Trdota predstavlja merilo odpornosti lesa proti prodiranju tršega telesa v njegovo notranjost in pogosto pogojuje uporabnost izbrane vrste lesa za določen namen uporabe. Poleg gostote, trdoto ...posamezne lesne vrste zelo pogojuje vlažnost lesa. V raziskavi smo ugotavljali trdoto lesa navadne smreke, uravnovešenega pri različnih relativnih zračnih vlažnostih. Meritve trdote smo izvedli z vtiskanjem kroglice v radialno površino lesa na inštrumentu za ugotavljanje mikromehanskih lastnosti materialov. Rezultati so pokazali, da se s poviševanjem vlažnosti lesa trdota lesa znižuje; vtisna trdota (HIT) in vtisni modul elastičnosti (EIT) sta tako pri absolutno suhem lesu znašala 110,8±11,7 MPa in 0,62±0,01 GPa, pri lesu z vlažnostjo točke nasičenja celičnih sten (29,4 %) pa 36,3±7,9 MPa in 0,40±0,05 GPa. Zniževanje trdote lesa s poviševanjem njegove vlažnosti se je pokazalo v povečevanju globine povzročenih vtisov in povečani hrapavosti površin vzorcev. Analiza lesnega tkiva z vrstičnim elektronskim mikroskopom je na območjih z vtisi razkrila usločenje celičnih sten lesa, njihovo gnetenje v lumne traheid, ter nastanek razpok znotraj celičnih sten.
Unlike the conventional calculation models of the hardness, a carburizing-quenching hardness model considers the influence of the carbon content on the phase transformation and hardness. The volume ...fraction model (VFM) and Jominy curve model (JCM) for calculating carburizing-quenching hardness of 20CrNi2Mo steel were built in this study, and the models were used to calculate the hardness of Jominy and gear samples. The hardness results of both models were compared, and the simulation results were verified with the corresponding test results. The results show that the hardness values obtained with both models have a certain calculation accuracy. But due to considering the influence of residual austenite (RA) on the hardness, the simulation accuracy of the VFM was better for the low Jominy distance and the hardened case, while the simulation accuracy of the JCM was better for the large Jominy distance and the low-carbon martensite region; the calculation of the latter is more convenient and its accumulated error is small.
We have studied the effects of different solution temperatures and holding times on the microstructure and room-temperature mechanical properties of the alloy using methods such as electron ...backscatter diffraction, hardness testing and tensile testing. The results showed that the average grain size increased significantly as the solution temperature increased, and many annealing twins appeared in the grains. The fraction of twin boundaries reached its maximum value at 1080 °C. The hardness, yield strength and tensile strength of the alloy decreased with an increase in the solution temperature, but abnormal yielding occurred at 1160 °C. The elongation after fracture and the area reduction increased with an increase in the solution temperature. The fracture morphology of the alloy was irregular, conical, accompanied by a large number of ductile dimples, and the material exhibited typical ductile fracture. At the same time, as the solution temperature increased, the number of dimples on the fracture surface continued to increase, the depth of the dimples gradually increased, and the distribution became more uniform.
In this paper, the alternate immersion corrosion test of Cr-Mo-V series SDCM steel for hot stamping was carried out, and different stresses were loaded with self-made fixture. The results shown that ...regardless of hardness and stress, the corrosion mode of the material is uniform corrosion. Stress could significantly increase the corrosion rate, with lower hardness and higher corrosion rate. Because of the existence of Corrosion Removal Layer (CRL), the maximum corrosion pit depth would be reduced. The maximum corrosion pit depth and Corrosion Pit density (CPD, ρv) were used to describe the degree of corrosion damage. From low to high hardness, the CPD ρv and corrosion resistance increased gradually. With the increased of tempering temperature, the hardness decreased, and the percentage of carbide area in the field of view increased from 16.36% to 24.32%. The irregular spherical carbide M23(C, N)6 rich in Cr coarsens and consumes Cr element in the material, which lead to the decrease of corrosion resistance. Through the polarization curve of the dynamic potential, we known that the current density was increased with the hardness decreased, from 28.53 μA/mm2 to 40.93 μA/mm2.
The changing dynamics of organic acids, sugars, phenolics and antioxidant potential in apples from technological to edible maturity was studied. During the time of storage, the content of citric and ...malic acids generally decreased. The content of sucrose, fructose and glucose decreased significantly in some varieties, while it increased in others. The content of total sugars changed only slightly over the storage period. In the apple pulp, the content level of single phenolics generally changed to a minor extent during storage. In the peel, the content levels of the rutin and quercetin-3-rhamnoside flavonoids remained generally constant during storage, while the level of p-coumaric acid increased slightly; on the other hand, the content levels of epicatechin and catechin decreased. In the pulp of most cultivars, there was no significant decrease in total phenolics at edible maturity. In contrast, the apple peel usually has a higher content level of total phenolics at edible maturity than at the time of technological maturity. Therefore, the antioxidant activity of the peel increased from technological to edible maturity.
Proučevali smo dinamiko spreminjanja organskih kislin, sladkorjev, fenolnih spojin in antioksidativnega potenciala jabolk od tehnološke do užitne zrelosti. Vsebnost citronske in jabolčne kisline se je med skladiščenjem na splošno zmanjševala. Vsebnost saharoze, fruktoze in glukoze se je v času skladiščenja pri nekaterih sortah značilno zmanjšala, pri drugih pa povečala. Vsebnost skupnih sladkorjev se je med skladiščenjem le malo spreminjala. Na splošno se je vsebnost posameznih fenolov v pulpi jabolk v času skladiščenja le malo spreminjala. V kožici je ostala vsebnost flavonoidov rutina in kvercetin-3-ramnozida v obdobju skladiščenja približno enaka, vsebnost p-kumarne kisline se je malo povečala, medtem ko se je količina epikatehina in katehina zmanjšala. Pri večini sort je opaziti v pulpi neznačilno zmanjšanje skupnih fenolov v užitni zrelosti. Nasprotno je kožica jabolk pri večini sort v užitni zrelosti imela večjo vsebnost skupnih fenolov kot v tehnološki zrelosti. Iz tega tudi izhaja, da se je antioksidativna aktivnost kožice od tehnološke do užitne zrelosti povečala.
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