Analysis of friction and cutting parameters when milling honeycomb composite structures

In machining, tool/workpiece interface parameters are complicated to estimate by experimental means alone. Numerical methods can then give critical solutions to predict and analyze the parameters influencing the machining. The friction between the tool and the cutter has a direct influence on the milling parameters. Therefore, it is necessary to understand the friction mechanism between the tool and the workpiece to estimate the milling parameters of Nomex honeycomb structures correctly. This work aims to present a 3D Finite Element numerical model allowing the prediction of the cutting forces correctly, the morphology of the chips, and the surface quality generated during the milling of this type of structure. These studies were obtained using the commercial software ABAQUS/Explicit. It has been demonstrated that the coupling between the isotropic elastoplastic approach and the Coulomb friction law can easily simulate the milling of Nomex honeycomb structures and gives excellent results in comparison with those obtained experimentally.

Frictional Sliding of Rough Surfaces Using a Quasi-static Approach to the Maxwell-slip Model

The Maxwell-slip model consists of independent mass-spring units that are slipped by a driver over a rigid, flat, fixed substrate. In the present study, the model is interpreted as a multi-asperity model and is used to study both the friction force and the mechanisms involved in the sliding of a rough elastic surface. Coulomb friction law is assumed at the single mass-spring level. A beta probability distribution function is used to generate the initial block positions randomly. The standard deviation of the initial lateral position of the blocks is interpreted as the surface roughness. The results show that when the surface is rough enough, the sequential slip of the blocks induces a steady friction force. On the other hand, when the surface is smooth enough, the collective slip of the blocks induces stick-slip. The border between the two regimes of sliding is sharply delineated by a specific roughness value. A tribological implication is that a sufficiently rough surface may bring about steady sliding. A geophysical implication is that a geological fault segment that undergoes aseismic creep may have a rougher surface compared to its locked counterpart.

Modeling Complex Contact Conditions and Their Effect on Blade Dynamics

Dry friction devices such as underplatform dampers are commonly included in turbine bladed disks designs to mitigate structural vibrations and avoid high cycle fatigue failures. The design of frictionally damped bladed disks requires adequate models to represent the friction contact. A widely used approach connects contact node pairs with normal and tangential springs and a Coulomb friction law. This simple model architecture is effective in capturing the softening behavior typically observed on frictionally damped structures subjected to increasing forcing levels. An unexpected hardening behavior was observed on the frequency response functions (FRFs) of a two-blades-plus-damper system tested by the authors in a controlled laboratory environment. The reason behind this unexpected behavior will be carefully analyzed and linked to the damper kinematics and to the dependence of contact elasticity on the contact pressure. The inadequacy of contact models with constant spring values will be discussed and alternatives will be proposed. The importance of being able to represent complex contact conditions in order to effectively predict the system dynamics is shown here using a laboratory demonstrator; however, its implications are relevant to any other case where large contact pressure variations are to be expected. The nonlinear steady-state simulations of the blades-plus-damper system will be carried out using an in-house code exploiting the multiharmonic balance method in combination with the alternating frequency time method.

Modeling Complex Contact Conditions and Their Effect on Blade Dynamics

Dry friction devices such as underplatform dampers are commonly included in turbine bladed disks designs to mitigate structural vibrations and avoid high cycle fatigue failures. The design of frictionally damped bladed disks requires adequate models to represent the friction contact. A widely used approach connects contact node pairs with normal and tangential springs and a Coulomb friction law. This simple model architecture is effective in capturing the softening behavior typically observed on frictionally damped structures subjected to increasing forcing levels. An unexpected hardening behavior was observed on the frequency response functions of two-blades-plus-damper system tested by the authors in a controlled laboratory environment. The reason behind this unexpected behavior will be carefully analyzed and linked to the damper kinematics and to the dependence of contact elasticity on the contact pressure. The inadequacy of contact models with constant spring values will be discussed and alternatives will be proposed. The importance of being able to represent complex contact conditions in order to effectively predict the system dynamics is shown here using a laboratory demonstrator, however its implications are relevant to any other case where large contact pressure variations are to be expected. The nonlinear steady state simulations of the blades-plus-damper system will be carried out using an in-house code exploiting the Multi-Harmonic Balance Method (MHBM) in combination with the Alternating Frequency Time (AFT) Method.

Modeling of partial dome collapse of La Soufrière of Guadeloupe volcano: implications for hazard assessment and monitoring

Over the past 9,150 years, at least 9 flank collapses have been identified in the history of La Soufrière of Guadeloupe volcano. On account of the volcano’s current unrest, the possibility of such a flank collapse should not be dismissed in assessing hazards for future eruptive magmatic as well as non-magmatic scenarios. We combine morphological and geophysical data to identify seven unstable structures (volumes ranging from 1 × 106 m3 to 100 × 106 m3), including one that has a volume compatible with the last recorded flank collapse in 1530 CE. We model their dynamics and emplacement with the SHALTOP numerical model and a simple Coulomb friction law. The best-fit friction coefficient to reproduce the 1530 CE event is tan(7°) = 0.13, suggesting the transformation of the debris avalanche into a debris flow, which is confirmed by the texture of mapped deposits. Various friction angles are tested to investigate less water-rich and less mobile avalanches. The most densely populated areas of Saint-Claude and Basse-Terre, and an area of Gourbeyre south of the Palmiste ridge, are primarily exposed in the case of the more voluminous and mobile flank collapse scenarios considered. However, topography has a prominent role in controlling flow dynamics, with barrier effects and multiple channels. Classical mobility indicators, such as the Heim’s ratio, are thus not adequate for a comprehensive hazard analysis.

Deformation Characteristics of the Sheet Metal in the Roll Gap for the Continuous Roll Forming Process

Continuous Roll Forming process (CRFP) is a newly developed technique applied to form 3D surface part with various transverse and longitudinal curvatures. In CRFP, the sheet metal is non-uniformly compressed in the roll gap between the upper and lower bendable rolls. The two bendable rolls rotate in opposite directions, and the sheet metal is bitten into the roll gap continuously. At the present, the deformation characteristics of the sheet metal in the deformation zoon (sheet metal between the upper and lower bendable roll) is discussed. The friction force in CRFP can be calculated according to the Coulomb friction law.

Analysis of a dynamic frictional contact problem for hyperviscoelastic material with non-convex energy density

Using the time approximation method we obtain the existence of a weak solution for the dynamic contact problem with damping and a non-convex stored elastic energy function. On the contact boundary we assume the normal compliance law and the generalization of the Coulomb friction law which allows for non-monotone dependence of the friction force on the tangential velocity. The existence result is accompanied by two numerical examples, one of them showing lack of uniqueness for the numerical solution.