A new approach to joining of bulk copper using microwave energy

Metallurgical joining of high thermal conductivity materials like copper has been technically challenging. This paper illustrates a novel method for joining of bulk metallic materials through microwave heating. Joining of copper in bulk form has been carried out using microwave energy in a multimode applicator at 2.45 GHz and 900 W. Charcoal was used as susceptor material to facilitate microwave hybrid heating (MHH). Copper in coin and plate forms have been successfully joined through microwave heating within 900 s of exposure time. A sandwich layer of copper powder with approximately 0.5 mm thickness was introduced between the two candidate surfaces. Near complete melting of the powder particles in the sandwich layer does take place during the microwave exposure leading to metallurgical bonding of the bulk surfaces. Characterisation of the joints has been carried out through microstructure study, elemental analysis, phase analysis, microhardness survey, porosity measurement and tensile strength testing. X-ray diffraction (XRD) pattern indicates that some copper powder particles got transformed into copper oxides. XRD analysis also reveals that the dominant orientation (3 1 1) in starting copper powder got transformed into a preferential orientation (1 1 1) in the joint. A dense uniform microstructure with good metallurgical bonds between the sandwich layer and the interface was obtained. The hardness of the joint area was observed to be 78 ± 7 Hv, while the porosity in the joint was observed to be 1.92%. Strength character of the copper joints shows approximately 29.21% elongation with an average ultimate tensile strength of 164.4 MPa.     

Investigation into effect of rubber bushing on stress distribution and fatigue behaviour of anti-roll bar

Anti-roll bars used in ground vehicle to reduce body roll by resisting any uneven vertical motion between the pair of wheels suffer from fatigue failure. In this study, several structural analyses of an anti-roll bar made of SAE 9262 were carried out by means of finite element (FE) technique to determine stress distributions. The result of FE analyses indicated that equivalent stress in the inner surface of the corner bend was the maximum; wherein the shear stress dominates. Fatigue tests that were carried out under 7° rotational loading also confirmed the failure location. In addition, the effects of hardness and wall thickness of rubber used in bushing on stress distribution were investigated for various polyurethane rubbers (75, 85, 90 and 95 Shore A) and bush wall thickness (5.25, 7 and 8.75 mm), systematically. It was found that both soft rubber and thick wall thickness tend to reduce stress in the critical region. Based on the results of FE analyses, several proof tests of anti-roll bars with specific bushing were planned. It was concluded that the reduction of equivalent stress in anti-roll bar accomplished by modifying the bushing provided a significant improvement in the fatigue life. Approximately 9% improvement in the fatigue life with respect to base bushing could be obtained by selecting relatively soft rubber materials. For the rubber hardness 75 Shore A, changing in wall thickness from 7 mm to 8.75 provided 11% improvement. Total improvement from the proof tests reached up to approximately 21% in the fatigue life.     

Plasma-carburization of nickel-based self-fluxing alloy

Surface hardening of Ni-based self-fluxing alloy was carried out using plasma-carburization. The carburization was performed utilizing methane glow discharge plasma on sintered Ni-based self-fluxing alloy (METCO 16C) at 977 °C and 1065 °C for 3.6 ks. The carburized surfaces were characterized by employing optical microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy and Vickers micro-hardness testing. The SEM and EPMA micrographs show that the thickness of the carburized hard layer increased with increasing temperature, to a depth of approximately 120-200 μm. Hard chromium carbide (Cr₃C₂) was found to precipitate near the surface on carburization at 977 °C more than at 1065 °C. Cr₃C₂ contributes to the surface hardening.     

Analysis of cold expanded fastener holes subjected to short time creep: Finite element modelling and fatigue tests

The beneficial effects of cold expansion have been well documented in previous studies, yet the performance of cold expanded plates exposed to elevated temperatures is an area of technical interest. In this research, finite element (FE) simulations along with experimental fatigue tests have been carried out to investigate the effect of exposure to elevated temperature on residual stress distribution and subsequent fatigue life of cold expanded fastener holes. According to the obtained results, creep stress relaxation occurs due to exposure to 120 °C for 50 h. FE results demonstrate a non-uniform residual stress relaxation regime through the plate thickness around the cold expanded hole and the fatigue test results show that the subsequent fatigue lives have significantly decreased.     

Enhanced wear and fatigue properties of Ti–6Al–4V alloy modified by plasma carburizing/CrN coating

In this study, a newly developed duplex coating method incorporating plasma carburization and CrN coating was applied to Ti–6Al–4V and its effects on the wear resistance and fatigue life were investigated. The carburized layer with approximately150 μm in depth and CrN coating film with 7.5 μm in thickness were formed after duplex coating. Hard carbide particles such as TiC And V₄C₃ were formed in the carburized layer. XRD diffraction pattern analysis revealed that CrN film had predominant [111] and [200] textures. The hardness (Hv) was significantly improved up to about 1,960 after duplex coating while the hardness value of original Ti–6Al–4V was 402. The threshold load for the modification and/or failure of CrN coating was measured to be 32 N using the acoustic emission technique. The wear resistance and fatigue life of duplex-coated Ti–6Al–4V improved significantly compared to those of un-treated specimen. The enhanced wear resistance can be attributed to the excellent adhesion and improved hardness of CrN coating film for the duplex-coated Ti–6Al–4V. The initiation of fatigue cracks is likely to be retarded by the presence of hard and strong layers on the surface, resulting in the enhanced fatigue life.     

The effect of composite damage on fatigue life of the high pressure vessel for natural gas vehicles

In order to examine how the damages such as scratches, cuts and gouges on the composite materials have effects on the fatigue life of NGV vessels, several experiments on real vessels were conducted and finite element analyses were applied. The flaw depths of COPV used in the experiments were 1.5 mm, 2.0 mm, 3.0 mm, and 4.0 mm, while the flaw lengths were 50 mm, 100 mm, and 200 mm. A flaw tolerance test defined by ANSI/IAS NGV2-2000 was performed on 12 vessels using a combination of these flaw depths and lengths. In the finite element analyses, stress analyses were performed using a commercial FEM program after the 3-D modelling of liner, hoop and helical layers by using MSC.PATRAN™. The result of the tests and analyses demonstrated that the effect of the flaw damages on the fatigue life of high pressure vessel for natural gas vehicles increases when the flaw depth is more than 3.0 mm and the flaw length is more than 100 mm.     

Failure Investigation of a Diesel Engine Piston Pin

Transverse and longitudinal cracking took place on a diesel engine piston-pin used in a truck in service. The external circle and internal hole surfaces of piston-pin are specified to be carburized. The cracks originated from the internal hole surface and propagated, by fatigue, towards the external circle. The microstructure and microhardness profiles indicate that the serious decarburization occurred on the internal hole surface and that the hardening case was not present. The occurrence of the decarburization in the surface region of the internal hole decreases the fatigue strength to levels far below those for a carburized surface so failure initiated easily at the internal hole surface. To assure against similar failures in the future, make sure that the region around the internal hole obtains the specified depth of hardened layer.     

Growth of 3C-SiC on 150-mm Si(100) substrates by alternating supply epitaxy at 1000 °C

To lower deposition temperature and reduce thermal mismatch induced stress, heteroepitaxial growth of single-crystalline 3C-SiC on 150 mm Si wafers was investigated at 1000 °C using alternating supply epitaxy. The growth was performed in a hot-wall low-pressure chemical vapor deposition reactor, with silane and acetylene being employed as precursors. To avoid contamination of Si substrate, the reactor was filled in with oxygen to grow silicon dioxide, and then this thin oxide layer was etched away by silane, followed by a carbonization step performed at 750 °C before the temperature was ramped up to 1000 °C to start the growth of SiC. Microstructure analyses demonstrated that single-crystalline 3C-SiC is epitaxially grown on Si substrate and the film quality is improved as thickness increases. The growth rate varied from 0.44 to 0.76 ± 0.02 nm/cycle by adjusting the supply volume of SiH₄ and C₂H₂. The thickness nonuniformity across wafer was controlled with ± 1%. For a prime grade 150 mm virgin Si(100) wafer, the bow increased from 2.1 to 3.1 μm after 960 nm SiC film was deposited. The SiC films are naturally n type conductivity as characterized by the hot-probe technique.     

A chevron specimen for the measurement of mixed-mode interface toughness of wafer bonds

Accurate characterization of interfacial adhesion is essential for the development of reliable wafer bonding processes. In most applications in which wafers are bonded, the interface experiences a combination of shear and normal loading (i.e., mixed-mode loading). When characterizing the fracture properties of a bond, it is important to measure the interface toughness under similar mixed-mode conditions. In the current work, a chevron test specimen composed of bonded cantilever layers of dissimilar thicknesses is analyzed, and the dependence of the mode mixity at the interface is determined as function of the layer thickness ratio. This test geometry is well-suited for the measurement of bonds between typical semiconductor substrates that range in thickness from 0.1 to 1 mm. A nominal specimen geometry with a total layer thickness of 0.5-2 mm and in-plane dimensions of 10 × 10 mm is analyzed using a 3-D finite element (FE) model in combination with the virtual crack closure technique. It is demonstrated that the phase angle (i.e. the degree of mode-mixity) at the interface can be varied from 0° to 35° by changing the layer thickness ratio from 1 to 0.1. The FE results have been fitted to an expression that allows the interface toughness to be easily calculated from experimental data.     

3D numerical simulations of sharp nosed projectile impact on ductile targets

Three-dimensional FE model is presented for perforation under normal and oblique impact of sharp nosed projectiles on single and layered ductile targets. Numerical simulations have been carried out to study the behavior of Weldox 460 E steel and 1100-H12 aluminum targets impacted by conical and ogive nosed steel projectiles respectively. Weldox 460 E steel targets of 12 mm thickness in single and double layered combination (2 × 6 mm) and 1100-H12 aluminum targets of 1 mm thickness in single and double layered combination (2 × 0.5 mm) impacted at 0°, 15° and 30° obliquity were considered for simulations. The results of monolithic and layered targets were compared for each angle of impact. Monolithic targets were found to have higher ballistic resistance than that of the layered in-contact targets of equivalent thickness. Failure of both the targets occurred through ductile hole enlargement. However, ogive nosed projectile failed 1 mm thick aluminum target through petal formation and conical nosed projectile failed 12 mm thick steel target through a circular or elliptical hole enclosed by a bulge at rear surface. The explicit algorithm of ABAQUS finite element code was used to carry out the numerical simulations. Various parameters which play critical role in numerical simulation such as element size and its aspect ratio have been studied.     

Producing nanostructured super-austenitic steels by friction stir processing

In the present work, friction stir processing (FSP) was used to produce the nanostructured super-austenitic steel. After preheating, the specimens were subjected to FSP using the rotation and traverse speed of 2600 rpm and 30 mm min⁻¹, respectively. The specimen temperature during FSP was about 950 ± 2 °C. The results show that a nanostructured layer of about 91 μm thick was produced on the specimen surface. The formed nanograins ranged from 50 to 90 nm. Besides, the hot severe deformation applied during FSP led to significant fragmentation of the coarse sigma particles to nanosize ones.The produced nanostructured layer was then characterized using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The formed nanostructure led to a twofold increase in the hardness. The formation of nanostructure resulted in an increase in hardness up to 350 Hv, comparing to 185 Hv pertaining to base structure of super austenitic steel.     

Improvement of thickness uniformity and crystallinity of AlN films prepared by off-axis sputtering

We improved both the thickness uniformity and crystallinity of Aluminum nitride (AlN) films deposited by off-axis sputtering. The results in thickness uniformity and X-ray rocking curve full-width at half-maximum (FWHM) of AlN (0 0 0 2) are achieved to be ±0.2% and 1.4°, respectively on a 100 mm Si (1 0 0) substrate. The residual stress can be controlled from tensile to compressive by varying sputtering parameters such as gas pressure, RF power and DC bias voltage applied to a substrate without degradation in the crystallinity and thickness uniformity.     

Perforation resistance of five different high-strength steel plates subjected to small-arms projectiles

Thin plates of high-strength steel are frequently being used both in civil and military ballistic protection systems. The choice of alloy is then a function of application, ballistic performance, weight and price. In this study the perforation resistance of five different high-strength steels has been determined and compared against each other. The considered alloys are Weldox 500E, Weldox 700E, Hardox 400, Domex Protect 500 and Armox 560T. The yield stress for Armox 560T is about three times the yield stress for Weldox 500E, while the opposite yields for the ductility. To certify the perforation resistance of the various targets, two different ballistic protection classes according to the European norm EN1063 have been considered. These are BR6 (7.62 mm Ball ammunition) and BR7 (7.62 mm AP ammunition), where the impact velocity of the bullet is about 830 m/s in both. Perforation tests have been carried out using adjusted ammunition to determine the ballistic limit of the various steels. In the tests, a target thickness of 6 mm and 6 + 6 = 12 mm was used for protection class BR6 and BR7, respectively. A material test programme was conducted for all steels to calibrate a modified Johnson–Cook constitutive relation and the Cockcroft–Latham fracture criterion, while material data for the bullets mainly were taken from the literature. Finally, results from 2D non-linear FE simulations with detailed models of the bullets are presented and the different findings are compared against each other. As will be shown, good agreement between the FE simulations and experimental data for the AP bullets is in general obtained, while it was difficult to get reliable FE results using the Lagrangian formulation of LS-DYNA for the soft core Ball bullet.     

Stress-dependence and time-dependence of the post-fatigue tensile behavior of carbon fiber reinforced SiC matrix composites

The major objective of this paper is to phenomenally report the stress-dependence and time-dependence of fatigue damage to C/SiC composites, and to tentatively discuss the effects of the fatigue stress levels and the fatigue cycles on the post-fatigue tensile behavior. Results show that compared with the virgin strength of the as-received C/SiC specimens, the tensile strengths of the as-fatigued specimens after 86,400 cycles were increased by 8.47% at the stresses of 90 ± 30 MPa, 23.47% at 120 ± 40 MPa, and 9.8% at 160 ± 53 MPa. As cycles continued, however, the post-fatigue strength of the composites gradually decreased after the peak of 23.47%, at which the optimal strength enhancement was obtained because the mean fatigue stress of 120 MPa was the closest to thermal residual stress (TRS), and caused TRS relieve largely during the fatigue. Most interestingly, there was a general inflexion appeared on the post-fatigue tensile stress-strain curves, which was just equal to the historic maximum fatigue stress acted upon the as-fatigued specimens. Below this inflexion stress the tensile curves revealed the apparent linear behavior with little AE response, and above that nonlinearity with new damage immediately emitted highly increase rate of AE activities. This ‘stress memory’ characteristic was strongly relevant to damaged microstructures of the as-fatigued composites in the form of the coating/matrix cracks, interface debonding/wear, and fiber breaking, which resulted undoubtedly in reduction of modulus but in proper increase of strength via TRS relief.     

Carbon particulate matter incineration in diesel engine emissions using indirect nonthermal plasma processing

One of the promising applications of nonthermal plasma (NTP) for environmental cleanup technology is low-temperature oxidation or incineration of carbon particulate matter (PM) in diesel engine emissions. In this process, NO₂ and activated radical species induced by NTP can incinerate carbon PM trapped by a diesel particulate filter (DPF) at low temperature (< 300 °C). In the present study, an experiment was carried out on indirect NTP DPF regeneration for real diesel engine emissions comprising CO₂ of several per cent, hydrocarbons of several hundreds of ppm and moisture of several tens of percentages. It was confirmed that DPF regeneration is possible for a real diesel emission at a low temperature of 280 °C. The removal energy efficiency was estimated to be 0.82 g/kW h. This electric power range is sufficient to meet the recently proposed long-term national regulation for diesel automobiles in Japan.     

Effect of retained austenite – Compressive residual stresses on rolling contact fatigue life of carburized AISI 8620 steel

In this study the rolling contact fatigue (RCF) of case carburized AISI 8620 steel was numerically and experimentally investigated. For the numerical study, a two dimensional finite element (FE) RCF model based on the continuum damage mechanics (CDM) was developed to investigate the fatigue damage accumulation, crack propagation and final fatigue life of carburized AISI 8620 steel under various operating conditions. A randomly generated Voronoi tessellation was used to model the effects of material microstructure topology. The boundaries of the Voronoi elements were assumed to be the weak planes where damage accumulates, cracks initiate and propagate to simulate inter-granular cracks. A series of torsional fatigue tests were conducted on carburized AISI 8620 steel specimens containing 0% and 35% retained austenite (RA) to determine fatigue load (S) vs. life (N) of the material. The S–N results were then used to determine the material parameters necessary for the rolling contact fatigue model. The torsional fatigue test results indicate that the carburized AISI 8620 specimens with higher RA demonstrate higher life than the specimens with lower RA. The RCF model also indicates that the material with higher level of compressive residual stresses (RS) and retained austenite demonstrates higher RCF life. In order to corroborate the results of RCF model, a three-ball-on-rod rolling contact fatigue test rig was used to determine the RCF lives of carburized AISI 8620 steels with different amounts of RA. The fatigue life and cracks evolution pattern from the numerical and experimental results were corroborated. The results indicate that they are in good agreement.     

Mechanical alloying behavior of Ti6Al4V residual scraps with addition of Al2O3 to produce nanostructured powder

The present investigation has been based on production and subsequent comparison of different physical, mechanical and thermal properties of nanostructured Ti6Al4V and Ti6Al4V/Al₂O₃ powders by means of high energy ball milling. In this regard, the structural and morphological changes of powders were investigated by X-ray diffraction, scanning electron microscopy and microhardness measurements. The results revealed that ball milling process reduced the grain size of Ti6Al4V and Ti6Al4V + 10 wt% Al₂O₃ to approximately 20 and 15 nm, respectively. For both compositions also a remarkable change in morphology and particle size occurred during ball milling of powders with different compositions. Moreover, phase evolution during milling and heat treatment was taken into consideration. The as-milled Ti6Al4V + 10 wt% Al₂O₃ powder exhibited higher microhardness (∼900 Hv) comparing to as-milled Ti6Al4V (∼536 Hv) and as-received samples (∼400 Hv).     

Optimum thickness of joints made of GFPR pultruded adherends and polyurethane adhesive

This paper presents results of experimental and numerical investigations on double-lap joints composed of pultruded GFRP profiles and polyurethane adhesive subjected to quasi-static axial tensile loading. The objective was to investigate the effect of the joint geometry on the structural response of adhesively-bonded joints and, in particular, to seek for experimental evidence of an optimum adhesive layer thickness. The influence of the adhesive thickness (0.3–10.0 mm) and the overlap length (50–200 mm) on the joint behavior was investigated. It was found that there is an optimum adhesive thickness of approximately 1.0 mm and joint strength consistently increases with the overlap length.     

Application of different concepts for fatigue design of welded joints in rotating components in mechanical engineering

Several concepts are used for the fatigue design of welded joints. In this paper investigations are presented, which were carried out in a joint project between five research institutes [1]. The aim is to investigate currently applied fatigue concepts with respect to their limitations, compatibility and reliability, in order to improve the accuracy of lifetime estimation and to simplify the choice of the optimum fatigue concept. Here, the results of the investigation of welded joints in rotating universal joint shafts are shown [2]. In the critical weld, a structural steel and a quenched and tempered steel are joined. In practice, stresses result from rotating bending, torsion and also residual stresses are sometimes present. Several welding techniques, MAG, TIG and laser welding, and two seam geometries were investigated with regard to their influence on fatigue strength. Experiments were conducted with welded tube specimens representative of the actual component application and with derived flat specimens as detail specimens. The welded sheet thickness was 5.5 mm. Fatigue strength was investigated from 10⁴ to 10⁷ numbers of cycles. In numerical analyses, nominal stress, structural hot spot stress and elastic notch stress with reference radii of 0.3 mm and 0.05 mm were calculated. In the comparison of the concepts, their respective advantages and disadvantages have been demonstrated. A comparison of the results with the IIW recommendation for fatigue design of welded joints and components [3] has been carried out and improvements have been suggested.