Quality Evaluation of Diffusion Bonded Joints by Electrical Resistance Measuring and Microscopic Fatigue Testing

2011 ◽  
Vol 24 (02) ◽  
pp. 187 ◽  
Author(s):  
Yujia LI
Keyword(s):  
Electrical Resistance ◽  
Quality Evaluation ◽  
Fatigue Testing ◽  
Bonded Joints

Electrical Resistance and Acoustic Emission During Fatigue Testing of Pristine and High Velocity Impact SiC/SiC Composites at Room and Elevated Temperature

2016 ◽  
Author(s):  
Zipeng Han ◽  
Gregory N. Morscher ◽  
Emmanuel Maillet ◽  
Manigandan Kannan ◽  
Sung R. Choi ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Acoustic Emission ◽  
Cyclic Loading ◽  
Electrical Resistance ◽  
Fatigue Testing ◽  
Early Stage ◽  
Loading Conditions ◽  
Initial Attempt ◽  
Matrix Cracks ◽  
Sic Composites

Electrical resistance (ER) is a relatively new approach for real-time monitoring and evaluating damage in SiC/SiC composites for a variety of loading conditions. In this study, ER of woven silicon carbide fiber-reinforced silicon carbide composite systems in their pristine and impacted state were measured under cyclic loading conditions at room and high temperature (1200C). In addition, modal acoustic emission (AE) was also monitored, which can reveal the occasion of matrix cracks and fiber. ER measurement and AE technique are shown in this study to be useful methods to monitor damage and indicate the failure under cyclic loading. Based on the slope of the ER evolution, an initial attempt has been made to develop a method allowing a critical damage phase to be identified. While the physical meaning of the critical point is not yet clear, it has the potential to allow the failure to be indicated at its early stage.

Fiber Breakage In Polymer-Matrix Composites During Static And Fatigue Loading, Observed By Electrical Resistance Measurement

1997 ◽  
Vol 503 ◽  
Author(s):  
Xiaojun Wang ◽  
D. D. L. Chung
Keyword(s):  
Electrical Resistance ◽  
Fatigue Testing ◽  
Polymer Matrix Composites ◽  
Fatigue Loading ◽  
Fiber Direction ◽  
Matrix Composites ◽  
Fiber Breakage ◽  
Static Tensile Loading ◽  
Static Tensile ◽  
Epoxy Matrix Composite

ABSTRACTBy measuring the electrical resistance of a continuous unidirectional carbon fiber epoxy-matrix composite along the fiber direction during loading in this direction, fiber breakage was progressively monitored in real time. Fiber breakage occurred in spurts involving 1000 fibers or more. It started at about half of the failure strain during static tensile loading and at about half of the fatigue life during tensiontension fatigue testing. Immediately before static failure, 35% of the fibers were broken. Immediately before fatigue failure, 18% of the fibers were broken. The fiber breakage was accompanied by decrease in modulus.

Fiber breakage in polymer-matrix composite during static and fatigue loading, observed by electrical resistance measurement

1999 ◽  
Vol 14 (11) ◽  
pp. 4224-4229 ◽  
Author(s):  
Xiaojun Wang ◽  
D. D. L. Chung
Keyword(s):  
Matrix Composite ◽  
Electrical Resistance ◽  
Fatigue Testing ◽  
Fatigue Loading ◽  
Fiber Direction ◽  
Fiber Breakage ◽  
Static Tensile Loading ◽  
Static Tensile ◽  
Epoxy Matrix Composite ◽  
Carbon Fiber Epoxy

By measuring the electrical resistance of a continuous unidirectional carbon fiber epoxy-matrix composite along the fiber direction during loading in this direction, fiber breakage was progressively monitored in real time. Fiber breakage occurred in spurts involving 1000 or more fibers. It started at about half of the failure strain during static tensile loading and at about half of the fatigue life during tension–tension fatigue testing. Immediately before static failure, at least 35% of the fibers were broken. Immediately before fatigue failure, at least 18% of the fibers were broken. The fiber breakage was accompanied by decrease in modulus.

New Electrical Potential Method for Measuring Crack Growth in Nonconductive Materials

2003 ◽  
Author(s):  
H. Nayeb-Hashemi ◽  
D. Swet ◽  
A. Vaziri
Keyword(s):  
Thin Layer ◽  
Crack Length ◽  
Crack Growth ◽  
Electric Potential ◽  
Electrical Resistance ◽  
Electrical Potential ◽  
Bonded Joints ◽  
Adhesively Bonded ◽  
Adhesively Bonded Joints ◽  
Adhesively Bonded Joint

D.C. electric potential technique has been used to monitor crack growth in conductive materials. A constant DC current is ppased through thesse materials and the crack length is measured through the changes in the electrical voltage at the crack mouth. However, this method is not applicable in crack growth measurement in nonconductive materials or adhesively bonded joints. For these materials, a new method is developed and is shown to provide a very accurate method for measuring the crack length. The surface of these materials is coated with a thin layer of carbon paint and the crack lenght is measured through the changes in the electrical resistance of the carbon paint, as the crack grows both in the base material and the thin layer carbon paint. In contrast to the D.C. electric potential technique where the position of the probes for measuring the crack length is very important for an accurate measurement of the crack length, the new technique is little sensitive to the probe location. Crack growth is measured in adhesively bonded joints subjected to creep loadings. A modified Compact tension specimen is cut in two pieces across its notch area. The pieces are then glued jusing an adhensive. The surface of the specimen is painted with a thin layer of carbon paint and the changes in its electrical resistance are monitored. It is shown that the carbon paint method provides a quiet sensitive method for monitoring the crack growth. The creep crack growth rate in the adhesively bonded joint is related to Mode I energy release rate, G1. It is shown that the crack grows in the middle of the adhesive layer rather than at the interface of the joint. Micromechanisms of the crack growth are studied using a scanning electron microscope. The damage consists of numerous crazed regions at the crack tip. Crack grows by the linkage of the crazed region.

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