Arthur Francisco

Untangling the environmental from the dietary: dust does not matter.

Both dust and silica phytoliths have been shown to contribute to reducing tooth volume during chewing. However, the way and the extent to which they individually contribute to tooth wear in natural conditions is unknown. There is still debate as to whether dental microwear represents a dietary or an environmental signal, with far-reaching implications on evolutionary mechanisms that promote dental phenotypes, such as molar hypsodonty in ruminants, molar lengthening in suids or enamel thickening in human ancestors. By combining controlled-food trials simulating natural conditions and dental microwear textural analysis on sheep, we show that the presence of dust on food items does not overwhelm the dietary signal. Our dataset explores variations in dental microwear textures between ewes fed on dust-free and dust-laden grass or browse fodders. Browsing diets with a dust supplement simulating Harmattan windswept environments contain more silica than dust-free grazing diets. Yet browsers given a dust supplement differ from dust-free grazers. Regardless of the presence or the absence of dust, sheep with different diets yield significantly different dental microwear textures. Dust appears a less significant determinant of dental microwear signatures than the intrinsic properties of ingested foods, implying that diet plays a critical role in driving the natural selection of dental innovations.

Seeds, browse, and tooth wear: a sheep perspective.

Abstract While grazing as a selective factor towards hypsodont dentition on mammals has gained a lot of attention, the importance of fruits and seeds as fallback resources for many browsing ungulates has caught much less attention. Controlled‐food experiments, by reducing the dietary range, allow for a direct quantification of the effect of each type of items separately on enamel abrasion. We present the results of a dental microwear texture analysis on 40 ewes clustered into four different controlled diets: clover alone, and then three diets composed of clover together with either barley, corn, or chestnuts. Among the seed‐eating groups, only the barley one shows higher complexity than the seed‐free group. Canonical discriminant analysis is successful at correctly classifying the majority of clover‐ and seed‐fed ewes. Although this study focuses on diets which all fall within a single dietary category (browse), the groups show variations in dental microwear textures in relation with the presence and the type of seeds. More than a matter of seed size and hardness, a high amount of kernels ingested per day is found to be correlated with high complexity on enamel molar facets. This highlights the high variability of the physical properties of the foods falling under the browsing umbrella.

Using Design of Experiments to Analyze the Connecting Rod Big-End Bearing Behavior

Reducing the frictional loss in internal combustion engines (ICE) represents a challenge, in which all car manufacturers are involved. This concern has two origins. The first one is the fuel cost, which increases over the years. The second is strongly linked to ecology: people feel more and more concerned by the greenhouse effect, partly resulting from fuel consumption. Many projects involving several laboratories and lead by car manufacturers have this particular point as main subject, with the goal to reduce the ICE fuel consumption by decreasing the friction power loss. This aim can be partly achieved with a better knowledge of the connecting rod big-end bearing functioning. A lot of theoretical and experimental studies have been carried out, resulting in efficient models for numerical simulations, but at the time, no known ambitious parametric study has been planned, to determine the most influent parameters and to quantify their effects on power loss. The present work is a first step to bridge the gap between the potential of recent numerical simulations and the need for a better understanding of the connecting rod big-end bearing functioning. To plan the numerical simulations, it will be taken advantage of design of experiment techniques, which provide an efficient way of preparing the series of experiments with a minimum of runs. Thus, these techniques are illustrated through the variable combination run, test results generated, and interpretations made to identify the dominate factors impacting the responses of interest.

Multilevel Solution of the Elastohydrodynamic Contact for the Water Lubricated Silicon Carbide 3D Line Contact

The aim of this work is to obtain the numerical solution of the isothermal elastohydodynamic lubrication problem for the finite line contact using high modulus material and very low viscous lubricant (Silicon Carbide lubricated with water). Generally, the cylinder length is assumed to be infinite, so the results are obtained within the field of plane strain. In this study, the whole cylinder will be taken into account, in order to determine the 3D minimum film thickness and the 3D maximum pressure. It will appear that the line contact results overestimate the minimum film thickness, compared to a 3D analysis. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in San Francisco, CA October 21–24, 2001

A hybrid method for fast and efficient rough surface generation

Since many years, the pioneering work of Hu and Tonder is used to generate rough surfaces with prescribed statistical moments (skewness and kurtosis) along with spatial properties (correlation lengths). The present work enlightens the drawbacks of this method and it proposes an original approach based on a hybrid analytical/numerical method. Simulations are conducted on very different surface specimens and the method is validated over a wide range of statistical moments. The results are obtained with high accuracy (beyond what is usually needed) and very short computing times (the order of a second).

Study of a Brittle Transparent Disk Under Dry RCF Conditions

Despite the numerous experimental works on rolling contact fatigue, dealing with two-disk contacts, some phenomena still remain badly understood. Most of the test benches, used for that purpose, impose the rotational speeds to the disks: global slipping occurs and the tangential force is measured. Even if this configuration is found in some mechanical contacts, it does not reflect situations, where only microslipping occurs with high tangential loads. For these reasons, an original bench has been designed: a specimen disk rotates a braked stainless steel disk under a normal load N. The tangential load T, due to the braked disk, is set below the global slipping value; the specimen disks are transparent for the cracks observation and brittle to avoid any plasticity complication. A typical run consists in carrying out a succession of steps of increasing the number of cycles. Each step ends with several measurements on the cracks: their counting and their width and depth measurements. The results are divided in two categories: general observations and quantitative results. The most evident observation concerns the crack shape since it propagates along an ellipse on the contact path. Furthermore, the direction of propagation inside the disk is perpendicular to the surface. Lastly, a regular primary network of well-defined cracks is observed with cracks less marked. Concerning the effects of varying loads, the higher the T, the faster the cracks initiate and propagate because of a higher tensile stress state. However, these effects can be partly overridden by N beneath the contact path. As the disk material is brittle, the crack behavior is quite similar to the one observed on metallic specimens. Even if the results are obtained in an epoxy resin, a reasonable transposition is possible. The disk transparency makes it possible to quantify the cracks growth and to propose original 3D photographs of the cracks.

A Methodology for the Connecting Rod Lubrication Optimization

The numerical optimization of the connecting rod big-end lubrication involves several main steps.The first, which can be considered as the most important one, is the identification of the main input factors and their varying range. In the same time, the meaningful resulting values have to be identified because the optimization will be performed on the basis of this choice.The computing time for a TEHD solution prevents from performing a huge amount of calculi to draw the Pareto-Front of the solutions. Thus, the next step is the creation of a metamodel, based on polynomials, with a good predictability property and a low computing cost.In the third step, a fast Multi Objective Optimization is performed on the metamodel. The Pareto-Front, which represents the best trade-offs of solutions, is identified: one can now easily choose the input parameters which will give a particular desired solution.In the last step, the robustness of the solutions has to be checked: if a given solution is chosen, the corresponding input parameters have to enclose a minimal uncertainty gap to be realistic. Otherwise, this wanted solution will never be reached, because in a real-life problem, the parameter values are not deterministic.© 2012 ASME

A New Approach for Rolling Contact Fatigue Numerical Study. Application to a Brittle Epoxy Resin

The background of the present study is the rolling contact fatigue (RCF) in a brittle polymer disk. The disk has been tested on a two disk machine, under controlled normal and tangential loads, with no global slip. After several million cycles and under different operating conditions, it has been observed that (1) the tangential load highly influences the RCF phenomenon, (2) a network of regularly spaced cracks appears, and (3) in the driving position, the RCF phenomenon develops faster. To explain these observations, a numerical model based on the finite element method (FEM) has been built: the cracks have been quite simply modeled, stick-slip has been chosen as the friction model, and the disk-on-disk contact has been replaced by a disk-on-plane contact. To study the influence of some of the operating conditions, the design of experiments (DOE) techniques has been used. The statistical postprocessing associated to DOE has confirmed the experimental observations with a good reliability. In addition, with some mechanical considerations, scenarios of what experimentally happens are proposed. The association FEM/DOE is an original and efficient way to explain phenomena in the field of RCF: the accuracy of the FEM coupled with DOE statistical treatments make it possible to have a good predictability despite some uncontrolled parameters.

Study of the Influence of Input Parameters on the Connecting Rod Big End Bearing Behavior

The present paper deals with the influence of functioning parameters on the connecting rod big end bearing behavior. The Design of Experiment (DOE) method is used to get the most of information from a given number of computations.Copyright