Black anodic coatings for space applications: study of the process parameters, characteristics and mechanical properties

Black inorganic anodized aluminium alloys are used for managing passive thermal control on spacecraft and for avoiding stray light in optical equipment. Spalling of these coatings has sometimes been observed after thermal cycling on 2XXX and 7XXX aluminium alloys. This phenomenon could generate particulate contamination in satellites and may affect mission lifetime. In this work, the influences of the four main steps of the process (pretreatments, sulphuric anodizing, colouring and sealing) on the coating characteristics have been studied for a 7175 T7351 aluminium alloy. The chemical heterogeneity of the coating has been underlined, and its mechanical behaviour observed through crazing. Scratch-testing, used to evaluate coating adhesion to its substrate, revealed the negative impact of thermal cycling

Investigations into the coefficient of thermal expansion of porous films prepared on AA7175 T7351 by anodizing in sulphuric acid electrolyte

The aim of this study was to investigate the Coefficient of Thermal Expansion (CTE) of anodic films on 7175 T7351 aluminium alloy and to evaluate the influence of the film characteristics on this value. In particular, effects of porosity and post-treatments, such as coloring and sealing, were studied. Beam bending analysis was used as the experimental method and a numerical finite element model was developed to verify theoretical relationships hypotheses. The values determined and the choice of experimental method were then validated by comparing the experimental cracking temperature of anodic films with a theoretical value directly depending on the previously determined CTE

Mechanical behavior of black anodic films on 7175 aluminium alloy for space applications

Because of their low outgassing and their thermo-optical properties, black anodized aluminium parts are often used near optical instruments to manage thermal control in space applications. However, critical cases of flaking of the film were observed after simulated thermal ageing. To understand the mechanisms leading to flaking, the influence of the initial porosity of the film on its mechanical behavior during and after the black anodizing process has been investigated. The decrease of limit tensile stress with the porosity, the coloring and the sealing combined to thermal stresses due to the difference of thermal expansion coefficients between film and substrate have been shown to cause crazing in articular conditions. For high initial porosity films, thermal cycling ageing has a detrimental influence on the adhesion measured by scratchtesting. Numerical simulation has been used to simulate the combined effects of thermal stresses and film cracking on the stress field at the interface

Introducing QoS support in Bluetooth Piconetwith a Class-Based EDF Scheduling

In this paper, we focus on the Bluetooth wireless network, analyzing its ability to support Quality of Service (QoS) requirements defined by the application. In particular, we are interested in two QoS parameters: (i) an application constraint denoting the importance degree of a message, and (ii) its delivery deadline. The QoS perceived by the application depends on the efficiency of the scheduling schemes chosen at the medium access layer. We define the minimal knowledge level required by a scheduling scheme to support these QoS constraints. As an example of classical scheduling schemes, we analyze performances of One-Round Robin (1-RR) and show that it does not provide a sufficient service differentiation. To achieve better service differentiation, we first present enhancements accounting locally for the two QoS parameters. These enhancements are applied to 1-RR scheduling scheme and we then give a comparison between the two versions. These comparisons are done by evaluating in each class, the average message response time and the percentage of messages missing their deadline. We then introduce enhancements in the intra-piconet scheduling. So, we define a new Bluetooth global scheduling, called Class-Based Earliest Deadline First (CB-EDF) that takes into account both locally and globally these two QoS parameters. Simulation results show that CB-EDF achieves a good service differentiation and allows the coexistence of messages with different application constraints on the same ACL link. Moreover, CB-EDF is a flexible solution that adapts itself to the provided knowledge level

Non-premptive Fixed Priority schedulingwith FIFO arbitration:uniprocessor and distributed cases

In this paper, we focus on non-preemptive Fixed Priority scheduling. We are interested in the worst case response time of flows, both in uniprocessor and distributed cases. On a processor, the number of available priorities is generally limited. If this number is less than the number of flows to be considered, several flows have to share the same priority. Such flows are assumed to be scheduled arbitrarily in the classical approach. We assume in this paper that these flows are scheduled FIFO. This assumption leads us to revisit classical results in the uniprocessor case. As we obtain response times less than or equal to the classical results, any flow set feasible with the classical approach is feasible with our approach. The converse is false, as shown by an example. Moreover, we determine the conditions leading to shorter response times. We then establish new results in a distributed context. We show how to compute an upper bound on the end-to-end response time of any flow. For this, we use a worst case analysis based on the trajectory approach

FP/EDF, a non-preemptive scheduling combiningfixed priorities and deadlines:uniprocessor and distributed cases

In this paper, we focus on a non-preemptive scheduling of sporadic flows, combining fixed priorities and deadlines. This scheduling is called FP/EDF. With any flow are associated a fixed priority denoting the importance of the flow and a delivery deadline. A packet m can be transmitted only if there is no waiting packet with a fixed priority higher than m and no waiting packet with the same fixed priority as m but with a smaller deadline. We are interested in the worst case response time of flows, both in uniprocessor and distributed cases. In the uniprocessor case, we prove that any sporadic flow set feasible with the classical Fixed Priority scheduling is feasible with FP/EDF. The converse is false, as shown by an example. Moreover, we show that when all flows sharing the same fixed priority have the same processing time, any sporadic flow set feasible with FP/FIFO is feasible with FP/EDF, but the converse is false. We then establish new results with FP/EDF in a distributed context, when all flows follow the same sequence of nodes. The absolute deadline of a packet that is considered by any scheduler is computed on the first node visited and then left unchanged by any other node. We show in such conditions how to compute an upper bound on the end-to-end response time of any flow. For this, we use a worst case analysis based on the trajectory approach. Results obtained for some configurations are exact. In all configurations, these results are compared with those provided by the classical holistic approach. We show that our results are largely better

A DiffServ-MPLS solution offering real-time end-to-end guarantees

In this paper, we are interested in providing deterministic end-to-end guarantees to real-time applications in the Internet. We focus on two QoS (Quality of Service) parameters: the end-to-end response time and the end-to-end jitter, parameters of the utmost importance for such applications. We propose a solution, very simple to deploy, based on a combination of DiffServ and . The Expedited Forwarding (EF) class of the Differentiated Services (DiffServ) model is well adapted for real-time applications as it is designed for flows with end-to-end real-time constraints. Moreover MultiProtocol Label Switching (MPLS), when applied in a DiffServ architecture, is an efficient solution for providing QoS routing. The results of our worst case analysis enable to derive a simple admission control for the class. Resources provisioned for the EF class but not used by this class are available for the other classes

Real-time end-to-end guarantees for the EF classwith and without traffic shaping

In this paper, we are interested in providing deterministic end-to-end guarantees to the Expedited Forwarding () class of the Differentiated Services (DiffServ) model. We focus on two Quality of Service (QoS) parameters: the end-to-end response time and the end-to-end jitter. As packets of any flow can experience variable network delays and sojourn times on each visited node, the inter-arrival times can be shorter than those on the source node and burst arrivals are possible. This flow distortion increases with the number of visited nodes. To cope with this distortion, traffic shaping has been introduced. We focus more particularly on two techniques of traffic shaping: jitter cancellation and token bucket. We then study the influence of traffic shaping on these two QoS parameters, independently of the scheduling policy for THEEF class. In this paper, we show how to compute the worst case end-to-end response time and jitter of any flow in the EF class with and without traffic shaping, assuming that the class has the highest priority and packets in this class are served FIFO. We then determine when each one of the three techniques (no traffic shaping, jitter cancellation and token bucket) is the most appropriate