Microstructure and mechanical properties of in situ TiB reinforced titanium matrix composites based on Ti–FeMo–B prepared by spark plasma sintering

The in situ synthesized TiB reinforced titanium matrix composites have been prepared by spark plasma sintering at 800–1200 °C under 20 MPa for 5 min. The effects of sintering temperature and reinforcement volume fraction on flexural strength, Young’s modulus and fracture toughness of the composites are investigated. The titanium matrix consists of -Ti and β-Ti phases, and the volume fraction of β-Ti increases with increasing sintering temperatures. The in situ synthesized TiB reinforcements are distributed randomly and uniformly in matrix. The transverse section of TiB has a hexagonal shape aligned along [0 1 0] direction, and the crystallographic planes of the TiB needles are always of the type . The 10 vol% TiB reinforced composite sintered at 1000 °C exhibits excellent mechanical properties. The flexural strength, Young’s modulus and fracture toughness of this composite are 1560 MPa, 137 GPa and 8.64 MPa · m^1/2, respectively.     

An experimental cum numerical technique to determine dynamic interlaminar fracture toughness

A method combining experimental and finite element analysis is developed to determine interlaminar dynamic fracture toughness. An interlaminar crack is propagated at very high speed in a double cantilever beam (DCB) specimen made of two steel strips which are bonded together by epoxy with a precrack of about 40 mm length. The face of the front cantilever is bonded to a large solid block and a special fixture is designed to apply impact load to the rear cantilever through a load bar. In the load bar, a compressive square shaped elastic stress pulse is generated by impacting it with a striker bar which is accelerated in an air gun. The rear cantilever is screwed to the load bar; when the incident compressive pulse reaches the specimen, a part of the energy is reflected into the load bar and the rest of it passes to the specimen. By monitoring the incident and the reflected pulses in the load bar through strain gauges, deflection of cantilever-end is determined. The crack velocity is determined by three strain gauges of 0.2 mm gauge length bonded to the side face of the rear cantilever. Further, the first strain gauge, bonded very close to the tip of the precrack, and the crack velocity determine the initiation time of crack propagation.

The experimental results are used as input data in a finite element (FE) code to calculate J-integral by the gradual release of nodal forces to model the propagation of the interlaminar crack. The initiation fracture toughness and propagation fracture toughness are evaluated for an interlaminar crack propagating with a velocity in the range of 850 to 1785 m/s. The initiation toughness and propagation toughness were found to vary between 90–200 J/m² and 2–13 J/m², respectively.     

Evaluation of interfacial fracture toughness of a flip-chip package and a bimaterial system by a combined experimental and numerical method

In this paper, the interfacial fracture toughness of a flip-chip package subjected to a constant concentrated line load and a bimaterial system under thermal loading condition were evaluated using a unique six-axis submicron tester, a thermal vacuum chamber and FEM modeling coupled with a high density laser moiré interferometry. The six-axis submicron tester was used to provide a constant concentrated line load, whereas the moiré interferometry technique was used to monitor the crack length during the test. In addition, a finite element technique was simultaneously used to determine the near crack tip displacement fields of the specimens. The interfacial fracture toughness and phase angle were computed by using these near tip displacement variables through the analytical energy release rate and phase angle expressions derived by authors. The interfacial fracture toughness and the phase angle of the flip-chip package considered at the interface where the passivated silicon chip meets the underfill are 35 J/m² and −65°, respectively, while the interfacial fracture toughness and the phase angle of the tested bimaterial specimen at the interface of the molding compound/silicon with the crack length of 3.3 mm under the temperature rise thermal load from room temperature (20°C) to 138°C are 20.02 J/m² and −54.8°, respectively.     

Manufacturing Influence on the Delamination Fracture Behavior of the T800H/3900-2 Carbon Fiber Reinforced Polymer Composites

'Torayca' T800H/3900-2 is the first material qualified on Boeing Material Specification (BMS 8-276) which utilizes the thermoplastic-particulate interlayer toughening technology. Two manufacturing processes, the autoclave process and the fast heating rated Quickstep™ process, were employed to cure this material. The Quickstep process is a unique composite production technology which utilizes the fast heat transfer rate of fluid to heat and cure polymer composite components. The manufacturing influence on the mode I delamination fracture toughness of laminates was investigated by performing double cantilever beam tests. The composite specimens fabricated by two processes exhibited dissimilar delamination resistance curves (R-curves) under mode I loading. The initial value of fracture toughness G_IC-INIT was 564 J/m² for the autoclave specimens and 527 J/m² for the Quickstep specimens. However, the average propagation fracture toughness G_IC-PROP was 783 J/m² for the Quickstep specimens, which was 2.6 times of that for the autoclave specimens. The mechanism of fracture occurred during delamination was studied under scanning electron microscope (SEM). Three types of fracture were observed: the interlayer fracture, the interface fracture, and the intralaminar fracture. These three types of fracture played different roles in affecting the delamination resistance curves during the crack growth. More fiber bridging was found in the process of delamination for the Quickstep specimens. Better fiber/matrix adhesion was found in the Quickstep specimens by conducting indentation-debond tests.     

Ion irradiation hardening of C60 thin films

The nanoindentation technique is used to measure the hardness and the Young’s modulus of ion irradiated C₆₀ films, 70 nm thick, deposited on a Silicon substrate. An increase of hardness from 1.3 GPa for the pristine sample to 10 GPa after irradiation with 800 keV Bi⁺ and N²⁺ ions was observed. The Young’s modulus also increases from 60–150 GPa after the irradiation. The results are discussed in terms of the damage and amorphization produced as consequences of the electronic and nuclear energy transference due to the irradiation.     

Finite element analysis of bi-material interface notch crack behaviour

The finite element method is extended to the analysis of the behaviour of an interface crack in bi-material specimen with a central hole. First, only the notch effect is considered, the field of stress and variation of the stress concentration factor as a function of the Young’s modulus ratio are determined. Secondly, the notch interface crack behaviour is investigated, the variations of the stress intensity factor versus the Young’s modulus ratio and crack length are shown as well as the distribution of stresses in the plate and along the interface.     

Evaluation of the internal friction and elastic modulus of the superhard films

In this paper, the vibrating-reed technique was used to measure the elastic modulus and internal fiction of the superhard thin films on the stainless steel substrate. The general formulas for evaluation of the internal fiction and the Young’s modulus of the film were derived for the sample with a rectangular section. The Young’s modulus of the nanocomposite superhard TiN/Si₃N₄ films on stainless steel is about 420–460 GPa at room temperature and decreases with increasing temperature. The internal fiction of the two-side deposited films is small and increases with temperature, while the internal friction of one-side deposited film is large and decreases with temperature due to the larger internal stress in the film.     

Mg0.27Al2.58O3.73N0.27透明陶瓷机械性能评价

MgAlON透明陶瓷具有优良的光学与机械性能, 在军用和民用领域均具有重要的应用潜力。本研究表征并评价了Mg_0.27Al_2.58O_3.73N_0.27透明陶瓷的机械性能, 实验测定了Mg_0.27Al_2.58O_3.73N_0.27透明陶瓷的维氏硬度、断裂韧性以及室温和高温断裂强度, 并使用Weibull函数对室温断裂强度测试结果进行统计。结果表明: 该透明陶瓷特征断裂强度为255 MPa、断裂韧性为2.56 MPa/m^1/2、杨氏模量为288 GPa、硬度为15.1 GPa。样品的Weibull模数为4.5, 1200℃下样品断裂强度达125 MPa。同时还测定了不同载荷下Mg_0.27Al_2.58O_3.73N_0.27透明陶瓷的硬度与不同载荷加载速率下的断裂强度。研究表明MgAlON光学透明陶瓷机械性能介于AlON和MgAl₂O₄之间。     

(SiCP/Cu)-铜箔叠层复合材料的制备与组织性能

采用浸涂法和热压烧结法制备了（SiC_P/Cu）-铜箔叠层复合材料,研究了SiC_P含量对材料组织结构、拉伸性能和断裂韧性的影响。结果表明,制备的（SiC_P/Cu）-铜箔叠层复合材料层间厚度均匀,界面结合力良好,增强颗粒SiC能够弥散分布于黏结相中和界面处。随着SiC_P体积分数的增加,（SiC_P/Cu）-铜箔叠层复合材料的抗拉强度和屈服强度都先增加后降低,当SiC_P的体积分数为20vol%（总体积为100）时,其抗拉强度和屈服强度达到最大值,分别为226.5 MPa和113.1 MPa,断裂方式主要为韧性断裂和部分脆性解理断裂。裂纹扩展方向平行于层界面时,材料的断裂韧性随SiC_P体积分数的增加略有减小,SiC_P体积分数为15%时达到最大值16.96 MPa·m^1/2;裂纹扩展方向垂直于层界面时,（SiC_P/Cu）-铜箔叠层复合材料的断裂韧性随SiC_P体积分数的增加逐渐减小,SiC_P体积分数为15%时达到最大值12.51 MPa·m^1/2。     

Structural and mechanical properties of well-relaxed amorphous–crystal interface in silicon: molecular dynamics study

Amorphous–crystal interface properties in silicon are key parameters for the control of the mechanical and electrical properties of polycrystalline thin film. We propose a method to calculate the interface properties of the well-relaxed amorphous–crystal interface by using structural parameters to evaluate the interface structures. The amorphous–crystal interface energies, γ^I=0.29 and 0.33 J/m², are obtained for (0 0 1) and (1 1 1) plane, respectively. Structural relaxation greatly influences those values. It is found that the interface energies are smaller than the surface energies and depend weakly on the crystal orientation. These findings agree very well with the experiments. The interface stress is small as compared with that of metal/metal interface and involves the scattering across a broad range. A critical nucleus size estimated by the calculated interface energy is slightly smaller than that estimated by the direct MD simulation for homogeneous nucleation. That small mismatch is thought to be caused by the limit of the classical nucleation theory.     

An investigation of non-linear elastic behavior of CFRP laminates and strain measurement using Lamb waves

This paper investigates the non-linear elastic behavior of unidirectional and cross-ply CFRP laminates and proposes a new method to measure tensile strain using Lamb waves. Young’s modulus was measured as a function of strain in situ using Lamb wave velocity during a tensile test. The stiffening effect of the carbon fibers on [0]₈ specimens and the softening effect of the epoxy matrix on [90]₈ specimens were accurately evaluated. Young’s modulus of the 0° ply was obtained as a quadratic function of strain. Using the function and the rule of mixture, the dependence of Young’s modulus on strain was accurately predicted for cross-ply laminates. Based on the results, the tensile strain was quantitatively correlated with the corresponding arrival time of the Lamb waves. The strains obtained from the proposed method agreed well with those from the strain gauge. Finally, the effect of transverse cracks on the in situ Young’s modulus of the cross-ply laminate under a tensile load was investigated. This method clearly detected even a small decrease in the Young’s modulus due to the transverse cracks in stiffening cross-ply laminate.     

Elasticity and resistivity study on the electromigration effects observed in aluminum–silicon–copper alloy thin films

The early electromigration (EM) processes in the Al–Si(Cu) thin films several tens of nanometers thick deposited on Si reed substrates were investigated by means of the simultaneous anelasticity and electrical resistivity measurements below 360 K. The grain growth, the shortening of a and the probable lengthening of a take place during the EM tests at the current density of 10⁸ A/m², where a and a denote the atomic plane spacing normal to and the one parallel to the film surface, respectively. The activation energy, E_GB, for the grain growth is found to be as low as 0.32 eV, possibly suggesting that E_GB in very thin nanometer-thick films is much lower than that found in thin micrometer-thick films. The increase in the Young’s modulus of the Al–Si(Cu) thin films takes place during the EM tests, suggesting that the grain growth is responsible for it. The decrease in Q⁻¹ observed at 330 and 360 K may be explained by a decrease in the grain boundary regions too. The increase in Q⁻¹ found during the EM tests at 300 K is possibly associated with an increase in a certain anelastic process in the grain boundary regions.     

Influence of in-plane fibre orientation on mode I interlaminar fracture toughness of stitched glass/polyester composites

The influence of in-plane fibre orientation on the mode I interlaminar fracture toughness, G_Ic of unstitched and stitched glass/polyester composites is investigated in this paper. The G_Ic of planar specimens depends on the fibre orientation, θ in the layers adjacent to the fracture plane, in addition to the property of matrix material. The mode I fracture toughness and fracture behavior of unstitched and stitched 0/0, 30/−30, 45/−45, 60/−60, 90/90 and 0/90 interfaces of unidirectional fibre mats (UD) and 30/−30, 45/−45 and 90/90 interfaces of woven roving mats (WRM) are studied. WRM layer orientation is represented by the direction of warp fibres. Stitching is done by untwisted Kevlar fibre roving of Tex 175 g/km at the stitch densities (number of stitches per unit area) of 10.24 and 20.48 stitches/inch². The specimens having same stitch density, but different stitch distributions are prepared, and the influence of stitch distribution on G_Ic is studied. Double cantilever beam (DCB) tests are carried out and the G_Ic is determined using modified beam theory. The G_Ic of both unstitched and stitched specimens increases with increase in orientation angle, θ upto 45° above which it decreases. The G_Ic values of unstitched 45/−45 delamination interface is around 2.4 times that of the unstitched 0/0 interfaces. The influence of fibre orientation on G_Ic is clearly observed in unstitched specimens, whereas in the stitched specimens, stitching plays an important role in improving the G_Ic and suppresses the influence of fibre orientation; degree of suppression increases with increasing stitch density. When the value of θ is above 45°, transverse cracks are observed in the delamination interface surrounded by UD layers; while in the delamination interface surrounded by WRM layers, transverse cracks are not initiated irrespective of the fibre orientation angle.     

Underlying mechanisms for unique elastic properties of nanocrystalline Au

In order to get an insight into the grain boundaries (GBs) in nanocrystalline (n-) metal, we prepared the high-density n-Au with ρ/ρ₀>99% by the gas-deposition method and carried out the vibrating reed measurements, where ρ/ρ₀ is the relative density referring to the bulk density. The strain amplitude dependence (SAMD) of the resonant frequency (f) and the internal friction (Q⁻¹) was measured for the strain () amplitude between 10⁻⁶ and 2×10⁻³ and for temperature between 5 and 300 K. No plastic deformations are detected for the present strain range, where f decreases for up to 10⁻⁴ and then turns to increase, showing saturation for between 10⁻⁴ and 2×10⁻³. The low temperature irradiation by 2 MeV electrons or 20 MeV protons causes an increase in the Young’s modulus at 6 K, which is surmised to reflect a modification of the anelastic process in the GB regions. In contrast, the SAMD of f is hardly modified by irradiation, suggesting that it is indicative of a collective motion of atoms in n-Au.     

Polymer-filler derived Mo2C ceramics

Manufacturing, microstructure and properties of novel reaction bonded Mo₂C materials derived from polymer/reactive filler mixtures were investigated. Mo powder was used as a filler to react with carbon bearing decomposition products of poly(methyl- and phenysiloxanes) during pyrolysis in nitrogen atmosphere. Microcrystalline composites with the filler reaction products Mo₃C, Mo₃Si, Mo₅Si₃ embedded in a silicon oxycarbide glass matrix could be formed with complex geometry owing to near net shape polymer/ceramic conversion. Depending on the precursor composition and pyrolysis conditions, ceramic hard materials with a density up to 97% theoretical density, a hardness of 10 GPa, a Young’s Modulus of 250 GPa, a fracture toughness of 5 MPam^1/2 and a flexural strength of 330 MPa were obtained.     

True and apparent Young’s modulus in ferrous porous alloys

Residual porosity in ferrous powder metallurgical alloys induces the phenomenon of localized yielding, or first yielding, during tensile testing. This gives rise to the existence of a true (E₁) and apparent (E₂) Young’s modulus. The true Young’s modulus is similar to the dynamic modulus (E_d) determined by the acoustic resonance method, whereas the apparent Young’s modulus is lower than both E₁ and E_d. For alloys with hard microstructures the apparent Young’s modulus turned out to be about 6% lower than the true Young’s modulus and a negligible influence of matrix hardness and pore morphology was highlighted. However, for ferritic or ferritic–pearlitic materials this difference was higher, ranging between 14 and 31% and it decreases as pore roundness is increased. For austenitic AISI 316L alloys both E₁ and E₂ are lower than E_d because of the presence of oxides on the powder surface, which favour early decohesion at the necks during tensile testing.     

Application of the dynamical flexural resonance technique to industrial materials characterisation

The determination of the Young’s modulus and damping coefficient Q⁻¹ by means of non-destructive vibrating techniques has been applied to bulk and coated industrial materials. Extensions of a previous analytic model of composite beam allow to determine accurately the macroscopic modulus of each component of multilayered structural materials as coated superalloys or nitride-hardened steels. Furthermore, the study of glasses and polymers has been investigated. An attempt of normalisation of the modulus versus temperature curves allows to establish master curves depending on the specific structure, from metallic glasses to polymeric glasses. Finally a comparison of dynamical modulus and Q⁻¹ values measured between resonant (>1 kHz) and subresonant techniques (10⁻³ to 10 Hz) in relation to the loading frequencies applied in real conditions has been under folder. For metallic materials such as forged or rolled titanium alloys, the brittle-to-fragile transition occurs abruptly or smoothly with a shift of 300 K following the range of excitation frequencies.     

Determination of interface properties from experiments on the fragmentation process in single-fiber composites

This paper attempts to quantify the fracture properties (strength and toughness) of the fiber–matrix interface in composites, using the fragmentation process and debonding growth for HI-Nicalon™ SiC single-fiber and T300 carbon single-fiber epoxy (Bisphenol-A type epoxy resin with triethylenetetramine (TETA) as curing agent) composite systems. This method is based on the numerical modeling for the microscopic damage and fragmentation process in single-fiber composite (SFC) tests, with a cohesive zone model (CZM). For the HI-Nicalon™ SiC single-fiber epoxy composite in which the major damage near a fiber break is interfacial debonding, interface properties were reasonably determined as (T_II,max, G_IIc) = (75 MPa, 200 J/m²). In contrast, for T300 carbon single-fiber epoxy composite, we could not determine unique interfacial properties, since the variation of the cohesive parameters hardly affects the microscopic damage process due to the transition to the damage pattern dominated by matrix cracking.     

Mechanical properties of U-0.95 mass fraction of Ti alloy quenching and aging treatment:a first principles study

First principles plane wave pseudopotential method was executed to calculate the mechanical properties with respect to the uranium-0.95 mass fraction of titanium(U-0.95 mass fraction of Ti) alloy for quenching and aging,including the elastic modulus,the value of shear modulus to bulk modulus(G/B) and the ideal tensile strength.The further research has also been done about the crack mechanism through Griffith rupture energy.These results show that the elastic moduli are 195.1 GPa for quenching orthorhombic a phase and 201.8 GPa for aging formed Guinier-Preston(G.P) zones,while G/B values are0.67 and 0.56,respectively.With the phase change of uranium-titanium(U-Ti) alloy via the quenching treatment,the ideal tensile strength is diverse and distinct with different crystal orientations of the anisotropic α phase.Comparison of quenching and short time aging treatment,both of the strength and toughness trend to improve slightly.Further analysis about electronic density of states(DOS) in the electronic scale indicates that the strength increases continuously while toughness decreases with the aging proceeding.The equilibrium structure appears in overaging process,as a result of decomposition of metastable quenching a phase.Thereby the strength and toughness trend to decrease slightly.Finally,the ideal fracture energies of G.P zones and overaging structure are obtained within the framework of Griffith fracture theory,which are 4.67 J/m2 and 3.83 J/m2,respectively.These results theoretically demonstrate strengthening effect of quenching and aging heat treatment on U-Ti alloy.     

Fracture behaviour of hybrid glass matrix composites: thermal ageing effects

The thermal aging of a glass matrix composite reinforced by short carbon fibres as well as by ZrO₂ particles (hybrid composite) was investigated at temperatures in the range 500–700 °C for exposure durations of 24 h in air. The mechanical properties of as-received and aged samples were evaluated at room temperature by using the three-point flexure chevron notch technique. The fracture toughness values of as-received specimens were in the range 2.6–6.4 MPa m^1/2. Fracture toughness was affected by the thermal aging conditions. For thermal aging at temperatures <700 °C, degradation of fibre–matrix interfaces occurred and therefore the apparent fracture toughness and flaw tolerant resistance decreased. For the most severe ageing conditions tested (700 °C/24 h), fracture toughness values dropped to 0.4 MPa m^1/2. Significant degradation of the material was detected for this aging condition, mainly characterised by porosity formation in the matrix as a result of softening of the glass and oxidation of the carbon fibres.