Microstructure and Mechanical Properties of Low-Cost SiC-Reinforced Aluminum and Al4Cu Matrix Composites Produced by Sintering in Vacuum.

Composite materials based on Al and Al4Cu with the addition of SiC particles (2.5; 5; 7.5; 10 wt.%) were produced in low-cost conventional powder metallurgy processes involving mixing, compacting with a pressure of 300 MPa, and sintering at 600 °C in a vacuum atmosphere. An attempt was made to create a relationship between the vacuum sintering and the microstructure and mechanical properties of Al/SiC composites. The strength of the matrix-reinforcing interface depends on the chemical composition of the components; therefore, the influence of 4 wt.% copper in the aluminum matrix was investigated. Comprehensive microstructural and mechanical properties (including Brinell hardness, compressive and flexural strength measurements) of the produced composites were measured. The addition of 2.5 wt.% SiC to the Al4Cu matrix improved the mechanical properties of the composites compared to the matrix. In the composite with the addition of 2.5 wt.% of SiC, while the addition of the reinforcement did not affect the hardness and compressive strength and caused a rapid decrease in the flexural strength compared to the aluminum matrix, the addition of Cu to the matrix of this composite improved hardness (from 25 to 49 HB), compressive strength (from 423 to 618 MPa), and flexural strength (from 52 to 355 MPa).

[Functional assessment in girls with Turner syndrome--preliminary results]. / Problemy funkcjonalne pacjentek z zespolem Turnera--doniesienie wstepne.

INTRODUCTION: About 10% of Turner's syndrome (TS) patients complain on persistent knee pain, and seek the orthopaedic help because of it. AIM OF STUDY: To evaluate the gait pattern of girls with TS. MATERIAL AND METHODS: Gait analysis was performed using VICON 460 system in 15 patients aged 7 to 20 years. The maximal isometric flexion and extension moments of the knee joints were measured. The knees were examined with X-ray and USG for possible anatomical or degenerative changes. RESULTS: All spatio-temporal parameters of the gait were within normal values. Only 3 patients had proper pelvic tilt, all the others had decreased tilt (from 2 to 9). Only 40% had proper knee flexion at initial contact, 1 patient had knee hyperextension, all the others increased knee flexion. In 50% of the patients the decreased knee range of motion together with decreased maximum knee flexion in swing phase was observed. In 30% there was a decreased hip range of motion. Clinical evaluation of body posture revealed that nearly all patients had trunk asymmetry, and various deformities of knees and feet. DISCUSSION: Nearly all TS patients had decreased pelvic tilt, which could be sign of the weakness of the muscles responsible for the pelvis orientation. The abnormalities of upper and lower body found during clinical evaluation of body posture also suggested decreased muscular strength. It is known that girls with TS have poorer motor development, which could result in decreased muscular strength and our findings support this thesis. Decreased muscular strength could also negatively influence the locomotor abilities.