Variation Of Contact Conditions Research Articles

Strength constrained topology optimization of hyperealstic structures with large deformation-induced frictionless contact

This paper developed a strength constrained topology optimization method for hyperelastic structures with large deformation-induced frictionless contact. The Neo-Hookean hyperelastic constitutive equation is adopted as the material model that incorporates both material and geometric nonlinearity. The large deforming contact is described by the node-to-segment algorithm. The topology optimization model is developed under the SIMP framework. Given the SIMP-related fictitious domain, we develop a nodal variable-based interpolation scheme to build smooth correlation between the contact force and nodal density variables, thus enabling the smooth transition and variation of contact conditions. Moreover, to guarantee the structure strength, local strain energy constraints are formulated and aggregated by the P-norm function. The details of sensitivity analysis are explicitly explained. At last, several benchmark examples are conducted that validate the proposed method.

Intergroup relationships with people who use drugs: A personal network approach

Positive and meaningful intergroup contact between people who use drugs and those with the potential to provide positive social interactions has been identified as an important pathway to address the burden of drug use by reducing stigmatizing views and behaviors. Traditional approaches to intergroup contact typically rely on laboratory experiments or survey vignettes to examine the consequences of variation in contact conditions and relationships. Although seldom measured, contact occurs naturally through individuals' personal social networks. Here, we apply this latter approach to examine how the characteristics of drug use and social roles are associated with positive and meaningful intergroup contact in daily life. We leverage unique data from a state representative sample of Indiana residents aged 18 or older (n = 926) that completed a personal network interview and separately reported people they know who have a drug use problem. We first identified the respondents who nominated a person who uses drugs as a member of their core personal network and then evaluated the relationship, disease, and individual characteristics that were associated with that person's inclusion in the personal network. We find that primary relationships (e.g., having a spouse or child who uses drugs) are associated with meaningful contact with people who use drugs but that intense manifestations of disease characteristics (severe or problematic, danger to self) can limit the likelihood of contact. These findings demonstrate how the nature of intergroup contact can shape the types of relationships that have been shown to help reduce stigmatizing attitudes and the behavioral barriers to recovery, such as social isolation. Thus, core networks present a valuable approach to defining the factors that likely contribute to effective intergroup contact.

Friction transitions and connections to third bodies for a Cd coating on steel substrate

Cd coating is used in aerospace industries from last five decades due to its sacrificial protection and lubrication properties. Although Cd coating is primarily used due to its sacrificial corrosion protection when applied on steel substrate, the added benefit of modifying the tribological behavior by acting as a lubricious layer gives it a leading-edge than other coatings. Often the measurement of friction coefficient (CoF) is reported as a value generated after full sliding cycle. This measurement of average CoF generally limits the study of local variation in CoF occurring within one sliding cycle, which can be significantly different with change in spatial position due to change in third body morphology. In this study, a linearly reciprocating sliding test is used to measure the CoF at a sampling rate of 800 Hz along the track length to generate triboscopic image with steel countersphere. The instantaneous CoF obtained with triboscopy is correlated with the wear track morphology using scanning electron microscope (SEM) and optical profilometer for variation in contact conditions. Tribological test performed in dry atmosphere shows an average CoF of 0.4 till the end of the test whereas with increase in relative humidity to 60%, the average CoF changes from 0.4 to 0.8 at the end of the test due to change in contact conditions. Soft Cd coating on low carbon steel substrate is used to study these variations in third body morphology.

Quantitative temperature distribution measurements by non-contact scanning thermal microscopy using Wollaston probes under ambient conditions.

Temperature measurement using Scanning Thermal Microscopy (SThM) usually involves heat transfer across the mechanical contact and liquid meniscus between the thermometer probe and the sample. Variations in contact conditions due to capillary effects at sample-probe contact and wear and tear of the probe and sample interfere with the accurate determination of the sample surface temperature. This paper presents a method for quantitative temperature sensing using SThM in noncontact mode. In this technique, the thermal probe is scanned above the sample at a distance comparable with the mean free path of ambient gas molecules. A Three-Dimensional Finite Element Model (3DFEM) that includes the details of the heat transfer between the sample and the probe in the diffusive and transition heat conduction regimes was found to accurately simulate the temperature profiles measured using a Wollaston thermal probe setup. In order to simplify the data reduction for the local sample temperature, analytical models were developed for noncontact measurements using Wollaston probes. Two calibration strategies (active calibration and passive calibration) for the sample-probe thermal exchange parameters are presented. Both calibration methods use sample-probe thermal exchange resistance correlations developed using the 3DFEM to accurately capture effects due to sample-probe gap geometry and the thermal exchange radii in the diffusive and transition regimes. The analytical data reduction methods were validated by experiments and 3DFEM simulations using microscale heaters deposited on glass and on dielectric films on silicon substrates. Experimental and predicted temperature profiles were independent of the probe-sample clearance in the range of 100-200 nm, where the sample-probe thermal exchange resistance is practically constant. The difference between the SThM determined and actual average microheater temperature rise was between 0.1% and 0.5% when using active calibration on samples with known thermal properties and between ∼1.6% and 3.5% when using passive calibration, which yields robust sample-probe thermal exchange parameters that can be used also on samples with unknown thermal properties.

Geometrical Modeling of the Sheet Metal Parts in the Incremental Shrinking Process

Shrinking is an incremental forming process and can be carried out using a driving machine, so called “Kraftformer”. It needs an upper and a lower shrinking tool, each of which has two moveable jaws as contact and force transform units. During every forming operation the tools clamp the metal sheet, so that the vertical forces from the upper tool are switched by the leverages inside the tools into the horizontal directions. The moveable jaws are practiced by the horizontal forces to compress the metal sheet. The shrinking of the metal sheet brings out the different three-dimensional forms. As a traditional manual forming method, economical productions can’t be reached for individualized sheet metal parts to achieve the customer’s demands. Hence, it is proposed to automate this forming process to reduce the manual work. The production strategies are to be deduced from the manual shrinking process. A direct way to get them is to simulate the forming process in a FEM-software environment. But within such a FEM-simulation it can take about even one hour only just to finish one forming step. Furthermore, an analytical modeling of the shrinking can’t be realized because of its complex procedures such as variation of contact conditions, material hardening. However, a pure geometric model can be established to demonstrate the change of the 3D-forms of the sheet metal parts. The respective forming parameters can be identified through the experiments. The simulation can take place only in a few seconds. This paper provides general information about the application of the manufacturing method and with it the qualification of shrinking as a manufacturing concept for the production of individualized sheet metal products.

Analysis of externally loaded bolted joints: Analytical, computational and experimental study

The behaviour of a simple single-bolted-joint under tensile separating loads is analysed using conventional analytical methods, a finite element approach and experimental techniques. The variation in bolt force with external load predicted by the finite element analysis conforms well to the experimental results. It is demonstrated that certain detailed features such as thread interaction do not need to be modelled to ensure useful results. Behaviour during the pre-loading phase of use agrees with previous long-standing studies. However, the pre-loading analysis does not carry over to the stage when external loading is applied, as is normally assumed and it is shown that the current, conventional analytical methods substantially over-predict the proportion of the external load carried by the bolt. The basic reason for this is shown to be related to the non-linear variation in contact conditions between the clamped members during the external loading stage.

Structure-borne sound transmission from machines into ribbed structures

The total structure-borne sound power of an installed machine is a function of the source activity and mobility, and the receiver mobility, at each contact and for each component of excitation. The data and computational requirements for prediction therefore are large. Manufacturers view their products as single entities and desire corresponding single values of source strength. A laboratory reception plate measurement procedure has been proposed which yields single equivalent values of source strength and source mobility. The source data, in combination with an estimate of the single equivalent value of receiver mobility, yields the approximate total installed power. The accuracy of the estimate is dependent on the spatial variation in contact conditions over the connections. In addition, phase information has been lost in the simplification. Case studies are described for multiple contact sources on a non-homogeneous plate (a timber-joist floor) where the approximate estimates of structure-borne power are compared with exact values obtained from full mobility formulations.

An application of a homogenization method to the estimation of effective thermal conductivity of a hydrogen storage alloy bed considering variation of contact conditions between alloy particles

A homogenization method is applied to the estimation of effective thermal conductivity of a hydrogen storage alloy bed. By including the contact conditions between the alloy particles, the effect of contact conditions on the thermal conductivity is investigated. When the pressure is lower than 1 bar, the effective thermal conductivity increases with an increase in the mean gap distance and the contact ratio of point contact. On the other hand, when the pressure is higher than 1 bar, the effective thermal conductivity increases with an increase in the contact ratio of plane contact and the Biot number. In addition, in the comparison of the parameters before and after charge and discharge cycles, it is shown that the mean gap, the contact ratio of plane contact and Biot number are involved in a decrease in effective thermal conductivity of the pulverized alloy particle bed.

Lateral contact of slender prismatic bodies

Many nominally two‐dimensional contact problems, such as the contact of parallel rollers or spur gears, exhibit slow axial variation in contact conditions due to manufacturing errors, misalignment or generalized beam deflections of the contacting bodies. In this paper, an asymptotic method is used to develop a solution to such problems, the inner problem being the two‐dimensional Hertzian contact theory and the outer problem the bending of the contacting bodies as beams separated by a nonlinear elastic foundation. The method is illustrated in the case of two cylindrical rollers that are slightly misaligned and pressed together by forces applied at their ends. The classical Hertzian elliptical contact area is obtained at low loads, but with increasing load the contact area evolves first into a dog‐bone shape and then into two separated contact areas surrounding the point forces that would be predicted by an elementary beam theory solution of the problem.