Fracture Features and Substructures of Ti-Al Ca Alloy

ＦｒａｃｔｕｒｅＦｅａｔｕｒｅｓａｎｄＳｕｂｓｔｒｕｃｔｕｒｅｓｏｆＴｉＡｌ＋ＣａＡｌｏｙＣａｏＰｅｎｇ，ＨｕａｎｇＢａｉｙｕｎ，ＨｅＹｕｅｈｕｉａｎｄＣｈｅｎＬｉｎｇｈｕｉ（曹鹏）（黄伯云）（贺跃辉）（陈令晖）ＣｅｎｔｒａｌＳｏｕｔｈＵｎｉｖｅｒ...     

Development and Application of Micromechanical Models for Ductile Fracture

材料微观力学模型可应用于研究各种不同材料，如结构钢，中子辐照脆化焊接材料，球墨铸铁和铝合金等的韧性断裂。因为这些模型是依据韧性断裂微观机制的物理描述而建立起来的，所以其应用不受特定负荷条件和试样（或零部件）几何形状的限制。与Ｊ积分的概念不同，微观力学模型可以用来估算如铁素体和奥氏体这样在融合线上性能变化梯度很大的材料界面上的裂纹萌生和传播行为。本文提出了一种结合试验数据和计算模拟确定微观力学参数的方法，并演示了应用微观力学模型预测实际构件整体性能和断裂行为的可能性。     

Nanoindentation Stress–Strain for Fracture Analysis and Computational Modeling for Hardness and Modulus

Stress–Strain plots based on nanoindentation load–depth curves were obtained to study phenomena like internal fracture and ductile to brittle transitions. Fracture phenomena during the indentation process were analyzed based on the stress–strain plots. A transition from ductile to brittle fracture was observed on increasing the depth or load of indenter penetration. A new approach with shape factors in the fracture studies based on radial crack branching and micro-cracking was done. Hardness and modulus plots were fitted with polynomials. The fitting parameters were varied to obtain different hardness and modulus responses.     

Fracture toughness and safety assessment of X65 offshore pipeline welded joints

0Introduction Weldedjointsaretheweaknesslocationinthewelded structureofoffshorepipeline.Duetothein servicecondi tionssuchaslowtemperatureandoceanwave,crackiniti ation,extensionandevencollapsearefrequentlyfoundin thejoints.Thematerialwithhightoughnessatl…     

Fracture in ferritic reactor steel—dynamic strain aging and cyclic loading

Ferritic steels commonly used for pressure vessels and reactor supports in light water reactors exhibit dynamic strain aging resulting in decreased ductility and toughness. In addition, recent work indicated decreased toughness during reverse-cyclicloading that has implications on reliability of these structures under seismic loading conditions. This paper summarizes the authors’ recent work on these aspects, along with synergistic effects of interstitial impurity atoms and radiation-induced point defects, which result in interesting beneficial effects of radiation exposure at appropriate temperature and strain-rate conditions. While the cyclic loading effects on toughness are studied in A516 steel, the dynamic strain aging and radiation-defect interactions were investigated on pure iron as well as several ferritic steels. In addition, studies on fast vs. total (thermal+fast) neutron spectra revealed unexpected results due to the influence of radiation exposure on source hardening component of the yield stress; grain size of pure iron plays a significant role in these effects. The paper concludes with future research needed to address these concerns. For more information, contact K.L. Murty, North Carolina State University, Box 7909, Raleigh, North Carolina 27695-7909; (919) 515-3657; fax (919) 515-5115; e-mail murty@eos.ncsu.edu.     

Effect of Hydride and Hydrogen—Induced Martensite on Fracture Toughness of TiNi Alloy

TiNi形状记忆合金在充氢时形成的氢致马氏体和氢化物可使合金的KIC明显下降，相对损失高达96％，但其氢致马氏体对KIC相对损失的贡献仅约1．8％，而且不随氢浓度而改变．因此氢致KIC下降几乎全部归因于氢化物．氢化物引起的相对损失ΔKIC^TiNiH／KIC和氢化物的含量(质量分数，%)WTiNiH有关，即ΔKIC^TiNiH/KIC(％)=93(1-eWTiNiH/9.5)．当充氢电流i≥15mA／cm^2时，在氢化物处能产生微裂纹，但微裂纹不会使断裂韧性进一步下降．     

Fracture of metal/ceramic laminates—II. Crack growth resistance and toughness

The propagation of cracks has been studied through Al/alumina, Cu/alumina and Ni/alumina laminates, with a range of metal and ceramic thicknesses. Two specimen orientations were chosen to propagate a crack either through the metal and ceramic layers in parallel or through the layers sequentially and perpendicular to the laminate. In both orientations a rising T-curve (toughness) was found with increasing crack length with a very steeply rising T-curve at large crack extensions. These observations can be explained by a large-scale bridging model with a crack closure traction imposed by the plastically deforming metal ligaments in the wake of the propagating crack. A simple model is derived which predicts the performance of the Ni/alumina laminates well. It does not predict the behaviour of the lower metal yield strength Cu/alumina and Al/alumina laminates so well, although it does account for the general trend of their behaviour.     

Microstructure Characterization and Fracture Toughness of Laves Phase-Based Cr–Nb–Ti Alloys

Three Laves phase-based alloys with nominal compositions of Cr2Nb–x Ti(x = 20,30,40,in at%) have been prepared through vacuum non-consumable arc melting.The results show that the microstructures of Cr2Nb-(20,30) Ti alloys are composed of the primary Laves phase C15–Cr2(Nb,Ti) and bcc solid solution phase,while the microstructure of Cr2Nb–40Ti alloy is developed with the eutectic phases C15–Cr2(Nb,Ti)/bcc solid solution.The measured fracture toughness of ternary Laves phase C15–Cr2(Nb,Ti) is about 3.0 MPa m1/2,much larger than 1.4 MPa m1/2for binary Laves phase Cr2 Nb.Meanwhile,the fracture toughness of Cr2Nb–x Ti(x = 20,30,40) alloys increases with increasing Ti content and reaches 10.6 MPa m1/2in Cr2Nb–40Ti alloy.The eutectic microstructure and addition of Ti in Cr2 Nb are found to be effective in toughening Laves phase-based alloys.     

Investigation of Adhesion and Fracture Toughness of Thermally Grown Oxide Scales by Interface Indentation Test

HIGH TEMPERATURE ALLOYS rely on theformation of a dense layer against oxidation.Howeverthe crack,spallation and detachment of oxide layeunder growth stress and thermal stress fromtemperature difference cause the failure of theprotective layer.Therefore,high temperature materialsare required forming a good oxide scale with highstrength and high interface bonding strength.Anappropriate measuring method and evaluation fooxide/metal interfacial adhesion is of great importanceto understand …     

Fracture and fatigue resistance of Mo–Si–B alloys for ultrahigh-temperature structural applications

Fracture and fatigue properties are examined for a series of Mo–Mo₃Si–Mo₅SiB₂ alloys, which utilize a continuous α-Mo matrix to achieve unprecedented room-temperature fracture resistance (>20 MPa√m). Mechanistically, these properties are explained in terms of toughening by crack trapping and crack bridging by the more ductile α-Mo phase.     

Fracture behavior of α-zirconium phosphate-based epoxy nanocomposites

The fracture behaviors of α-zirconium phosphate (α-ZrP) based epoxy nanocomposites, with and without core-shell rubber (CSR) toughening, were investigated. The state of exfoliation and dispersion of α-ZrP nanofiller in epoxy were characterized using X-ray scattering and various microscopy tools. The level of enhancement in storage moduli of epoxy nanocomposite against neat epoxy is found to depend on the state of exfoliation of α-ZrP as well as the damping characteristics of the epoxy matrix. The fracture process in epoxy nanocomposite is dominated by preferred crack propagation along the weak intercalated α-ZrP interfaces, and the presence of α-ZrP does not alter the fracture toughness of the epoxy matrix. However, the toughening using CSR can significantly improve the fracture toughness of the nanocomposite. The fracture mechanisms responsible for such a toughening effect in CSR-toughened epoxy nanocomposite are rubber particle cavitation, followed by shear banding of epoxy matrix. The ductility and toughenability of epoxy do not appear to be affected by the incorporation of α-ZrP. Approaches for producing toughened high performance polymer nanocomposites are discussed.     

Fracture Characteristics of SiC(p) / Al Composites

ＦｒａｃｔｕｒｅＣｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆＳｉＣ（ｐ）／ＡｌＣｏｍｐｏｓｉｔｅｓＧｕＨｏｎｇｗｅｉ；ＣａｏＬｉ；ＹｕａｎＧｕａｎｓｅｎ；ＬｉｕＡｎｓｈｅｎｇ；ＷｕＺｉｑｉｎａｎｄＣｈｅｎＬａｎｆｅｎｇ（古宏伟），（曹利），（袁冠森），（刘安生...     

Micromechanism of Cleavage Fracture of Weld MetalsEI北大核心CSCD

Cleavage fracture is the most dangerous form of fracture. Cleavage fracture usually happens well before general yielding at low nominal fracture stress and strain. Cleavage fracture is often spurred by low temperature and determines the toughness in the lower shelf temperature region. This paper describes a new framework for the micromechanism of cleavage fracture of high strength low alloy (HSLA) steel weld metals. Cleavage fracture not only determines the impact toughness in the lower shelf but also plays a decisive role on the impact toughness in the transition temperature region. The toughness is determined by the extending length of a preceding fibrous crack which is terminated by cleavage fracture. Three non-stop successive stages, i.e. crack nucleation, propagation of a second phase particle-sized crack across the particle/grain boundary, propagation of a grain-sized crack across the grain/grain boundary are explained. The "critical event" of cleavage fracture is emphasized which offers the greatest difficulty during crack formation and controls the cleavage process. The critical event indicates the weakest microstructural component and its critical size which specifies the local cleavage fracture stress sigma(f) for cleavage fracture. In toughness-study it is paramount important to reveal the critical events for various test specimens. Three criteria for crack nucleation, for preventing crack nucleus from blunting and for crack propagation are testified. An active region specified by these criteria is suggested where the combined stress and strain are sufficient to trigger the cleavage fracture. It can be used in statistical analyses. A case study, using the new framework of micromechanism for analyzing toughness of 8% Ni steel welding metals is presented to analyze the experimental results.     

Fracture behaviour of diffusion bonded bimaterial Ti–Al joints

Abstract

Failure modes of constrained metal foils between two elastic solids are rather different from those in the unconstrained condition. If the interface adhesion is strong between materials, a lower strength thin metal (plastic) foil between two much higher strength metals (elastic) can undergo substantial plastic deformation and fail with high triaxiality induced ductile fracture. Experiments have been conducted to explore the modes of failure and the factors governing fracture in such a constrained metal interlayer. In the present work, the effects of soft inter layer thickness and brittle reaction layer on the fracture behaviour of four point bend specimens have been investigated. A series of solid state diffusion bonds were produced between 25 × 25 mm section titanium bars using pure aluminium foils of different thickness (50, 457, 914, and 2000 μm) as the soft constrained inter layer. All four point bend specimens containing an ～ 2 μm thick intermetallic reaction layer TiAl₃ between the titanium and aluminium failed in ductile fracture mode within the soft aluminium interlayer next to the interface. A number of void formations were observed ahead of the crack tip next to the interface. No evidence of interface debonding was observed. However, the specimens containing an 8 μm thick TiAl₃ layer failed by brittle fracture along the interface between the titanium substrate and the TiAl₃ layer. It was found that decreasing the soft interlayer thickness from 2000 to 457 μm increased the load carrying capacity and decreased the fracture toughness caused by constrained plastic deformation (high triaxiality) of the interlayer.     

Fracture behaviors of AZ80 magnesium alloy during multiple forging processes

1 Introduction Pure magnesium and magnesium alloys are the lowest density metals used as structural materials and have excellent specific strength and stiffness, machinability, dimensional stability, and excellent recycling capability. They are, therefor…     

Fracture behavior of B2-ordered iron aluminide with Mn addition

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｒｅｈａｓｂｅｅｎｍｏｒｅａｎｄｍｏｒｅｒｅｓｅａｒｃｈｅｓｏｎｏｒ ｄｅｒｅｄｉｒｏｎａｌｕｍｉｎｉｄｅｓｂａｓｅｄｏｎｔｈｅＦｅ Ａｌｓｙｓｔｅｍｉｎｒｅｃｅｎｔｙｅａｒｓ .Ｔｈｅｏｒｄｅｒｅｄｉｒｏｎａｌｕｍｉｎｉｄｅ     

Fracture behavior of DO_3-ordered Fe-Al alloy with V addition

1　INTRODUCTIONTherehasbeenmoreandmoreresearchontheorderedironaluminidesbasedontheFe Alsysteminrecentyears .TheironaluminideFe3Aloccurswhenthecontentofaluminumisintherangeof 2 4 % 32 %(massfraction) .Ithastwoorderedstructures :DO3 orderedstructurewhichexistsbelowthecriticaltem peratureof 5 40℃andB2 orderedstructurebetween5 40and 76 0℃ .Theorderedironaluminideshaveexcellentoxidationresistance ,lowcost ,enrichmentinresourcesandsomeotheradvantages ,whichleadsthemtomanyengineeringapplic…     

Modeling of Fracture Toughness of Electroless Nickel (EN) Coatings

INDENTATION TEST is one of the methods forestimate fracture toughness of brittle coatings.According to this method,fracture toughness,KC[MPa.m],can be determined by the followingrelation[l,2]:(1)where P is the applied load[N],a the half diagonal ofthe indent[mm]and U the generated crack length alongeach tip of indenter[p.m].If the other cracks appeararound the indent,so U is definded an equivalent cracklength by dividing by4the total crack length,!,[!]:(2)where has a linear relation to…