Enhanced Damping Capacity in Graphene-Al Nanolaminated Composite Pillars Under Compression Cyclic Loading

Cyclic compression tests were conducted on 2.5-μm-diameter nanolaminated graphene-aluminum (Al) composite pillars. The composite possessed three times higher damping coefficient than its pure Al counterpart, which was rationalized by the enhanced dislocation hindrance at the graphene/Al interfaces in the composites. Moreover, the cyclic compression of micro-pillars produced similar damping coefficients as the corresponding bulk sample, providing a novel and convenient approach to assess the cyclic deformation behavior and damping properties of structural materials.

     

Domain Reorientation as a Damping Mechanism in Ferroelastic-Reinforced Metal Matrix Composites

The damping behavior of a model ferroelastic-reinforced–metal matrix composite (FR-MMC) system was examined through the incorporation of barium titanate (BaTiO₃) particles into a Cu-10 wt pct Sn (bearing bronze) matrix. The damping properties of the resulting FR-MMC were investigated vs frequency, temperature (above and below the Curie temperature of the ferroelastic reinforcement), and number of strain cycles. Dynamic mechanical analysis (DMA) indicates that the incorporation of the ferroelastic-capable reinforcement significantly augments the damping capability relative to the matrix alone, and also with respect to the damping that would result from the presence of passive composite reinforcements. Neutron diffraction data demonstrate a strong correlation of domain reorientation activity to imposed stress level and demonstrate a degree of reversibility important to the potential practical application of this mechanism of damping.     

Entropy of Alloy Phases: A Macroscopic Perspective

This study presents a comprehensive analysis of the entropy of condensed phases, its temperature, pressure, and composition dependence on a macroscopic correlative platform. Two principal contributions to total nonconfiguration entropy (S_T) are outlined. They are: (i) the pure thermal (S_th) contribution arising from the isochoric temperature dependence of Gibbs energy (G_T) and (ii) the elastic contribution (S_el) representing the dilatational volume effects. It is then argued that entropy variation among a group of alloy phases can be exclusively related to molar volume, only when both thermal pressure (p_th) and thermal entropy terms assume common values for all members. This argument is extended to establish a linear relationship between transformation entropy (ΔS_tr) and transformation-induced volumetric strain (ΔV_tr/V). The temperature and pressure dependencies of entropy have been discussed in terms of the complementing roles of S_th and S_el and simple approximations to these effects are suggested. A macroscopic power law relation for systematizing the standard entropy variation using a composite scaling parameter (MV^2/3/T_m) has been proposed, and its validity is demonstrated for both solid and liquid metals. This power law correlation has been exploited to deduce the following outcome: (i) a simple approximation for the initial slope (dp/dT_m) of p–T_m melting curve, (ii) self-consistent correlation of entropy with specific heat and Debye temperature, (iii) estimation of entropy of metastable phases, and (iv) correlating dilute solution entropy with volume effects of alloying.

     

Damping and acoustic harmonics in cracked laminated composites

This article reports on a novel experimental technique conceived and used to study damping and generation of acoustic harmonics in a cracked laminated composite. The cracked jaws of a double cantilever specimen with an interlaminar crack were vibrated symmetrically at 22.5 kHz; damping in the specimen and acoustic harmonics in the vicinity of the crack tip were measured as functions of amplitude of vibration. At low amplitudes, the damping was linear(i.e., independent of amplitude) with no detectable acoustic harmonics. At high amplitudes, the damping was nonlinear with generation of acoustic harmonics up to the fifth. Among known models for harmonic generation, the best choice to explain these data seems to be smooth motion of dislocations in graphite vibrating within a potential well of small asymmetry. Formerly Graduate Student, Columbia University, New York, NY 10027. This article is based on a presentation given in the Mechanics and Mechanisms of Material Damping Symposium, October 1993, in Pittsburgh, Pennsylvania, under the auspices of the SMD Physical Metallurgy Committee.     

Damping properties of consolidated iron and graphite powders

Upon increasing the strain amplitude, the damping capacity of sintered (800°C, 1 h) pure iron powders changes slowly at low strain amplitudes, increases at a threshold strain amplitude of about 8 × 10⁻⁵, reaches a maximum, and then decreases. This behavior is the same for sintered graphite powders as well as for mixtures of graphite and iron powders except that the threshold strain amplitude is lower (2 × 10⁻⁵) for the composite. However, the low threshold is similar to that of the cast iron. With increasing graphite content, the modulus of the composite decreases, but the damping capacity increases. Both the damping capacity and Young's modulus of the composite are comparable to those of cast iron.     

Numerical modeling of the damping capacity of Al/SiC(<Emphasis Type="Italic">p</Emphasis>)

In the present article, the damping behaviors of Al/SiC particulate-reinforced metal-matrix composites (PMMCs) at room temperature are investigated by the numerical modeling method. Through the cell method (CM) and finite-element method (FEM), the influences of particulate shape and distribution on the damping capacity of Al/SiC(p) composite are studied. Also, the case of multiparticulate with random distribution and random size is investigated as a comparison with the single-particulate case. At last, the simulation results are compared with the experimental results, which show that they are consistent with each other in quality.     

Damping properties of austenitic stainless steels containing strain-induced martensite

Damping properties of two austenitic stainless steel grades, EN 1.4318 and EN 1.4301, were investigated. The test materials were cold rolled to different reductions and damping capacity was measured as a function of temperature with an internal friction method. Microstructures of the test materials were studied by means of X-ray diffraction (XRD) and magnetic measurements. The results showed that damping capacity of the studied materials depended on the amounts of strain-induced ε- and α′-martensite phases. At temperatures around 0 °C, highest damping capacity was achieved with cold rolling reduction of 10 to 15 pct. This behavior is related to the existence of ε-martensite and stacking faults. Internal friction peak due to α′-martensite phase was present at the temperature of 130 °C. Strain aging heat treatment at 200 °C for 20 minutes decreased the damping capacity in the entire studied temperature range.     

Driveability of FRP Composite Piling

Fiber-reinforced polymer (FRP) composites represent an alternative construction material without many of the performance disadvantages of traditional materials. Although composite materials present a number of difficulties related to pile driving, including low stiffness, high damping, and low strength, the use of FRP as a pile material can eliminate deterioration problems of conventional piling materials in waterfront environments and aggressive soils. This paper is a theoretical parametric study of the effect of various pile properties and soil conditions on the driveability of FRP composite piling in a typical waterfront site. All analyses performed show that composite piling could be driven to reasonable capacities for load-bearing piles. The parameters studied include the effect of pile modulus, damping ratio, unit weight, residual stresses, and hammer type on the efficiency of driving of FRP piling relative to conventional piling materials.     

Analysis of damping in particle-reinforced superplastic zinc composites

The damping behavior of superplastic zinc (SPZ) particulate composites with up to 42.5 vol pct spherical TiC particles (3 Μm in diameter) was studied in the 25 ‡C to 330 ‡C temperature range using a low frequency torsion pendulum. The observed damping at room temperature was modeled as a combination of a diffusion-controlled dislocation relaxation and a grain boundary relaxation. Addition of TiC produced a lower dislocation damping contribution at room temperature, but this loss was offset by an increased contribution from the grain boundary relaxation. An increase in the elastic modulus was also observed for the composite. The validity of a theoretical model for predicting changes in the grain boundary relaxation peak temperature resulting from the introduction of large nondeforming particles was tested. This study demonstrates that grain sliding in SPZ alloys occurs by cooperative sliding of grain clusters containing three to five grains. The activation energy for this process was found to be 111 kJ/mole (1.15 eV), which is in agreement with previously published values for grain sliding in SPZ. A second internal friction peak at a temperature just below the eutectoid transformation temperature was also observed and this peak was associated with recrystallization.     

On the application of magnetomechanical models to explain damping in an antiferromagnetic copper-manganese alloy

The Smith-Birchak model for magnetoelastic damping was successfully applied to model the damping observed in an antiferromagnetic Cu-48Mn-1.5Al (wt pct) alloy. Antiferromagnetic domains were developed by solution treatment at 820 ‡C and subsequent aging at 400 ‡C for 4, 10, and 16 hours. Damping capacity and dynamic elastic modulus were measured as a function of strain amplitude and temperature. A maximum in the strain-amplitude-dependent damping was obtained for the 4-hour-aged sample for which a magnetostriction constant, λ, equal to 4.65 × 10^-4, was derived. An exact fit for the Smith-Birchak model was obtained at low strains, whereas the model predicted lower damping than was observed for strains greater than 1.1 × 10^-3. This discrepancy was attributed to an additional damping mechanism at high strain amplitudes,i.e., dislocation damping. A magnetostriction constant equal to 3.23 × 10^-4 was also calculated based upon the Néel temperature and the observed microstructure.     

Effects of Fe Addition on the Snoek-Type Damping Behavior of Surface-Oxidation-Treated Ti-Mo Alloys

Effects of Fe addition on the oxygen diffusion and the Snoek-type relaxation damping behavior of the Ti-15 wt pct Mo alloy were investigated in this study. After surface oxidation treatment, the Ti-15 wt pct Mo-1 wt pct Fe alloy exhibits a higher damping capacity compared to the Ti-15 wt pct Mo alloy. The dual-phase zone and the oxygen-enriched β-phase zone in the surface-oxidation-treated Ti-Mo alloys were determined by electron backscattered diffraction (EBSD) and hardness measurements. Based on the oxygen distributions in both alloys obtained through a diffusion model, the relative damping capacity of different zones contributing to the beam sample damping was estimated to be proportional to the thickness of the oxygen dissolved zones. On the other hand, the substitutional solute of Fe in the Ti-Mo-Fe alloy is considered to affect the oxygen distribution by lengthening the oxygen diffusion zone and increasing the oxygen concentration in this zone. As a result, the addition of Fe in Ti-Mo alloy improves the damping capacity of the surface-oxidation-treated alloys.     

Vibration damping characteristics of laminated steel sheet

The use of laminated steel sheets as vibration damping materials was studied. The laminate consisted of a viscoelastic layer which was sandwiched between two steel sheets. The study sought to identify parameters affecting the damping efficiency of the laminate. Two viscoelastic materials, a copolymer based on ethylene and acrylic acid (PEAA) and polyvinyl butyral (PVB), were used. A frequency analyzer was used to measure the loss factor of the laminates. A theoretical analysis of damping efficiency based on a model described by Ungar^[2] was also carried out. The results showed that the loss factor of the PEAA-based laminates increased monotonically with increasing thickness of the viscoelastic layer and leveled off at 25.9 pct of total thickness. Ungar’s theory predicted a higher loss factor than the experimental data. This might have resulted from interfacial adhesive bonding, a nonuniform viscoelastic layer thickness, and the extrapolation of the rheological data from low to high frequencies. The loss factor of the laminate increased with increasing temperature, reached a maximum value, and then decreased. An optimum temperature for maximum damping was found for each laminate configuration. The PEAA-based laminates possessed higher damping efficiency than the PVB-based laminates at room temperature. The symmetric laminate (with the same steel sheet thickness) possessed a better damping efficiency than asymmetric laminates. The maximum damping peak of the laminates using a polymer blend, when compared to the laminates using unblended resin, exhibited a lower loss factor value, became broader, and occurred at a temperature between theT _g’s of the individual components of the polymer blend. This paper is based on a presentation made in the symposium “Acoustic/Vibration Damping Materials” presented during the TMS Fall Meeting, Indianapolis, IN, October 1–5, 1989, under the auspices of the TMS Physical Metallurgy Committee.     

Enhancing the Damping Behavior of Dilute Zn-0.3Al Alloy by Equal Channel Angular Pressing

The effect of grain size on the damping capacity of a dilute Zn-0.3Al alloy was investigated. It was found that there was a critical strain value (≈1 × 10⁻⁴) below and above which damping of Zn-0.3Al showed dynamic and static/dynamic hysteresis behavior, respectively. In the dynamic hysteresis region, damping resulted from viscous sliding of phase/grain boundaries, and decreasing grain size increased the damping capacity. While the quenched sample with 100 to 250 µm grain size showed very limited damping capacity with a loss factor tanδ of less than 0.007, decreasing grain size down to 2 µm by equal channel angular pressing (ECAP) increased tanδ to 0.100 in this region. Dynamic recrystallization due to microplasticity at the sample surface was proposed as the damping mechanism for the first time in the region where the alloy showed the combined aspects of dynamic and static hysteresis damping. In this region, tanδ increased with increasing strain amplitude, and ECAPed sample showed a tanδ value of 0.256 at a strain amplitude of 2 × 10⁻³, the highest recorded so far in the damping capacity-related studies on ZA alloys.

     

Damping and Viscoelastic Dynamic Response of RC Flexural Members Strengthened with Adhesively Bonded Composite Materials

A theoretical approach for the dynamic viscoelastic response of reinforced concrete (RC) beams and one-way slabs strengthened with adhesively bonded composite materials is developed. The analytical model is based on variational principles, dynamic equilibrium, and compatibility of deformations between the structural components (RC beam/slab, adhesive, composite material). The model accounts for the deformability of the adhesive layer and for its high order stress and displacement fields. The equations of motion and the boundary, continuity, and initial conditions are derived via the extended Hamilton’s principle. The Kelvin-Voigt approach is adopted for the consideration of the viscoelastic response of the adhesive material and the internal damping in the composite material and the RC member. The Rayleigh damping model is used for the external viscous damping of the RC member. The dynamic governing equations are solved using the Newmark time integration and a multiple shooting algorithm is used for the solution in space. A numerical example is presented to examine the capabilities of the model, to highlight the unique phenomena associated with the viscoelastic response of the adhesive material, and to demonstrate its influence on the local and global behavior. The results obtained using the analytical model show that the viscoelastic response of the adhesive material may significantly modify the critical shear and peeling stresses at the interfaces of the adhesive layer.     

High-damping metals and alloys

High-Damping Metals (HIDAMETS) are the physical metallurgist’s answer to unwanted noise and vibrations. However, the characterization of the damping properties of metals and alloys is neither simple nor straightforward. This is mainly because the damping mechanisms involved depend upon the stress-induced movement of defects in the metal in question which, in turn, implies a dependence upon the microstructure (thermomechanical history) of the sample. To properly characterize the damping performance of a HIDAMET in a well-defined structural state, one must measure the mechanical damping as a function of vibration frequency, temperature, vibration strain amplitude, and static bias load over the ranges of these variables to be encountered in the application in question. This requires the use of a variety of equipment adapted to different modes of vibration and their overtones, especially when the damping is nonlinear (amplitude-dependent). Our approach to this problem is described and illustrated by test results obtained on several HIDAMETS. This paper is based on a presentation made in the symposium “Acoustic/Vibration Damping Materials” presented during the TMS Fall Meeting, Indianapolis, IN, October 1–5, 1989, under the auspices of the TMS Physical Metallurgy Committee.     

Damping characteristics of TiNi shape memory alloys

The damping characteristics of TiNi SMAs have been systematically studied by using techniques of resonant-bar and low-frequency inverted torsion pendulum. Experimental results show that both the martensite phase (M) and R phase (R) have high damping due to the movement of twin boundaries. Because the B2 parent phase (B2) has smaller damping, it is suggested that this may come from the dynamic ordering process of lattice defects. In the transformation re-gions of B2 ↔ M, B2 ↔ R, and R ↔ M, there are maxima of the damping capacity which are attributed to two contributions. One arises from the plastic strain and twin-interface move-ment during the thermal transformation, which obeys a linear variation of peak heightsQ ⁻¹ _max vst att ≥ 1 °C/min. The other originates from the stress-induced transformation formed by the applied external stress which dominates atT < 1 °C/min. The elastic modulusE of martensite and the R phase is lower than that of the B2 phase, and a modulus minimum appears in the transformation region.     

Calorimetric studies of 7000 series aluminum alloys: I. Matrix precipitate characterization of 7075

Both differential scanning calorimetry (DSC) and hot stage transmission electron microscopy were used to characterize the solid state reactions accompanying heating of the highest strength (T651) and overaged (T7351) tempers of 7075 aluminum alloy. Each of the observed endothermic or exothermic reactions that occurs over the 20 to 500°C temperature range has been ascribed to the dissolution or formation of a specific precipitate. The dissolution of each matrix phase,i.e., GP zones, ή and ή, can be characterized by a distinguishable dissolution temperature, dissolution enthalpy, activation energy, and activation entropy. The values of activation energy and activation entropy for the dissolution of the initial matrix precipitate of these phases indicate that the relative stability of the matrix precipitates is primarily influenced by the entropy rather than the energy term. This investigation provides a basis for the use of DSC analysis in the rapid, quantitative identification of the matrix microstructure of 7075 aluminum alloy as well as in the characterization of the matrix microstructure of other 7000 series aluminum alloys.     

Synthesis of nanocomposite thin films based on the Mo-Si-C ternary system and compositional tailoring through controlled ion bombardment

A major advantage of sputtering processes compared to evaporation processes is the possibility of synthesizing films that replicate the composition of the source (target) material,particularly in the case of alloy targets. This is related to the unique feature of sputtering, viz, formation of an “altered layer” which facilitates reproduction of the target composition in the thin film. An exciting and novel area of research deals with the synthesis of nanocomposite thin films by sputtering composite targets. In this article, the feasibility of depositing a composite thin film based on the Mo-Si-C temary system through RF magnetron sputtering of a MoSi₂+XSiC target, and the possibility of modifying the film composition by controlled ion bombardment (i.e., “ion plating” or “bias sputtering”), will be discussed. In this context, the role of the sputter yields for Mo, Si, and C will be examined with respect to the ability to vary the composition of as-deposited films. In addition, the modifications which were required to sputter a 58.4-mm-diameter composite target (produced inhouse, by different synthesis reactions) using a 127×381-mm Vac Tec cathode will be discussed. Details of Auger electron spectroscopy (AES) scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses of the as-deposited films will be presented.     

Room-temperature tensile and high-cycle-fatigue strength of fine TiB particulate-reinforced Ti-22Al-27Nb composites

To further improve the mechanical properties of a Ti-22Al-27Nb (mol pct) alloy, based on the ordered orthorhombic Ti₂AlNb (O phase), a TiB particulate-reinforced Ti-22Al-27Nb matrix composite was prepared using the gas-atomized powder metallurgy method. Because of the rapid solidification during the gas atomization process, the TiB particulates dispersed in the composite were extremely fine, with an average diameter of less than 1 μm and lengths ranging up to 5 μm. This composite (PM composite) showed higher tensile and high-cycle-fatigue properties at room temperature than both an unreinforced Ti-22Al-27Nb matrix alloy and a Ti-22Al-27Nb/TiB composite produced using a conventional ingot metallurgy method (IM composite) with relatively coarse (average diameter 5 μm and average length 40 μm) TiB particulates. These coarse TiB particulates in the IM composite were thought to provide only classical composite strengthening effects. On the other hand, the fine TiB particulates in the PM composite showed additional effects, such as blocking the movement of dislocations.     

Solid particle erosion of Al alloy and Al-alloy composites: Effect of heat treatment and angle of impingement

Erosive wear behavior of the as-cast and heat-treated Al alloy and the Al-alloy-SiC particle composite against Al₂O₃ erodent has been examined at different angles of impingement (15 to 90 deg). It has been noted that the cast Al alloy exhibited a higher erosion rate than the heat-treated alloy and composites irrespective of the angle of impingement. It is noted that the as-cast and heat-treated Al alloy exhibited a maximum wear rate at the 45 deg angle of impingement, whereas the composite, in as-cast as well as in heat-treated conditions, showed a maximum erosion rate at the 60 deg angle of impingement. Subsurface studies of the alloy and composite confirm that the material loss, during erosive wear, is primarily due to microcutting/microplowing (i.e., abrasive-type) and microfracture (i.e., impact-type) actions. At a low angle of impingement, the abrasive type is the dominating factor for material removal, and at a higher angle of impingement, both the impact-type and abrasive-type actions play critical roles. The impact type is mainly localized at the tip of the erosion profile, while the abrasive type takes place along the sidewalls of the profile. This is explained on the basis of the erosion mechanism using a schematic diagram.