Ultrasonic Friction Research Articles

Novel elastico-mechanoluminescence materials CaZnOS:Mn2+ and CaZr(PO4)2:Eu2+

This paper highlights our work on the recent progress in novel elastico-mechanoluminescence (EML) materials CaZnOS : Mn 2+ and CaZr ( PO 4)2: Eu 2+, which can simultaneously "feel" (sense) and "see" (image) the applied mechanical stress as an intense and proportional luminescence. CaZnOS : Mn 2+ can sense various types of mechanical stress, including ultrasonic vibration, impact, friction and compression because of the large piezoelectric coefficient. CaZr ( PO 4)2: Eu 2+ with multiple trap levels shows a broad measurement range for dynamic load. Both of CaZnOS : Mn 2+ and CaZr ( PO 4)2: Eu 2+ belong to the defect-controlled type piezoelectric phosphors, and their EML mechanisms could be explained using the piezoelectrically induced carrier de-trapping model.

Measurement of local internal friction in metallic glasses

Atomic force acoustic microscopy (AFAM), an advanced scanning probe microscopy technique, has been used to measure local elastic properties with a spatial resolution given by the tip-sample contact radius. AFAM is based on inducing out-of-plane vibrations in the specimen. The vibrations are sensed by the AFM cantilever from by the photodiode signal when its tip is in contact with the material under test. To measure local damping, the inverse quality factor Q−1 of the resonance curve is usually evaluated. Here, from the contact-resonance spectra obtained, we determine the real and imaginary part of the contact stiffness k* and from these two quantities the local damping factor Qloc−1 is obtained which is proportional to the imaginary part γ of the contact stiffness. The evaluation of the data is based on the cantilever's mass distribution with damped flexural modes and not on an effective point-mass approximation for the cantilever’s motion. The given equation is simple to use and has been employed to study the local Qloc−1 of amorphous PdCuSi metallic glass and its crystalline counterpart as a function of position of the AFM tip on the surface. The width of the distribution changes dramatically from the amorphous to the crystalline state as expected from the consequences of the potential-energy landscape picture. The center value of the distribution curve for Qloc−1 coincides very well with published data, based on global ultrasonic or internal friction measurements. This is compared to Qloc−1 measured in crystalline SrTiO3, which exhibits a narrow distribution, as expected.

Friction Stir Welding of Dissimilar 5xxx to 6xxx Al Alloys: A Review

Many engineering applications in aerospace and automotive field require joining of dissimilar 5xxx to 6xxx Al alloys. Dissimilar Al alloy joints are used for industrial applications due to technical & economic reasons. However, due to different metallurgical behaviour & mechanical properties, joining of dissimilar Al alloys presents a number of challenges. Due to high temperature generation most of the fusion welding techniques are not suitable. In addition, other pressure welding techniques such as – Ultrasonic welding, Roll bonding, Diffusion bonding and Friction welding have some limitation. Hence, friction stir welding (FSW) can be considered to be the most suitable method to join dissimilar Al alloys due to solid-state nature of the process. Since invention, friction stir welding has been a matter of research and investigation for years. In its history of two decades, Friction Stir welding was investigated for joining dissimilar Al alloys during the last decade. Most of studies demonstrated that good quality joints between dissimilar Al alloys can be produced by the Friction Stir Welding (FSW) process. The present study is a chronological & critical review of recent studies on joining of dissimilar 5xxx to 6xxx Al alloys by friction stir welding.

Elastic–plastic cube model for ultrasonic friction reduction via Poisson's effect

Ultrasonic friction reduction has been studied experimentally and theoretically. This paper presents a new elastic–plastic cube model which can be applied to various ultrasonic lubrication cases. A cube is used to represent all the contacting asperities of two surfaces. Friction force is considered as the product of the tangential contact stiffness and the deformation of the cube. Ultrasonic vibrations are projected onto three orthogonal directions, separately changing contact parameters and deformations. Hence, the overall change of friction forces. Experiments are conducted to examine ultrasonic friction reduction using different materials under normal loads that vary from 40N to 240N. Ultrasonic vibrations are generated both in longitudinal and vertical (out-of-plane) directions by way of the Poisson effect. The tests show up to 60% friction reduction; model simulations describe the trends observed experimentally.

An intense elastico-mechanoluminescence material CaZnOS:Mn^2+ for sensing and imaging multiple mechanical stresses

The elastico-mechanoluminescence (EML) properties of CaZnOS:Mn2+ are investigated. The CaZnOS:Mn2+/epoxy resin composite can simultaneously "feel" (sense) and "see" (image) various types of mechanical stress over a wide energy and frequency range (ultrasonic vibration, impact, friction and compression) as an intense red emission (610 nm) from Mn2+ ions. Further, the accurate linear relation between emission intensity and different stress parameters (intensity, energy and deformation rate) are confirmed. The EML mechanism is explained using a piezoelectrically induced trapped carrier excitation mode. All the results imply that CaZnOS:Mn2+ has potential as a stress probe to sense and image multiple mechanical stresses and decipher the stress intensity distribution.

Evaluation of Discontinuities in A36 Steel Repairs with Friction Hydro Pillar Processing Using Different Axial Forces

Friction welding techniques are widely used in several industrial sectors. A non-destructive inspection is mandatory in post-processing for repair quality evaluation. The present study examines through conventional ultrasonic technique Friction Hydro Pillar Processing (FHPP) repairs on ASTM A36 low carbon steel plates. The repairs were made using four different axial forces, 200, 250, 300 and 350 kN with constant rotational speed of 1000 rpm. The features of the echogram signals obtained made possible to identify and distinguish microcracks, lack of bound, clustered inclusions and isolated inclusions, forming three critical regions within the weld. It was seen that high processing forces increases probability to generate microcracks from discontinuities. These ultrasonic results were related and validated with micrographic analysis and it was possible to make a relationship between echograms features and micrographs to differentiate the discontinuities founded within the repairs. This information could be used as a guideline for operating procedure to locate discontinuities.

An elastico-mechanoluminescence material CaZnOS:Mn2+ for sensing and imaging various mechanical stresses

We have investigated the novel elastico-mechanoluminescence (EML) properties of CaZnOS:Mn2+ for sensing and imaging various mechanical stresses. The CaZnOS:Mn2+ indicators encapsulated in an optically transparent epoxy resin matrix can simultaneously “feel” (sense) and “see” (image) various types of mechanical stress over a wide energy and frequency range (including ultrasonic vibration, impact, friction and compression) as intense and short-lived red fluorescence emission (610nm) from the 4T1(4G)→6A1(6S) transition of Mn2+ ions. Further, the accurate linear relation between emission intensity and different stress parameters (such as intensity, energy and strain rate) are confirmed. The EML characteristics of CaZnOS:Mn2+ could be explained using a model of piezoelectrically induced trapped carrier excitation according to the unusual entirely non-centrosymmetric crystal structure of CaZnOS:Mn2+ and the existence of carrier traps with an appropriate depth. All the results imply that the investigated EML material has potential as a touch sensor or smart skin to sense and image various mechanical stresses and decipher the stress intensity distribution.

Modeling study of thermosonic flip chip bonding process

Thermosonic flip chip (TSFC) bonding is a developing area-array microelectronic package technology. To better understand the bonding formation mechanism, a dynamic finite element model of the TSFC bonding process was developed, where the soften effect caused by the heat stage and ultrasonic vibration was considered in the constitutive relation of the gold bump. With this model, the strain evolution processes for the bump and the bump/pad interface were obtained and compared, and it was found that the deformation of the bump is always larger than that of the bonding interface; this may decrease the Allowable I/O pitch and bonding strength. To increase the ratio of the strain of the bonding interface to that of the bump, parameter studies are carried out, and the effects of ultrasonic vibration amplitude, bonding force, and static friction coefficient on the plastic deformation and strain distribution on the bump and the bump/pad contact interface were studied. Based on the simulation results, the effects of the parameters on the strain distribution were obtained, and some recommendations for parameter optimization are given. This FE simulation study may assist in process window development for fine pitch TSFC bonding.

Mechanical Spectroscopy of Hyperstabilized Martensites

The internal friction of the hyperstabilized martensite demonstrates very low values, both above and below the nominal martensitic transformation temperature, due to a pronounced pinning effect. Over a wide temperature range it is comparable with the level of damping in the parent phase. A study of the temperature dependence of the non-linear ultrasonic internal friction and its strain amplitude hysteresis indicates that the diffusion, assisted by dislocations/interfaces, is quite pronounced and in Ni-Fe-Ga and Cu-Al-Be alloys it operates at temperatures around 20 K. The renucleation of the lamellar parent phase during the reverse martensitic transformation close to 600 K is accompanied by an internal friction peak which demonstrates a substantial transitory contribution. After renucleation of the parent phase the samples recover a conventional martensitic transformation with the internal friction level in the martensite comparable to the one in non-stabilized samples. Observations of a relaxation peak in the parent phase of different alloys for temperatures just below the renucleation stage of the reverse transformation point to the essential role of diffusion in the nucleation of the parent phase in hyperstabilized martensites.

Research on Dynamic Grinding Force in Ultrasonic Honing Chatter

The power ultrasonic vibration honing is one typical method with low speed grinding precision work. Compared with traditional honing, the ultrasonic vibration honing is of the advantages such as higher precision of surface quality, small roughness, higher processing efficiency, easy to process hard crisp material, etc. In the process of power ultrasonic vibration honing, with the increased ultrasonic surging force, the grinding force becomes extremely complex and changes along with the operating condition. Its flutter belongs to the nonlinear time-variable vibration, its flutter mechanism is more complex and the harm is more serious. In order to repress the chatter phenomenon, exploring the supersonic honing chatter mechanism through the research on the grinding force's tendency change rule. Through the analysis, draws the following conclusion: the radial component, which is caused by the added ultrasonic action on the oilstone, may be possible completely or partly to counteract the dynamic grinding force caused by the thickness effect; the axial componentmay be possible to remove the cross mark’s peak effectively of the ordinary honing and enhance the surface-supporting length ratiotpwithout changing the roughness; the added ultrasonic influences mutual friction between oilstone and work piece in honing process.

Effect of Ultrasonic Vibration on Friction and Wear Properties of GCr15/45# Steel Frictional Pairs under Oil Lubrication

Ultrasonic vibration friction and wear experiments were carried out by MFT-R4000 reciprocating friction and wear tester bonded with ultrasonic device. The surface morphologies of wear scars were examined by scanning electron microscope (SEM). The influences of ultrasonic vibration on friction reduction and anti-wear properties of GCr15/45# steel frictional pairs under different loads were discussed. The experimental results showed that, the friction of GCr15/45# steel frictional pairs could be reduced by ultrasonic vibration, and the reduction of friction coefficient became more obvious as the loads increasing. The friction coefficient measured under ultrasonic vibration is 12% lower than it measured without ultrasonic vibration when the load was 50N. However, the wear of frictional pairs increased under ultrasonic vibration, and the amplitude of wear volume enlarged with the loads increase, which is 63% at the load of 50N.

Ultrasonic friction power during thermosonic Au and Cu ball bonding

The ultrasonic friction power during thermosonic ball bonding with Au and Cu wires, both 25 µm in diameter, is derived with an improved method from experimental measurements during the bonding process. Experimental data include the current delivered to the ultrasonic transducer and the tangential force measured using piezoresistive microsensors integrated close to the Al bonding pad. The improvement results from a new, more accurate method to derive the mechanical compliance of the ultrasonic system. The method employs a bond process modification in which the ultrasonic current is ramped up sequentially in three steps. In the first two steps, the ultrasonic current is set to levels that are too low to cause sliding. The bonding takes place during the third step, when the current is ramped up to the optimum value required for making good quality bonds. The ultrasonic compliance values are derived from the first two steps and are 8.2 ± 0.5 µm N−1 and 7.7 ± 0.5 µm N−1 for the Au and Cu processes, respectively. These values are determined within an average error estimate of ±6%, substantially lower than the ±10% estimated with a previously reported method. The ultrasonic compliance in the case of Au is 6% higher due to the lower elastic modulus of Au compared with that of Cu. Typical maximum values of relative sliding amplitude of ultrasonic friction at the interface are 655 nm and 766 nm for the Au and Cu processes. These values are 81% of the free-air vibration amplitude of the bonding capillary tip for the respective ultrasonic current settings. Due to bond growth, which damps relative motion between the ball and the pad, the final relative amplitude at the bond interface is reduced to 4% of the equivalent free-air amplitude. Even though the maximum value of relative amplitude is 17% higher in the Cu process compared with the Au process, the average total interfacial sliding is 519 µm in the Cu process, which is 31% lower than that in the Au process (759 µm). The average maximum interfacial friction power is 10.3 mW and 16.9 mW for the Au and Cu ball bonding processes, respectively. The total sliding friction energy delivered to the bond is 48.5 µJ and 49.4 µJ for the Au and Cu ball bonding cases, respectively. These values result in average friction energy densities of 50.3 mJ mm−2 and 54.8 mJ mm−2 for Au and Cu ball bonding, respectively.

Silver pick up during tail formation in thermosonic wire bonding process

Cu ball bonding processes are significantly less robust than Au ball bonding processes. One reason for this are higher variations observed, e.g. in the free-air ball (FAB) formation process. There is a strong influence the tail bond process has on subsequent FAB formation. Tail tips and bond fractographs made with Cu and Au wires are investigated using scanning electron microscopy. Au and Cu wires pick up Ag material (Ag pick up) from the Ag metallization of Cu leadframe diepads during wire tail breaking. Ag pick up by Cu wire is more dominant than that by Au wire. Ultrasonic friction energy is necessary in order for Ag material pick up to occur. The impact force plays an important role for Ag pick up; less pick up is observed with a higher impact force. The hardness of the free-air ball (FAB) with Ag pick up is reduced by up to 4% compared to that of a FAB made from a tail broken at the neck of a ball bond and therefore having no Ag pick up. No significant change of FAB diameter is observed in these two cases.

Modeling of copper wire bonding process on high power LEDs

In this paper, a couple thermal mechanical transient dynamic finite element framework of copper wire bonding process on high power lighting emitting diodes (LEDs) is developed, which considers the thermal heating effects of friction and plastic deformation. The whole wire bonding process is simplified to consist of impact and ultrasonic vibration stages. Parametric studies are also carried out to examine the effects of ultrasonic vibration amplitude and bonding force on stress/strain distribution and friction thermal heating effect during wire bonding process. Different friction coefficients of interface between the free air ball (FAB) and the bond pad are taken in the simulation to examine the effects of friction on the stress and strain level of electrode structure. Modeling results show that the stress/strain distribution and temperature evolution of wire bonding system are significant influenced by the ultrasonic vibration amplitudes, bonding forces and friction coefficients. Discussion and comparison are conducted between the copper and the gold wire bonding processes on the high power LEDs by numerical simulation. The results have disclosed that higher stress/strain in the bond pad and the ohmic contact layer is induced during the copper wire bonding process. Therefore, the process parameters of copper wire bonding should be controlled carefully. This numerical simulation work may provide guidelines for the copper wire bonding process virtual window development of high power LEDs packaging.

Novel Approaches to Friction Spot Welding Thin Aluminium Automotive Sheet

Conventional welding methods, like resistance spot welding, are inefficient and difficult to apply to light alloys. Two alternative new solid state friction joining techniques, which have not yet been fully optimized, are high power Ultrasonic Spot and Friction Stir Spot Welding (USW & FSSW). Here we have compared the performance for these two processes for producing ‘keyhole-less’ welds in thin aluminium automotive closure panels. For friction stir spot welding this was achieved through using a novel ‘pinless’ tool to create a joint without a retained keyhole and reduce the weld cycle time. The properties of the welds that can be produced by each technique are compared, together with the stages of weld formation, and the relationship between welding conditions and joint performance.

Ultrasonic friction power during Al wire wedge-wedge bonding

Al wire bonding, also called ultrasonic wedge-wedge bonding, is a microwelding process used extensively in the microelectronics industry for interconnections to integrated circuits. The bonding wire used is a 25μm diameter AlSi1 wire. A friction power model is used to derive the ultrasonic friction power during Al wire bonding. Auxiliary measurements include the current delivered to the ultrasonic transducer, the vibration amplitude of the bonding tool tip in free air, and the ultrasonic force acting on the bonding pad during the bond process. The ultrasonic force measurement is like a signature of the bond as it allows for a detailed insight into mechanisms during various phases of the process. It is measured using piezoresistive force microsensors integrated close to the Al bonding pad (Al–Al process) on a custom made test chip. A clear break-off in the force signal is observed, which is followed by a relatively constant force for a short duration. A large second harmonic content is observed, describing a nonsymmetric deviation of the signal wave form from the sinusoidal shape. This deviation might be due to the reduced geometrical symmetry of the wedge tool. For bonds made with typical process parameters, several characteristic values used in the friction power model are determined. The ultrasonic compliance of the bonding system is 2.66μm∕N. A typical maximum value of the relative interfacial amplitude of ultrasonic friction is at least 222nm. The maximum interfacial friction power is at least 11.5mW, which is only about 4.8% of the total electrical power delivered to the ultrasonic generator.

Ultrasonic Friction Power in Microelectronic Wire Bonding

An integrated sensor method is used to measure interfacial temperature profiles with an ultrasonic friction test process. The profiles are compared to numerical results obtained by a transient thermal 2D axisymmetric finite elements (FE) analysis. In the experiments, the 50 $m diameter gold balls used in wire bonding are deformed by the capillary tool during impacting on the flat surface of a silicon chip (contact zone). The deformed balls then are pressed onto the SiO2 layer on the chip and vibrated with various amplitudes of 128 kHz ultrasonics. The 52 $m diameter contact zone is surrounded in 14 $m distance by a 50 aluminum resistor which is used as a resistive temperature detector. Temperature increases of typically 0.18 K and up to 0.3 K are measured by the sensor close to the heat source at the contact zone, corresponding to 3.1 K and 5.2 K at the interface as suggested by the FE model. With typical bonding parameters, the contact zone friction power is determined to be 4.4 mW which is less than 2 % of the electrical energy delivered to the used ultrasonic transducer type.

Mechanical-Diode Mode Ultrasonic Friction Force Microscopy

We report on a novel technique, Mechanical-Diode Mode Ultrasonic Friction Force Microscopy, based on the study of the additional ultrasound-induced torsion of a cantilever when the cantilever tip scans in contact with a sample surface at low frequency in the presence of shear surface ultrasonic vibration of sufficiently high amplitude (lateral mechanical-diode effect). Data recorded on Si(111) are discussed. The results can be understood by considering the interaction of the tip with the lateral surface sample potential, and the presence of an ultrathin viscous liquid layer at the tip-sample contact which develops hydrodynamic pressure when sheared at ultrasonic velocities.

Characterization of elasticity, friction, anelasticity, and adhesion with nm lateral resolution, using the ultrasonic vibration modes of atomic force microscope cantilevers

Ultrasound is combined with atomic force microscopy to achieve the lateral resolution of scanning probes for imaging. Atomic force acoustic microscopy (AFAM) and ultrasonic friction force microscopy (UFFM) exploit the vibrational modes of AFM cantilevers which extend from 10 kHz to several MHz. In the AFAM mode the cantilever vibrates in contact mode in one of its flexural resonances. Images can be obtained with the contrast depending on the local indentation modulus, which can be obtained quantitatively from the contact resonance frequencies. The lateral resolution is defined by the tip‐sample contact radius and is 10 nm. At large ultrasonic amplitudes nonlinear effects that are related to adhesion become important. In UFFM shear stiffness and friction phenomena can be examined by evaluating the torsional cantilever resonances. At low lateral surface amplitudes, the sensor tip remains in elastic contact and the cantilever behaves like a linear torsional oscillator with damping. If the amplitude exceeds a critical value, the resonance develops a plateau due to stip‐slick in the tip‐sample contact, allowing one to monitor friction. Ultrasonic C‐scan images and the corresponding contact resonance spectra will be shown and compared to theory. Applications of the AFAM techniques to measure local piezoelectricity and anelasticity will be discussed as well.

Jaguar “Roadmap” rethinks self‐piercing technology

PurposeDescribes how Jaguar Cars is evaluating a technology roadmap to assess future manufacturing processes.Design/methodology/approachDescribes the major production line technologies that are under close scrutiny for the next ten years for use in the Jaguar Cars' production plants at Castle Bromwich and at Halewood, Merseyside, both in the UK. Technologies under review include ultrasonic welding, friction stir spot welding, laser welding and self‐piercing rivets.FindingsThe use of self‐piercing rivets is already used in production at Jaguar for the aluminium‐bodied XJ saloon. But developments of the process are already underway in readiness for the next new model. However, at the same time, engineers are examining other techniques including ultrasonic joining and friction stir spot welding, both of which at the subject of research work in the US and the UK. Use of pedestal guns and blow feeding devices is expected to bring improvements in cost.Research limitations/implicationsEngineers at Jaguar are carrying out research and development, both in‐house and with various research bodies and universities to establish the most beneficial processes for the joining of aluminium sheet, extrusion and cast components that go to form an aluminium car body. For successful joining aluminium requires low heat input solutions. At present, self‐piercing rivets offer the best solution, but Jaguar engineers are looking at other processes including ultrasonic joining and friction stir spot welding. The aim is to find processes that are fast and cost‐effective. In the meantime, Jaguar will continue to use self‐piercing rivets for aluminium structures.Practical implicationsThe practical implications of the work will lead to reduced cycle times which in turn will help to make the manufacture of aluminium car bodies more cost‐effective.Originality/valueBMW claims it is the first car maker to make use of bowl‐feeding self‐piercing rivets for the manufacture of aluminium body‐in‐white.