandwich Panel Theory Versus Elasticity

Buckling of Thick Orthotropic Cylindrical Shells Under External Pressure