A mixed-mode bending apparatus for delamination testing

A mixed-mode delamination test procedure was developed combining double cantilever beam mode I loading and end notch flexure mode II loading on a split unidirectional laminate. By loading the specimen with a lever, a single applied load simultaneously produces mode I and II bending loads on the specimen. This mixed mode bending (MMB) test was analyzed using both finite element procedures and beam theory to calculate the mode I and II components of strain energy release rate, G sub I and G sub II, respectively. The analyses showed that a wide range of G sub I/G sub II ratios could be produced by varying the applied load position on the loading lever. As the delamination extended, the G sub I/G sub II ratios varied by less than 5 percent. The simple beam theory equations were modified to account for the elastic interaction between the two arms of the specimen and to account for shear deformations. The resulting equations agreed closely with the finite element results and provide a basis for selection of G sub I/G sub II test ratios and a basis for computing the mode I and II components of measured delamination toughness. The MMB specimen analysis and test procedures were demonstrated using unidirectional laminates

Effects of reciprocal full-sib selection in maize

Fifty full-sib families and 100 S(,1) lines were developed from randomly chosen parents in each of the maize (Zea mays L.) populations BS10C0, BS10(FR)C6, BS11C0, and BS11(FR)C6 to investigate the effects of six cycles of reciprocal full-sib selection on population means and variances. Progenies were evaluated in experiments at two Iowa locations in 1983 and 1984. Data were collected for grain yield, ears per plant, percentage of root and stalk lodged plants, date of 50% silk emergence, ear and plant height, and number of tassel branches;Significant increases in yield and ears per plant among full-sib families and S(,1) lines were detected from the C0 to C6 cycles of BS10 and BS11. At both inbreeding levels, population means were significantly reduced from the C0 to C6 cycles for percentage of stalk lodging in both populations, and for percentage of root lodging and silking date in BS11. Among full-sib families in BS10 and BS11 mean ear and plant height decreased from the C0 to C6 cycles. Increases in mean ear and plant height were observed among S(,1) lines from BS10C0 to BS10(FR)C6, while population means of these traits decreased significantly from BS11C0 to BS11(FR)C6. At both inbreeding levels, population means for number of tassel branches increased from BS10C0 to BS10(FR)C6 and decreased from BS11C0 to BS11(FR)C6;Inbreeding depression for most traits decreased in response to selection. Reductions were significant for ear and plant height in BS10, and for yield, silking date, plant height, and number of tassel branches in BS11;For most traits, magnitudes of variances among full-sib families and S(,1) lines responded similarly to reciprocal full-sib selection. Magnitudes of additive genetic variance tended to decrease from the C0 to C6 cycles of BS10 and BS11 for yield, percentage of stalk lodging, ear and plant height, and number of tassel branches and seemed to increase for ears per plant and percentage of root lodging from BS10C0 to BS10(FR)C6 and for plant height from BS11C0 to BS11(FR)C6. Estimates of dominance variance generally increased, but decreases were observed for percentage of root lodging in BS10 and for yield, percentage of stalk lodging, and plant height in BS11. If actual changes in genetic variances have occurred, they have been small. Several negative estimates of dominance, environments x additive, and environments x dominance variances were obtained

User-Defined Material Model for Progressive Failure Analysis

An overview of different types of composite material system architectures and a brief review of progressive failure material modeling methods used for structural analysis including failure initiation and material degradation are presented. Different failure initiation criteria and material degradation models are described that define progressive failure formulations. These progressive failure formulations are implemented in a user-defined material model (or UMAT) for use with the ABAQUS/Standard1 nonlinear finite element analysis tool. The failure initiation criteria include the maximum stress criteria, maximum strain criteria, the Tsai-Wu failure polynomial, and the Hashin criteria. The material degradation model is based on the ply-discounting approach where the local material constitutive coefficients are degraded. Applications and extensions of the progressive failure analysis material model address two-dimensional plate and shell finite elements and three-dimensional solid finite elements. Implementation details and use of the UMAT subroutine are described in the present paper. Parametric studies for composite structures are discussed to illustrate the features of the progressive failure modeling methods that have been implemented

Flight Measurements of Flying Qualities of a P-47D-30 Airplane (AAF No. 43-3441) to Determine Longitudinal Stability and Control and Stalling Characteristics

Flight tests have been made to determine the longitudinal stability and control and stalling characteristics of the P-47.E-30 airplane. The teat results show the airplane to be unstable stick free in any power-on condition even at the most forward center-of-gravity position tested. At the rearward center-of-gravity position tested the airplane also had neutral to negative stick-fixed stability with power on. The characteristics in accelerated flight were acceptable at the forward center-of-gravity position at low and high altitudes except at high speed where the control-force variations with acceleration were high. At the rearward center-of-gravity position, elevator-force reversals were experienced in turns at low speeds, and the force per g was low at all the other speeds. Ample stall warning was afforded in all the conditions tested and the stalling characteristics were very satisfactory except in the approach and wave-off conditions

Lessons Learned from Recent Failure and Incident Investigations of Composite Structures

During the past few decades, NASA Langley Research Center (LaRC) has supported several large-scale failure and incident investigations and numerous requests for engineering consultations. Although various extenuating circumstances contributed to each of these incidents, in all cases, the failure resulted from accumulation and/or propagation of damage that reduced the load carrying capability of the structure to a level below that which was needed to sustain structural loads. A brief overview of various failure and incident investigations supported by LaRC, including some of the computational and experimental methodologies that have been applied, is presented. An important outcome of many of these failure and incident investigations is the development of an improved understanding of not only the state-of-the-art in experimental and analytical methods but also the state-of-the-art in the design and manufacturing processes that may contribute to such failures. In order to provide insight into such large-scale investigations, a series of lessons learned were captured. Awareness of these lessons learned is highly beneficial to engineers involved in similar investigations. Therefore, it is prudent that the lessons learned are disseminated such that they can be built upon in other investigations and in ensuing research and development activities

Food Insecurity and Depression Among US Adults: NHANES 2005–2016

A growing body of evidence suggests that food insecurity is associated with adverse mental health outcomes such as depression and anxiety. In this study, the relationship between food insecurity and depression was examined using data from the 2005–2016 National Health and Nutrition Examination Survey (NHANES). Food insecurity was assessed with the 18-item United States Food Security Survey Module with zero affirmative responses indicating high food security, 1 or 2 affirmative responses indicating marginal food security, and ≥3 affirmative responses indicating food insecurity. Depression was assessed with the Patient Health Questionnaire-9 with scores ≥10 indicating depression. Data were analyzed from 28,448 adult participants aged 20 or older. Food insecurity was present in 19.2% of the sample population (n = 5452). Food security status was significantly associated with gender, race, education level, marital status, smoking status, and BMI (Rao-Scott chi-square, p \u3c 0.05). Fully food secure and very low food security adults experienced depression at a rate of 5.1% and 25.8%, respectively (Rao-Scott chi-square, p \u3c 0.0001). Participants with very low food security had a significantly greater odds of depression than food secure adults, OR = 3.50 (95% CI: 2.98, 4.12). These findings suggest that food insecurity is a significant risk factors for depression in US adults over 20 years of age. To address this issue in our citizenry, police initiatives and public health interventions addressing both food access and mental health should be prioritized

Phylogenetic insights on evolutionary novelties in lizards and snakes: sex, birth, bodies, niches

Abstract Squamate reptiles (lizards and snakes) are a diverse clade in which there appear to have been multiple origins of many remarkable traits, including (a) parthenogenetic reproduction, (b) viviparity, (c) snake-like, limb-reduced body form, (d ) herbivory, and (e) venom. These repeated transitions make squamates an outstanding/excellent system for addressing many fundamental questions in evolutionary biology. For example, they are the only vertebrate group with true parthenogenesis (with at least 40 separate origins), they have more origins of viviparity than any other group of vertebrates, and they have undergone dramatic changes in body form (lizard-like to snake-like) dozens of times. New molecular phylogenies for squamates have overturned many traditional hypotheses and taxonomies based on morphology and are now revealing exciting new insights into the evolution of many of these traits at both higher and lower taxonomic levels. In this review, we summarize many of these new insights and outline important areas for future research