Mechanical Properties of T650-35/AFR-PE-4 at Elevated Temperatures for Lightweight Aeroshell Designs

Considerable efforts have been underway to develop multidisciplinary technologies for aeroshell structures that will significantly increase the allowable working temperature for the aeroshell components, and enable the system to operate at higher temperatures while sustaining performance and durability. As part of these efforts, high temperature polymer matrix composites and fabrication technologies are being developed for the primary load bearing structure (heat shield) of the spacecraft. New high-temperature resins and composite material manufacturing techniques are available that have the potential to significantly improve current aeroshell design. In order to qualify a polymer matrix composite (PMC) material as a candidate aeroshell structural material, its performance must be evaluated under realistic environments. Thus, verification testing of lightweight PMC's at aeroshell entry temperatures is needed to ensure that they will perform successfully in high-temperature environments. Towards this end, a test program was developed to characterize the mechanical properties of two candidate material systems, T650-35/AFR-PE-4 and T650-35/RP46. The two candidate high-temperature polyimide resins, AFR-PE-4 and RP46, were developed at the Air Force Research Laboratory and NASA Langley Research Center, respectively. This paper presents experimental methods, strength, and stiffness data of the T650-35/AFR-PE-4 material as a function of elevated temperatures. The properties determined during the research test program herein, included tensile strength, tensile stiffness, Poisson s ratio, compressive strength, compressive stiffness, shear modulus, and shear strength. Unidirectional laminates, a cross-ply laminate and two eight-harness satin (8HS)-weave laminates (4-ply and 10-ply) were tested according to ASTM standard methods at room and elevated temperatures (23, 316, and 343 C). All of the relevant test methods and data reduction schemes are outlined along with mechanical data. These data contribute to a database of material properties for high-temperature polyimide composites that will be used to identify the material characteristics of potential candidate materials for aeroshell structure applications

Investigating Differences between Graphical and Textual Declarative Process Models

Declarative approaches to business process modeling are regarded as well suited for highly volatile environments, as they enable a high degree of flexibility. However, problems in understanding declarative process models often impede their adoption. Particularly, a study revealed that aspects that are present in both imperative and declarative process modeling languages at a graphical level-while having different semantics-cause considerable troubles. In this work we investigate whether a notation that does not contain graphical lookalikes, i.e., a textual notation, can help to avoid this problem. Even though a textual representation does not suffer from lookalikes, in our empirical study it performed worse in terms of error rate, duration and mental effort, as the textual representation forces the reader to mentally merge the textual information. Likewise, subjects themselves expressed that the graphical representation is easier to understand

High-Temperature Structures, Adhesives, and Advanced Thermal Protection Materials for Next-Generation Aeroshell Design

The next generation of planetary exploration vehicles will rely heavily on robust aero-assist technologies, especially those that include aerocapture. This paper provides an overview of an ongoing development program, led by NASA Langley Research Center (LaRC) and aimed at introducing high-temperature structures, adhesives, and advanced thermal protection system (TPS) materials into the aeroshell design process. The purpose of this work is to demonstrate TPS materials that can withstand the higher heating rates of NASA's next generation planetary missions, and to validate high-temperature structures and adhesives that can reduce required TPS thickness and total aeroshell mass, thus allowing for larger science payloads. The effort described consists of parallel work in several advanced aeroshell technology areas. The areas of work include high-temperature adhesives, high-temperature composite materials, advanced ablator (TPS) materials, sub-scale demonstration test articles, and aeroshell modeling and analysis. The status of screening test results for a broad selection of available higher-temperature adhesives is presented. It appears that at least one (and perhaps a few) adhesives have working temperatures ranging from 315-400 C (600-750 F), and are suitable for TPS-to-structure bondline temperatures that are significantly above the traditional allowable of 250 C (482 F). The status of mechanical testing of advanced high-temperature composite materials is also summarized. To date, these tests indicate the potential for good material performance at temperatures of at least 600 F. Application of these materials and adhesives to aeroshell systems that incorporate advanced TPS materials may reduce aeroshell TPS mass by 15% - 30%. A brief outline is given of work scheduled for completion in 2006 that will include fabrication and testing of large panels and subscale aeroshell test articles at the Solar-Tower Test Facility located at Kirtland AFB and operated by Sandia National Laboratories. These tests are designed to validate aeroshell manufacturability using advanced material systems, and to demonstrate the maintenance of bondline integrity at realistically high temperatures and heating rates. Finally, a status is given of ongoing aeroshell modeling and analysis efforts which will be used to correlate with experimental testing, and to provide a reliable means of extrapolating to performance under actual flight conditions. The modeling and analysis effort includes a parallel series of experimental tests to determine TSP thermal expansion and other mechanical properties which are required for input to the analysis models

Onboard Evolution of Understandable Swarm Behaviors

Designing the individual robot rules that give rise to desired emergent swarm behaviors is difficult. The common method of running evolutionary algorithms off‐line to automatically discover controllers in simulation suffers from two disadvantages: the generation of controllers is not situated in the swarm and so cannot be performed in the wild, and the evolved controllers are often opaque and hard to understand. A swarm of robots with considerable on‐board processing power is used to move the evolutionary process into the swarm, providing a potential route to continuously generating swarm behaviors adapted to the environments and tasks at hand. By making the evolved controllers human‐understandable using behavior trees, the controllers can be queried, explained, and even improved by a human user. A swarm system capable of evolving and executing fit controllers entirely onboard physical robots in less than 15 min is demonstrated. One of the evolved controllers is then analyzed to explain its functionality. With the insights gained, a significant performance improvement in the evolved controller is engineered

Loneliness, social relations and health and wellbeing in deprived communities

There is growing policy concern about the extent of loneliness in advanced societies, and its prevalence among various social groups. This study looks at loneliness among people living in deprived communities, where there may be additional barriers to social engagement including low incomes, fear of crime, poor services and transient populations. The aim was to examine the prevalence of loneliness, and also its associations with different types of social contacts and forms of social support, and its links to self-reported health and wellbeing in the population group. The method involved a cross-sectional survey of 4,302 adults across 15 communities, with the data analysed using multinomial logistic regression controlling for sociodemographics, then for all other predictors within each domain of interest. Frequent feelings of loneliness were more common among those who: had contact with family monthly or less; had contact with neighbours weekly or less; rarely talked to people in the neighbourhood; and who had no available sources of practical or emotional support. Feelings of loneliness were most strongly associated with poor mental health, but were also associated with long-term problems of stress, anxiety and depression, and with low mental wellbeing, though to a lesser degree. The findings are consistent with a view that situational loneliness may be the product of residential structures and resources in deprived areas. The findings also show that neighbourly behaviours of different kinds are important for protecting against loneliness in deprived communities. Familiarity within the neighbourhood, as active acquaintance rather than merely recognition, is also important. The findings are indicative of several mechanisms that may link loneliness to health and wellbeing in our study group: loneliness itself as a stressor; lonely people not responding well to the many other stressors in deprived areas; and loneliness as the product of weak social buffering to protect against stressors