Induce Plastic Deformation Research Articles

Stress distribution in mechanically surface treated Ti-2.5Cu determined by combining energy-dispersive synchrotron and neutron diffraction

Mechanical surface treatments such as shot peening (SP) or ball-burnishing (BB) induce plastic deformation close to the surface resulting in work-hardening and compressive residual stresses. It enhances the fatigue performance by retarding or even suppressing micro-crack growth from the surface into the interior. SP and BB were carried out on a solution heat treated (SHT) Ti-2.5Cu. The investigations of compressive and balancing tensile residual stresses need a combination of energy-dispersive synchrotron (ED) and neutron diffraction. Essential for the stress distribution is the stress state before surface treatments which was determined by neutron diffraction. Results show that the maximum compressive stress and its depth play an important role to improve the fatigue performance.

Toughening of poly(L‐lactide) by melt blending with rubbers

AbstractPoly(L‐lactide) (PLA) was melt‐blended with four rubber components—ethylene–propylene copolymer, ethylene–acrylic rubber, acrylonitrile–butadiene rubber (NBR), and isoprene rubber (IR)—in an effort to toughen PLA. All the blend samples exhibited distinct phase separation. Amorphous PLA constituted a topologically continuous matrix in which the rubber particles were dispersed. According to Izod impact testing, toughening was achieved only when PLA was blended with NBR, which showed the smallest particle size in its blend samples. In agreement with the morphological analysis, the value of the interfacial tension between the PLA phase and the NBR phase was the lowest, and this suggested that rubber with a high polarity was more suitable for toughening PLA. Under the tensile stress conditions for NBR and IR blend samples, these rubbers displayed no crosslinking and showed a high ability to induce plastic deformation before the break as well as high elongation properties; this suggested that the intrinsic mobility of the rubber was important for the dissipation of the breaking energy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

A Comparative Study of Nanosilica/Poly(propylene) Composites Prepared by Reactive Compatibilization

AbstractA comparative study of nano‐SiO2/PP composites prepared by reactive compatibilization was conducted. Nano‐SiO2 was first grafted with three polymers bearing specific reactive groups. The grafted particles were then melt‐compounded with functionalized and matrix PP. Due to the reaction between the grafted polymers and functionalized PP, nano‐SiO2 was covalently connected to the matrix and the mechanical properties of the nanocomposites were significantly improved. It was found that chain flexibility of the graft polymers is critical for inducing plastic deformation of the matrix, provided that interfacial chemical bonding has been built up.magnified image

Bending Deformation of Single-Walled Carbon Nanotubes Caused by 5–7 Pair Couple Defect

The characteristics of 5–7 pair couple defects formed in single-walled carbon nanotubes were investigated. For armchair nanotubes with diameters from 6.8 to 13.6 Å, such defects were formed by removing atoms. Structural optimization, which was carried out using tight-binding molecular dynamics, resulted in the bending deformation of the nanotubes due to the defects. The resulting stable structure was found to change with the number of atoms removed, showing a bending angle of 16.6° for a diameter of 10.7 Å. The dependence of bending angle on the diameter of nanotubes was analysed using a simple model. As results, several sets of 5–7 pair couple defects were found to be necessary in order to induce plastic deformation that was experimentally observed in nanotubes.

Phenomenological Mechanism of Transformation Plasticity and the Constitutive Law Coupled with Thermo-Mechanical Plasticity

Phenomenological mechanism of transformation plasticity is proposed in the first part of the paper by use of simple model why stress in mother phase increases to reach yielding due to progressing new phase and to induce plastic deformation even under small applied stress. Based on the discussion, a unified constitutive model including transformation-induced and ordinal thermomechanical plastic strain rates by introducing an effect of varying phases during phase transformation into yield function. Thus derived constitutive equation is applied to describe strain response under varying temperature and stress with some discussions as well as metallo-thermo-mechanical simulation of quenching.

Effect of vibration on flow properties of fine glass beads

AbstractAn estimation of cohesion C and angle of internal friction φ of fine glass beads, which have been previously subjected to small intensity vertical vibrations of controlled frequency and amplitude for a fixed period of time, is presented. In the range of vibration intensities tested previbration causes powder compaction. Experimental measurements to obtain C and φ have been performed by means of a centrifuge powder tester in which the previbrated powder bed is rotated around its vertical axis. At a critical rotation velocity the shear stress induced by rotation is large enough to drive material avalanches. From a theoretical analysis of these avalanches, based on the Coulomb's method of wedges, C and φ are derived. We have found a significant increase of cohesion, and a slight decrease of the angle of internal friction as the effective consolidation stress due to previbration is increased. The estimated interparticle cohesion force ft from the experimental measurements, and using a Rumpf's averaging equation, is in agreement with the calculated interparticle attractive force due to van der Waals and capillary interaction for the unconsolidated beds. Moreover ft increases as the effective consolidation stress is increased in agreement with estimations from theoretical models based on contact plasticity. This result suggests that, at the microscopic level of asperities, compaction due to previbration is able to induce plastic deformation of the contacts. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Modeling Crack Initiation and Propagation in Nickel Base Superalloys

Nickel base superalloys are the primary class of materials used in the manufacture of high temperature components for gas turbine aeroengines, including combustion casings and liners, guide vane and turbine blades and discs, etc. These components are subjected to complex cyclic loading induced by the combination of mechanical loading, changing temperatures and thermal gradients, inducing plastic deformation and creep, that ultimately may lead to crack initiation and propagation. The purpose of the present paper is to provide a necessarily brief overview of recent modeling activities in this field, including polycrystalline crystal plasticity modeling for the study of crack initiation, coupled non-local damage-plasticity modeling for crack initiation and propagation studies, and the incorporation of time and environment dependent processes (creep and oxidation) in the predictive modeling of fatigue crack growth rates in nickel base superalloys.

Friction and Wear Mechanisms of Nanocrystalline Nickel in Ambient and Inert Atmospheres

The role of testing environment on the friction and wear behavior of nanocrystalline (nc) Ni with a grain size of 15 ± 3 nm and a hardness of 519 ± 11 Hv has been studied in comparison with microcrystalline (mc) Ni with a grain size of 20 ± 5 μm and a hardness of 122 ± 5 Hv. Coefficients of friction (COFs) and wear rates were measured in ambient air and argon environments using a pin-on-disc tribometer operated at a constant load of 2 N and a sliding speed of 0.1 m/s against a spherical Al2O3 counterface (H = 1,900 ± 40 Hv). The initial contact pressure exerted by the counterface (1.56 GPa) was sufficiently high to induce plastic deformation on the contact surface of the mc Ni but not on the surface of the nc Ni for which the initial wear rate in the first eight cycles was almost two orders of magnitude smaller (Wi (mc) = 7.88 × 10−3 mm3/m, and Wi (nc) = 0.16 × 10−3 mm3/m). Both samples showed higher wear rates when tested in argon, but again the initial wear rate of the nc Ni was much lower (i.e., during the first eight cycles, WiAr (mc) = 9.97 × 10−3 mm3/m and WiAr (nc)= 0.22 × 10−3 mm3/m). In both atmospheres, the COF curves increased rapidly and exhibited a peak before they decreased to a steady-state value. The peak value of the COF for the nc Ni was less than that of the mc Ni in air (COFp (mc) = 0.71, and COFp (nc) = 0.58) as well as in argon (COFpAr (mc) = 1.14, and COFpAr (nc) = 0.77). Steady-state wear conditions in both samples were reached earlier in air than in argon. Compared to the mc Ni, the nc Ni maintained lower steady-state wear rates in both air (Wss (mc) = 0.13 × 10−3 mm3/m, and Wss (nc) = 0.03 × 10−3 mm3/m) and argon (WssAr (mc) = 0.18 × 10−3 mm3/m, and WssAr (nc) = 0.07 × 10−3 mm3/m) environments. The wear track of the nc Ni was continuously widened by the scratching action of the counterface. In the ambient atmosphere, oxidized debris particles became agglomerated, forming a compacted protective tribolayer on the top of the wear track of the nc Ni. In the argon atmosphere, the tribolayers were discontinuous, covering about half of the wear tracks, and had lower hardness because of their lesser oxide content, resulting in higher steady-state wear rates and COF values (COFss (nc) = 0.41, and COFssAr (nc) = 0.58).

Special Issue on the Magnetic and Electric Field Effects at the Micro- and Nano-Scale Systems and Flows in Material Processing

Special Issue on the Magnetic and Electric Field Effects at the Micro- and Nano-Scale Systems and Flows in Material Processing

Effect of oxygen content and microstructure on the thermo-mechanical response of three Ti–6Al–4V alloys: Experiments and modeling over a wide range of strain-rates and temperatures

Results from a series of experiments on three different titanium alloys, under quasi-static and dynamic loading conditions are presented. The Ti–6Al–4V titanium alloys include the ELI version and two with higher oxygen contents. The strain-rates are varied from 10 −6 to 3378 s −1 while observations are made at temperatures from 233 to 755 K. The alloys initial and deformed photomicrographs and various deformation mechanisms responsible for the induced plastic deformation, are presented and discussed. Differences in the responses of these alloys are observed in terms of thermal softening, work hardening, and strain-rate and temperature sensitivities. The Khan–Huang–Liang (KHL) model is used to effectively simulate the observed responses obtained from these experiments. The model, with the constants determined from these experiments, is then used to predict strain-rate jump experimental results, and also high temperature dynamic experiments for one of the alloys; the predictions are found to be very close to the observations.

Combining high-speed laser perforation and cold roll forming for the production of biomedical microfiltration membranes

A novel high speed two-step technique capable of performing large matrices of very small pores with micron dimensions in large sheets of thin stainless steel foils has been developed. This process combination is initiated by high-speed “on-the-fly” laser perforation. A 100 W fiber laser is capable of a very high drilling rate making it an attractive option for the creation of large drilling matrices and pore widths <20 μm. The second step consists in cold-roll forming of the previously laser microperforated foil. This mechanically induced plastic deformation leads to a pore size reduction in one dimension perpendicular to the rolling direction. The minimum pore width determines the filtration parameters and the 5 μm pore width achieved here is well suited for the removal of spherical particles.

Shape memory behavior of Ti–Ni–Cu thin films

Three kinds of Ti-rich Ti–Ni–Cu thin films (Ti 51.9Ni 41. 6Cu 6.5, Ti 51.6Ni 36.8Cu 11.6, Ti 51.5Ni 33.1Cu 15.4) and three kinds of (Ni, Cu)-rich Ti–Ni–Cu thin films (Ti 48.9Ni 44.9Cu 6.2, Ti 48.5Ni 40.0Cu 11.5, Ti 48.6Ni 35.9Cu 15.5), numbers indicate at.%, were prepared by sputtering and annealed at 773, 873 and 973 K for 1 h. X-ray diffraction patterns showed that the Ti-rich thin films contain Ti 2Ni and Ti 2Cu phases, while the (Ni, Cu)-rich thin films contain a TiNiCu phase. The B2 → B19′ martensitic transformation occurred below 10 at.% Cu, while the B2 → B19 martensitic transformation occurred above 10 at.% Cu. The transformation temperature increased with increasing Cu content and annealing temperature. The temperature hystereses were small compared with those of Ti–Ni binary alloy thin films. The maximum recoverable strain decreases with increasing annealing temperature. It also decreases with increasing Cu content when the Cu content is more than 10 at.%. The critical stress for inducing plastic deformation increases with decreasing annealing temperature and increasing Cu content.

Nanoindentation-induced deformation in Al–Pd–Mn single quasicrystals

Nanoindentation experiments were performed at room temperature on Al–Pd–Mn single quasicrystals to induce plastic deformation in very localized areas and to examine microscopic mechanisms taking place in the bulk. Nanoindentation imprints investigated by transmission electron microscopy revealed the presence of grains and crystalline phases, but did not provide any evidence of dislocation activity. Pop-in events observed on the nanoindentation curves support the idea of grain formation and phase transformation just beneath the indenter, as shown by transmission electron microscopy.

Hydrodynamic impact: Numerical and experimental investigations

This paper deals with the slamming phenomenon experienced by ships during impact between the bow and the water free surface. Slamming loads on ships may be sufficiently important to induce plastic deformation of the hull external structure. For extreme loading cases, they have been identified as the cause of ship loss. The problem to be solved is transient and highly nonlinear due to the complex water flow conditions. In the present paper, the three-dimensional Wagner problem is solved numerically using the finite element method. A numerical analysis is performed for both rigid and deformable structures. After this numerical analysis, an original experimental investigation is presented. It consists of a series of free fall drop-tests of rigid and deformable cone-shaped samples with different deadrise angles and thickness. Distribution and evolution of pressure are analyzed. Finally, our numerical results are successfully compared with experimental data.

Thermodynamic Theory of Light-Induced Material Transport in Amorphous Azobenzene Polymer Films

It was discovered 10 years ago that the exposure of an initially flat layer of an azobenzene-containing polymer to an inhomogeneous light pattern leads to the formation of surface relief structures, accompanied by a mass transport over several micrometers. However, the driving force of this process is still unclear. We propose a new thermodynamic approach that explains a number of experimental findings including the light-induced deformation of free-standing films and the formation of surface relief gratings for main inscription geometries. Our basic assumption is that under homogeneous illumination, an initially isotropic sample should stretch itself along the polarization direction to compensate the entropy decrease produced by the photoinduced reorientation of azobenzene chromophores. The magnitude of the elastic stress, estimated by taking the derivative of the free energy over the sample deformation, is shown to be sufficient to induce plastic deformation of the polymer film. Orientational distributions of chromophores predicted by our model are compared with those deduced from Raman intensity measurements.

Width reduction of laser microdrillings by subsequent mechanically induced plastic deformation

This work reports a novel process combination, which is capable of forming large hole matrices (100 pores/mm2) in thin stainless steel foils (10 μm<dfoil<300 μm) maintaining high processing rates and pore widths smaller than 5 μm. This technique perforates stainless steel foils with high-speed ‘on-the-fly’ laser perforation (60000 drillings/min) followed by a cold-roll forming of the laser-treated foil. The cold-roll forming leads to a pore-size reduction (in one dimension) perpendicular to the rolling direction. For the laser processing a diode-pumped, q-switched and frequency-tripled Nd:YAG laser (λ=355 nm, τ=30 ns), and a flashlamp-pumped Nd:YAG laser (λ=1064 nm, τ=57 μs) were applied. Using this process combination, minimum pore sizes of 3.5 μm have been achieved. At present, the processing efficiency of cold-rolled percussion drillings inserted with nanosecond pulse durations is lower in comparison with single-pulse ‘on-the-fly’ perforation, but in terms of quality (straight pore channel, low standard deviation of pore widths and pore widths smaller than 5 μm) well suited for various fields in filtration (e.g. particle removal) .

Micromechanics approach to the magnetoelectric properties of laminate and fibrous piezoelectric/magnetostrictive composites

We use a micromechanics approach to study the magnetoelectric (ME) properties of the piezoelectric/magnetostrictive composite with a 2–2 laminate structure and a 3–1 fibrous structure. It is found that the 3–1 composite has a higher ME coefficient than the 2–2 one, if the volume ratio of piezoelectric material is the same. The reason is that the 3–1 fibrous composite makes use of the longitudinal piezoelectric response and the piezoelectric voltage constant g33 is 2–3 times that of g31. Generally, a smaller volume ratio of the piezoelectric material will generate a higher ME response. The tensile stress at the piezoelectric/magnetostrictive interface of the 3–1 fibrous composite, however, could be high enough to induce plastic deformation or microcracks, which leads to a ME coefficient lower than the theoretically predicted one.

Plastic deformation of wadsleyite: I. High-pressure deformation in compression

We have studied the plastic deformation of Mg2SiO4 wadsleyite polycrystals. Wadsleyite was synthesized from a forsterite powder in a multianvil apparatus. It was then recovered and placed in a second multianvil assembly designed to induce plastic deformation by compression between two hard alumina pistons. After the deformation experiment, the microstructures are characterized by transmission electron microscopy (TEM) and large-angle convergent beam electron diffraction (LACBED). Deformation experiments have been carried out at 15–19 GPa and at temperatures ranging from room temperature to 1800–2000 °C. Five different dislocation types have been identified by LACBED: [100], 1/2〈111〉, [010], 〈101〉 and [001]. The [001] dislocations result from dislocation reactions and not from activation of a slip system. The [010] dislocations are activated under high stresses at the beginning of the experiments and further relax by decomposition into 1/2〈111〉 dislocations or by dissociation into four 1/4[010] partial dislocations. The following slip systems have been identified: 1/2〈111〉{101}, [100](010), [100](001), [100]{011}, [100]{021}, [010](001), [010]{101} and 〈101〉(010).

Continuous in situ measurement of quenching distortions using computer vision

A heat treatment vacuum furnace equipped with a CCD camera is used to follow the shape evolution of two axisymmetric steel samples during gas cooling. The experimental results are compared with numerical simulations performed with the finite element technique. A good agreement is obtained between the theoretical predictions and experiments. The shape evolution of metallic samples are measured experimentally and simulated numerically during all the cooling processes. The accuracy of the measurement is 0.01 mm, while the dimensions of the samples are 40 mm diameter and 80 mm height. Stepwise increasing hole diameters are used in the samples to amplify the shape changes during quenching. The first steel sample does not exhibit phase changes during cooling. The shape evolution is only due to thermal shrinking. Since residual distortions are not observed, the thermal gradients generated during these experiments are not large enough to induce plastic deformation. The second steel sample presents a martensitic transformation during cooling. The shape changes are thus due to both thermal shrinking and phase changes. The residual distortions observed can be attributed to transformation plasticity. It turns out that this physical phenomenon can be studied by the experimental set-up described in this paper.

Plastic deformation of minerals under extreme pressure using a multi-anvil apparatus

We describe recent progress in the achievement of high-pressure deformation experiments using the multi-anvil apparatus. This equipment allows experiments to be performed on samples that are several cubic millimeters in volume at pressures up to 26 GPa, corresponding to the uppermost lower mantle of the earth (700 km depth), and temperatures up to 2500 K. The high-pressure assemblies have been modified to induce plastic deformation under high-P, high-T conditions.