A nonlinear viscoelastic approach to durability predictions for polymer based composite structures

Current industry approaches for the durability assessment of metallic structures are briefly reviewed. For polymer based composite structures, it is suggested that new approaches must be adopted to include memory or viscoelastic effects which could lead to delayed failures that might not be predicted using current techniques. A durability or accelerated life assessment plan for fiber reinforced plastics (FRP) developed and documented over the last decade or so is reviewed and discussed. Limitations to the plan are outlined and suggestions to remove the limitations are given. These include the development of a finite element code to replace the previously used lamination theory code and the development of new specimen geometries to evaluate delamination failures. The new DCB model is reviewed and results are presented. Finally, it is pointed out that new procedures are needed to determine interfacial properties and current efforts underway to determine such properties are reviewed. Suggestions for additional efforts to develop a consistent and accurate durability predictive approach for FRP structures is outlined

The nonlinear viscoelastic response of resin matrix composite laminates

Possible treatments of the nonlinear viscoelastic behavior of materials are reviewed. A thermodynamic based approach, developed by Schapery, is discussed and used to interpret the nonlinear viscoelastic response of a graphite epoxy laminate, T300/934. Test data to verify the analysis for Fiberite 934 neat resin as well as transverse and shear properties of the unidirectional T300/934 composited are presented. Long time creep characteristics as a function of stress level and temperature are generated. Favorable comparisons between the traditional, graphical, and the current analytical approaches are shown. A free energy based rupture criterion is proposed as a way to estimate the life that remains in a structure at any time

Method and apparatus for measuring the strain developed in a coated surface

A method and apparatus are provided for determining the strain developed in a coated surface. A beam with a coating on a surface thereof is mounted as a cantilever and a force is applied to the free end of the beam to cause deflection of the beam until the coating on the beam fails. The strain in the beam, and hence in the coating at the point of failure, is determined based on the dimensions of the beam, the point along the beam where failure of the coating occurs and the amount of deflection of the beam, and this determination is made independently of the temperature of the beam and the material from which the beam is made. The determination is made based on the equation E= 1.5hdx/l(exp 3), where E is strain, h is the beam thickness, d is the beam deflection, x is the distance from the free end of the beam to the point where failure of the coating occurred, and l is the length of the beam

Improving the measurement of prosociality through aggregation of game behavior

Prior research has found that people's choices in economic games are often only modestly related to their prosocial personality traits and to mundane prosocial behaviors. The present article reviews the recent literature showing that the strength of these relationships depends on the level of aggregation. Specifically, we demonstrate an increase in behavioral consistency after horizontal aggregation (across multiple game types), vertical aggregation (across multiple game variants), and a combination thereof. Moreover, we show that aggregation increases the magnitude of the relationships of game behavior with prosocial personality and mundane prosocial behavior. These findings illustrate that economic games can genuinely capture a core facet of human prosociality - but that their capacity for doing so is greater when multiple game behaviors are considered

Multiconfiguration Loads Analysis for Missions with an Uncertain Rideshare Manifest

Rideshare or “multi-manifest” missions – where several smaller “rideshare” spacecraft are launched together, usually with a larger “forward” spacecraft – are becoming increasingly common. In many cases, the properties or configuration of the rideshare spacecraft are not well-defined during initial launch manifesting and may not be finalized until a few months before launch. In this paper, a multiconfiguration loads analysis (MLA) process is presented that can enable flexibility in the mission manifesting process by allowing for uncertainty in the final rideshare configuration, including late manifest changes or swaps, without requiring additional loads analyses to those specified in the Load Cycle Process. By applying the MLA process, a set of adequately conservative loads can be generated for the forward spacecraft, launch vehicle, and potential rideshare spacecraft that account for uncertainty in the rideshare manifest and minimize the potential for issues late in the process. The MLA process will also define a mission-specific dynamic properties envelope that would allow rideshare spacecraft that “fit” within the envelope to be swapped. If all parts of the system are verified to match the models used in analysis and designed to survive the bounding loads, the launch manifest can be changed after analyses are completed, much closer to launch, without incurring increased risk

Design and Development of a Dynamically Deforming Leading Edge Airfoil for Unsteady Flow Control

ICIASF '97 RECORD, IEEE Publication No. 97CH36121, pp. 132-140.A novel approach to unsteady flow separation and dynamic stall control using a dynamically deforming leading edge airfoil is described. The design details of a carbon-fiber composite skin airfoil having a thickness of 0.002 in. at the leading edge and capable of deforming at 20 Hz in unsteady flow at freestream Mach numbers of up to 0.45, are discussed. Implementation of the scheme at model scales places extraordinary demands on the design, material and fabrication of such an airfoil. Rate scaling further requires very-rapid-response instrumental ion, measurement techniques and data acquisition schemes. The special instrumentation control system developed for these experiments as well as the fluid dynamic results of successful flow control that was achieved using this method, are also discussed.U.S. Army Research Office ARO MIPR 133-94, ARO 32480.11-EGU.S. Army Research Office ARO MIPR 133-94, ARO 32480.11-E

Durable Advanced Flexible Reusable Surface Insulation

An improved flexible blanket includes a nickel-based alloy foil layer brazed to a nickel-based alloy fabric layer. The fabric layer is stitched to an underlying ceramic insulation layer

Cooperation in mixed-motive games: the role of individual differences in selfish and social orientation

In mixed-motive games, people must choose between acting upon selfish interests and concerns for others. Yet, the consistency of people’s behavior across these various games is still unclear. If the same conflict between self and others is at the core of all mixed-motive situations, three hypotheses can be stated: (1) behaviors in different mixed-motive games should be substantially related, (2) all these games should substantially appeal to dispositional variables th

Risk Factors for Positive Deep Pelvic Nodal Involvement in Patients with Palpable Groin Melanoma Metastases: Can the Extent of Surgery be Safely Minimized?: A Retrospective, Multicenter Cohort Study

Background: Patients with palpable melanoma groin metastases have a poor prognosis. There is debate whether a combined superficial and deep groin dissection (CGD) is necessary or if superficial groin dissection (SGD) alone is sufficient. Aim: The aim of this study was to analyze risk factors for deep pelvic nodal involvement in a retrospective, multicenter cohort of palpable groin melanoma metastases. This could aid in the development of an algorithm for selective surgery in the future. Methods: This study related to 209 therapeutic CGDs from four tertiary centers in The Netherlands (1992–2013), selected based on complete preoperative imaging and pathology reports. Analyzed risk factors included baseline and primary tumor characteristics, total and positive number of inguinal nodes, inguinal lymph node ratio (LNR) and positive deep pelvic nodes on imaging (computed tomography [CT] ± positron emission tomography [PET], or PET − low-dose CT). Results: Median age was 57 years, 54 % of patients were female, and median follow-up was 21 months (interquartile range [IQR] 11–46 months). Median Breslow thickness was 2.10 mm (IQR 1.