Interfaces and fatigue damage in a metastable beta titanium matrix composite

The transverse behavior of 1140ϩ/Ti-6-4 and SCS-6/Ti-␤21s composites has been investigated using conventional tensile testing in air. Acoustic emission (AE) has also been used to assess and to locate the position of damage. Few AE events can be detected in 1140ϩ/Ti-6-4 composites below the stress of ϳ250 MPa, whereas for SCS-6/Ti-␤21s composites, AE events are found almost immediately on loading. Many AE events of high energy were detected over a range of stresses, which appear to be associated with debonding. Continuous AE events are obtained with an increase of stress, and this suggests that debonding is an incremental process: a ring crack (formed by premature debonding at the surface) penetrates into the depth along interface "tubes." The peak energy of AE events obtained in SCS-6/Ti-␤21s composites is ϳ650 arbitrary units, which is approximately 4 times that obtained in 1140ϩ/Ti-6-4 composites. Distinct AE events have also been deduced to correspond to cracking of carbon coating layers and fiber/matrix reaction products. A change of fiber volume fraction from 8 to 21 pct for the 1140ϩ/Ti-6-4 composites has no effect on the characteristics or distribution of AE events received.

Section: Introductionmentioning

confidence: 99%

Transverse behavior and acoustic-emission analysis of titanium metal-matrix composites under tensile loading

Wu¹,

Mori

Bowen

2001

“…Diffusion of the matrix alloying elements into the fiber/matrix interface is responsible for the coarsening of the reaction layer, which was also observed in SiC fiber-reinforced Ti-15V-3Cr-3Al-3Sn matrix composite. [20,21] B.…”

Section: Resultsmentioning

confidence: 99%

Interface-controlled fatigue cracking of SCS-6/Ti-22Al-23Nb “orthorhombic” titanium aluminide composite

Her

Wang

Yang

1998

The effect of aging at elevated temperature on interfacial stability and fatigue behavior of a SCS-6/Ti-22Al-23Nb ''orthorhombic'' (O) titanium aluminide composite is investigated. The composite was heat treated in vacuum at 900 ЊC for up to 250 hours to change the microstructural characteristics. The stability of the matrix alloy and interfacial reaction zone after extended thermal exposure was analyzed. The effect of interface on fatigue behavior, including stiffness degradation, evolution of fatigue damage, and crack growth rates, was characterized. Finally, a modified shear-lag model was used to predict the saturated matrix crack spacing in the composite under fatigue loading. The results demonstrate that aging at elevated temperature affects the stability of the interfacial reaction zone, which, in turn, degrades the fatigue properties of the composite. However, fatigue crack will not develop from the ruptured interfacial reaction layer until the thickness of the reaction zone or the maximum applied stress exceeds a critical value.

“…The debonding length is Fatigue tests were carried out in a scanning electron microscope (SEM) mounted on a hydraulic fatigue test machine allowed to slide on cyclic loading. As the importance of the RL in matrix crack initiation has frequently been under load-controlled mode, with a frequency of 2 Hz and a stress ratio of R ϭ 0.1 (where R is the ratio of the minimum reported, [3,4,6,7,9,10] it is treated as a distinct body with the material properties of Ti x C. [16] This model is analyzed under applied stress ( min ) over the maximum applied stress ( max )). The test environment was kept in a vacuum of about plane-strain conditions, in accordance with Dundurs and Markenscoff's findings that plane-strain conditions are more 2 ϫ 10 Ϫ3 Pa at a temperature of T ϭ 823 K. A tungstencoil d.c. current filament was used to heat the specimen, reasonable than plane-stress conditions when dealing with interface problems.…”

Section: A Finite-element Modelingmentioning

confidence: 99%

“…The observed results are of great general interest, because fiber exposure in a composite occurs during service or due to mechanical machining and polishing. [3,4,6,9,10] The previous test for SCS-6-reinforced Ti-15-3 at high temperature shows that the initial crack after surface-fiber breaks tends to deflect and propagate along the interface. The effects of the deflected-interface crack propagation on matrix crack initiation will be investigated in the following sections.…”

Section: Introductionmentioning

confidence: 98%

“…The objective of the current crack propagation at room and high temperatures. [1][2][3][4][5][6][7][8] Interwork is to consider the effects of interface debonding and face debonding and sliding are required to achieve fiber sliding on matrix crack initiation based on detailed observabridging, and interface debonding may be initiated due to tion of the fatigue damage process in an un-notched SiC localized stress intensification when the matrix crack front (SCS-6) fiber-reinforced Ti-15-3 composite at high temperreaches the fiber-matrix interface in a notched specimen [4][5][6] ature. Emphasis is placed on the modeling and analysis and/or due to the brittle reaction-layer (RL) cracking of how the interface-debonding growth influences matrix between the matrix and outermost carbon coating in an cracking during isothermal fatigue testing of an un-notched unnotched specimen.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of interfacial debonding and sliding on matrix crack initiation during isothermal fatigue of SCS-6/Ti-15-3 composites

Liu

Tanaka

Masuda

2000

Direct observation of initial damage-evolution processes occurring during cyclic testing of an unnotched SCS-6 fiber-reinforced Ti-15-3 composite has been carried out. The aligned fibers break at an early stage, followed by debonding and subsequent sliding along the interface between the reaction layer (RL) and Ti-15-3 alloy matrix. Matrix cracking initiation from the initial broken fiber and RL was avoided. This fracture behavior during cyclic loading is modeled and analyzed by the finiteelement method, with plastic deformation of the matrix being considered. The plastic strain in the matrix at the initial crack and at the deflected crack tips, when the interface crack is deflected into the RL after extensive interface debonding propagation, is characterized. The effects of interfacial debond lengths and test temperatures on the matrix cracking mechanism are discussed, based on a fatigue-damage summation rule under low-cycle fatigue conditions. The numerical results provide a rationale for experimental observations regarding the avoidance and occurrence of the matrix cracking found in fiber-reinforced titanium composites.