Material Design & Processing Communications最新文献

First published: 08 August 2019 https://doi.org/10.1002/mdp2.101

The authors would like to draw attention to the following error:

In Section 2.1: Prototypes configuration and materials, the thickness of the foils was incorrectly stated as 50 mm. The correct value is 50 μm.

The paragraph should appear as follows:

‘Two types of prototypes were built, either with a single or double target material cylinders. The single-cylinder prototypes were produced to study the target to cladding materials bonding whilst the double-cylinder prototypes were produced to study the target to target materials bonding. Ta foils were eventually introduced between the materials as diffusion interfacial aids. The foils’ thickness was fixed in 50 μm, following literature recommendations, to maximize the bonding strength.14, 18 The two types of prototypes are represented in Figure 2 with their respective components'.

The authors apologise for any misunderstanding arising from this error.

Fretting and fretting fatigue are important considerations to be made in the design and development of medium-speed reciprocating engines. Predictive capabilities for safe-life design often rely on very simple empirical parameters and experience. Practices are briefly reviewed, and opportunities for more sophisticated methodologies are highlighted. It is concluded that more research into fretting fatigue with complex load sequences are needed.

Early observations of cracks protect the teeth. The crack in teeth initiates due to the flaws, defect, or inappropriate fillings design. The brittleness allows the crack to extend from any notches over the enamel due to the lower plasticity. Therefore, in this issue, linear elastic fracture mechanics (LEFM) assumptions will be used instead of the elastic–plastic fracture mechanics (EPFM). Traditionally, the vertical crack in the teeth is predominated. The load distributions over the crown and the cyclic loading will propagate the crack. There are limited works trying to simulate the crack in the teeth. In this work, the crack path (CP) and the fracture behavior of the tooth have been simulated. It was shown that LEFM is sufficient for such simulation.

In this research, numerical simulations have been performed for carbon/epoxy laminated composites. Two methods were utilized: the extended finite element method and the cohesive zone modeling approach. In addition, experimental works were done according to the ASTM-D5528 standard for double cantilever beam specimens under Mode I displacement-controlled tensile loading. Besides, the loading rate was considered as 0.05, 0.5, 5, and 50 mm/min. During testing, a charge-coupled device (CCD) camera was used to detect the crack length and the initial crack tip opening displacement by the digital image correlation technique. Experimental data were analyzed to find fracture properties by the compliance calibration method, the modified compliance calibration approach, and the modified beam theory. Consequently, there was a good adaptation between numerical and experimental results, obtained by the cohesive zone modeling approach and the extended finite element method, for predicting the maximum force, the energy release rate, and also the initial crack tip opening displacement, under different loading rates. Moreover, the results of the extended finite element method had higher errors than those of the cohesive zone modeling approach.

It is well known that fretting fatigue promotes crack initiation and propagation in structural components, thus causing the failure of mechanical systems. Nowadays, many palliatives such as shot peening are used in order to prevent such ruptures. Nevertheless, when such treatments are applied, the fatigue assessment of the component becomes more complex. In the present paper, a methodology implementing the critical plane-based criterion by Carpinteri et al. for fretting fatigue is employed in order to estimate both endurance strength and fatigue life of Al 7075-T651 alloy shot-peened specimens subject to partial slip fretting fatigue loading.

The strain energy is one of the significant factors in geo-structure nonlinear analysis. The design quality in geotechnical earthquake engineering associates with the accuracy of the numerical simulation and the high quality of the seismic response prediction. In this study, the embankment-subsoil Models A and B are modeled with the same geometry and two different meshes. To predict the strain mechanism of the embankment-subsoil model, the hexahedral and tetrahedral meshes are used in nonlinear numerical simulation. To control the quality of the numerical simulation, the statistical analysis was made. The results of the statistical analysis illustrate that mesh shape governs the accuracy of the numerical simulation. The finding of this study improves the simulation of strain mechanism in embankment-subsoil seismic analysis.

In the present investigation the aptness of the HYB process for butt welding of 4mm AA6082-T6 profiles is evaluated and benchmarked against one gas metal arc (GMA) weld and one friction stir (FS) weld, representing best practice for both methods. The tensile testing shows that the yield strength of the HYB weld exceeds that of the GMA weld and is comparable with that of the FS weld. When it comes to impact toughness the HYB weld is the superior one of the three. Since the subsequent transverse bend testing did not reveal any evidence of bonding defects or crack formation, it means that the 4mm AA6082-T6 HYB butt weld meets all acceptance criteria being specified by Equinor for offshore use.

Fracture behavior of additively manufactured (AM) Ti-6Al-4V has been investigated under quasistatic and impact loading. Taylor cylinder impact tests, on material printed along different directions, have been performed at various velocity to determine high-rate material deformation and impact velocity for damage initiation. Test results revealed that, although the AM material under quasistatic loading condition shows better characteristics than the corresponding wrought material grade, under impact condition, fracture in AM material occurred at an impact velocity almost half of that of wrought grade and at a strain 10 time less of the quasistatic uniaxial fracture strain. Microscopy investigation seems to indicate that pre-existing microvoids produced by the AM process promote shear band development under impact loading causing fracture at much lower strain.

Carbon fiber-reinforced plastics were manufactured with embedded fiber optic Bragg grating (FOBG) sensors for strain monitoring purposes. A novel manufacturing concept was applied to decrease the possibility to induce damage on the ingress/egress point of the fiber to the laminate structure. Specimens without embedded sensors were manufactured as well, and quasi-static mechanical tests showed that FOBG embedding did not decrease the tensile mechanical properties. Coupons with embedded fiber were tested under different loading spectrum (ranging from 20% and up to 60% of ultimate tensile strength), and the differences between the loadings of the surface-attached strain gauge and the embedded sensor were less than 2.0% and for all the applied peak loads. Application of 65,000 fatigue cycles on several coupons was assessed to simulate the fatigue loading of the coupons over their life span. The already fatigued coupons were tested at the same loading spectrum, and their strain measurements were compared against the respective loading spectrum without prior fatigue. The differences at peak loads were less than 1.0%, and therefore, it can be assumed that fatigue damage after65,000 cycles was not accumulated in the sensing area of the Bragg grating sensor. To this end, the investigated FOBG embedding procedure and the proposed manufacturing methodology do not impose damage on the laminate composite.

Additive manufacturing (AM) techniques are under constant development and selective laser melting (SLM) is among the most promising ones. However, widespread use of AM techniques in many industries is limited by the different/unusual mechanical properties of AM metallic parts, with respect to traditionally processed ones, especially when dealing with complex fatigue loading conditions. In fact, crack formation and propagation mechanisms are mainly affected by the development of internal defects, residual stresses, and microstructural changes. This is actually one of the major issues the materials engineering community is facing today. In many applications, AM components are subjected to multiaxial fatigue loads, arising from operating conditions and/or from complex geometries, that unavoidably generate crack initiation and propagation mechanisms. The aim of this study is to investigate the multiaxial fatigue behavior of additively manufactured Ti6Al4V samples, made by SLM. Fatigue tests, combining proportional axial and torsional loads, were performed on thin-walled tubular specimens. Full-field measurement techniques, such as the infrared thermography and digital image correlation, were also used to capture temperature and strain evolutions, at both local scales and global scales. Fatigue results highlighted damage mechanisms, and failure modes are strongly related to the applied stress level.