The modified life law applied to SAE-1045 steel

Miner's rule is seen to hold probabilistic significance. Erroneous predictions must therefore be caused by using inadequate data in the damage summation. Improved predictions can be made if the modified life law concept is applied. The modified life curve arises from the threshold lowering effect of compressive load cycles. In experimentation with 3-level block loads under varied frequency of application, points on the modified life curve can be found. In solving for points on the modified curve, steps must be taken to reduce scatter amplification. Minimum modified life curves plotted from experimental data were used in the prediction of lives. Lives were verified by experiment. For peak loads corresponding to the peak load level used in establishing the modified life curve, predictions fell within expected accuracy limits. Implementation of the modified life curves gives a significant improvement in life predictions

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Résumé On constate que la loi de Miner a une signification probabiliste et que, dès lors, des prédictions erronnées peuvent résulter de l'utilisation de données inadéquates dans la somme des dommage. Si on adopte un concept d'endurance modifiée, on peut réaliser des prédictions améliorées. La courbe d'endurance modifiée procède du seuil d'abaissement du dommage, constitué par la portion compressive des cycles de charge. On a déterminé expérimentalement les points de la courbe d'endurance modifiée en appliquant dans des essais des séquences de trois niveaux de mise en charge, suivant des fréquences diverses. Lors de l'ajustage des points sur la courbe modifiée, on procède par étapes de manière à éviter une amplification de la dispersion. Pour prédire les vies en fatigue, on porté des courbes d'endurance minimales à partir de données expérimentales, et les vies effectives ont été vérifiées par les essais. Les prédictions se sont révélées tomber dans les limites d'exactitude attendues, pour des contraintes de crète correspondant aux niveaux de crète utilisés pour établir la courbe modifiée. Par le recours à la courbe d'endurance modifiée, on obtient une amélioration appréciable dans la prédiction des vies en fatigue

     

Effect of drought and irrigation on the fate of nitrogen applied to cut permanent grass swards in lysimeters: Nitrogen balance sheet and the effect of sward destruction and ploughing on nitrogen mineralisation

Fuor years after ¹⁵N labelled fertiliser nitrogen (as Ca(NO₃)₂ and equivalent to 400 kg N ha^?1) was applied to permanent grass swards growing in lysimeter monoliths, approximately one-quarter remained immobilised in soil organic matter. In the intervening years similar but non-labelled applications were made. Although differing rainfall regimes applied during the experiment had significantly affected nitrogen uptake by plants and nitrate loss in drainage, they caused no significant effect on the tracer nitrogen remaining in the soil, the ranges were 85–97 kg N ha^?1 and 79–94 kg N ha^?1 respectively for the 135 cm deep clay and silt loam soil monoliths. Labelled nitrogen unaccounted for in crop, drainage or soil was presumed to have been denitrified. These losses averaged 62 and 49 kg N ha^?1 on the clay and silt loam soils respectively; again the differing rainfall regimes caused no significant differences. The ratio between estimates of labelled nitrogen denitrified and of annual nitroux oxide loss was approximately 9:1 for both soils. The conversion from permanent grass to winter wheat in autumn 1981, involving killing and then burying the sward, resulted in no pronounced increase in net mineralisation of labelled nitrogen. However, the balance between crop uptake and the quantity leached did change. Labelled nitrogen assimilated was less for the wheat (growing without addition of fertiliser nitrogen) than for the grass in its last year, and the quantity leached was considerably greater than under grass swards that were supplied with an average rainfall distribution. Following the first wheat harvest total nitrogen leached averaged 51 and 44 kg N ha^?1 on the clay and silt loam soils respectively. Rates of nitrous oxide emissions during the autumn following sward destruction were greater than in earlier years, but this enhanced loss was of short duration. The crop clearly benefited from the succession of nitrogen applications made to grass, as grain yield and total nitrogen uptake exceeded 7 t ha^?1 and 120 kg N ha^?1 respectively on both soils. These quantities exceed the national averages for winter wheat and are also considerably greater than for crops from lysimeters which received no nitrogen fertiliser throughout the experiment.     

Nitrous oxide emission from permanent grass swards

Emissions of nitrous oxide from permanent grass swards growing on monoliths of clay (Salop series) or silt loam (Bromyard series) soils contained in lysimeters (80 cm diameter, 135 cm deep), were measured between October 1977 and August 1980. With no added fertiliser nitrous oxide emissions were small (equivalent to 10–30 μg N m^?2 h^?1), but after application of nitrate fertiliser (400 kg N ha^?1 year^?1) during the spring and summer months, emissions increased to peak values ca 1000 μg N m^?2 h^?1. The peaks were associated with nitrogen applications and rainfall/irrigation events, but persisted only for 3–7 days. Nitrous oxide production in the soil was mostly restricted to the upper 30 cm of the soil profile. Total annual nitrous oxide losses amounted to 6–8 kg N ha^?1 from the Salop clay soil and 4–6 kg N ha^?1 from the Bromyard silt loam.     

椅子的新意

或许你天天都在和椅子打交道，却又一直忽略了它，但是，当你的视线接触到如此富有新意的椅子时，一定再也无法转移。     

桌之新意

在这个创意漫天飞的年代，即使只是一张简单的桌子，也可以与许多精彩的词语相关，譬如：自然、回忆、科技、未来……     

银色旋律

银色，有着与生俱来的优雅，犹如曼妙的旋律，内敛却充满情感，令小小的物品也能气质动人。     

The uptake of 15N-labelled fertiliser by winter wheat and its immobilisation in a clay soil after direct drilling or ploughing

The uptake of fertiliser nitrogen (N) by winter wheat was measured using ¹⁵N-labelled calcium nitrate applied at 80 kg N ha-¹ rate in May to the soil in microplots contained by sections of rigid PVC tube (30 cm diameter, 20 cm long), inserted into a calcareous clay soil (Evesham series). The microplots and surrounding plots had been subjected to either 5 or 6 years of continuous ploughing or direct drilling or 1 and 2 years of direct drilling after 4 years of deep-tined cultivation. The recovery of fertiliser N labelled with ¹⁵N in the crop plants at harvest was in the range 60–67% of that applied in the first year and 0.5–0.7% in the second year; there were no significant treatment differences. The ‘apparent’ recovery of fertiliser based on a comparison of plots with and without fertiliser N was greater and ranged from 77–111 % of that applied. Estimates of the contribution of non-fertiliser N to the crop by means of ¹⁵N analysis suggest that if this N had been utilised with the same efficiency as that of fertiliser N about 120 kg N ha-¹ was available to the plants. This represents about 1% of the total N in the soil to 80 cm depth. Soil analysis (0–15 cm) showed that about 8% of the applied ¹⁵N was retained in the upper layers of the soil; there were no treatment differences. Any changes due to mineralisation of the soil organic matter during the 2 years of the experiment were within the errors of the experiment.     

Effect of drought and irrigation on the fate of nitrogen applied to cut permanent grass swards in lysimeters: Experimental design and crop uptake

The effect of drought and irrigation on the yield and fertiliser nitrogen uptake by cut permanent grass swards was investigated using lysimeters containing monoliths (80 cm diam., 135 cm deep) of two soil types (Salop series, clay loam and Bromyard series, silt loam). Over the five summers 1977–81 swards were treated with four dressings of calcium nitrate at rates of 0 and 100 kg N ha^?1 after each cut; in the first year, the nitrogen was labelled with ¹⁵N. Rainfall equivalent to the long-term average gave mean yields of 12.9 t dry matter ha^?1 for Salop and 14.3 t dry matter ha^?1 for Bromyard. Irrigation (to 120% of average summer rainfall) gave a non-significant increase of 8–9% in herbage yield on both soils. When the average rainfall distribution was modified to create periods of drought for 4 weeks duration immediately before each cut and fertiliser application, yields were significantly depressed, by 12% on Salop soil and 20% on Bromyard soil. Adjustment of the drought so that cutting and nitrogen application fell mid-way in the dry period resulted in only a small non-significant depression of yield on both soils (yield 95–96% of average rainfall treatment). The recovery of applied ¹⁵N labelled fertiliser in herbage during the first year of the experiment was in the range 45–47% for the Salop soil and 39–52% for the Bromyard soil. In the Salop soil the recovery of the labelled nitrogen was not significantly affected by imposition of drought conditions or by irrigation. However, in the Bromyard soil the drought treatment resulted in a significant reduction in the recovery of fertiliser nitrogen to 79% of that of the average rainfall treatment and irrigation increased the recovery to 106%. The contrasting results from the two soils was due to the imposed drought treatments which were more effective in creating differing soil water status in the Bromyard soil. This was due to its good drainage and lower water holding capacity. On both soils, fertiliser nitrogen constituted 53–60% of the total nitrogen content of the herbage. This experiment indicates that on clay soils with poor drainage status, the pattern of rainfall distribution has relatively little impact on the productivity of the sward and its utilisation of fertiliser nitrogen. On freely-draining soils, however, heavy rainfall after drought following cutting and nitrogen application can substantially depress yield and fertiliser use.