A quantitative study on using digital photoelasticity for characterising the effect of the stretching speed on the necking phenomenon

AbstractThe digital photoelastic technique is used to characterise the necking behaviour of isotactic polypropylene (iPP) fibres. The effect of stretching rate on necking initiation is studied. The birth of necking is observed using photoelastic patterns of the stretched fibres to understand how the localised difference between the principle stresses grows to form a necking region. Finally, the formation of multiple necking regions is characterised photoelastically. These multiple necks are initiated using the same formation mechanism and conditions as if there is only a single necking region. It was evident that, fast stretching causes faster arrangement of molecular chains and hence decreases the time required for necking initiation. Recommendations are suggested for optimum mechanical processing conditions of iPP fibres to avoid failure by necking. Photoelastic patterns are given for illustration.

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Ball Grid Array Thermomechanical Response During Reflow Assembly

Journal of Electronic Packaging ◽

10.1115/1.2792155 ◽

1996 ◽

Vol 118 (4) ◽

pp. 214-222 ◽

Cited By ~ 3

Author(s):

T. E. Voth ◽

T. L. Bergman

Keyword(s):

Process Model ◽

Experimental Studies ◽

Ball Grid Array ◽

Mechanical Processing ◽

Processing Conditions ◽

System Behavior ◽

Reflow Soldering ◽

Thermomechanical Response ◽

Model Predictions ◽

Representative System

The thermomechanical response of ball-grid array assemblies during reflow soldering is considered here. Experiments are performed to investigate the thermomechanical response of a representative system and the results are used to validate a numerical model of system behavior. The conclusions drawn from the experimental studies are used to guide development of a process model capable of describing more realistic BGA soldering scenarios. Process model predictions illustrate the system’s thermomechanical response to thermal and mechanical processing conditions, as well as component properties. High thermal conductivity assemblies show the greatest sensitivity to mechanical loading conditions.

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Review of Quantitative Study of Rill Morphology on Slope

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1010-1012.1125 ◽

2014 ◽

Vol 1010-1012 ◽

pp. 1125-1128

Author(s):

Pan Zhang ◽

Wei Ying Sun ◽

Wen Yi Yao

Keyword(s):

Soil Erosion ◽

Dynamic Response ◽

Quantitative Study ◽

Formation Mechanism ◽

Research Direction ◽

Morphological Development ◽

Existing Problems ◽

Response System ◽

Quantized Fields ◽

The Future

Morphological development of rill at hillslope formed a microrelief dynamic response system with soil erosion driven by rainfall. To reveal the formation mechanism of this system, scientifically quantification is the key problem. In recent years, domestic and foreign scholars had achieved fruitful results in rill evolution and quantized fields. This paper analysised the existing problems in the present research based on summarizing the current existing methods of rill morphology quantitation, and put forward the research direction in the future.

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Effects of Selective Attention on Perceptual Filling-in

Journal of Cognitive Neuroscience ◽

10.1162/jocn.2006.18.3.335 ◽

2006 ◽

Vol 18 (3) ◽

pp. 335-347 ◽

Cited By ~ 16

Author(s):

P. De Weerd ◽

E. Smith ◽

P. Greenberg

Keyword(s):

Selective Attention ◽

Frequency Distribution ◽

Peripheral Vision ◽

Response Times ◽

Cognitive Factors ◽

Surface Perception ◽

Visual Processes ◽

Time Required ◽

Directing Attention ◽

As If

After few seconds, a figure steadily presented in peripheral vision becomes perceptually filled-in by its background, as if it “disappeared”. We report that directing attention to the color, shape, or location of a figure increased the probability of perceiving filling-in compared to unattended figures, without modifying the time required for filling-in. This effect could be augmented by boosting attention. Furthermore, the frequency distribution of filling-in response times for attended figures could be predicted by multiplying the frequencies of response times for unattended figures with a constant. We propose that, after failure of figure–ground segregation, the neural interpolation processes that produce perceptual filling-in are enhanced in attended figure regions. As filling-in processes are involved in surface perception, the present study demonstrates that even very early visual processes are subject to modulation by cognitive factors.

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The influence of structure and processing conditions on engineering mechanical properties in bulk crystallized isotactic polypropylene

Journal of Applied Polymer Science ◽

10.1002/app.1976.070200102 ◽

1976 ◽

Vol 20 (1) ◽

pp. 9-24 ◽

Cited By ~ 17

Author(s):

J. H. Reinshagen ◽

R. W. Dunlap

Keyword(s):

Mechanical Properties ◽

Isotactic Polypropylene ◽

Processing Conditions

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Numerical Analysis of Influence of Mechanical Processing Conditions on Stress-Deformed State of Large-Size Thin-Wall Complex Parts

Intellekt Sist Proizv ◽

10.22213/2410-9304-2018-3-17-21 ◽

2018 ◽

Vol 16 (3) ◽

pp. 17

Author(s):

S D Kugultinov ◽

A V Shchenyatskii ◽

A S Zhilyaev

Keyword(s):

Numerical Analysis ◽

Thin Wall ◽

Mechanical Processing ◽

Processing Conditions ◽

Large Size ◽

Deformed State ◽

Complex Parts

Многие предприятия приборостроительной, машиностроительной, авиакосмической отрасли сталкиваются с трудностями механической обработки крупногабаритных тонкостенных деталей сложной формы из алюминиевых сплавов, отвечающих за работоспособность всего изделия. К рассматриваемой группе деталей предъявляются повышенные требования по точности и качеству изготовления, к ним относятся несущие элементы конструкции летательных аппаратов, корпуса, волноводы, радиаторы. Зачастую допуск формы на поверхностях данных деталей не превышают 0,01 мм при площади поверхности 1-2 м2. Для обеспечения выпуска качественной продукции без увеличения производственного цикла и затрат на отработку технологии необходимо применение численного инженерного анализа для моделирования сложных технологических процессов. Статья содержит обоснование актуальности исследования взаимосвязи режимов механической обработки, схемы и усилия закрепления с технологическими остаточными напряжениями и деформациями детали. Представлены результаты анализа напряженно-деформированного состояния (НДС), возникающего в процессе фрезерования под воздействием силы и температуры резания, методом конечных элементов (МКЭ). На основе расчетов методом МКЭ показано, что в процессе фрезерования под действием силы резания в детали формируются сжимающие остаточные напряжения, приводящие к короблению поверхностей деталей. Разработана имитационная модель механического воздействия концевой фрезы на обрабатываемую деталь. Полученные результаты в дальнейшем планируется применить для формирования управляющих воздействий на параметры технологического процесса с целью повышения качества обработки и минимизации цикла производства деталей.

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