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Hutchinson, John

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Hutchinson

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Hutchinson, John
Author's Publications: search.filters.isAuthorOfPublication.8bff5543-dba9-4bb2-82db-4495930a0898

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    Technical Brief: Knockdown Factor for the Buckling of Spherical Shells Containing Large-Amplitude Geometric Defects
    (ASME International, 2017-01-24) Jiménez, Francisco López; Marthelot, Joel; Lee, Anna; Hutchinson, John; Reis, Pedro M.
    We explore the effect of precisely defined geometric imper- fections on the buckling load of spherical shells under exter- nal pressure loading, using finite element analysis that was previously validated through precision experiments. Our nu- merical simulations focus on the limit of large amplitude de- fects and reveal a lower bound that depends solely on the shell radius to thickness ratio and the angular width of the defect. It is shown that, in the large amplitude limit, the buck- ling load depends on an single geometric parameter, even for shells of moderate radius to thickness ratio. Moreover, nu- merical results on the knockdown factor are fitted to an em- pirical, albeit general, functional form that may be used as robust design guideline for the critical buckling conditions of pressurized spherical shells.
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    Buckling of a Pressurized Hemispherical Shell Subjected to a Probing Force
    (ASME International, 2017-10-19) Marthelot, Joel; López Jiménez, Francisco; Lee, Anna; Hutchinson, John; Reis, Pedro M.
    We study the buckling of hemispherical elastic shells sub- jected to the combined effect of pressure loading and a prob- ing force. We perform an experimental investigation using thin shells of nearly uniform thickness that are fabricated with a well-controlled geometric imperfection. By systemat- ically varying the indentation displacement and the geome- try of the probe, we study the effect that the probe induced deflections have on the buckling strength of our spherical shells. The experimental results are then compared to finite element simulations, as well as to recent theoretical predic- tions from the literature. Inspired by a nondestructive tech- nique that was recently proposed to evaluate the stability of elastic shells, we characterize the nonlinear load-deflection mechanical response of the probe for different values of the pressure loading. We demonstrate that this nondestructive method is a successful local way to assess the stability of spherical shells.
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    Wrinkling Phenomena in Neo-Hookean Film/Substrate Bilayers
    (American Society of Mechanical Engineers, 2012) Cao, Yanping; Hutchinson, John
    Wrinkling modes are determined for a two-layer system comprised of a neo-Hookean film bonded to an infinitely deep neo-Hookean substrate with the entire bilayer undergoing compression. The full range of the film/substrate modulus ratio is considered from the limit of a traction-free homogeneous substrate to very stiff films on compliant substrates. The role of substrate prestretch is considered wherein an unstretched film is bonded to a prestretched substrate with wrinkling arising as the stretch in the substrate is relaxed. An exact bifurcation analysis reveals the critical strain in the film at the onset of wrinkling. Numerical simulations carried out within a finite element framework uncover advanced post-bifurcation modes including period-doubling, folding and a newly identified mountain ridge mode.
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    Generalizing \(J_2\) Flow Theory: Fundamental Issues in Strain Gradient Plasticity
    (Springer Verlag, 2012) Hutchinson, John
    It has not been a simple matter to obtain a sound extension of the classical \(J_2\) flow theory of plasticity that incorporates a dependence on plastic strain gradients and that is capable of capturing size-dependent behaviour of metals at the micron scale. Two classes of basic extensions of classical \(J_2\) theory have been proposed: one with increments in higher order stresses related to increments of strain gradients and the other characterized by the higher order stresses themselves expressed in terms of increments of strain gradients. The theories proposed by Muhlhaus and Aifantis in 1991 and Fleck and Hutchinson in 2001 are in the first class, and, as formulated, these do not always satisfy thermodynamic requirements on plastic dissipation. On the other hand, theories of the second class proposed by Gudmundson in 2004 and Gurtin and Anand in 2009 have the physical deficiency that the higher order stress quantities can change discontinuously for bodies subject to arbitrarily small load changes. The present paper lays out this background to the quest for a sound phenomenological extension of the rateindependent \(J_2\) flow theory of plasticity to include a dependence on gradients of plastic strain. A modification of the Fleck-Hutchinson formulation that ensures its thermodynamic integrity is presented and contrasted with a comparable formulation of the second class where in the higher order stresses are expressed in terms of the plastic strain rate. Both versions are constructed to reduce to the classical \(J_2\) flow theory of plasticity when the gradients can be neglected and to coincide with the simpler and more readily formulated \(J_2\) deformation theory of gradient plasticity for deformation histories characterized by proportional straining.
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    Lifetime Assessment for Thermal Barrier Coatings: Tests for Measuring Mixed Mode Delamination Toughness
    (John Wiley & Sons, 2011) Hutchinson, Robert G.; Hutchinson, John
    Mechanisms leading to degradation of the adherence of thermal barrier coatings (TBC) used in aircraft and power generating turbines are numerous and complex. To date, robust methods for the lifetime assessment of coatings have not emerged based on predictions of the degradation processes due to their complexity. In the absence of mechanism-based predictive models, direct measurement of coating adherence as a function of thermal exposure must be a component of any practical approach toward lifetime assessment. This paper outlines an approach to lifetime assessment of TBC that has taken shape in the past few years. Most TBC delaminations occur under a mix of mode I and mode II cracking conditions, with mode II delamination being particularly relevant. Direct measurement of TBC delamination toughness has been challenging, but recent progress has made this feasible. This paper surveys a range of potentially promising tests for measuring the mode dependence of delamination toughness with particular emphasis on toughness under mode II conditions.
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    Deformation and Fracture of Impulsively Loaded Sandwich Panels
    (Elsevier, 2013) Wadley, Haydn N. G.; Børvik, Tore; Olovsson, Lars; Wetzel, John J.; Dharmasena, Kumar P.; Hopperstad, Odd Sture; Deshpande, Vikram; Hutchinson, John
    Light metal sandwich panel structures with cellular cores have attracted interest for multifunctional applications which exploit their high bend strength and impact energy absorption. This concept has been explored here using a model 6061-T6 aluminum alloy system fabricated by friction stir weld joining extruded sandwich panels with a triangular corrugated core. Micro-hardness and miniature tensile coupon testing revealed that friction stir welding reduced the strength and ductility in the welds and a narrow heat affected zone on either side of the weld by approximately 30%. Square, edge clamped sandwich panels and solid plates of equal mass per unit area were subjected to localized impulsive loading by the impact of explosively accelerated, water saturated, sand shells. The hydrodynamic load and impulse applied by the sand were gradually increased by reducing the stand-off distance between the test charge and panel surfaces. The sandwich panels suffered global bending and stretching, and localized core crushing. As the pressure applied by the sand increased, face sheet fracture by a combination of tensile stretching and shear-off occurred first at the two clamped edges of the panels that were parallel with the corrugation and weld direction. The plane of these fractures always lay within the heat affected zone of the longitudinal welds. For the most intensively loaded panels additional cracks occurred at the other clamped boundaries and in the center of the panel. To investigate the dynamic deformation and fracture processes, a particle-based method has been used to simulate the impulsive loading of the panels. This has been combined with a finite element analysis utilizing a modified Johnson–Cook constitutive relation and a Cockcroft–Latham fracture criterion that accounted for local variation in material properties.The fully coupled simulation approach enabled the relationships between the soil-explosive test charge design, panel geometry, spatially varying material properties and the panel's deformation and dynamic failure responses to be explored. This comprehensive study reveals the existence of a strong instability in the loading that results from changes in sand particle reflection during dynamic evolution of the panel's surface topology. Significant fluid–structure interaction effects are also discovered at the sample sides and corners due to changes of the sand reflection angle by the edge clamping system.
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    Cohesive Traction-Separation Laws for Tearing of Ductile Metal Plates
    (Elsevier, 2012) Nielsen, K. L.; Hutchinson, John
    The failure process ahead of a mode I crack advancing in a ductile thin metal plate or sheet produces plastic dissipation through a sequence of deformation steps that include necking well ahead of the crack tip and shear localization followed by a slant fracture in the necked region somewhat closer to the tip. The objective of this paper is to analyze this sequential process to characterize the traction–separation behavior and the associated effective cohesive fracture energy of the entire failure process. The emphasis is on what is often described as plane stress behavior taking place after the crack tip has advanced a distance of one or two plate thicknesses. Traction–separation laws are an essential component of finite element methods currently under development for analyzing fracture of large scale plate or shell structures. The present study resolves the sequence of failure details using the Gurson constitutive law based on the micromechanics of the ductile fracture process, including a recent extension that accounts for damage growth in shear. The fracture process in front of an advancing crack, subject to overall mode I loading, is approximated by a 2D plane strain finite element model, which allows for an intensive study of the parameters influencing local necking, shear localization and the final slant failure. The deformation history relevant to a cohesive zone for a large scale model is identified and the traction–separation relation is determined, including the dissipated energy. For ductile structural materials, the dissipation generated during necking prior to the onset of shear localization is the dominant contribution; it scales with the plate thickness and is mesh-independent in the present numerical model. The energy associated with the shear localization and fracture is secondary; it scales with the width of the shear band, and inherits the finite element mesh dependency of the Gurson model. The cohesive traction–separation laws have been characterized for various material conditions.
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    Crossover Patterning by the Beam-Film Model: Analysis and Implications
    (Public Library of Science, 2014) Zhang, Liangran; Liang, Zhangyi; Hutchinson, John; Kleckner, Nancy
    Crossing-over is a central feature of meiosis. Meiotic crossover (CO) sites are spatially patterned along chromosomes. CO-designation at one position disfavors subsequent CO-designation(s) nearby, as described by the classical phenomenon of CO interference. If multiple designations occur, COs tend to be evenly spaced. We have previously proposed a mechanical model by which CO patterning could occur. The central feature of a mechanical mechanism is that communication along the chromosomes, as required for CO interference, can occur by redistribution of mechanical stress. Here we further explore the nature of the beam-film model, its ability to quantitatively explain CO patterns in detail in several organisms, and its implications for three important patterning-related phenomena: CO homeostasis, the fact that the level of zero-CO bivalents can be low (the “obligatory CO”), and the occurrence of non-interfering COs. Relationships to other models are discussed.
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    Simulations of Ductile Fracture in an Idealized Ship Grounding Scenario Using Phenomenological Damage and Cohesive Zone Models
    (Elsevier, 2013) Woelke, Pawel B.; Shields, Michael D.; Abboud, Najib N.; Hutchinson, John
    Two complementary simulation methodologies for ductile fracture in large sheet metal components are presented and evaluated in this paper. The first approach is based on the phenomenological dilatational plasticity-damage model developed by Woelke and Abboud [68], which accounts for pressure-dependent volumetric damage growth through a scalar damage variable. The damage function represents phenomenologically micromechanical changes the material undergoes during the process of necking. Secondly, the cohesive zone model with an opening mode traction-separation law is employed to simulate the same ductile fracture problems accounting for significant variation of the multiaxial stress state along the crack path. Both methods are examined as to their capabilities to reproduce and predict the outcome of large scale experimental fracture tests of welded and unwelded ductile plates subjected to large-scale penetration, simulating an idealized ship grounding (Alsos and Amdahl, [1, 2]). The results of the current study indicate that, with appropriate calibration, both approaches can be successfully employed to simulate ductile fracture in structural components under multiaxial stress. The advantages and shortcomings of each approach is discussed from the point of view of post-test numerical investigation as well as its predictive capabilities as an engineering tool.
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    Necking Modes in Multilayers and their Influence on Tearing Toughness
    (SAGE Publications, 2013) Hutchinson, John
    Periodic bifurcation modes that occur in ductile multilayered plates or sheets stretched in plane strain tension are analyzed to reveal whether necks are likely to localize at the scale of the thickness of individual layers or at the scale of the full thickness of the multilayer. The energy dissipated in tearing a ductile multilayer scales with the extent of the localized thinning region in the tensile direction. If plates or sheets with high tearing toughness are desired, the combination of layers should be chosen to suppress necking localization at the scale of individual layers. Insight into the properties and thicknesses of the layers required to suppress short wavelength necking is revealed by a bifurcation analysis of multilayers comprised of metal layers having different strength and hardening behaviors and multilayers combining metal and elastomer layers. Several examples suggest that when localization takes place at the scale of the individual layers it may occur in the form of a band inclined through the thickness.