SNOEK-Kê-K■STER PEAK OF INTERNAL FRICTION IN Fe-P-N ALLOYS

The internal friction and precipitate phases of the deformed Fe-P-N alloys have been investigated. It has been found that the ratio of depends on the content of P and the relation holds if the content of N is lower than 30wt.ppm and the content of P is lower than 640wt.ppm. It shows that the intercept K2 is related to the presence of the atomic pairs and clusters of P in the alloy matrix.

Internal friction peak and damping mechanism in high damping aluminium alloy laminate

A new aluminium alloy laminate characterized by high damping, corrosion resistance and weldablity was developed. The laminate designed for required aforesaid functions was actually a composite material, which was made of two anti corrosive layers (Al), two damping layers (ZnAl alloy) and one reinforcing layer (AlMg alloy) by hot rolling. The damping characteristics were studied and it was found that there was an internal friction peak at about 50 ℃ on internal fraction vs temperature curve for the laminate. For this reason, the activation energy of the peak was calculated. The origin and damping mechanism for this peak was researched by means of SEM, TEM, X ray and DSC. It is considered that the peak is caused by the interaction between dislocations and point defects in damping layers (AlZn alloy). i.e. by the movement of dislocations dragging point defects under the action of thermal activation. The laminate is remained at room temperature for a long time, it will weaken or even disappear with the restoration of the crystal microstructure and the reduction of the dislocation density in the ZnAl alloy layers. The mechanism of the peak is in conformity with that of the dislocation induced damping. [

Relationship between Relaxation Internal Friction Peak at about 200℃(f≈1Hz)and Bainitic Transformation In a CuZnAl Alloy

The present investigation showed that the re- laxation peak at about 200℃ (f≈1Hz) was related to bainitic transformation in a CuZnAl alloy.The peak decreased when bainite precipitated.The activation energy of the peak was the same as the apparent activation energy of bainitic transforma- tion.According to the relations between the peak and the bainitic transformation,the mechanism of the peak has been discussed.

Controversy about the Origin of the Grain Boundary Internal Friction Peak and Its Clarification

In the seventies some scientific workers from France and Italy suggested that the grain boundary internal friction peak (named the K (e) over cap peak in the literature) widely accepted as a grain boundary process, is originated from the motion of lattice dislocations. Since this problem is one of fundamental importance, this controversy has drawn much international attention. Started from 1982, the Hefei research group made a critical analysis of the large amount of literature concerning this problem and,performed a series of crucial experiments to clarify the controversy. It is concluded that the irrelevant evidence suggested by the controverters comes from the farfetched interpretation and the mis-identification of the internal friction peaks appeared under various experimental conditions and different states of the specimens.

Strain amplitude-dependent internal friction of as-cast high damping magnesium alloy during cyclic vibration

An investigation on strain amplitude-dependent internal friction （IF） of an as-cast high damping Mg-7 wt% Ni alloy was carried out. In the range of our tested strain amplitudes, whether the strain amplitude is increasing or decreasing, the strain amplitude-dependent IF curve can be divided into two stages： one is the strain amplitude weakly dependent part and the other is the strain amplitude strongly dependent part. However, after several cyclic vibrations, the IF values measured during the strain amplitude increasing are smaller than those obtained during the strain amplitude decreasing. The phenomenon is also observed at 100 C. Partial dislocations generate a short-range slip under the cyclic stress to be responsible for it.

Combined effects of topography and bottom friction on shoaling internal solitary waves in the South China Sea

A numerical study to a generalized Korteweg-de Vries (KdV) equation is adopted to model the propagation and disintegration of large-amplitude internal solitary waves (ISWs) in the South China Sea (SCS). Based on theoretical analysis and in situ measurements, the drag coefficient of the Chezy friction is regarded as inversely proportional to the initial amplitude of an ISW, rather than a constant as assumed in the previous studies. Numerical simulations of ISWs propagating from a deep basin to a continental shelf are performed with the generalized KdV model. It is found that the depression waves are disintegrated into several solitons on the continental shelf due to the variable topography. It turns out that the amplitude of the leading ISW reaches a maximum at the shelf break, which is consistent with the field observation in the SCS.Moreover, a dimensionless parameter defining the relative importance of the variable topography and friction is presented.

EFFECT OF AGING ON INTERNAL FRICTION,ELASTIC MODULUS AND MECHANICAL PROPERTIES OF TERNARY Mn-Cu-Al ALLOYS

Internal friction and elastic modulus of ternary Mn-Cu-Al alloys containing 56—60 wt-% Mn,0-3.59 wt-% Al were measured with acoustic frequency,1 kHz,in the tempera- ture range of-150 to 150℃.It was found that when the specimen was aged in the temperature range under the spinodal curve within the miscibility gap(400—500℃),the internal fric- tion increases with an increase of the aging time and reaches a maximum value at a certain ag- ing time which is shorter with a higher aging temperature.Two internal friction peaks which did not appear before the aging were observed above room temperature after a definite aging time.These are respectively the martensitic tranformation peak and the relaxation peak orig- inating from the stress-induced movement of the twin boundaries.The former peak shifts to- ward higher temperatures with an increase of the aging time,whereas the relaxation peak ap- pearing at 15℃,is independent of the aging time and temperature.The activation energy as- sociated with the relaxation peak was found to be 0.56 eV which is about the same as that of the relaxation peak in binary alloy containing 90 wt-% Mn.It was also found that the hardness,strength and the brittleness of the specimen increase when aged below the spinodal curve within the miscibility gap.The addition or Al enhances the strength but reduces the in- ternal friction of the specimen.A choice of suitable aging time and temperature can give an optimum compromise of high strength and high internal friction.Analysis of experimental re- sults suggests that spinodal decomposition leads to Mn-rich zones in the specimen and thus causes the phase transformation and the change of mechanical properties of the specimen.

Internal Friction in Rail Waist of BNb and BNbRE Steels

The internal frictions of the specimens in the waist centre of the commercial BNb and BNbRE rails, which were left in air for two years, were measured. It is found that there is an obvious Snoek-Kê-Koester （SKK） peak in both steels, and still exists a measurable deformation-enhanced Shock peak（DESP） in the specimens of the BNbRE steel. The internal frictions in the deformed specimens of the both steel rails were also measured. Unlike the case of the tread specimens showing a decrease of SKK damping due to deformation, the SKK damping of the rail waist specimens increases after deformation; and the specimens containing rare earth（RE） show more noticeable damping increase than those without RE. The results of the internal friction measured during ascending and descending temperature under 700℃ show that there is a high temperature damping which can be completely disappeared during descending temperature for both steels.

Experimental Study and Fatigue Analysis of Vortex-Induced Vibration of Umbilical Cable Considering Internal Friction

In order to investigate the effect of internal friction of umbilical cable on its vortex-induced vibration(VIV)responses,the experimental study on VIV of bond umbilical cable(BUC)and un-bond umbilical cable(UBUC)was carried out in an experimental tank.A current generator in the laboratory simulated the uniform current,and the current velocities were observed in real time by using a Doppler Velocimeter.In addition,different sizes of top tension were applied to the umbilical cable model.The VIV responses of the umbilical cable model were measured by using Fiber Bragg grating(FBG)strain sensors.The displacement responses of umbilical cable model were reconstructed based on the experimental strain data processed by modal superposition method.In this paper,the traveling wave characteristics,the spatial-temporal distribution characteristics of frequency and fatigue damage of the BUC and UBUC under VIV are studied.The experimental results show that there are obvious differences between BUC and UBUC in the response characteristics of VIV.The UBUC appears the traveling wave sooner than BUC,but its standing wave characteristics are more obvious than those of BUC at high velocities.Compared with BUC,the spatial-temporal distribution of UBUC frequencies appears wide-band distribution sooner,but has narrower bandwidth in the"lock-in"state.The level of fatigue damage of BUC was approximately the same as that of UBUC.

Influence of temperature rate on transitory internal friction during reverse martensitic transformation for Ti_(50)Ni_(27)Cu_(23) alloy

Internal friction （IF） spectra during reverse martensitic transformation from 35 to 135°C at different temperature rates of 0.5,0.75,and 1°C/min for Ti50Ni27Cu23 shape memory alloy （SMA） samples were measured with a dynamic mechanical analyzer,respectively.The IF spectra were characterized by IF peak increasing progressively and peak shifting toward high temperature with an increase in temperature rate.An iterative approach was used to calculate the precise intrinsic and approximate transitory IF contributions to the normal IF spectrum.The quantitatively analyzed results indicate that the transitory IF of this alloy is nonlinearly dependent on the temperature rate and obeys a power law with a power coefficient of 0.55.The predicted and experimental IF spectra at different temperature rates of 0.75 and 1°C/min agree well with each other,respectively.

Fe–Al Phase Formation Studied by Internal Friction during Heating Process

We systematically investigate the internal friction properties of a Fe-(43 at.%)Al powder mixture compact during the heating process with the expectation to understand the phase formation and transition process.Three internal friction peaks are successively observed during the heating process from room temperature to 750℃,but almost completely disappear in the subsequent cooling process.Three internal friction peaks exhibit obvious measuring frequency dependence,which increases with decreasing the frequency.The first internal friction peak originates from the micro-sliding of weak bonding interface between Al particles corresponding to a recr.ystallization process of deformed Al particles.The second internal friction peak is attributed to a phase formation process associated with the formation of the intermediate phase Fe2Al5.The third internal friction peak is considered to result from the formation of the FeAl intermetallic compound owing to the reaction of Fe2Al5 and residual Fe initiated by a dramatic thermal explosion reaction.

Effect of precipitation on internal friction of AZ91 magnesium alloy

The effect of precipitation on the internal friction(IF)of AZ91 magnesium alloy was investigated by using X-ray diffraction(XRD)analysis,scanning electron microscope(SEM)observation,and dynamic mechanical analysis(DMA).Six different states of alloy were prepared by applying different heat treatment processes:as-cast,in-complete solid solution,complete solid solution,micro-precipitation,continuous precipitation and continuous-discontinuous precipitation.It was found that the internal friction of in-completely solid-solutionized,completely solid-solutionized and micro-precipitated specimens showed a similar characteristic,and the grain boundary relaxation is completed depressed due to the Al atoms supersaturated in theα-Mg solution.However,a thermal relaxation internal friction peak was observed for continuously precipitated and continuously-discontinuously precipitated specimens at around 438 K and frequency of about 1 Hz,which was attributed to the grain boundaries relaxation.Furthermore,it was found that the relaxation of theβ-Mg17Al12/α-Mg phase interfaces should give its contribution to the background internal friction in the as-cast,continuously precipitated and continuously-discontinuously precipitated specimens.

Internal Friction in a Shape Memory Alloy Cu-Zn-Al under Equilibrium Condition

1. Introduction CuZnAl shape memory alloys have beenextensively studied as a new type of material.Dejonghe[1]et al. firstly reported theirresults on the internal friction (IF) of CuZnAlalloys in 1975. Later, some researchershave done much work on internal friction.But most of them were concerned withphase transformation internal frictionof martensite and reverse martensite andfew of them were about internal friction

INTERNAL FRICTION OF GRAIN BOUNDARIES IN Fe-P AND Fe-P-La ALLOYS CONTAINING TRACE Cu

The grain boundary internal friction(GBIF)in Fe-P and Fe-P-La alloys containing trace Cu has been studied.It is found that an addition of 0.584—0.722 wt-% La obviously reduces the IF,shifts grain boundary peaks towards higher temperatures,and produces a small addi- tional peak at even higher temperature.The mechanism of GBIF is explained as the movement of defects of atomic size,namely point defects,at gram boundaries and/or their clusters un- der stress.

EFFECT OF BIAS STRESS ON NON-LINEAR INTERNAL FRICTION OF Al-Mg ALLOY

The influence of longitudinal and torsional bias stresses on anomalous amplitude-dependent internal friction was studied.The longitudinal bias stress may always weaken the anomalous amplitude-dependent effect,while the torsional one may induce different effects from differ- ent directions applied.Bias stress effect exhibits only in properly heat treated and cold worked ahoy specimens.The anomalous amplitude-dependent internal friction peaks,P_3,P_2 and P_1, are found to be related closely to slant dislocation kink chains.Thus,the application of bias stress to internal friction would be contributed to the study on dislocation structure.

Investigation on Behavior of Rare Earth Element Cerium in Aluminum-Lithium Alloys by Internal Friction Method

The behavior of rare earth element Ce in 2090 Al Li alloys was studied by the method of low frequency internal friction.The results showed that rare earth element Ce can increase the activation energy of grain boundary and improve the grain boundary strength of alloys.Rare earth element Ce can decrease the tendency of softening of elastic modulus of 2090 Al Li alloys after heat cycle and keep high elastic modulus of initial state.

EFFECT OF SLIP ORIENTATION ON STRESS RESPONSE,INTERNAL FRICTION AND ULTRASONIC ATTENUATION DURING CYCLIC DEFORMATION IN Al SINGLE CRYSTALS

The variation of cyclic stress,internal friction and ultrasonic attenuation during cyclic deformation and relations among them have been investigated with different slip orientation Al single crystals.The results indicate that the value of cyclic stress σ,internal friction Q^(-1)and ultrasonic attenuation △α depend obviously on the slip orientation.There are large differences in above three parameters for different slip orientation Al crystals.In early stage of fatigue life,σ and △α increase and Q^(-1)decreases with cycles N,and △α reached maxi- mum before σ,while Q^(-1)and σ get the valley and the peak,respectively,at same cycles.

CHARACTERISTICS OF INTERNAL FRICTION AND MODULUS ASSOCIATED WITH NON-EQUILIBRIUM DIFFUSION-TYPE PHASE TRANSFORMATION IN EUTECTOID Al-Zn ALLOY

The characteristics of the low frequency internal friction and the modulus effect associated with the non-equilibrium spinodal pretransformation and the following discontinuous trans- formation was investigated in an as-quenched eutectiod Al-Zn alloy.It was observed that the loss of the stability in the lattice,which corresponded to the large-amplitude long-wavelength static concentration wave in the non-equilibrium spinodal pretransformation,did not induce any effect of localized soft modulus.Although there are two aging internal friction peaks in phase transformation which correspond to the appearance and disappearance of the coherency in spinodal pretransformation and the maximum of the interface area in the discontinuous transformation respectively,the effect of localized soft modulus did not take place yet.

EFFECT OF RARE EARTH ON MEDIUM-TEMPERATURE INTERNAL FRICTION OF COMMERCIALLY PURE IRON

The strong effect of rare earth(RE)on medium-temperature internal friction(IF)of commercially pure iron is closely related to the heat treatment.The RE added into iron has an alloying effect.The Snoek-Ke-Kster(briefly SKK)peak lower as the aging temperature in- creases from 150℃ to 450℃,but it still exists even aged at 600℃.However,the SKK peak temperature T_p does not simply falls as the ascending of aging temperature,it rises again at 600℃ aging.