This work studies the effect of incorporating a mix of reinforcement particles of a hard and soft nature on the microstructure and mechanical and physical properties of a high-strength aluminum alloy, AA7075. A friction stir processing technique was used for compositing the surface of this alloy. The vanadium carbide (VC) was selected to be the hard reinforcement, while the boron nitride (BN) and graphene nanoplates (GNPs) were chosen as soft reinforcements. Mono VC, hybrid reinforcements combined of 50 vol.% VC and 50 vol.% BN, and triple reinforcements combined of 33.4 vol.% VC, 33.3 vol.% BN, and 33.3 vol.% GNPs were used for producing the composites. Intensive grain refinement was observed, 930%, in the composite with triple reinforcements. The microhardness and the ultimate compressive strength were improved and reached b0, 29%, respectively, in composites that contained GNPs. The thermal properties were significantly improved, and the coefficients of thermal expansion (CTE) and thermal conductivity decreased to 88% and 15%, respectively. The composite’s electrical conductivity was decreased by 58% with triple reinforcements.

Improving the mechanical durability and wear resistance of aluminum alloys is a research challenge that can be solved by their reinforcement with ceramics. This article is concerned with the improvement of the mechanical properties and wear resistance of the AA2024 aluminum alloy surface. Surface composites were prepared by incorporating a hybrid of heavy particles (tantalum carbide (TaC), light nanoparticles, and boron nitride (BN)) into the AA2024 alloy using the friction stir process (FSP) approach. Three pattern holes were milled in the base metal to produce the composites with different volume fractions of the reinforcements. The effects of the FSP and the reinforcements on the microstructure, mechanical properties, and wear resistance are investigated. In addition to the FSP, the reinforced particles contributed to greater grain refinement. The rolled elongated grains became equiaxed ultrafine grains reaching 6 ± 1 µm. The refinement and acceptable distribution in the reinforcements significantly improved the hardness and wear resistance of the produced composites. Overall, the hardness was increased by 60% and the wear resistance increased by 40 times compared to the base alloy.

Crack orientation, a critical parameter, significantly affects the dynamic properties of composite structures. Experimental free vibration tests were conducted on carbon fiber–reinforced polymer (CFRP) composite plates at room temperature with different crack orientations. Dynamic properties such as damping ratio, natural frequency, and storage modulus were measured using a four-channel dynamic pulse analyzer. Multi-sensors were mounted on the test plate to pick up the vibration signals. Experimental modal analysis was performed to identify the first three mode shapes of the defective plates. A numerical model using ANSYS software was developed via parametric investigation to predict the correlation between crack orientation and resonant frequencies with corresponding mode shapes. The orientation of the introduced cracks had a significant effect on the dynamic properties of CFRP composites. Vertical cracks had the most significant influence on the eigenvalues of the mode shape frequencies. Furthermore, the damping ratio was an effective method to detect the cracks in CFRP composites.

Background Spinal cord injury (SCI) is a significant cause of morbidity and mortality with an incidence of 40-83/million/year. Sympathetic denervation in SCI leads to cardiovascular abnormalities including orthostatic hypotension, rhythm disturbance and repolarization changes. Electrocardiographic (ECG) findings include brady-arrhythmias, ectopic beats, long QT interval and ST-T changes that may be mistaken for myocardial ischemia. Case Summary A patient in their 40s with free past medical history was referred to our center with the diagnosis of non-ST elevation acute coronary syndrome. On presentation, chest pain was diffuse and radiating to the back. 12-lead Electrocardiogram (ECG) showed deep symmetrical T wave inversion. Echocardiography and cardiac troponin were normal. The patient was scheduled for multi-slice CT coronary angiography which was normal, however, a few hours after admission, the patient developed rapidly progressive motor weakness in both lower limbs with urine retention. Examination revealed motor power grade 1 in both lower limbs. All sensations were diminished with a sensory level at T6. Urgent MRI spine revealed neoplastic infiltration of the whole vertebrae with D5/D6 fracture exerting spinal cord compression. The patient was referred for urgent decompression surgery. Conclusion ECG changes could be the earliest sign for ongoing SCI. ST elevation is reported in higher levels of complete injury, while ST depression and inverted T waves can occur independent of lesion level or severity. Misinterpretation of these changes may cause a delay in reaching the correct diagnosis. We highlight the importance of considering neurological causes for ischemic-like ECG changes, as early recognition could prevent irreversible functional loss.