ABSTRACT
The objective of this study was to compare three methods for determining the Young's modulus of polylactic acid (PLA) and acrylonitrile-butadiene-styrene (ABS) samples. The samples were manufactured viathe fused filament fabrication/fused deposition modeling (FFF/FDM) 3D printing technique. Samples for analysis were obtained at processing temperatures of 180 °C to 230 °C. Measurements were performed with the use of two nondestructive techniques: the impulse excitation technique (IET) and the ultrasonic (US) method. The results were compared with values obtained in static tensile tests (STT), which ranged from 2.06 ± 0.03 to 2.15 ± 0.05 GPa. Similar changes in Young's modulus were observed in response to the processing temperatures of the compared methods. The values generated by the US method were closer to the results of the STT, but still diverged considerably, and the error exceeded 10% in all cases. Based on the present findings, it might be concluded that the results of destructive and nondestructive tests differ by approximately 1 GPa.
ABSTRACT
The aim of the study was to investigate the effect of ultrasound treatment and freezing/thawing on the physical properties of blueberries (Vaccinium corymbosum L.). Fruits were subjected to ultrasound treatment, mechanical freezing/thawing, and freezing/thawing with subsequent ultrasound treatment. Moisture, density, porosity, hardness, springiness, cohesiveness, chewiness, gumminess, and color of blueberries were analyzed. Ultrasound treatment and freezing/thawing significantly decreased particle density and increased porosity of blueberries (p < 0.05). Ultrasound treatment and freezing/thawing produced significantly softer, less chewy and gummy berries in relation to control sample (p < 0.05). All techniques induced considerable changes in the color of blueberries. The results indicates that ultrasound treatment performed after freezing/thawing, didn't exert any effect on the fruits in relation to freezing/thawing alone (p > 0.05); however, it is an interesting technique for processing fresh blueberries and an alternative to freezing/thawing, when the preservation of product quality is a priority or when rapid textural damage is required before diffusion processes.
ABSTRACT
Non-destructive ultrasonic methods for testing biological materials are applied in medicine as well as in food engineering to determine the physical parameters and the quality of agricultural products and raw materials such as meat. The purpose of this work was to identify the simplest and the most accurate of five methods for sound velocity determination across the fibers of the porcine longissimus dorsi muscle. The through-transmission technique (TT) was used for ultrasound signal acquisition with 2MHz transducers. The first two methods (M1, M2) are based on the acquisition of a single ultrasound signal in the analyzed material, another two methods (M3, M4) rely on the acquisition of two ultrasound signals in samples with different thicknesses (two-distance method) and the last method (M5) involves the acquisition of a single ultrasound signal in the analyzed material and the acquisition of a single ultrasound signal in distilled water at the same distance between ultrasonic transducers (relative method). The results were processed by the nonparametric Kruskal-Wallis test and compared with published data. The mean values of sound velocity obtained with the use of the above methods in pork samples at post-storage, room and vital temperatures were as follows: method M1-1549.2/1581.7/1597.4m/s, method M2-1477.7/1509.8/1597.4m/s, method M3-1552.0/1599.0/1623.3m/s, method M4-1557.4/1598.3/1623.6m/s, method M5-1554.3/1583.7/1598m/s. The experiment indicates that the choice of method for determining sound velocity significantly influences the results. Two of the five analyzed methods (namely M3 and M4), which involved measurements of the time of sound wave propagation through samples of the same material with varied thickness, produced velocity values most consistent with published data.
