scholarly journals Mode I and II Interlaminar Fracture in Laminated Composites: A Size Effect Study

2019 ◽  
Vol 86 (9) ◽  
Author(s):  
Marco Salviato ◽  
Kedar Kirane ◽  
Zdeněk P. Bažant ◽  
Gianluca Cusatis
Keyword(s):  
Size Effect ◽  
Process Zone ◽  
Laminated Composites ◽  
Nonlinear Effects ◽  
Effect Study ◽  
Mode I ◽  
Brittle Behavior ◽  
Linear Elastic ◽  
Nominal Strength ◽  
Significant Difference

This work investigates the mode I and II interlaminar fracturing behavior of laminated composites and the related size effects. Fracture tests on geometrically scaled double cantilever beam (DCB) and end notch flexure (ENF) specimens were conducted. The results show a significant difference between the mode I and mode II fracturing behaviors. The strength of the DCB specimens scales according to the linear elastic fracture mechanics (LEFM), whereas ENF specimens show a different behavior. For ENF tests, small specimens exhibit a pronounced pseudoductility. In contrast, larger specimens behave in a more brittle way, with the size effect on nominal strength closer to that predicted by LEFM. This transition from quasi-ductile to brittle behavior is associated with the size of the fracture process zone (FPZ), which is not negligible compared with the specimen size. For the size range investigated in this study, the nonlinear effects of the FPZ can lead to an underestimation of the fracture energy by as much as 55%. Both the mode I and II test data can be captured very accurately by the Bažant’s type II size effect law (SEL).

scholarly journals The role of the material fracture properties in the size-effect law of concrete structures

1996 ◽  
Vol 18 (1) ◽  
pp. 40-48
Author(s):  
V. Tran Tu
Keyword(s):  
Size Effect ◽  
Process Zone ◽  
Crack Opening ◽  
Concrete Structures ◽  
Fracture Propagation ◽  
Fracture Properties ◽  
Nominal Strength ◽  
Material Fracture ◽  
General Size

The size effect of the nominal stress at failure in concrete structures is dealt within general. An existence of a rather large fracture process zone in front of crack tip is proved to be the main reason leading to the size effect of the nominal strength. On the basis of the new general size-effect law and numerical results of fracture propagation, a particularly proposed size effect law for beams in bending is developed, in which the role of each material fracture characteristic, especially the shape of the stress - crack opening curve, is elaborated clearly.

scholarly journals Scaling of Quasi-Brittle Fracture and the Fractal Question

1995 ◽  
Vol 117 (4) ◽  
pp. 361-367 ◽  
Author(s):  
Zdeneˇk P. Bazˇant
Keyword(s):  
Size Effect ◽  
Composite Laminates ◽  
Process Zone ◽  
Asymptotic Properties ◽  
Material Strength ◽  
Fractal Nature ◽  
Quasibrittle Materials ◽  
Large Size ◽  
Fracture Simulation ◽  
Nominal Strength

The paper represents an extended text of a lecture presenting a review of recent results on scaling of failure in structures made of quasibrittle materials, characterized by a large fracture process zone, and examining the question of possible role of the fractal nature of crack surfaces in the scaling. The problem of scaling is approached through dimensional analysis, the laws of thermodynamics and asymptotic matching. Large-size and small-size asymptotic expansions of the size effect on the nominal strength of structures are given, for specimens with large notches (or traction-free cracks) as well as zero notches, and simple size effect formulas matching the required asymptotic properties are reported. The asymptotic analysis is carried out, in general, for fractal cracks, and the practically important case ofnonfractal crack propagation is acquired as a special case. Regarding the fractal nature of crack surfaces in quasibrittle materials, the conclusion is that it cannot play a signification role in fracture propagation and the observed size effect. The reason why Weibull statistical theory of random material strength does not explain the size effect in quasibrittle failures is explained. Finally, some recent applications to fracture simulation by particle models (discrete element method) and to the determination of size effect and fracture characteristics of carbon-epoxy composite laminates are briefly reviewed.

Size Effect and Fracture Characteristics of Composite Laminates

1996 ◽  
Vol 118 (3) ◽  
pp. 317-324 ◽  
Author(s):  
Zdeneˇk P. Bazˇant ◽  
Isaac M. Daniel ◽  
Zhengzhi Li
Keyword(s):  
Size Effect ◽  
Composite Laminates ◽  
Process Zone ◽  
Fiber Composite ◽  
Maximum Load ◽  
Two Dimensions ◽  
Effective Length ◽  
Smooth Transition ◽  
Fracture Characteristics ◽  
Nominal Strength

Measurements of the size effect on the nominal strength of notched specimens of fiber composite laminates are reported. Tests were conducted on graphite/epoxy crossply and quasi-isotropic laminates. The specimens were rectangular strips of widths 6.4, 12.7, 25.4 and 50.8 mm (0.25, 0.50, 1.00 and 2.00 in.) geometrically similar in two dimensions. The gage lengths were 25, 51, 102 and 203 mm (1.0, 2.0, 4.0 and 8.0 in.). One set of specimens had double-edge notches and a [0/922]s crossply layup, and another set had a single-sided edge notch and a [0/±45/90]s, quasi-isotropic layup. It has been found that there is a significant size effect on the nominal strength. It approximately agrees with the size effect law proposed by Bazˇant, according to which the curve of the logarithm of the nominal strength versus the logarithm of size represents a smooth transition from a horizontal asymptote, corresponding to the strength criterion (plastic limit analysis), to an inclined asymptote of −0.5 slope, corresponding to linear elastic fracture mechanics. Optimum fits of the test results by the size effect law are obtained, and the size effect law parameters are then used to identify the material fracture characteristics, particularly the fracture energy and the effective length of the fracture process zone. Finally, the R-curves are also identified on the basis of the maximum load data. The results show that in design situations with notches or large initial traction-free cracks the size effect on the nominal strength of fiber composite laminates must be taken into account.

Field measurements of snowdrift characteristics on reduced scale building roofs based on the size effect study

Structures ◽  
2021 ◽  
Vol 32 ◽  
pp. 2020-2031
Author(s):  
Guolong Zhang ◽  
Qingwen Zhang ◽  
Feng Fan ◽  
Shizhao Shen
Keyword(s):  
Size Effect ◽  
Field Measurements ◽  
Effect Study ◽  
Reduced Scale

scholarly journals Comparative study of elastic properties and mode I fracture energy of carbon nanotube/epoxy and carbon fibre/epoxy laminated composites

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Jyotikalpa Bora ◽  
Sushen Kirtania
Keyword(s):  
Carbon Nanotube ◽  
Carbon Fibre ◽  
Fracture Energy ◽  
Elastic Properties ◽  
Volume Fraction ◽  
Laminated Composites ◽  
Laminated Composite ◽  
Fe Analysis ◽  
Mode I ◽  
Mode I Fracture

Abstract A comparative study of elastic properties and mode I fracture energy has been presented between conventional carbon fibre (CF)/epoxy and advanced carbon nanotube (CNT)/epoxy laminated composite materials. The volume fraction of CNT fibres has been considered as 15%, 30%, and 60% whereas; the volume fraction of CF has been kept constant at 60%. Three stacking sequences of the laminates viz.[0/0/0/0], [0/90/0/90] and [0/30/–30/90] have been considered in the present analysis. Periodic microstructure model has been used to calculate the elastic properties of the laminated composites. It has been observed analytically that the addition of only 15% CNT in epoxy will give almost the same value of longitudinal Young’s modulus as compared to the addition of 60% CF in epoxy. Finite element (FE) analysis of double cantilever beam specimens made from laminated composite has also been performed. It has been observed from FE analysis that the addition of 15% CNT in epoxy will also give almost the same value of mode I fracture energy as compared to the addition of 60% CF in epoxy. The value of mode I fracture energy for [0/0/0/0] laminated composite is two times higher than the other two types of laminated composites.

Color-Tunable ZnO Quantum Dots Emitter: Size Effect Study and a Kinetic Control of Crystallization

2013 ◽  
Vol 2 (1) ◽  
pp. 11-19 ◽  
Author(s):  
Chengbo Zhang ◽  
Shihong Zhou ◽  
Keyan Li ◽  
Shuyan Song ◽  
Dongfeng Xue
Keyword(s):  
Quantum Dots ◽  
Size Effect ◽  
Effect Study ◽  
Kinetic Control ◽  
Color Tunable ◽  
Zno Quantum Dots
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