Recovering Nonisothermal Physical Aging Shift Factors Via Continuous Test Data: Theory and Experimental Results

For isothermal physical aging, a few simple tests to characterize the aging shift factors allow reasonable prediction of the mechanical response. In this paper, a new technique is developed to extract aging shift factors from creep data during a nonisothermal history. Previous methods have generated discrete experimental shift factors by a series of short-term creep tests, in which the load portion alone is used for evaluation; this is particularly time consuming for nonisothermal histories, since many data points (requiring several tests) may be needed for an adequate characterization of the response. This paper presents a new continuous shift factor (CSF) method, based on the validity of effective time theory, which generates a continuous experimental shift factor curve from a single test. Results are presented for this method when applied to a polyimide/carbon fiber composite material tested in shear under temperature jump conditions; this nonisothermal aging data for a polymer matrix composite is shown to exhibit similar response to that of homogeneous polymers. The new CSF technique will be useful in the development of models to predict the shift factor due to coupled aging and thermal history.

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Mechanical response of carbon fiber composite sandwich panels with pyramidal truss cores

Composites Part A Applied Science and Manufacturing ◽

10.1016/j.compositesa.2012.11.011 ◽

2013 ◽

Vol 47 ◽

pp. 31-40 ◽

Cited By ~ 54

Author(s):

Tochukwu George ◽

Vikram S. Deshpande ◽

Haydn N.G. Wadley

Keyword(s):

Carbon Fiber ◽

Mechanical Response ◽

Fiber Composite ◽

Sandwich Panels ◽

Carbon Fiber Composite ◽

Composite Sandwich Panels ◽

Composite Sandwich ◽

Pyramidal Truss

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Dynamics of Structural Recovery and Mechanical Response of Polymeric Liquids Near to the Glass Transition

MRS Proceedings ◽

10.1557/proc-407-227 ◽

1995 ◽

Vol 407 ◽

Author(s):

D. M. Colucci ◽

C. R. Schultheisz ◽

G. B. Mckenna

Keyword(s):

Aging Time ◽

Time Scales ◽

Physical Aging ◽

Mechanical Response ◽

Configurational Entropy ◽

Shift Factor ◽

Temperature History ◽

Time Shift ◽

Torsional Response ◽

Structural Recovery

ABSTRACTResults from the NIST torsional dilatometer have indicated that after a temperature step from equilibrium, the volume (structure) and mechanical response (physical aging) can evolve at different rates, depending on the temperature history. The torsional dilatometer results have been modeled in two ways. First, it was assumed that the volume and mechanical response are governed by different clocks, with the principle of time-aging time superposition employed to evaluate an aging time shift factor atc from the torsional response, which was then compared to a structural shift factor aδ calculated from the evolution of the volume. These results were also investigated using a thermoviscoelastic model based on rational thermodynamics and configurational entropy; this model does not include an explicit assumption of separate time scales, but different time scales for the structure and mechanical properties appear to arise naturally from the formulation. The results from the thermoviscoelastic model show good qualitative agreement with the torsional dilatometer results, although more material data is needed to make an exact comparison.

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Flexural Strength and Fatigue Characterization of Exotensioned Composite Beams

Journal of Mechanics ◽

10.1017/jmech.2014.3 ◽

2014 ◽

Vol 30 (3) ◽

pp. N1-N3 ◽

Cited By ~ 1

Author(s):

B. J. Rael ◽

Y.-L. Shen

Keyword(s):

Structural Integrity ◽

Mechanical Response ◽

Bending Strength ◽

Fiber Composite ◽

Low Cost ◽

Carbon Fiber Composite ◽

High Tension ◽

Structural Applications ◽

Load Carrying

ABSTRACTAn exotensioned composite structure is developed as a light-weight and low-cost load carrying members for structural applications. The beam body, consisting of carbon-fiber composite skeletons with insertions of high-tension fiber strands, is externally weaved to provide extra structural integrity. Monotonic and cyclic flexural loading experiments are performed in this study to quantify the basic mechanical response of the structure. The bending strength, ductility, and fatigue resistance are specifically assessed.

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Physical Aging in Long Term Creep of Polymeric Composite Laminates

Journal of Mechanics ◽

10.1017/s1727719100001283 ◽

2007 ◽

Vol 23 (3) ◽

pp. 245-252 ◽

Cited By ~ 12

Author(s):

H. W. Hu

Keyword(s):

Aging Time ◽

Composite Laminates ◽

Physical Aging ◽

Creep Compliance ◽

Polymeric Composite ◽

Reference Curve ◽

Creep Tests ◽

Time Model ◽

Term Creep

AbstractThis paper presents a complete approach to characterize physical aging in long term creep of composite laminates using short term creep test. Carbon/epoxy composite IM7/977−3 was use to make the coupon specimens of unidirectional fiber orientation and symmetrical laminates. Creep tests were conducted on the specimens to obtain momentary compliances at isothermal conditions. Physical aging in elastic and in creep compliances were modeled respectively. Momentary creep compliances in various aging times were shifted to superpose a reference curve by introducing shift factors for both relaxation time and shape factor of a power law model. Linear relations between shift factors and aging time in log-log scale were found and defined as shift rates. By using reference curve associated with the shift rates, momentary creep compliance in any given aging time can be predicted. By introducing a time dependent shift factor, momentary creep compliance can be modified and turned into an effective time model, which can successfully predict the long term creep of composite laminates at isothermal aging. This approach only requires the test data of momentary creep, and no material properties in each lamina are needed.

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Towards Highly Reconfigurable Carbon Fiber Composite

ASME 2019 Conference on Smart Materials, Adaptive Structures and Intelligent Systems ◽

10.1115/smasis2019-5677 ◽

2019 ◽

Author(s):

Arnaldo Casalotti ◽

Giulia Lanzara ◽

Matthew P. Snyder

Keyword(s):

Carbon Fiber ◽

Mechanical Response ◽

Shape Change ◽

Fiber Composite ◽

Fiber Composites ◽

Mechanical Tests ◽

Carbon Fiber Composites ◽

Carbon Fiber Composite ◽

Experimental Campaign ◽

Stiffness Variation

Abstract This article discusses an approach to develop innovative carbon fiber composites that have the capability to change shape according to a prescribed input. The approach is based on the study of specific stacking sequences of unidirectional fiber plies cured on a curved mold. The effects of the above-mentioned aspects are investigated on the manufactured specimen. The combined thermo-mechanical response is investigated by performing mechanical tests at various prescribed temperatures and the intensity of the shape change is evaluated together with the corresponding stiffness variation. The experimental campaign is mostly devoted to characterize the response of the manufactured sample and demonstrate the great capability of the proposed approach to develop a smart material with enhanced shape and stiffness variation according the prescribed input.

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Characterization of electro-mechanical response in novel carbon fiber composite materials

Journal of Composite Materials ◽

10.1177/0021998319839113 ◽

2019 ◽

Vol 53 (19) ◽

pp. 2675-2686 ◽

Cited By ~ 2

Author(s):

Riley Sherman ◽

Vijaya Chalivendra ◽

Asha Hall ◽

Mulugeta Haile ◽

Latha Nataraj ◽

...

Keyword(s):

Composite Materials ◽

Carbon Fibers ◽

Mechanical Response ◽

Fiber Composite ◽

Three Dimensional ◽

Tensile Load ◽

Tensile Loading ◽

Electrical Measurements ◽

Carbon Fiber Composite ◽

Short Carbon

A comprehensive experimental parametric study is performed to investigate the electro-mechanical response of novel three-dimensional conductive multi-functional carbon/epoxy composite materials. Three-dimensional conductive network is generated by embedding multi-wall carbon nanotubes in the epoxy matrix and reinforcing short carbon fibers between the carbon fabric laminates. An open mold compression method is utilized to fabricate the composite materials. Wet electro-up-flocking technology is employed to reinforce 150-µm and 350-µm length carbon fibers vertically at varying densities (500, 1000, 1500, 2000 fibers/mm2) between each laminate to analyze the effects these parameters have on electrical resistivity, tensile properties, and electro-mechanical response to quasi-static tensile loading. A high-resolution four-point circumferential ring probe is used to obtain electrical measurements. The resistivity of the composites having 150 µm flocked carbon fibers did not show significant change with increase in flock density; however, composites of 350-µm length carbon fibers showed a clear decrease in resistivity by a factor of 10 when the flock density increased from 500 to 2000 fibers/mm2. The electro-mechanical response of composites without short carbon fibers is inconsistent and jagged compared to that of flocked composites. The composites having 350-µm long carbon fibers showed a longer duration of initially decreasing resistance due to the applied tensile load when compared to that of 150 µm flocked carbon fibers. However, composites with no short carbon fibers registered maximum value of percentage change in resistance at the break point of tensile loading.

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