Interface elements based on cohesive formulations provide an effective numerical tool for the sim... more Interface elements based on cohesive formulations provide an effective numerical tool for the simulation of the decohesion processes occurring during delamination and debonding phenomena. Although a large number of cohesive models has been proposed in the literature, many of them exhibit limitations or drawbacks in dealing with mixed-mode loading conditions with variable mode ratios. Accurately predicting the delamination growth requires the cohesive law to respect some basic thermodynamic requirements, such as producing a positive dissipation under any loading path, to properly describe the mode interaction, and to correctly reproduce the experimentally measured dissipated energy under any loading path. Several experimental studies point out that the fracture energy significantly increases in passing from pure Mode I to pure Mode II [1]. A new cohesive model, specifically conceived for the description of mixed-mode delamination and based on an isotropic damage formulation, is propo...
Delamination, i.e. the decohesion between layers, is one of the main failure modes in composite m... more Delamination, i.e. the decohesion between layers, is one of the main failure modes in composite materials. Making use of robust and accurate numerical tools is fundamental to reliably predict the delamination growth. The finite element simulation of these problems is often dealt with by the insertion between adjacent layers of interface elements, whose constitutive behavior is described by a cohesive model in terms of a traction-opening displacement law. In the literature, there exists a variety of works devoted to the formulation of cohesive laws (see [1] for a comparative review of some models), although many of them exhibit a number of shortcomings, such as the need of strong assumptions on the loading path and on the mixed-mode failure properties, or the lack of thermodynamic consistency. Real-life delamination processes are indeed often characterized by mixed-mode loading conditions with varying mode ratio. In addition, several experimental results show that the fracture energy...
In questo lavoro viene presentata una strategia numerica dedicata alla simulazione agli elementi ... more In questo lavoro viene presentata una strategia numerica dedicata alla simulazione agli elementi finiti di fenomeni di taglio e delaminazione in strutture sottili a uno o più strati. Sebbene lo studio di queste due problematiche sia di interesse in molteplici settori ingegneristici, l’applicazione che ha motivato lo sviluppo del codice di simulazione riguarda laminati impiegati nell’industria del packaging alimentare.
Delamination is among the most frequent failure mechanism in laminated composite materials, often... more Delamination is among the most frequent failure mechanism in laminated composite materials, often characterized by mixed-mode loading conditions. As underlined in [1, 2], classical cohesive models, formulated under the hypothesis of small openings, are not able to describe the delamination growth either in the presence of extensive fiber-bridging phenomena or when large relative displacements are involved. As shown by a number of DCB tests performed on fiber-reinforced composites, large-scale fiber bridging causes an increment in the fracture energy, typically expressed by an R-curve in which the toughness gradually increases until a steady-state value is reached. In this work the cohesive model proposed in [3] for the simulation of mixed-mode delamination problems under the assumption of small openings is extended to handle the transition between small and large openings and to account for large-scale bridging or interfacial fibrilation. Consistently with the fact that fiber bridgi...
Paperboard is one of the most widely used materials in industrial processes, notably for packagin... more Paperboard is one of the most widely used materials in industrial processes, notably for packaging purposes. Packages are obtained through a continuous forming process, in which a flat laminated sheet is converted into the final 3-D solid. In the package forming process, it is common practice to score the paperboard laminate with crease lines, in order to obtain folds with sharp edges and to minimize the initiation and propagation of flaws during the subsequent folding procedures. In this work, a constitutive model for the mechanical response of crease lines is proposed and validated on the basis of experimental tests available in the literature.
I principj ed i metodi generali esposti dal sommo Lagrange nella Meccanica Analitica vennero in m... more I principj ed i metodi generali esposti dal sommo Lagrange nella Meccanica Analitica vennero in molta parte abbandonati dai geometri che dopo di lui trattarono questioni di Matematica applicata. L’essere alcuni di quei principj, o non dimostrati, o dimostrati incompletamente, pare sia la cagione principale di quell’abbandono, e ne abbiamo quasi una prova nel vedere adoperate tuttora le formole date da Lagrange nella Sezione IV della seconda parte, le quali, appunto perche rigorosamente dimostrate, non vennero lasciate in disparte anche dopo i lavori di Hamilton e di Jacobi sullo stesso argomento. Fra questi principj il piu importante per le applicazioni e certamente quello indicato dall’autore nella Sezione II, ed esposto con maggior chiarezza nella Sezione IV della prima parte della M. A., intorno al modo di introdurre l’effetto delle forze interne nella equazione generale per l’equilibrio e pel moto, e che il difetto di dimostrazione rese quasi sterile pei successori di Lagrange.
In beams with full-end constraints, loaded transversely by short pressure pulses, the effect of e... more In beams with full-end constraints, loaded transversely by short pressure pulses, the effect of extensional plastic deformation is to make possible instabilities related to snap buckling in the elastic-plastic recovery after the first peak displacement (Symonds and Yu, 1985). In the present paper we make use of a damped, Shanley-type model to study the calculation of the final displacement, reached asymptotically. We show that plots of the elastic strain energy and of the total energy as functions of the displacement help to guide thinking. They provide clarification of previously observed phenomena (Genna and Symonds, 1988) that appear complex at small damping, and lead to lower and upper bounds on the load parameter such that anomalous responses are observed. The response is calculable with the usual accuracy in problems where bifurcations are concerned.
Interface elements based on cohesive formulations provide an effective numerical tool for the sim... more Interface elements based on cohesive formulations provide an effective numerical tool for the simulation of the decohesion processes occurring during delamination and debonding phenomena. Although a large number of cohesive models has been proposed in the literature, many of them exhibit limitations or drawbacks in dealing with mixed-mode loading conditions with variable mode ratios. Accurately predicting the delamination growth requires the cohesive law to respect some basic thermodynamic requirements, such as producing a positive dissipation under any loading path, to properly describe the mode interaction, and to correctly reproduce the experimentally measured dissipated energy under any loading path. Several experimental studies point out that the fracture energy significantly increases in passing from pure Mode I to pure Mode II [1]. A new cohesive model, specifically conceived for the description of mixed-mode delamination and based on an isotropic damage formulation, is propo...
Delamination, i.e. the decohesion between layers, is one of the main failure modes in composite m... more Delamination, i.e. the decohesion between layers, is one of the main failure modes in composite materials. Making use of robust and accurate numerical tools is fundamental to reliably predict the delamination growth. The finite element simulation of these problems is often dealt with by the insertion between adjacent layers of interface elements, whose constitutive behavior is described by a cohesive model in terms of a traction-opening displacement law. In the literature, there exists a variety of works devoted to the formulation of cohesive laws (see [1] for a comparative review of some models), although many of them exhibit a number of shortcomings, such as the need of strong assumptions on the loading path and on the mixed-mode failure properties, or the lack of thermodynamic consistency. Real-life delamination processes are indeed often characterized by mixed-mode loading conditions with varying mode ratio. In addition, several experimental results show that the fracture energy...
In questo lavoro viene presentata una strategia numerica dedicata alla simulazione agli elementi ... more In questo lavoro viene presentata una strategia numerica dedicata alla simulazione agli elementi finiti di fenomeni di taglio e delaminazione in strutture sottili a uno o più strati. Sebbene lo studio di queste due problematiche sia di interesse in molteplici settori ingegneristici, l’applicazione che ha motivato lo sviluppo del codice di simulazione riguarda laminati impiegati nell’industria del packaging alimentare.
Delamination is among the most frequent failure mechanism in laminated composite materials, often... more Delamination is among the most frequent failure mechanism in laminated composite materials, often characterized by mixed-mode loading conditions. As underlined in [1, 2], classical cohesive models, formulated under the hypothesis of small openings, are not able to describe the delamination growth either in the presence of extensive fiber-bridging phenomena or when large relative displacements are involved. As shown by a number of DCB tests performed on fiber-reinforced composites, large-scale fiber bridging causes an increment in the fracture energy, typically expressed by an R-curve in which the toughness gradually increases until a steady-state value is reached. In this work the cohesive model proposed in [3] for the simulation of mixed-mode delamination problems under the assumption of small openings is extended to handle the transition between small and large openings and to account for large-scale bridging or interfacial fibrilation. Consistently with the fact that fiber bridgi...
Paperboard is one of the most widely used materials in industrial processes, notably for packagin... more Paperboard is one of the most widely used materials in industrial processes, notably for packaging purposes. Packages are obtained through a continuous forming process, in which a flat laminated sheet is converted into the final 3-D solid. In the package forming process, it is common practice to score the paperboard laminate with crease lines, in order to obtain folds with sharp edges and to minimize the initiation and propagation of flaws during the subsequent folding procedures. In this work, a constitutive model for the mechanical response of crease lines is proposed and validated on the basis of experimental tests available in the literature.
I principj ed i metodi generali esposti dal sommo Lagrange nella Meccanica Analitica vennero in m... more I principj ed i metodi generali esposti dal sommo Lagrange nella Meccanica Analitica vennero in molta parte abbandonati dai geometri che dopo di lui trattarono questioni di Matematica applicata. L’essere alcuni di quei principj, o non dimostrati, o dimostrati incompletamente, pare sia la cagione principale di quell’abbandono, e ne abbiamo quasi una prova nel vedere adoperate tuttora le formole date da Lagrange nella Sezione IV della seconda parte, le quali, appunto perche rigorosamente dimostrate, non vennero lasciate in disparte anche dopo i lavori di Hamilton e di Jacobi sullo stesso argomento. Fra questi principj il piu importante per le applicazioni e certamente quello indicato dall’autore nella Sezione II, ed esposto con maggior chiarezza nella Sezione IV della prima parte della M. A., intorno al modo di introdurre l’effetto delle forze interne nella equazione generale per l’equilibrio e pel moto, e che il difetto di dimostrazione rese quasi sterile pei successori di Lagrange.
In beams with full-end constraints, loaded transversely by short pressure pulses, the effect of e... more In beams with full-end constraints, loaded transversely by short pressure pulses, the effect of extensional plastic deformation is to make possible instabilities related to snap buckling in the elastic-plastic recovery after the first peak displacement (Symonds and Yu, 1985). In the present paper we make use of a damped, Shanley-type model to study the calculation of the final displacement, reached asymptotically. We show that plots of the elastic strain energy and of the total energy as functions of the displacement help to guide thinking. They provide clarification of previously observed phenomena (Genna and Symonds, 1988) that appear complex at small damping, and lead to lower and upper bounds on the load parameter such that anomalous responses are observed. The response is calculable with the usual accuracy in problems where bifurcations are concerned.
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