Search results

This paper aims to deal with the study of interaction between multiple cracks in an aluminum alloy under static loading. Self-similar as well as non-self-similar crack growth has been observed which depends on the relative crack positions defined by crack offset distance and crack tip distance. On the basis of experimental observations, the conditions for crack coalescence, crack shielding, crack interaction, crack initiation, etc. are discussed with respect to crack position parameters. Considering crack tip distance, crack offset distance, crack size and crack inclination with loading axis as input parameter and crack initiation direction as output parameter, an artificial neural network (ANN) model is developed. The model results were then compared with the experimental results. It was observed that the model predicts the crack initiation direction under monotonic loading within a scatter band of ±0.5°.

The study is based on the experimental observations. Growth studies are made from the growth initiation from two cracks in a rectangular aluminium plate under static loading. The present study is focused on the influence of crack position defined by crack offset distance and crack tip distance on growth direction. In addition to this, ANN has been used to predict crack growth direction in multiple crack geometry under static loading. The predicted results have been compared with the experimental data.

The influence of the interaction between multiple cracks on crack extension angle greatly depends on the relative position of cracks defined by crack tip distance S, crack offset distance H and crack inclinations with respect to loading direction. The intensity of the crack interaction can be described according to degree of crack extension angle and relative crack position factors. It is also observed that the progress of the outer and inner crack tip direction is different which mainly depends on the relative crack position.

It is limited to static loading only. Under fatigue loading findings may differ.

It is important to investigate the growth behaviour under multiple cracks and also to know the effect of crack statistics on the growth behaviour to estimate the component life. The study also focused on the development of a high quality predictive method.

The results show trends that vary with crack geometry condition and the ANN and empirical solution provides a possible solution to assess crack initiation angle under multiple crack geometry.

The purpose of this paper is to examine the formation of surface damage associated with the ultrasonic consolidation (UC) of single ply 150 μm thick 3003‐H18 foil to a 3003‐18 build plate and the relationship between the development of this damage state with the linear weld density (LWD) achieved during consolidation.

The influence of the consolidation control variables on the area fraction of the sonotrode induced top foil surface damage is established through application of a full factorial three‐level design‐of‐experiment methodology, the control variables limits being fixed by the capability of the UC system.

Detailed analysis of the foil top surface structure after consolidation reveals the presence of two characteristic, damaged and undamaged, regions. The former corresponded to plastically deformed areas, these being formed as a result of interaction of the foil top surface with the sonotrode, while the latter corresponded to the original foil surface. Sonotrode normal load, vibrational amplitude and its rotational velocity are found to have an interdependent affect on the development of the sonotrode‐induced top surface damage. Top surface damage initiates upon impression of the sonotrode into the foil surface followed by the commencement of oscillatory and forward rotational motion of the sonotrode. Finally, evidence is presented that the degree of sonotrode induced top surface damage bears a direct relationship with the linear ultrasonic weld density developed at the foil‐build plate interface, increasing top surface damage being associated with increased LWD.

A linear relationship between the degree of bonding at the foil‐build plate interface and the plastically deformed area on the foil top surface is established, this correlation demonstrating that bond formation between foils during UC depends on effective frictional conditions at the sonotrode‐foil interface.

This chapter briefly summaries research over the past four decades (and prior) associated with black men and mental health in the UK. The chapter also examines some responses to the research. This is because we unfortunately remain in a situation where black men in Britain are 17 times more likely than white counterparts to be diagnosed with a psychotic illness. Research into the mental health needs of black men has been conducted repeatedly in the UK, with each new generation hopeful for change. By briefly exploring some policies that have emerged to address this inequality, this chapter highlights the barriers to change.

The parameters solution temperature, intermediate treatment and cooling rate (from high temperature and after tempering) were examined by statistical multiple factor analysis. Tempering temperature (200 to 650°C) and duration (4 to 64 h) were graded exhaustively.

Quasi shear and tensile mode stress‐rupture and quasi shear mode creep behaviours were investigated for aged production surface mount soldered connections of 127 mm pitch, rigid gullwing and J‐bend configurations at ambient and 60°C (on limited specimens) environments. These joints were manufactured by the vapour phase reflow soldering process using a 63Sn‐37Pb solder composition. Metallographic examinations and fractrographic studies were also performed on appropriate specimens to characterise the metallurgical attributes of the solder and the joint failure. A relatively coarse solder microstructure was observed with both joint configurations. The steady‐state creep data of both soldered joints exhibited two distinct creep regimes. A grain boundary‐controlled regime at low loads with a slope of 042 for gullwing and 0?50 for J‐bend joints was followed by a dislocation climb‐controlled regime at high loads with a slope of 0?13 and 0?24 for gullwing and J‐bend configurations, respectively. The log‐log plot of applied load varied linearly with rupture time for the entire load range for the respective soldered joints for both modes of testing at room temperature. A transgranular fracture morphology was found to predominate for the entire load regime for the quasi shear mode tested gullwing joints. A mixed‐mode fracture morphology with predominantly transgranular features was observed for both low and high loading conditions for quasi shear mode tested J‐bend specimens. The steady‐state creep elongation in shear showed a strong dependence on the applied load for both types of soldered joints. This was primarily attributed to the presence of relatively large creep transients, especially at higher loads.

Telecom equipment is subject to thermal cycles caused by both variations in temperature between day and night and variations in the telephone traffic. To simulate such thermal excursions, accelerated thermal cycle testing between — 10°C and 100°C has been established as a standard method within Ericsson Telecom. Thermal cycle tests have been carried out for frequencies ranging from one cycle per day to 30 cycles per hour in order to cover the different thermal excursions that occur in telecom equipment. It has been found that the life of a surface mounted PWB assembly can be predicted from the accelerated testing results using a frequency modified Coffin‐Manson relation. Factors which influence the fatigue life of solder joints such as solder material, compliant leads, compliant surface layers and mismatch between package and board are discussed. Based on results from accelerated testing it is suggested that the optimal PWB design for leadless ceramic chip carriers should be a moderate TCE matching combined with a compliant surface layer.

This paper aims to investigate the influence of laser energy density on microstructure and mechanical properties of the selective laser melted (SLMed) Ti6Al4V to complement the existing knowledge in additive manufacturing of Ti6Al4V for future application of selective laser melting (SLM) in fabricating Ti6Al4V parts.

Ti6Al4V alloy is fabricated by SLM by adopting various energy densities. Microstructures and mechanical properties of the Ti6Al4V deposited using different energy densities are characterized.

Both high relative densities and microhardness can be obtained in the optimized processing window. The decrease of martensite width and spacing can improve the microhardness on both XOY and XOZ sections when the applied E_V (defined as the laser energy per unit volume) increases. The width of the columnar grain increases with E_V, resulting in a stronger anisotropy in microhardness between XOY and XOZ sections. Residual tensile stresses exist in the SLMed Ti6Al4V and increase with an increasing E_V. A tensile strength of 1,268 MPa, a yield strength of 1,030 MPa, and an elongation of 4% can be obtained by using the optimized range of E_V.

The microstructure of SLMed Ti6Al4V is quantitatively analysed by measuring the size of columnar grains and the martensites. The anisotropy of microstructures and properties in SLMed Ti6Al4V is characterized and its dependence on laser energy density is established. The residual stress in SLMed Ti6Al4V is characterized and its dependence on laser energy density is established. An optimized processing window to deposit Ti6Al4V alloy by SLM is proposed.

The purpose of this technical paper is to investigate the friction and wear behaviour of heat treated Al 6061 alloy and Al 6061 SiC‐graphite particulate reinforced hybrid composites subjected to different ageing durations.

The composites have been prepared by stir casting process with varying percentages of SiC and graphite particles. The cast 6061 alloy and its composites were subjected to solutionising treatment at a temperature of 803 K for 1 hr followed by quenching in water. The quenched samples were then subjected to artificial ageing for different durations of 4, 6, 8 hr at a temperature of 448 K. Tests were performed on heat treated Al 6061 alloy and its composites using pin‐on‐disc apparatus. Hardness measurements were also made on the specimens. The wear surfaces of the composites were analyzed using scanning electron microscopy.

During wear test of specimens the wear resistance of the hybrid composites was found to increase with increase in ageing durations. The microscopic examination of the wear surfaces shows that the base alloy and composites wear primarily because of abrasion and delamination. The hardness result shows that the hardness of the composites increased with decreasing weight percentage of graphite particles.

The content of this paper is fully research oriented and the finding from this investigation will be useful for society and also the automobile industries, especially in the making of brake drums.

This paper aims to study the wear properties of electron beam melted Ti6Al4V (EBM-Ti6Al4V) in simulated body fluids for orthopedic implant biomedical applications compared with wrought Ti6Al4V (Wr-Ti6Al4V).

Wear properties of EBM-Ti6Al4V compared with Wr-Ti6Al4V against ZrO₂ and Al₂O₃ have been investigated under dry friction and the 25 Wt.% newborn calf serum (NCS) lubricated condition using a ball-on-disc apparatus reciprocating motion. The microstructure, composition and hardness of the samples were characterized using scanning electron microscopy (SEM), x-ray diffraction and a hardness tester, respectively. The contact angles with 25 Wt.% NCS were measured by a contact angle apparatus. The wear parameters, wear 2D and 3D morphology were obtained using a 3D white light interferometer and SEM.

EBM-Ti6Al4V yields a higher contact angle than the Wr-Ti6Al4V with the 25 Wt.% NCS. EBM-Ti6Al4V couplings exhibit lower coefficients of friction compared with the Wr-Ti6Al4V couplings under both conditions. There is only a slight difference in the wear resistance between the Wr-Ti6Al4V and EBM-Ti6Al4V alloys. Both Wr-Ti6Al4V and EBM-Ti6Al4V suffer from similar friction and wear mechanisms, i.e. adhesive and abrasive wear in dry friction, while abrasive wear under the NCS condition. The wear depth and wear volume of the ZrO₂ couplings are lower than those of the Al₂O₃ couplings under both conditions.

This paper helps to establish baseline bio-tribological data of additively manufactured Ti6Al4V by electron beam melting in simulated body fluids for orthopedic applications, which will promote the application of additive manufacturing in producing the orthopedic implant.

There is still a need for a comprehensive investigation into how wire and arc manufactured (WAAM) parts fail under cyclic loading. This study investigates the effect of process-induced defects on the high-cycle fatigue performance of WAAM-processed Ti-6Al-4V with dedicated thermal treatment. Furthermore, the study assesses the applicability of the fatigue life prediction model, which was originally developed and validated for laser beam-welded Ti-6Al-4V joints, to WAAM-fabricated structures.

The fatigue life assessment model was adapted to WAAM-fabricated Ti-6Al-4V. This model is based on the NASGRO equation, which considers short crack growth from internal and surface defects, such as lack of fusion defects and pores. The model was used to create artificial Wöhler curves, and the results from stress intensity factor range-decreasing fatigue crack propagation rate tests are compared to the experimental data in the form of a Kitagawa–Takahashi (KT) diagram.

The results demonstrate that the model can accurately predict the minimum fatigue life of specimens extracted from WAAM structures. When considering that the crack from internal defects grows in a vacuum-like environment, accurate Wöhler curves are predicted. The experimental data does not follow the expected trends of the KT diagram. Nonetheless, the measured long crack threshold stress intensity factor range produces a suitable estimate of defect severity.

The study results in a model with which a probabilistic computation of the fatigue life of additively manufactured samples based on the defect size distribution is possible. Furthermore, the KT diagram as a criterion for the assessment of defect severity is evaluated.