bluuebunny/crossref_metadata_2025 huggingface dataset:
One-Month-Lead Predictability of Asian Summer Monsoon Indices Based on the Zonal Winds by the APCC Multimodel Ensemble
Authors: Park Hye-Jin , Kryjov Vladimir N. , Ahn Joong-Bae
Published: September 2018

The seasonal predictability of Asian summer monsoon indices characterizing horizontal and vertical zonal wind shear is investigated using 1-month-lead hindcast datasets from seven coupled global circulation models (CGCMs) participating in the operational multimodel ensemble (MME) seasonal prediction system of the Asia–Pacific Economic Cooperation Climate Center (APCC) for the 1983–2010 period. The summer monsoon indices analyzed in this study represent the South Asian summer monsoon (SASM), western North Pacific summer monsoon (WNPSM), and the newly defined northeastern Asian summer monsoon (NEASM). For the WNPSM and NEASM indices, we also analyze the prediction skill of the index components separately. The study demonstrates that the operational APCC MME system reliably predicts most of the summer monsoon indices and their components, with correlation coefficients exceeding the 99% confidence level. Analysis of the ocean sources of the prediction skill of the indices reveals that the strong relationships of most of the monsoon indices and their components with sea surface temperature (SST) are not confined to the equatorial Pacific but rather are dispersed throughout the World Ocean, with the leading role played by the north Indian Ocean SST anomalies. This conclusion is supported by the analysis of correlations between the monsoon indices and the tropical SST indices. The correlations between the SST anomalies and all the summer monsoon indices in the MME predictions are stronger than those in the observations. However, overestimation of the role of the ENSO-related SST anomalies in the seasonal model hindcasts results in some predictability deterioration of the SASM and NEASM indices.
The Dynamics of Intimate Partner Violence and the Risk of Pregnancy during the Transition to Adulthood
Authors: Barber Jennifer S. , Kusunoki Yasamin , Gatny Heather H. , Budnick Jamie
Published: September 2018

Using a reproductive coercion framework, we investigate the role of intimate partner violence (IPV) in pregnancy during the transition to adulthood. We use two types of data from a population-based sample of 867 young women in a Michigan county: a 60-minute survey interview with 2.5 years of weekly follow-up surveys, and semi-structured interviews with a subsample of 40 pregnant women. The semi-structured interviews illustrate the violence women experienced. Discrete-time logit hazard models demonstrate that threats and physical assault are associated with higher pregnancy rates during ages 18 to 22. However, this holds only when the violence is recent; violence occurring more than a month earlier is not associated with higher pregnancy rates. These associations are independent of violent experiences with prior partners, which are also associated with higher pregnancy rates. Fixed-effects models show that during violent weeks, women perceive more pregnancy desire from their partners, have more sex, and use less contraception than during nonviolent weeks. Finally, mediation analyses and the semi-structured interviews are consistent with reproductive coercion: violent young men are more likely to want their girlfriends pregnant, and they use threats and physical assault to implement their preferences via sex and contraceptive non-use, which in turn increase pregnancy rates.
Efficacy of antenna engineering research orientation among graduate students at Mekelle University Ethiopian Institute of Technology
Authors: Mohammed Mohammed I
Published: September 2018

The continual growth of antenna-based technologies has created an exponential demand for well-qualified workforce of antenna engineer/researchers, but the expertise for a smooth transition into job market is lagging. This study presents the effectiveness of using hybrid-flipped model integrated with educational technologies in a graduate Antenna Theory and Design course, and the influence it has on orienting students toward antenna research. This is important because graduate research in emerging technologies with good results will open the gateway for job and the prospect of a scholarship for higher education. The effectiveness of the proposed study is evaluated using the following metrics: (a) student response to the hybrid-flipped learning, (b) impact of educational technology on student learning, and (c) educational outcome toward antenna engineering research. Result of the study indicates that the number of students choosing antenna research increased from 14% in 2014–15 to 42% in 2015–16 and reaching to 70% in 2016–17, and the number of students for year 2017–18 is 77% Results of the study also reflect research in diverse antenna technologies with good research output to merit publication in journals of international repute.
More Reform of the English National Health Service: From Competition Back to Planning?
Authors: Lewis Richard Q.
Published: September 2018

The period of sustained financial austerity since 2009 has led to a shift in competition policy within the English National Health Service. Policymakers have directed their attention away from the preexisting priority to support quicker access to routine and planned hospital care and have focused instead on improving emergency, cancer, and general practitioner services. This has prompted the development of a new policy framework and, in particular, a desire to create collaborative health systems focused on specific populations. In addition, previous policy initiatives to engage the leadership of general practitioners in planning services have been revisited. The overall effect has been to shift emphasis away from competitive markets and back toward a planning approach.
Universal, Normative, and Indispensable: Exploring the Emphasis on Eurocentric Literary-Critical Perspectives in the Criticism of the Black Zimbabwean Novel
Authors: Gwekwerere Tavengwa
Published: September 2018

Literary-critical discourse on the Black Zimbabwean novel constitutes one of several platforms on which the self-other dialectic in Zimbabwe finds expression. This is especially the case at the level of literary-critical theory where the tendency is to advance arguments that frame Afrocentric and Eurocentric literary-critical theories as mutually exclusive. In this article, I explore the scholarship of Flora Veit-Wild and Ranka Primorac on the Black Zimbabwean novel with a view to discoursing the ways in which it can be argued that in their discussion of the corpus, the two scholars are anchored in the Eurocentric framework. In pursuing this objective, I focus on the critics’ reliance on Eurocentric literary-critical theories and apparent discomfiture with Afrocentric benchmarks in their criticism of the Black Zimbabwean novel. Thus, I argue in this article that while the version of critical discourse discussed here speaks to the complex and contradictory ways in which cultures find places of translation and dialogic engagement where history is made, the overall impression created by Veit-Wild and Primorac in their criticism of the Black Zimbabwean novel is that Eurocentric perspectives are universal, normative, and indispensable.
Race, Class, Gender, and Rhymes: Hip-Hop as Critical Pedagogy
Authors: Karvelis Noah
Published: September 2018

Hip-hop is a truly African-American art form in every sense of the phrase. Multiple decades after its development into the genre that we recognize it as today, hip-hop firmly remains a fundamental and unique element of African-American culture that has experienced international presence and regard. As a direct result of deep involvement with African-American culture, hip-hop is uniquely placed as a tool for developing rich, critical understandings of an array of complex social issues. Through thoughtful inclusion and the music classroom, the lyrics, culture, and history of hip-hop can be taught in a manner that augments education, particularly in areas relating to race, gender, and class in society.
Evaluation of the Factor Structure of the Adolescent Stress Questionnaire in Chinese Adolescents
Authors: Ye Tianpeng , Cui Naixue , Yang Wen , Liu Jianghong
Published: September 2018

This study evaluated the psychometric properties of the Chinese version of Adolescent Stress Questionnaire ( ASQ-CN) in a sample of Chinese middle school students ( N = 420; 52.14% boys and 47.86% girls). Iterated principal factor analysis and multiple-group principal components cluster analysis supported a six-factor model with 42 items out of 58 items in the ASQ-CN. The internal consistency was from .82 to .90. Girls reported lower stress levels in one subscale, Stress of romantic relationship, whereas no gender differences were found in the other five subscales. Compared with other studies of the ASQ in Westernized countries, the ASQ-CN showed a distinct factor structure that may be explained by cross-cultural differences. Scales constructed from factor analysis related negatively to measures of mindfulness and positively to a measure of behavioral problems, suggesting that they were valid for Chinese adolescent stress. The study did not support a higher order construct of the ASQ-CN. Altogether, our findings suggest that the ASQ-CN is adequate for assessing stressors in Chinese adolescents.
Emotional State Can Affect Inflammatory Responses to Pain Among Rheumatoid Arthritis Patients: Preliminary Findings
Authors: Graham-Engeland Jennifer E. , Song Sunmi , Mathur Ambika , Wagstaff David A. , Klein Laura Cousino , Whetzel Courtney , Ayoub William T.
Published: September 2018

In a novel pilot study, we investigated how emotional state is related to inflammatory responses to acute pain among women with rheumatoid arthritis. Nine women completed four 5-hour visits that varied only by manipulation of emotion (anger, sadness, happiness, vs. control); in each visit, acute pain was elicited, with blood draws at baseline, 10 minutes, 60 minutes, and 100 minutes post-pain. We examined the effects of within-subjects factors on circulating inflammatory biomarkers interleukin (IL)-6, IL-10, tumor necrosis factor-α, C-reactive protein, and cortisol. There was a main effect of state anger on IL-6, with higher reported anger associated with higher IL-6 across conditions. Further, there were several interactions between state emotion and condition. For example, when individuals reported higher state anger in the sadness condition compared to their own average, they showed higher levels of IL-6 and cortisol. Findings are discussed within a larger literature suggesting that mixed emotional states can contribute to psychological stress and inflammatory responses.
Study on the effect of organic phosphonic compounds on disulfide bonds in wool
Authors: Li Bo , Yao Jinbo , Niu Jiarong , Liu Jianyong , Wang Le , Feng Mao , Sun Yanli
Published: September 2018

In this study a new type of organic phosphonic compound named LKS-610, a kind of reducing agent, was used to cleave disulfide bonds in wool fibers. Research into the extraction of keratin from wool and processing into useful textile materials is a hot topic in the field of textiles. Wool fibers are rich in disulfide bonds which are the main chemical cross-linkage to maintain the fiber's secondary structure. If the disulfide bonds between molecular chains can be sufficiently disrupted, it will facilitate to obtain the keratin solution suitable for the regenerated materials preparation. The reaction mechanism and effect were analyzed through scanning electron microscopic test (SEM), X-ray photoelectron spectroscopy test (XPS) and amino acid content test. After a period of processing time, the valence state of sulfur element on fiber surface changed significantly; this result shows that the disulfide bonds reacted with LKS-610 reagent and generated thiol groups. Amino acid analysis demonstrated that for wool fibers treated for 60 min at 80℃, the quality percentage of cystine in wool was reduced from 10.09% to 1.05%, the majority of disulfide bonds had been cleaved. In this case, fiber scales were almost completely stripped and the cortical layer was not significantly damaged but became prone to swelling. This indicated that LKS-610 reagent could disrupt the disulfide bonds in the wool thoroughly and efficiently, and reduce these bonds to thiol groups. Wool fibers pretreated by LKS-610 reagent can be dissolved readily to prepare keratin solution; this keratin solution with high dissolution ratio and large molecular weight can be used in research into modification and preparation of regenerated protein materials.
The Urban Development Corporation’s “Imaginative Use of Credit”: Creating Capital for Affordable Housing Development
Authors: Peterson Eric David
Published: September 2018

Heralded as an innovative if short-lived builder of affordable housing, in 1975, the New York State Urban Development Corporation (UDC) defaulted on more than $2 billion in debt obligations and narrowly avoided bankruptcy. Offering the first detailed examination of its finances, this article argues the UDC was prescient of a new model for public-private housing finance that in the 1980s emerged in the ashes of conventional, state-financed public housing. In response to many of the long-standing challenges with government-produced housing, particularly inadequate funding, the UDC’s creation presaged the debt-driven model of development which would mature in the subsequent decades. While many scholars continue to reify criticism of government-created housing projects often on the basis of design or policy defects, the UDC’s failure highlights the importance of financial and political support in shaping the success of subsidized housing.
Replicating a National Survey on Statistical Training in Undergraduate Psychology Programs
Authors: Friedrich James , Childress Julia , Cheng David
Published: September 2018

This study describes a close replication of Friedrich, Buday, and Kerr’s late 1990s survey of statistics instruction in undergraduate psychology programs. Disciplinary reform efforts at that time such as the report of the APA Task Force on Statistical Inference, together with recent progress in the new statistics movement, raise important questions about whether undergraduate instruction has kept pace. Other than increases in effect size coverage, instructors’ estimates of class time devoted to critical reform topics have changed relatively little over nearly two decades, with significant attention often reserved for a rarely offered second-level, advanced class. We consider the importance of addressing the statistics curriculum in ways that meet the reading access, critical thinking, and research skill needs of current majors.
Reciprocal Relationships Between Workplace Childcare Initiatives and Collective Turnover Rates of Men and Women
Authors: Piszczek Matthew M.
Published: September 2018

Work-family practice research has largely been focused on individual outcomes, despite their theorized importance for organizational performance. Additionally, studies of the effectiveness of work-family practices are dominated by cross-sectional designs that are unable to rule out additional causal arguments for observed relationships. Finally, childcare initiatives that help employees better address family demands have received little research attention relative to other work-family practices, and these studies have produced mixed results. Grounded in context-emergent turnover theory, the present study assesses the relationship between establishment childcare initiatives and collective turnover rates of men and women in 24,888 observations of German establishments between 2002 and 2012. Findings indicate childcare initiatives are associated with lower female collective turnover rates in following years and that higher female collective turnover rates are also associated with a higher likelihood of adopting a childcare initiative in subsequent years. These results provide support for the argument that childcare initiatives can improve collective turnover rates of women and are not adopted only by already-high-performing organizations.
Assange vs Zuckerberg: Symbolic Construction of Contemporary Cultural Heroes
Authors: Blanco-Gracia Antonio
Published: September 2018

Myth is a meta-language that shapes our cultures and the way we individually and collectively make sense of reality. This paper presents the methodologies of French anthropologist and sociologist Gilbert Durand as a way to unveil how ancient myths contribute to the symbolic construction of societal leaders in times of crisis. To do so, it analyses the controversy of the selection of Time magazine’s Person of the Year, which confronted the figures of Julien Assange and Mark Zuckerberg. The myth analysis of their Wikipedia biographies will show that despite the fact these two personalities are considered almost opposites, the structure of the collective shared narratives about each of them follow the structure of the myth of Hermes, one shaping the grand narrative of the postmodern era. Realizing why and how the myth of Hermes promotes our contemporary leaders, sometimes apparent antagonists, contributes to better understanding of the unconscious drives of their symbolic construction, and enabling critical engagement with the rationales of their emergence.
Acute Kidney Injury (AKI)—The Toxicologic Pathologist’s Constant Companion
Authors: Crabbs Torrie A.
Published: September 2018

This article provides a brief overview of the second scientific session of the 37th Annual Symposium of the Society of Toxicologic Pathology in Indianapolis, Indiana, on June 18, 2018. The session was entitled “Acute Kidney Injury (AKI): The Toxicologic Pathologist’s Constant Companion” and was co-chaired by Drs. Zaher Radi and Torrie Crabbs. The fundamentals of tubule and interstitial anatomy were covered by Dr. Kevin McDorman, followed by a review of International Harmonization of Nomenclature and Diagnostic Criteria, Standard for Exchange of Nonclinical Data, and Drug-Induced Kidney Injury terminology, which was presented by Dr. Torrie Crabbs. Dr. Bruce Molitoris gave a talk on renal hemodynamics, microcirculation, and ischemia. Advances and challenges on new therapies and clinical targets of AKI were presented by Dr. Brad Rovin, and the session ended with a review from Dr. Zaher Radi on immunopathology of AKI.
Brief Synopsis: Review of Renal Tubule and Interstitial Anatomy and Physiology and Renal INHAND, SEND, and DIKI Nomenclature
Authors: Crabbs Torrie A. , McDorman Kevin S.
Published: September 2018

This article provides a synopsis of the first two presentations from the second scientific session of the 37th Annual Symposium of the Society of Toxicologic Pathology in Indianapolis, Indiana, on June 18, 2018; the session focused on acute kidney injury. The first presentation, given by Dr. Kevin McDorman, focused on “Fundamentals of Renal Tubule and Interstitial Anatomy and Physiology.” Several common background findings from toxicity studies were additionally discussed. Lastly, factors that impact the relevance and usefulness of historical control data, such as quality and consistency of histopathology, were discussed. The second presentation, given by Dr. Torrie Crabbs, provided a review of International Harmonization of Nomenclature and Diagnostic Criteria (INHAND), Standard for Exchange of Nonclinical Data (SEND), and drug-induced kidney injury (DIKI) nomenclature. INHAND is a global collaborative project that provides internationally accepted standardized nomenclature and diagnostic criteria for proliferative and nonproliferative changes in laboratory animals in toxicity and carcinogenicity studies. SEND is currently a required standard for data submission to the Food and Drug Administration (FDA). Since the FDA has indicated its preference for INHAND nomenclature, SEND will predominately use INHAND terminology; thus, familiarity with INHAND terminology is critical for toxicologic pathologists. The diagnostic features of three common DIKI findings, in addition to several complicated INHAND terminologies, were reviewed.
Foam Extrusion of PS Blown with a Mixture of HFC-134a and Isopropanol
Authors: Gendron Richard , Vachon Caroline , Champagne Michel F. , Delaviz Yadi
Published: September 2018

Use of mixtures of blowing agents in foam extrusion has gained interest in the past few years. Reasons for blending physical foaming agents (PFA) are numerous. The incentives may be economical, environmental or technical. With respect to that latter factor, blending suitable PFAs is often regarded as providing a better control of processing conditions. For example, a specific PFA could be selected for its inflation performance and blended with other co-blowing agents chosen for their stabilizing role. Although considerable amount of work has been done in that area, very little information has been disclosed in open literature.

1,1,1,2-tetrafluoroethane (HFC-134a) has been reported as an interesting candidate for polystyrene (PS) foaming, although low densities cannot be easily obtained and stable processing conditions are difficult to achieve. This work studies the effect of blending HFC-134a with isopropanol as a co-blowing agent for PS. Off-line solubility data, on-line rheology measurements and extrusion foaming performance of this mixture will be discussed. The function of each blowing agent during the process will be analyzed with respect to the plasticization, nucleation, expansion and stabilization phases. Attention will also be paid to interaction involving the two PFA components.
Microcellular Foaming with Supercritical CO2 in Injection Moulding
Authors: Goodship V. , Stewart R.L. , Hansell R. , Ogur E.O. , Smith G.F.
Published: September 2018

This paper discusses the systems for microcellular injection moulding developed and patented by Trexel and IKV. It then introduces a third design with initial findings and recommendations for modifications. The results suggest that microcellular foaming is possible introducing supercritical carbon dioxide in the nozzle providing certain design criteria are met such as a sufficient pressure drop from the plastication unit to the mould to enable rapid nucleation. Results from experiments with polystyrene are presented with consideration for pressure drop, weight reduction and injection speed.
Polyethylene-Kevlar Composite Foams II: Mechanical Properties
Authors: Zhang Yaolin , Rodrigue Denis , Aït-Kadi Abdellatif
Published: September 2018

Polyethylene-Kevlar composite foams were prepared by polymerization-compounding and melt blending to investigated and understand the effect of fibers. In the first part of this study (Zhang et al., Cellular Plastics, 22, (2003), 279), we reported on the preparation and morphology of these composite foams. In this second part, the effect of fibers on the mechanical properties of composite foams is investigated. Using several models for particulate composites, it was found that the normalized modulus of our composite foams can be well predicted by the simple Moore's empirical equation to take into account the foam morphology in combination with Berlin's approach and Rosen's model for critical fiber aspect ratio to account for the effect of fibers.
Evaluation of HFC-245fa as an Alternative Blowing Agent for Extruded Low-Density Polyethylene
Authors: Vachon Caroline
Published: September 2018

HFC-245fa was investigated as a blowing agent in low-density polyethylene (LDPE). Ultrasonic monitoring showed that this blowing agent has degassing pressures systematically lower in LDPE than those reported in polystyrene, in agreement with solubility measurements performed on other polymer-gas systems. Based on these results, HFC-245fa would have solubility properties similar to HCFC-22 both in polyolefins and in polystyrene.

Foams were produced in extrusion using gas concentrations ranging from 3 to 7.7 wt.%. Extrusion profiles show that foam growth in LDPE is very slow and that adding a nucleating agent is required to trigger the expansion process. Using an optimal concentration of gas and talc, it was possible to produce foam samples below 100 kg/m3.
Morphology and Physico-Mechanical Properties of Closed Cell Microcellular EPDM Rubber Vulcanizates: Effect of Conductive Carbon Black and Blowing Agent
Authors: Mahapatra S.P. , Tripathy D.K.
Published: September 2018

The morphology of the composite based on a new controlled long chain branching grade, oil extended EPDM (Keltan 7341A) and highly conductive carbon black (vulcanXC72) filled compound has been studied from SEM photomicrographs with variation of blowing agent and conductive carbon black filler loading. The average cell size, maximum cell size and cell density varies with variation of blowing agent and filler loading. Physical properties like relative density, hardness, tensile strength, modulus, tear strength decreases with blowing agent concentration. Enclosed gas pressure in a closed cell increases relative modulus at higher strain. Elongation at break decreases with blowing agent loading at higher filler loading. At lower filler loading it increases both with filler and blowing agent loading. The elastic nature of closed cells reduces the hysteresis loss compared to solid compounds. The stress relaxation behavior is independent of blowing agent loading.
The Effect of Skin Thickness on the Mechanical Properties of Structural Foams
Authors: Blanchet Jean-François , Rodrigue Denis
Published: September 2018

The flexural, shear and tensile modulus of high density polyethylene structural foams were measured in order to determine the effect of skin thickness on their response under load. Data for foam density between 424 and 725 kg/m3 and skin thickness between 3 and 57% are compared with different models taken from the literature. It is found that the I-beam model of Hobbs and the simple square power-law of Moore are the best models for the flexural and tensile modulus, respectively. For the shear modulus, all the models tested performed equally well.
Selection of Energy Absorbing Materials for Automotive Head Impact Countermeasures
Authors: Juntikka Rickard , Hallström Stefan
Published: September 2018

Material candidates for energy absorption in head impact countermeasures for automotive applications are evaluated using both quasi-static and dynamic test methods. Ranking of different materials turns out to be difficult since the mechanical response of a material could vary considerably with temperature, especially for polymers. Twenty-eight selected materials, including foams, honeycombs and balsa wood are tested and evaluated. The materials are subjected to a sequence of tests in order to thin out the array systematically. Quasi-static uni-axial compression is used for initial mapping of the selected materials, followed by quasi-static shear and dynamic uni-axial compression. The quasi-static test results show that balsa wood has by far the highest energy absorption capacity per unit weight but the yield strength is too high to make it suitable for the current application. The subsequent dynamic compression tests are performed for strain rates between 56 s−1 and 120 s−1 (impact velocities between 1.4 and 3 m/s) and temperatures in the range −20 - 60 °C. The test results emphasize the necessity of including both strain rate and temperature dependency to acquire reliable results from computer simulations of the selected materials.
Polyethylene-Kevlar Composite Foams III: Torsion Properties
Authors: Zhang Yaolin , Rodrigue Denis
Published: September 2018

High density closed-cell Kevlar-polyethylene composite foams (17 - 30% void fraction) were prepared by compression molding and characterized via torsion rectangular tests in order to determine the effect of thin unfoamed skins and Kevlar content on shear modulus. It was found that structural foam models gave better results than uniform foam models indicating that thin skins have an important effect on the shear modulus of polymer foams. The normalized modulus of our composite structural foams can be predicted by a sandwich model in combination with Berlin's approach and Rosen's model for the aspect ratio of the fibres.
The Effect of Clay Content on PMMA-Clay Nanocomposite Foams
Authors: Manninen Allan R. , Naguib Hani E. , Nawaby A. Victoria , Liao Xia , Day Michael
Published: September 2018

In this study the CO2sorption at 45 °C in PMMA nanocomposite films containing 2 wt.% of nanoclay has been measured using an in-situ gravimetric technique. The films examined were prepared by compression moulding material obtained by dry-blend and solvent co-precipitation techniques. The CO2diffusion coefficients were found to be higher for the dry-blended nanocomposite due to the larger agglomerations of the organoclay agglomerations, which prevented the polymer chains from fully wetting and intercalating the clay particles. The Tg-p profile for PMMA nanocomposite containing 2 wt.% nanoclay in the presence of CO2was also measured using high-pressure DSC. The glass transition phase envelope was shifted vertically by approximately 10 °C when compared to the value reported in the literature for neat PMMA. This result suggests that the nanoclay affects the plasticization behaviour of PMMA under high-pressure CO2conditions. The cellular morphologies obtained for these PMMA nanocomposite foams produced by batch processing with subcritical CO2are strongly dependent upon the clay content and the dispersion of the nanoclay in the material. In the case of intercalated nanocomposites, most clay particles exist as agglomerated stacks of silicate sheets. On foaming the cells tend to form around the clay particles causing either irregular-shaped cells or layers to be produced. As a result, the cell density increases and the mean cell size decreases in the foamed nanocomposite on increasing the nanoclay content. Accordingly, the resulting cell structures are highly non-uniform and show large variations in cellular morphologies throughout the foam.
Constrained Solid-State Foaming of Microcellular Panels
Authors: Nadella Krishna , Kumar Vipin , Li Wei
Published: September 2018

This paper presents a novel constrained foaming process to produce microcellular panels. A systematic study of various process variables is conducted using a two-stage, sliding-level design of experiment approach. The resulting microcellular sheets have thicknesses in the 5 – 15 mm range and densities reductions as low as 92%. It is shown that an unfoamed integral skin of desired thickness can be produced with a microcellular core at various densities. These microcellular panels are envisioned for use in advanced panel systems and sandwich structures, such as in housing construction and other load-bearing applications.
Effect of Processing Parameters on Cellular Structures and Mechanical Properties of PMMA Microcellular Foams
Authors: Fu Jin , Jo Choonghee , Naguib Hani E.
Published: September 2018

In this study, the effect of processing parameters on the cellular morphologies and mechanical properties of PMMA microcellular foams is investigated. Microcellular closed cell Poly(methyl-methacrylate) (PMMA) foams were prepared using a two stage batch process method. The foam structure was controlled by altering the processing parameters such as foaming temperature, foaming time and saturation pressure. The foam morphologies were characterized in terms of the average cell size, cell density and foam density. Elastic modulus, tensile strength and elongation at break were studied as functions of the different foaming parameters. The mechanical properties were found to be greatly affected by the foaming parameters and vary with changing the cell morphologies. The experimental results were compared with existing analytical models to validate them and to predict the mechanical properties of microcellular polymeric PMMA foams prepared with different processing parameters. A constitutive equation for the nonlinear elastic behavior of polymeric microcellular foams was developed based on the Maxwell viscoelastic model. The results of this work can help designers optimize the foam processing parameters and achieve desired foam morphology and mechanical properties.
Compressive Deformation and Energy Absorption Characteristics of Conductive Carbon Black Reinforced Microcellular EPDM Vulcanizates
Authors: Mahapatra S.P. , Tripathy D.K.
Published: September 2018

Compressive stress-strain properties of unfilled and conductive carbon black (VulcanXC 72) filled oil extended EPDM (keltan 7341A) microcellular vulcanizates were studied as a function of blowing agent (density) and filler loading. With decrease in density, the compressive stress-strain curves for microcellular vulcanizates behaved differently from those of solid vulcanizates. The compressive stress-strain properties were found to be strain rate dependent. The log-log plots of relative density of the microcellular vulcanizates showed a fairly linear correlation with the relative modulus. The compression set at a constant stress increased with decrease in density. The efficiency of energy absorption E, was also studied as a function of filler and blowing agent loading. From the compressive stress-strain plots the efficiency E and the ideality parameter I, were evaluated. These parameters were plotted against stress to obtain maximum efficiency and the maximum ideality region, which will make these materials suitable for cushioning and packaging applications in electronic devices.
Prediction of Cushion Curves for Closed Cell Polyethylene-Based Foams. Part I. Modelling
Authors: Ruiz-Herrero J.L. , Rodríguez-Pérez M.A. , de Saja J.A.
Published: September 2018

The possibility of prediction of the cushioning performance of closed cell foams under compressive impacts has been analyzed, using simple theoretical models. Several corrections have been introduced into the models previously proposed by Burgess. These corrections take into account the variation of gas volume in the foam with density, they incorporate the effect of the falling weight into the calculations, and finally they consider the base polymer effect. Even though the predictability of the model is not complete it provides a useful tool from the practical viewpoint.
Critical Issues in Extrusion Foaming of Plastic/Woodfiber Composites
Authors: Rizvi G.M. , Guo G. , Park C.B. , Kim Y.S.
Published: September 2018

Foaming of wood-fiber/plastic composites (WPC) with a fine-celled structure can offer benefits such as improved ductility and impact strength, lowered material cost, and lowered weight, which can improve their utility in many applications. However, foaming of WPC is still a poorly understood art. This paper presents a review of material published, which address the various critical issues particularly in extrusion foaming of WPC, and the proposed processing techniques and strategies, for producing artificial wood with enhanced properties.
Finite Element Models for the Viscoelasticity of Open-Cell Polyurethane Foam
Authors: Mills N.J.
Published: September 2018

Finite Element Analysis (FEA) was used to model viscoelastic effects in the compression of polyurethane (PU) foam. Modelling of the impact compression of foam cubes predicted that a compressed region propagated through the sample, causing step increases in the stress traces. Modelling of head impacts on gymnastic ‘crash’ mats, made of PU chip foam, revealed that the majority, but not all, of the energy losses could be attributed to the polymer viscoelasticity.

The Gibson-Ashby micromechanics model was used to show that the hysteresis in a viscoelastic foam could be higher than in the parent polymer. A wet Kelvin foam, with a better foam geometry, was then used for viscoelastic analysis. The lattice of uniform-sized cells, in a Body Centred Cubic array, were compressed in the [111] direction. With the PU treated as a linear viscoelastic material, the predicted hysteresis in the cyclic stress-strain curve was slightly smaller than that measured for a PU flexible foam.
The Effect of Composition on Impact Properties of Foamed HDPE/PP Blends
Authors: Estrada-Núñez S.A. , González-Núñez R. , Rodrigue D.
Published: September 2018

In this study, high density polyethylene and polypropylene were blended and foamed using azodicarbonamide as a chemical blowing agent, zinc oxide as an accelerator, and Kraton D1102 as a compatibilizer. Gardner impact resistance of injection molded samples is reported as a function of blend composition for foamed and unfoamed samples. The results show that Kraton addition had negligible effect on impact strength of unfoamed samples while foamed samples were more resistant. A change in fracture behavior was also observed and related to the morphology of the material.
Processing and Characterization of Nanophased Polyurethane Foams
Authors: Mohammed Aleem A. , Hosur M.V. , Jeelani S.
Published: September 2018

Nanophased polyurethane foams were prepared with the inclusion of 0.5% and 1% nanoclay. Samples were subjected to static and dynamic compression loading. Compression behavior of neat (without nanoclay) and nanophased foams were compared. Quasi-static compression testing was carried out using MTS system whereas a Split Hopkinson's Pressure Bar (SHPB) was used to characterize the high strain rate behavior at three different strain rates of approximately 1000, 1450, 1750 s−1. It was found that by increasing the strain rate peak stress and modulus of foams increased. Nanoclay filled polyurethane foam exhibited improved mechanical properties over the neat system. Microstructural analysis revealed that cell wall thickness of nanoclay filled foam was more than that of the neat foam which caused an increase in the cell density (number of cells per unit area) resulting in increased mechanical properties.
On the Bulk Modulus of Open Cell Foams
Authors: Moore B. , Jaglinski T. , Stone D.S. , Lakes R.S.
Published: September 2018

Bulk properties of open cell polyurethane foam are studied in a hydrostatic compression experiment under strain control. A linear region of behaviour is observed in the stress-strain curve, followed by a non-monotonic region corresponding to a negative incremental bulk modulus. The bulk modulus in the linear region is in reasonable agreement with the value calculated from compressional Young's modulus and Poisson's ratio. The linear region of behaviour in hydrostatic compression corresponds to less than half the axial strain range observed in axial compression.
Low Density Sub-Critical CO2-Blown Solid-State PLA Foams
Authors: Wang Xiaoxi , Kumar Vipin , Li Wei
Published: September 2018

This paper presents a characterization of the PLA-CO2 system for solid-state foaming process with a particular goal of producing low density foams. The diffusivity of CO2 in PLA increases with increasing saturation pressures. The results show that low relatively density (lower than 10%) can be achieved in a wide processing window. The cell size can vary from tens of microns to several hundreds of microns depending on the solid-state foaming process parameters. There are significant differences in relative density and cell size for 2 and 3 MPa saturation cases, which are likely due to the much higher crystallinity at 3 MPa (26.4%) compared to 2 MPa (9.7%). Foams with cell size of around 300 μm and relative density of 3% were produced at 2 MPa saturation.

It was observed that the higher the gas pressure, the higher the rate of gas-induced crystallization. Further, the gas-induced crystallization as well as the gas concentration in PLA during sorption reach their respective maximum values at approximately the same time for all gas pressures explored. For specimens saturated at 2 MPa, there is a substantial jump in crystallinity (from 5.2% to 23.4%) after foaming.
Influence of the Foam Core Material on the Indentation Behavior of Sandwich Composite Panels
Authors: Rizov V. , Mladensky A.
Published: September 2018

Foam core sandwich composite materials have been used more and more frequently in various engineering applications in recent decades. Due to the increased usage of these materials, the concern about their strength and reliability has gained momentum. One of the basic disadvantages of the sandwich structures is their sensitivity to failure by the application of localized lateral loads. The main aim of this work is to investigate the influence of the foam core material on the indentation response of flat sandwich panels. For this purpose, quasi-static indentation test are conducted on sandwich panel specimens that are manufactured with glass fiber reinforced plastic (GFRP) face sheets and three types of Divinycell foam core material (H60, H100 and HCP100). The load is applied through a steel spherical indentor with diameter of 25 mm. The load-displacement diagram for both loading and unloading steps is obtained from the experiments. A numerical modeling of the elastic-plastic indentation response of sandwich structures is performed using the ABAQUS finite element program. In order to predict the residual dent magnitude, both indentation and unloading phases are analyzed. The finite element results demonstrate good agreement with the experimental data. It is found that the load (at a given indentation) is the highest for sandwich panels with the HCP100 foam core, and is the lowest for sandwich panels with the H60 foam core. The load (at the same indentation) for panels with the H100 foam core has intermediate magnitude.
Characterization of the Binder Phase in a Three-Phase Carbon Microballoon Syntactic Foam
Authors: Carlisle K.B. , Gladysz G.M. , Chawla K.K. , Koopman M. , Lewis M.
Published: September 2018

In three-phase syntactic foams, the (often polymeric) binder phase plays the vital role of holding the compressive load bearing microballoon components in place. When characterizing three-phase syntactic foams, it is important to characterize this binder phase. To obtain thermal and mechanical properties, we have performed differential scanning calorimetry and nanoindentation on samples of the binder in a three-phase carbon microballoon syntactic foam system. The binder is a specific variety of bismaleamide, APO-BMI, differing from the prototypical bismaleamide by an extra methyl group and two sulfur atoms between the central benzene rings. Through differential scanning calorimetry, we determined that the melting temperature of neat APO-BMI is 120 °C and that curing begins at 230 °C. The presence of carbon microballoons was seen to affect the curing reaction of APO-BMI, reducing the onset of curing temperature. The Young's modulus of cured APO-BMI was determined by nanoindentation to be 6.6 GPa.
Analysis of the Mechanical Response of Rigid Thermoplastic Foams
Authors: Michaeli Walter , Sastre Laura Flórez , Cramer Axel
Published: September 2018

Rigid thermoplastic foams, also known as structural foams, have been produced since decades to enhance specific properties, reduce material consumption and avoid shrinkage of thermoplastic injection molded parts. A good understanding of their behaviour is needed to properly design and predict their performance for a given set of functional requirements. While the variation of mechanical properties in dependence of the density reduction has been the traditional approach to characterise the mechanical performance of this type of materials, little attention has been paid to the variation of properties depending on the foam morphology.

As the second part of a research where the effects of the injection molding parameters on the foam morphology are analyzed, mechanical tests were conducted to study the variation of the properties along an injection molded plate. The correlations between the foam morphology and the tensile and flexural modulus of elasticity are studied.
Properties of Polyurethane Foams Modified with Natural Oil-Based Polyols
Authors: Prociak Aleksander
Published: September 2018

Polyols based on natural oils (NOPs) can be used in formulations of various polyurethane materials including foams with the cell structure and properties required for their typical applications. Vegetable oils such as rapeseed, soybean, sunflower and linseed oils may be applied as raw materials but first, they need to be transformed. The transformations of the double bonds of triglycerides to hydroxyls make such products capable for reaction with isocyanates. Taking into account that European countries have a vast potential regarding cultivation of oil plants, the investigations may result in a significant source of modern, sustainable, and more ecological polymers.

In the presented work, the properties of various polyurethane foams modified with NOPs were investigated. The cellular materials with apparent densities ca. 27–43 kg/m3 were moulded. The influence of the type and amount of oil-based polyol on cell structure, mechanical and heat insulating properties of the foams is discussed.
Effects of Microstructure of Mesophase Pitch Precursor on the Compression Behaviour of Carbon Foam
Authors: Wang Yong , Gao Jin , An Qingqing , Xu Zhi , Wang Yimin
Published: September 2018

The compression behaviour of carbon foams derived from synthetic naphthalene based and coal tar based mesophase pitch is studied. After carbonization and graphitization, the structure of carbon foam is modified obviously and compression behaviour decreased dramatically due to the transition of foam from two-dimensional turbostratic structures to graphite structures. The SEM, X-Ray diffraction and compression behaviour are used in the study of modification of mechanical properties. The results show that the compressive strength of carbon foam obtained from synthetic mesophase pitch is only 30% of the foam obtained from coal tar based mesophase pitch. The SEM shows that the length of micro-cracking of foam derived from synthetic mesophase pitch is as high as 5 μm and that of foam derived from coal tar based mesophase pitch is less than 2 μm. The causes of the differences in properties focused on rod structure of naphthalene based pitch transformed easier to three-dimensional sandwich structure.
Microcellular Injection Molding of PP and PC/ABS with Precision Mold Opening and Gas Counterpressure
Authors: Bledzki Andrzej K. , Kühn Joanna , Kirschling Hendrik , Pitscheneder Walther
Published: September 2018

The injection molding of microcellular polymers is expected to be increasable promise for engineering applications. The combined effect of precision mold opening and gas counterpressure process produced uniform microfoam structure with a maximal cell diameter less than 10 μm/1/. The nature of microcellular PP and PC/ABS was analyzed. It was observed that the mechanical properties, the morphology and the application of microcellular PP were influenced by the degree of crystallinity and the conditions of foaming process. The viscoelastic behavior of materials and their correlation between process, foam structure and properties of PP foam and PC/ABS foam were investigated by DMA.
Pressure Profile in Annular Die using PP/CO2 Solution Viscosity
Authors: Wang Jing , Park Chul B.
Published: September 2018

In this paper, a rheological die with a rectangular channel was designed to determine the solution viscosity of supercritical CO2 in non-crosslinked high-melt-strength (HMS) polypropylene (PP). The shear viscosity of this solution was modeled as a function of temperature, pressure, gas content, and shear rate. With interest in producing highly-expanded foamed wire coatings using an annular die, an analysis of the annular die pressure profile using the measured viscosity data and an analytical method was also conducted.