6,820 research outputs found
The effect of contact on the decohesion of laminated beams with multiple microcracks
No full textThe problem of interface decohesion in laminated beams is addressed with reference to the debonding double cantilever beam test geometry (DCB). The paper deals with the analysis of the influence of nonuniform bonding properties or interfacial defects on the crack propagation process and its stability. To this aim, the classical analytical approach based on the Euler–Bernoulli beam on an elastic foundation is extended to the presence of a general distribution of microcracks ahead of the macrocrack tip. The main features and limitations of this approach are carefully analyzed. In particular, it is shown that this simplified approach does not consider the unilateral contact condition along the interface, thus admitting a penetration between the two arms of the beam. A comparison with a finite element formulation is proposed to assess if this violation of the constraints inequalities, usually adopted in the case of uniform bonding, is still acceptable when interfacial defects are present. In order to fully describe the whole nonlinear behavior of the interface, a generalized interface constitutive law is used. The models comparison shows that, in the presence of interfacial defects, the effect of contact plays a crucial role in the description of the mechanical response of the joint
Snap-back instability in micro-structured composites and its connection with superplasticity
No full textInstability phenomena occurring in the microstructure of micro-structured composites are numerically investigated. To this aim, an interface constitutive law is proposed to describe both decohesion and contact at bi-material interfaces. These formulations are implemented in the FE code FEAP. Then, by applying dimensional analysis, the nondimensional parameters governing the macroscopic response of the composite are identified. According to this model, transverse debonding with respect to the fiber direction is simulated and the transition from snap-back instability in case of coarse fiber diameters, to a stable mechanical response for finer reinforcements is quantified. These results provide a possible quantitative explanation to the role played by the size of the reinforcement on the instability phenomena experimentally observed during superplastic deformation
A numerical model for the analysis of decohesion at bi-material interfaces with random properties
No full textSoftening and snap-back instability in superplastic deformation
No full textThe mechanical behavior of micro-structured composites has been experimentally and theoretically proven to be strongly dependent on the size of the reinforcement. In other words,
keeping constant the reinforcement volumetric fraction and the mechanical properties of the constituent materials, size effects on the mechanical response are observed by varying the diameter of the inclusion. From the technological point of view, an important example where this
size effect is noticed is represented by superplasticity (Langdon, 1995). Instability phenomena occurring in the microstructure of micro-structured composites are
numerically investigated in this paper. To this aim, an interface constitutive law is proposed to
describe both decohesion and contact at bi-material interfaces. These formulations are
implemented in the FE code FEAP. Then, by applying dimensional analysis (Carpinteri, 1989),
the nondimensional parameters governing the macroscopic response of the composite are
identified. According to this model, transverse debonding with respect to the fiber/particle
direction is simulated and the transition from snap-back instability in case of coarse inclusion
diameters to a stable mechanical response for finer reinforcement is quantified. These results
provide a possible quantitative explanation to the role played by the size of the reinforcement on
the instability phenomena experimentally observed during superplastic deformation
Theoretical and numerical investigation on internal instability phenomena in composite materials
No full textA unified interface constitutive law for the study of fracture and contact problems in heterogeneous materials
No full textA unified interface constitutive law for the description of contact and decohesion at bi-material interfaces is proposed. To this aim, a synthesis of the nonlinear models pertaining to Fracture and Contact Mechanics is presented. The issues pertinent to the implementation within the FE discretization framework are also discussed in detail. Finally, a numerical example of fatigue modeling at the mesoscopical level in a fiber-reinforced composite is provided
Theoretical and numerical investigation on internal instability phenomena in composite materials
No full textInstability phenomena occurring in the microstructure of composite materials are investigated. To this aim, a complete description of the mechanical behavior of bi-material interfaces in composite materials requires the definition of both a cohesive law involving damage for the debonding stage, and a contact model during the closure of the interface. Both formulations are herein presented and implemented in the FE code FEAP. Numerical examples showing the transition from a snap-back instability to a stable mechanical response are presented
A coupled contact and decohesion analysis of laminated beams
No full textThe problem of interface decohesion in laminated beams is addressed with reference to the double cantilever beam (DCB) geometry. The paper deals with the analysis of the influence of non-uniform bonding properties or interfacial defects on the crack propagation process and its stability. In spite of the relative simplicity of the considered case study, which is under pure Mode I deformation, a contact problem takes place due to the decohesion. The occurrence of contact makes the problem highly non-linear, since the extension of the contact area is a priori unknown. The finite element method with a generalized interface constitutive law is used to enforce the contact constraint along the interface and to model the progress of the delamination process
Cusp-catastrophe interpretation of the stick-slip behaviour of rough surfaces
No full textThe stick-slip instability is a typical manifestation of the nonlinearity of the frictional response of rough surfaces. As recently demonstrated by several researchers, the problem of contact loss is also inherently connected to the stick-slip instability and it has been detected both in elastically soft materials, such as rubber or gelatine, and in elastic stiff materials, such as for earthquake faults. Treating the problem of tangential contact in the framework of micromechanical contact models, the effect of the phenomenon of contact loss on the micro-slip behavior of rough surfaces is herein investigated. To this aim, the stick and slip components of the total applied tangential force and of the total real contact area are properly determined as functions of the total applied tangential force. A comparison with the behavior of smooth surfaces, such as spheres, cylinders and flat surfaces, is presented. Then, simulating the problem of tangential loading followed by a reduction of the applied normal force, it will be shown that the phenomenon of contact loss gives rise to energy release due to snap-back instability in the diagram relating the tangential force to the sliding displacement. This result provides for the very first time an explanation to the phenomenon of stick-slip according to the Catastrophe Theory, in close analogy with the cusp-catastrophe instability of Mode I crack propagation in cohesive solids
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