This paper presents the results of an investigation of the possibility of the reliable determination of the residual stress–strain state in polymers and composites using a combination of bridge curvature, optical scanning, and finite element methods. A three-factor experiment was conducted to determine the strength of printed PLA plastic products. The effect of the residual stresses on the strength of the printed products was evaluated. By comparing the values of the same strength stresses, a relationship between the nature of the stresses and the strength of the samples was found. A tendency of the negative influence of tensile stresses and the opposite strengthening effect of compressive stresses was obvious, so at the same values of tensile strength, the value of residual stress of 42.9 MPa is lower than that of the fibre compression at the value of 88.9 MPa. The proposed new methods of the residual stress determination allow obtaining a complete picture of the stressed state of the material in the investigated areas of the products. This may be necessary in confirming the calculated models of the residual stress–strain state, clarifying the strength criteria and assessing the quality of the selected technological modes of manufacturing the products.

This study proposes a novel computational method, employing the integral dynamics of multibody systems to simulate the transverse vibrations of the rotor in a cantilever-type centrifugal pump. This method was applied to the kinematic assembly of the rotor and its supports, with the latter modeled as springs possessing stiffness and damping properties equivalent to those of real bearings supporting the shaft in an actual design. To investigate transverse vibrations within the system, three key observation points were defined—at the locations of the left and right bearings, as well as at the rotor’s center of mass—to allow for a thorough dynamic analysis. Additionally, the influence of motor rotational speed and the impeller’s eccentricity on the transverse vibrations of the supports and the shaft was examined. The results have revealed that transverse vibrations significantly affect the system’s dynamics at lower rotational speeds, leading to the classification of the shaft as flexible. As the rotational speed increases, the system exhibits enhanced dynamic stability. Furthermore, it was found that for impellers with a diameter less than 300 mm, the unbalanced forces are negligible and can be disregarded in pump design. To reduce vibration levels, an elastic damping ring was selected and incorporated into the system. This novel method provides an effective tool for analyzing the transverse vibrations of centrifugal pump rotors and for optimizing vibration mitigation strategies.

The application of carbon fiber-reinforced polyetheretherketone (CFR-PEEK) composites in osteosynthesis implants represents a promising approach to mitigating the stress-shielding effect associated with the high stiffness of conventional metallic implants. This study aimed to experimentally and numerically evaluate the effects of short carbon fiber content and the orthotropic mechanical properties of CFR-PEEK on the structural strength of osteosynthesis plates and load distribution within the bone–plate system. The investigation employed a multiscale approach integrating micromechanical modeling using the Mori–Tanaka homogenization method in Digimat-MF, experimental mechanical testing of FDM-fabricated CFR-PEEK specimens containing 10 wt.% carbon fibers, and finite element analysis of osteosynthesis plates made of CFR-PEEK with 10 and 30 wt.% carbon fibers and Ti-6Al-4V using MSC Patran/Marc. CFR-PEEK 30% specimens were neither fabricated nor experimentally tested. Their mechanical properties were predicted using Digimat-MF by applying correction factors derived from experimental data obtained for CFR-PEEK 10%. The results demonstrated that increasing the carbon fiber content from 10 to 30 wt.% enhanced the longitudinal elastic modulus. Experimental testing of CFR-PEEK containing 10 wt.% carbon fibers revealed an elastic modulus ranging from 1.76 to 3.10 GPa and a tensile strength of 47–54 MPa. Following process-related adjustments to the material properties, finite element simulations of the bone–plate system were performed under an axial load of 50 N. The calculated load shielding indices were 94.3% for Ti-6Al-4V, 28.6% for CFR-PEEK 10%, and 54.3% for CFR-PEEK 30%, indicating the potential of composite implants to improve mechanical load transfer to the surrounding bone tissue. A preliminary strength assessment based on the three-dimensional Tsai–Hill failure criterion yielded failure indices of 15.577 and 1.112 for CFR-PEEK 10% and CFR-PEEK 30%, respectively, under the assumed material strength parameters. Critical stress concentrations were predominantly localized around the fixation holes. These findings highlight the trade-off between reducing stress shielding and ensuring the structural integrity of composite osteosynthesis plates. The results further emphasize the need for localized optimization of fixation regions to improve mechanical reliability without increasing the overall implant thickness.