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Additive manufacturing is used to build three-dimensional parts from a CAD model. The parts are layered constructed and selectively consolidated by laser or electron beam. This method enables the production of complex geometries of versatile materials parts. In this study, a powder laser bed fusion technique was used to create AlSi10Mg extrusion billets. The AM billets were subjected to stress relief heat treatment (HT) and hot extrusion process. The mechanical properties and microstructure of the extruded AM billets and aged hardened were evaluated. A significant improvement of the extruded sample’s mechanical properties was found compared to cast and as-built material. In some cases, the yield stresses, tensile stresses, and elongation increased by 30–40%. Extrusion of additive manufactured billets can be used as a technique to gain better mechanical properties of heavy-duty products.

Fiber-reinforced metal laminate (FRML) composites are currently used as a structural material in the aerospace industry. A common FRML, glass layered aluminum reinforced epoxy (Glare), possesses a set of mechanical properties which was achieved by designing its layup structure to combine metal alloy and fiber-reinforced polymer phases. Beyond static and dynamic mechanical properties at the material characterization phase, however, the need exists to develop methods that could assess the evolving material state of Glare, especially in a progressive failure context. This paper presents a nondestructive approach to monitor the damage at the material scale and combine such information with characterization and postmortem evaluation methods, as well as data postprocessing to provide an assessment of the failure process during monotonic loading conditions. The approach is based on multiscale sensing using the acoustic emission (AE) method, which was augmented in this paper in two ways. First, by applying it to all material components separately in addition to actual Glare specimens. Second, by performing testing and evaluation at both the laboratory scale as well as at the scale defined inside the scanning electron microscopy. Such elaborate testing and nondestructive evaluation results provided the basis for the application of digital signal processing and machine learning methods which were capable to identify data trends that are shown to be correlated with the evolution of failure modes in Glare.

Aim To evaluate the prevalence of scapular dyskinesis (SD) in competitive swimmers during training sessions. Methods Repeated measurement observational study.20 young competitive swimmers were filmed before, at midpoint and at the end of a training session, performing shoulder flexion and abduction. SD was examined separately by two assessors. Demographic and Quick Disabilities of the Arm, Shoulder, and Hand questionnaires were collected. Results SD was observed in 30% of the swimmers before training, in 70%, an hour later, and in 80%, upon completion of the training session. The difference between the baseline and mid-practice was close to significance (p-value = 0.055), and between mid-practice and end of practice was significant (p = 0.004). Conclusions This study confirmed that the prevalence of SD increases throughout a training session in most swimmers. The main reason might be fatigue of the muscles which stabilize the scapula, therefore, when examining a sportsmen's shoulder, it is important to examine the SD post-training or following simulation of the training session in the clinic.

Three mixed mode failure initiation criteria at reentrant corners in brittle elastic materials are examined. Prediction of failure load and crack initiation angle are compared to experimental observations carried out on PMMA (polymer) and MACOR (glass ceramic) V-notched specimens. Since the mode mixity ratio influences greatly both the failure load and crack initiation angle, a detailed experimental procedure has been followed, focusing on obtaining a wide range of mode mixity ratios. It is demonstrated that by assuming a sharp V-notch tip some failure criteria predict reasonably well both the crack initiation angle and failure load.

This article presents the advantages of combining Acoustic Emission (AE) and Digital Image Correlation (DIC) in nondestructive testing (NDT) applications focusing on in situ damage monitoring. This data-fusion approach is used herein to characterize the mechanical and damage behavior of a fiber metal laminate (Glare 1A) tested in both tension and fatigue. Furthermore, the approach is used to investigate the structural behavior of partially grouted reinforced masonry walls. The obtained AE datasets were post-processed, in combination with DIC and mechanical information, using signal processing and pattern recognition techniques to investigate progressive failure of the Glare 1A. In the case of the masonry wall specimens, DIC clearly identified critical damage areas as a function of applied loading, while AE was capable to monitor the damage process and reveal changes in the overall behavior. The presented analysis demonstrates the potential of integrating AE and DIC in data-driven damage mechanics investigations at multiple time and length scales.

Low temperature superplastic (SP) behavior (mechanical and deformation mechanisms) of two commercial Mg-based alloys (AZ31 and ZK60) was characterized. The two alloys were tested in the as extruded condition with initial grain size of 15 μm (AZ31) and fine (2 μm) and coarse (25 μm) grains mixed randomly for the ZK60. Strain rate was activated in the range 10−5–1 s−1 at 450 K (0.49Tm) in order to determine the deformation capacity curves (elongation to failure vs. strain rate), and to evaluate the strain rate sensitivity coefficient, m, from the stress versus strain rate curves. Optical, scanning and transmission electron microscopy observations (SEM and TEM) were performed to elaborate on the dynamic recrystallization (DRX) grain growth, fracture modes and deformation mechanisms at the SP mode. In addition, X-ray diffraction was utilized to track for microstructural classification. Although low temperature was applied, the ZK60 exhibited superplastic-like behavior and the maximum peak of elongation (220%) was detected at 1×10−5 s−1 with m equal to 0.2. In AZ31 SP behavior was suppressed due to grain growth, while for ZK60, DRX was detected. However, for the latter alloy, it was observed that the coarse/fine grain interface was the trigger for microcracking initiation. Actually, this phenomenon reduces the SP capacity of the ZK60 alloy. Surface observations and TEM findings indicate that grain boundary sliding with homogeneous character is the controlling SP deformation mode. Typical dislocation features have supported this deformation mode, mainly by grain boundary dislocation pile-ups. More sophisticated extrusion processes as equal angular channel extrusion (EACE) is likely to be considered in the future as a mean to improve grain homogeneity and produce ultra fine grain microstructure.

Mechanical characterization combined with micro feature observations provide a successful method in elucidating micromechanisms of plastic deformation. As such, the present study is centered on some aspects as related to slip/twinning mechanisms in uranium base systems. Most of the findings emerged from a broad experimental/theoretical program particularly in a lean U-Ti alloy. Within this framework, the interrelationship between slip and mechanical twinning onset was mainly developed. In fact, the key issue remains in defining the critical role of plasticity on the local stress field. Better understanding of this concept has already been explored through several types of failure events in elastic-plastic solids. For such material of low crystal structure symmetry, better understanding of concomitant slip/twinning behavior is essential regarding deformation and fracture resistance. Thus, incentives to shed light on these basic issues becomes apparent. At least it is desirable to follow the sequence of micro-events as the level of plasticity proceeds in this U-Ti alloy which is characterized by a DBT. To assist this extrinsic dominant variables such as state of loading, temperature and strain rate were included.

In the framework of a broader experimental/theoretical investigation regarding the crack initiation stage, the current study was centered on fatigue crack nucleation. Polycrystalline commercially pure copper was selected with attention directed toward fine scale surface features. Phenomenologically, observational findings regarding the role of residual stresses were explored by utilizing scanning electron microscopy (SEM) and atomic force microscopy (AFM). Experimental results are described and analyzed with some modeling aspects and simulation attempts, even as far as environmental/plasticity interactions.

Aqueous Corrosion/Deformation Interactions (ACDI) in uranium and uranium alloys actually exhibit complicated mechanical damage processes. In this context, the exploration of the dominant micromechanical mechanisms vis- a -vis experimental confirmations remain an unsettled issue. Various mechanisms might be involved in such environmental effects, starting from stress corrosion cracking (SCC) hydrogen embrittlement, up to brittle film fracture or film-induced cleavage, enhanced or inhibited by diffusion barriers. These on top of hydride formation which potentially affects the local mechanical/chemical driving field. Thus, beside the driving force modifications, the reduction of the fracture resistance requires appropriate evaluations. The main objective in the current phenomenological investigation was, to provide additional findings as related to damage evolution in specific ACDI systems. In fact, the present selected systems allowed further insights into a low symmetry, orthorhombic crystal structure case. Experimentally, sustained load, slow strain rate (SSR), monotonic and fatigue tests in fracture mechanics framework were performed, supplemented by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observations. In addition, X-ray, Fourier Transform Infrared spectroscopy (FTIR) techniques and acoustic emission (AE) tracking were utilized. Experimental findings are analyzed and discussed with emphasis to fractographic observations and kinetics associated with the crack propagation stage. These beside developments in modeling aspects founded on a stepwise decohesion processes.

In U-Ti alloys, a simplified dislocation shielding model might represent the lower shelf regime of fracture toughness as a function of microstructure, temperature and strain rate. This proposed shielding model centers on the local back-stress for shielding and, as such, depends on the friction stress and its strain rate sensitivity. Shielding concepts might be applicable to some brittle lower symmetry crystal structures obeying similar trends typical to thermally activated deformation mechanisms.

Frequency effects in fatigue as related to structural reliability of electronic materials/devices still remain a long term goal. Here, complexities arise by realizing that more than a single time dependent micromechanism might dominate. To achieve some progress, intensive experimental activities were conducted in different crystal - structures and in non-metallic systems. The study found that at least in metals. under isothermal conditions, the fatigue crack propagation rate (FCPR) actually increased as the frequency decreased even without environmental interactions. These effects become substantial in materials in which the activation enthalpy for deformation exceeded values of about 0.5e.v, which accentuated at low temperatures. In metals, these issues are analyzed in the light of crack-tip dislocation-interaction model with emphasis to some proposed constitutive equations. Attempts for more realistic simulation techniques in metals, ceramics and polymers might give insights into the generic frequency effects in cyclic damage.