起重機設(shè)計外文翻譯---龍門式起重機金屬材料的疲勞強度預(yù)測

1、<p><b>　　附錄A</b></p><p><b>　　英文原文：</b></p><p>　　Fatigue life prediction of the metalwork of a travelling gantry</p><p><b>　　crane</b></p&

2、gt;<p>　　V.A. Kopnov</p><p>　　P.O. Box 64, Eknteriuburg 620107, Russian</p><p>　　Received 3 April 1998; accepted 29 September 1998</p><p><b>　　Abstract</b></p&

3、gt;<p>　　Intrinsic fatigue curves are applied to a fatigue life prediction problem of the metalwork of a traveling gantry crane. A crane, used in the forest industry, was studied in working conditions at a log yar

4、d, an strain measurements were made. For the calculations of the number of loading cycles, the rain flow cycle counting technique is used. The operations of a sample of such cranes were observed for a year for the averag

5、e number of operation cycles to be obtained. The fatigue failure analysis ha</p><p>　　Key words: Cranes; Fatigue assessment; Strain gauging</p><p>　　1. Introduction</p><p>　　Fatigue

6、 failures of elements of the metalwork of traveling gantry cranes LT62B are observed frequently in operation. Failures as fatigue cracks initiate and propagate in welded joints of the crane bridge and supports in three-f

7、our years. Such cranes are used in the forest industry at log yards for transferring full-length and sawn logs to road trains, having a load-fitting capacity of 32 tons. More than 1000 cranes of this type work at the ent

8、erprises of the Russian forest industry. The problem </p><p>　　2. Analysis of the crane operation</p><p>　　For the analysis, a traveling gantry crane LT62B installed at log yard in the Yekaterin

9、burg region was chosen. The crane serves two saw mills, creates a log store, and transfers logs to or out of road trains. A road passes along the log store. The saw mills are installed so that the reception sites are und

10、er the crane span. A schematic view of the crane is shown in Fig. 1.</p><p>　　1350-6307/99/$一see front matter 1999 Elsevier Science Ltd. All rights reserved.</p><p>　　PII: S 1 3 5 0一6307(98) 00

11、041一7</p><p>　　A series of assumptions may be made after examining the work of cranes:</p><p>　　·if the monthly removal of logs from the forest exceeds the processing rate, i.e. there is a

12、creation of a log store, the crane expects work, being above the centre of a formed pile with the grab lowered on the pile stack;</p><p>　　·when processing exceeds the log removal from the forest, the c

13、rane expects work above an operational pile close to the saw mill with the grab lowered on the pile;</p><p>　　·the store of logs varies; the height of the piles is considered to be a maximum;</p>

14、<p>　　·the store variation takes place from the side opposite to the saw mill;</p><p>　　·the total volume of a processed load is on the average k=1.4 times more than the total volume of remo

15、val because of additional transfers.</p><p>　　2.1. Removal intensity</p><p>　　It is known that the removal intensity for one year is irregular and cannot be considered as a stationary process.

16、The study of the character of non-stationary flow of road trains at 23 enterprises Sverdlesprom for five years has shown that the monthly removal intensity even for one enterprise essentially varies from year to year. Th

17、is is explained by the complex of various systematic and random effects which exert an influence on removal: weather conditions, conditions of roads and lorry fleet,</p><p>　　Therefore, the less possibility

18、of removing wood in the season between spring and autumn, the more intensively the wood removal should be performed in winter. While in winter the removal intensity exceeds the processing considerably, in summer, in most

19、 cases, the more full-length logs are processed than are taken out.</p><p>　　From the analysis of 118 realizations of removal values observed for one year, it is possible to evaluate the relative removal int

20、ensity g(t) as percentages of the annual load turnover. The removal data fisted in Table 1 is considered as expected values for any crane, which can be applied to the estimation of fatigue life, and, particularly, for an

21、 inspected crane with which strain measurement was carried out (see later). It would be possible for each crane to take advantage of its load turnover</p><p>　　The distribution of removal value Q(t) per mont

22、h performed by the relative intensity q(t) is written as</p><p>　　where Q is the annual load turnover of a log store, A is the maximal designed store of logs in percent of Q. Substituting the value Q, which

23、for the inspected crane equals 400,000 m3 per year, and A=10%, the volumes of loads transferred by the crane are obtained, which are listed in Table 2, with the total volume being 560,000 m3 for one year using K,.</p&

24、gt;<p>　　2.2. Number of loading blocks</p><p>　　The set of operations such as clamping, hoisting, transferring, lowering, and getting rid of a load can be considered as one operation cycle (loading bl

25、ock) of the crane. As a result to investigations, the operation time of a cycle can be modeled by the normal variable with mean equal to 11.5 min and standard deviation to 1.5 min. unfortunately, this characteristic cann

26、ot be simply used for the definition of the number of operation cycles for any work period as the local processing is extremely </p><p>　　The volume of a unit load can be modeled by a random variable with a

27、distribution function(t) having mean22 m3 and standard deviation 6;一3 m3, with the nominal volume of one pack being 25 m3. Then, knowing the total volume of a processed load for a month or year, it is possible to determi

28、ne distribution parameters of the number of operation cycles for these periods to take advantage of the methods of renewal theory [1].</p><p>　　According to these methods, a random renewal process as shown i

29、n Fig. 2 is considered, where the random volume of loads forms a flow of renewals: </p><p>　　In renewal theory, realizations of random:，，，having a distribution function F(t), are understood</p><p

30、>　　as moments of recovery of failed units or request receipts. The value of a processed load:，，after</p><p>　　}th operation is adopted here as the renewal moment.</p><p>　　Let F(t)=P﹛＜t﹜. The

31、 function F(t) is defined recurrently,</p><p>　　Let v(t) be the number of operation cycles for a transferred volume t. In practice, the total volume of a transferred load t is essentially greater than a uni

32、t load, and it is useful therefore totake advantage of asymptotic properties of the renewal process. As follows from an appropriate</p><p>　　limit renewal theorem, the random number of cycles v required to t

33、ransfer the large volume t has</p><p>　　the normal distribution asymptotically with mean and variance.</p><p>　　without dependence on the form of the distribution function月t) of a unit load (the

34、 restriction is</p><p>　　imposed only on nonlattice of the distribution).</p><p>　　Equation (4) using Table 2 for each averaged operation month,function of number of load cycles with parameters

35、m,. and 6,., which normal distribution in Table 3. Figure 3 shows the average numbers of cycles with 95 % confidence intervals. The values of these parameters</p><p>　　for a year are accordingly 12,719 and 4

36、20 cycles.</p><p>　　3. Strain measurements</p><p>　　In order to reveal the most loaded elements of the metalwork and to determine a range of stresses, static strain measurements were carried out

37、 beforehand. Vertical loading was applied by hoisting measured loads, and skew loading was formed with a tractor winch equipped with a dynamometer. The allocation schemes of the bonded strain gauges are shown in Figs 4 a

38、nd 5. As was expected, the largest tension stresses in the bridge take place in the bottom chord of the truss (gauge 11-45 MPa). The top c</p><p>　　being less compressed than the top one (gauge 17-75 and 10-

39、20 MPa). The other elements of the bridge are less loaded with stresses not exceeding the absolute value 45 MPa. The elements connecting the support with the bridge of the crane are loaded also irregularly. The largest c

40、ompression stresses take place in the carrying angles of the interior panel; the maximum stresses reach h0 MPa (gauges 8 and 9). The largest tension stresses in the diaphragms and angles of the exterior panel reach 45 MP

41、a</p><p>　　The elements of the crane bridge are subjected, in genera maximum stresses and respond weakly to skew loads. The suhand, are subjected mainly to skew loads.1, to vertical loads pports of the crane

42、 gmmg rise to on the other</p><p>　　The loading of the metalwork of such a crane, transferring full-length logs, differs from that of</p><p>　　a crane used for general purposes. At first, it inv

43、olves the load compliance of log packs because of</p><p>　　progressive detachment from the base. Therefore, the loading increases rather slowly and smoothly.The second characteristic property is the low prob

44、ability of hoisting with picking up. This is conditioned by the presence of the grab, which means that the fall of the rope from the spreader block is not permitted; the load should always be balanced. The possibility of

45、 slack being sufficient to accelerate an electric drive to nominal revolutions is therefore minimal. Thus, the forest traveling gant</p><p>　　When a high acceleration with the greatest possible clearance in

46、the joint between spreader andgrab takes place, the tension of the ropes happens 1 s after switching the electric drive on, the</p><p>　　clearance in the joint taking up. The revolutions of the electric moto

47、rs reach the nominal value in</p><p>　　O.}r0.7 s. The detachment of a load from the base, from the moment of switching electric motors</p><p>　　on to the moment of full pull in the ropes takes 3

48、-3.5 s, the tensions in ropes increasing smoothly</p><p>　　to maximum. The stresses in the metalwork of the bridge and supports grow up to maximum</p><p>　　values in 1-2 s and oscillate about an

49、 average within 3.5%.</p><p>　　When a rigid load is lifted, the accelerated velocity of loading in the rope hanger and metalwork</p><p>　　is practically the same as in case of fast hoisting of a

50、 log pack. The metalwork oscillations are characterized by two harmonic processes with periods 0.6 and 2 s, which have been obtained from spectral analysis. The worst case of loading ensues from summation of loading ampl

51、itudes so that the maximum excess of dynamic loading above static can be 13-14%.Braking a load, when it is lowered, induces significant oscillation of stress in the metalwork, which can be }r7% of static loading. Moving

52、over</p><p>　　4. Fatigue loading analysis</p><p>　　Strain measurement at test points, disposed as shown in Figs 4 and 5, was carried out during the work of the crane and a representative number

53、of stress oscillograms was obtained. Since a common operation cycle duration of the crane has a sufficient scatter with average value } 11.5min, to reduce these oscillograms uniformly a filtration was implemented to thes

54、e signals, and all repeated values, i.e. while the construction was not subjected to dynamic loading and only static loading occurred, we</p><p>　　Fig. 6 where the interior sequence of loading for an operati

55、on cycle is visible. At first, stresses</p><p>　　increase to maximum values when a load is hoisted. After that a load is transferred to the necessary location and stresses oscillate due to the irregular cran

56、e movement on rails and over rail joints resulting mostly in skew loads. The lowering of the load causes the decrease of loading and forms half of a basic loading cycle.</p><p>　　4.1. Analysis of loading pro

57、cess amplitudes</p><p>　　Two terms now should be separated: loading cycle and loading block. The first denotes one distinct oscillation of stresses (closed loop), and the second is for the set of loading cyc

58、les during an operation cycle. The rain flow cycle counting method given in Ref. [2] was taken advantage of to carry out the fatigue hysteretic loop analysis for the three weakest elements: (1) angle of the bottom chord(

59、gauge 11), (2) I-beam of the top chord (gauge 17), (3) angle of the support (gauge 8). Statistical</p><p>　　4.2. Numbers of loading cycles</p><p>　　During the rain flow cycle counting procedure,

60、 the calculation of number of loading cycles for the loading block was also carried out. While processing the oscillograms of one type, a sample number of loading cycles for one block is obtained consisting of integers w

61、ith minimum and maximum observed values: 24 and 46. The random number of loading cycles vibe can be described</p><p>　　by the Poisson distribution with parameter =34.</p><p>　　Average numbers of

62、 loading blocks via months were obtained earlier, so it is possible to find the appropriate characteristics not only for loading blocks per month, but also for the total number of loading cycles per month or year if the

63、central limit theorem is taken advantage of. Firstly, it is known from probability theory that the addition of k independent Poisson variables gives also a random variable with the Poisson distribution with parameter k},

64、. On the other hand, the Poisson distribut</p><p>　　5. Stress concentration factors and element endurance</p><p>　　The elements of the crane are jointed by semi-automatic gas welding without pre

65、liminary edge preparation and consequent machining. For the inspected elements 1 and 3 having circumferential and edge welds of angles with gusset plates, the effective stress concentration factor for fatigue is given by

66、 calculation methods [3], kf=2.}r2.9, coinciding with estimates given in the current Russian norm for fatigue of welded elements [4], kf=2.9.</p><p>　　The elements of the crane metalwork are made of alloyed

67、steel 09G2S having an endurance limit of 120 MPa and a yield strength of 350 MPa. Then the average values of the endurance limits of the inspected elements 1 and 3 are ES一l=41 MPa. The variation coefficient is taken as 0

68、.1, and the corresponding standard deviation is 6S-、一4.1 MPa.</p><p>　　The inspected element 2 is an I-beam pierced by holes for attaching rails to the top flange. The rather large local stresses caused by l

69、ocal bending also promote fatigue damage accumulation. According to tables from [4], the effective stress concentration factor is accepted as kf=1.8, which gives an average value of the endurance limit as ES一l=h7 Map. Us

70、ing the same variation coiffing dent th e stand arid d emit ion is =6.7 MPa.</p><p>　　An average S-N curve, recommended in [4], has the form:</p><p>　　with the inflexion point No=5·106 an

71、d the slope m=4.5 for elements 1 and 3 and m=5.5 for element 2.</p><p>　　The possible values of the element endurance limits presented above overlap the ranges of load amplitude with nonzero probability, whi

72、ch means that these elements are subjected to fatigue damage accumulation. Then it is possible to conclude that fatigue calculations for the elements are necessary as well as fatigue fife prediction.</p><p>

73、　　6. Life prediction</p><p>　　The study has that some elements of the metalwork are subject to fatigue damage accumulation.To predict fives we shall take advantage of intrinsic fatigue curves, which are deta

74、iled in [5]and [6].</p><p>　　Following the theory of intrinsic fatigue curves, we get lognormal life distribution densities for the inspected elements. The fife averages and standard deviations are fisted in

75、 Table 5. The lognormal fife distribution densities are shown in Fig. 7. It is seen from this table that the least fife is for element 3. Recollecting that an average number of load blocks for a year is equal to 12,719,

76、it is clear that the average service fife of the crane before fatigue cracks appear in the welded elem</p><p>　　7. Conclusions</p><p>　　The analysis of the crane loading has shown that some elem

77、ents of the metalwork are subjectedto large dynamic loads, which causes fatigue damage accumulation followed by fatigue failures.The procedure of fatigue hfe prediction proposed in this paper involves tour parts:</p&g

78、t;<p>　　(1) Analysis of the operation in practice and determination of the loading blocks for some period.</p><p>　　(2) Rainflow cycle counting techniques for the calculation of loading cycles for a p

79、eriod of standard operation.</p><p>　　(3) Selection of appropriate fatigue data for material.</p><p>　　(4) Fatigue fife calculations using the intrinsic fatigue curves approach.</p><

80、p>　　The results of this investigation have been confirmed by the cases observed in practice, and the manufacturers have taken a decision about strengthening the fixed elements to extend their fatigue lives.</p>

81、<p>　　References</p><p>　　[1] Feller W. An introduction to probabilistic theory and its applications, vol. 2. 3rd ed. Wiley, 1970.</p><p>　　[2] Rychlik I. International Journal of Fatigue

82、1987;9:119.</p><p>　　[3] Piskunov V(i. Finite elements analysis of cranes metalwork. Moscow: Mashinostroyenie, 1991 (in Russian).</p><p>　　[4] MU RD 50-694-90. Reliability engineering. Probabili

83、stic methods of calculations for fatigue of welded metalworks.</p><p>　　Moscow: (iosstandard, 1990 (in Russian).</p><p>　　[5] Kopnov VA. Fatigue and Fracture of Engineering Materials and Structu

84、res 1993;16:1041.</p><p>　　[6] Kopnov VA. Theoretical and Applied Fracture Mechanics 1997;26:169.</p><p><b>　　附錄B</b></p><p><b>　　中文翻譯</b></p><p&g

85、t;　　龍門式起重機金屬材料的疲勞強度預(yù)測</p><p>　　v.a.科普諾夫郵箱64 ，郵編 620107 ，俄</p><p>　　收到1998年4月3日;接受1998年9月29日</p><p><b>　　摘要</b></p><p>　　內(nèi)在的疲勞曲線應(yīng)用到龍門式起重機金屬材料的疲勞壽命預(yù)測問題。起重機，用

86、于在森林工業(yè)中，在伐木林場對各種不同的工作條件進行研究，并且做出相應(yīng)的應(yīng)變測量。對載重的循環(huán)周期進行計算，下雨循環(huán)計數(shù)技術(shù)得到了使用。在一年內(nèi)這些起重機運作的樣本被觀察為了得到運作周期的平均數(shù)。疲勞失效分析表明，一些元件的故障是自然的系統(tǒng)因素，并且不能被一些隨意的原因所解釋。1999年Elsevier公司科學(xué)有限公司。保留所有權(quán)利。</p><p>　　關(guān)鍵詞：起重機;疲勞評估;應(yīng)變測量</p>&

87、lt;p>　　1.緒論  頻繁觀測龍門式起重機LT62B在運作時金屬元件疲勞失效。引起疲勞裂紋的故障沿著起重機的橋梁焊接接頭進行傳播，并且能夠支撐三到四年。這種起重機在森林工業(yè)的伐木林場被廣泛使用，用來轉(zhuǎn)移完整長度的原木和鋸木到鐵路的火車上，有一次裝載30噸貨物的能力。 這種類型的起重機大約1000臺以上工作在俄羅斯森林工業(yè)的企業(yè)中。限制起重機壽命的問題即最弱的要素被正式找到之后，預(yù)測其疲勞強度，并給制造商建

88、議，以提高起重機的壽命。</p><p>　　2.起重機運行分析  為了分析，在葉卡特琳堡地區(qū)的林場碼頭選中了一臺被安裝在葉卡特琳堡地區(qū)的林場碼頭的龍門式起重機LT62B， 這臺起重機能夠供應(yīng)兩個伐木廠建立存儲倉庫，并且能轉(zhuǎn)運木頭到鐵路的火車上，這條鐵路通過存儲倉庫。這些設(shè)備的安裝就是為了這個轉(zhuǎn)貨地點在起重機的跨度范圍之內(nèi)。一個起重機示意圖顯示在圖1中 。 1350-6307/99 /元，

89、看到前面的問題。 1999年Elsevier公司科學(xué)有限公司保留所有權(quán)利。 PH:S1350-6307(98)00041-7</p><p>　　V.A.Kopnov|機械故障分析6（1999）131-141</p><p><b>　　圖1起重機簡圖</b></p><p>　　檢查起重機的工作之后，一系列的假設(shè)可能會作出： ·

90、如果每月從森林移動的原木超過加工率，即是有一個原木存儲的倉庫，這個起重機期待的工作，也只是在原木加工的實際堆數(shù)在所供給原木數(shù)量的中心線以下；·當(dāng)處理超過原木從森林運出的速度時，起重機的工作需要在的大量的木材之上進行操作，相當(dāng)于在大量的木材上這個鋸木廠賺取的很少；·原木不同的倉庫;大量的木材的高度被認為是最高的; ·倉庫的變化，取替了一側(cè)對面的鋸軋機; ·裝載進程中總量是平均為K=1.4倍大

91、于移動總量由于額外的轉(zhuǎn)移。</p><p>　　2.1 搬運強度  據(jù)了解，每年的搬運強度是不規(guī)律的，不能被視為一個平穩(wěn)過程。非平穩(wěn)流動的道路列車的性質(zhì)在23家企業(yè)中已經(jīng)研究5年的時間，結(jié)果已經(jīng)表明在年復(fù)一年中，對于每個企業(yè)來說，每個月的搬運強度都是不同的。這是解釋復(fù)雜的各種系統(tǒng)和隨機效應(yīng)，對搬運施加的影響：天氣條件，道路條件和貨車車隊等，所有木材被運送到存儲倉庫的木材，在一年內(nèi)應(yīng)該被處理。

92、 因此，在春季和秋季搬運木頭的可能性越來越小，冬天搬運的可能性越來越大，然而在冬天搬運強度強于預(yù)想的，在夏天的情況下，更多足夠長的木材就地被處理的比運出去的要多的多。</p><p>　　V.A.Kopnov|機械故障分析6（1999）131-141</p><p><b>　　表1</b></p><p><b>　　搬運強度（%

93、）</b></p><p><b>　　表2</b></p><p><b>　　轉(zhuǎn)移儲存量</b></p><p>　　通過一年的觀察，從118各搬運值的觀察所了解到的數(shù)據(jù)進行分析，并且有可能評價相關(guān)的搬運強度（噸）參考年度的裝載量的百分比。該搬運的數(shù)據(jù)被記錄在起重機預(yù)期值表1中，它可以被應(yīng)用到估計疲勞壽命，

94、尤其是為檢查起重機應(yīng)變測量（見稍后） 。將有可能為每個起重機，每一個月所負荷的載重量，建立這些數(shù)據(jù)，無需特別困難的統(tǒng)計調(diào)查。此外，為了解決這個問題的壽命預(yù)測的知識是未來的荷載要求， 在類似的操作條件下，我們采取起重機預(yù)期值。</p><p>　　每月搬運價值的分布Q（t） ，被相對強度q（t）表示為  其中Q是每年的裝載量的記錄存儲，是設(shè)計的最大存儲原木值Q以百分比計算，其中為考察起重機等于40.0萬

95、立方米每年， 和容積載重搬運為10 ％ 的起重機，得到的數(shù)據(jù)列在表2 中，總量56000立方米每年，用K表示。</p><p>　　2.2 .裝載木塊的數(shù)量  這個運行裝置，如夾緊，吊裝，轉(zhuǎn)移，降低，和釋放負載可被視為起重機的一個運行周期（加載塊）。參照這個調(diào)查結(jié)果，以操作時間為一個周期，作為范本，由正常變量與平均值11.5分相等等，標(biāo)準(zhǔn)差為1.5分鐘。不幸的是，這個特點不能簡單地用于定義運

96、作周期的數(shù)目，任何工作期間的載重加工是非常不規(guī)則。使用運行時間的起重機和評價周期時間，，與實際增加一個數(shù)量的周期比，很容易得出比較大的誤差，因此，最好是作為如下。   測量一個單位的載荷，可以作為范本，由一個隨機變量代入分布函數(shù)得出，并且比實際一包貨物少然后，明知總量的加工負荷為1個月或一年可能確定分布參數(shù)的數(shù)目，運作周期為這些時期要利用這個方法的更新理論</p><p>　　V.A.Kop

97、nov|機械故障分析6（1999）131-141</p><p>　　圖2隨機重建過程中的負荷</p><p>　　根據(jù)這些方法，隨機重建過程中所顯示的圖。二是考慮到， （隨機變量）負荷，形成了一個流動的數(shù)據(jù)鏈：</p><p>　　在重建的理論中，隨機變量：，有一個分布函數(shù)f（t）的，可以被理解為在失敗的連接或者要求收據(jù)時的恢復(fù)時刻。過程的載荷值，作為下一次的動作

98、的通過值，被看作是重建的時刻。</p><p>　　設(shè)。函數(shù)f （ t ）反復(fù)被定義，</p><p>　　假設(shè)V （ t ）是在運作周期內(nèi)轉(zhuǎn)移貨物的數(shù)量。實踐中，總轉(zhuǎn)移貨物的總噸數(shù)，基本上是大于機組負荷，，由于利用漸近性質(zhì)的重建過程所以式有益的。根據(jù)下面適當(dāng)?shù)南拗浦亟ǘɡ恚枰D(zhuǎn)移大量噸數(shù)。已正態(tài)分布漸近與均值和方差，確定抽樣數(shù)量的周期v</p><p>　　而

99、不依賴于整個的形式分布函數(shù)的， （只對不同的格式分配進行限制）。  利用表2的每個月平均運作用方程（ 4 ）表示，賦予正態(tài)分布功能的數(shù)量，負載周期與參數(shù)m和6。在正態(tài)分布表3中 。圖3顯示的平均人數(shù)周期與95 ％的置信區(qū)間某一年的相應(yīng)的值為12719和420個周期。</p><p><b>　　表3</b></p><p><b>　　

100、運作周期的正太分布</b></p><p>　　3 .應(yīng)變測量  為了顯示大多數(shù)金屬的負載元素，并且確定一系列的壓力，事前做了靜態(tài)應(yīng)變測量。垂直載荷用來測量懸掛負載，并且斜交加載由一個牽引力所形成，配備了一臺測力計。靜態(tài)應(yīng)力值分布在圖4和5中 。同樣地預(yù)計，梁上的最大的拉應(yīng)力，發(fā)生在底部的桁架上（值為11-45 MPA ）。頂端的桁架受到最大的壓縮應(yīng)力。 此處的彎曲應(yīng)力所造成的壓

101、力，車輪起重機，手推車等被添加到所說的橋梁和負荷的重量。這些壓力的結(jié)果，在底部的共振的的I梁那么壓縮應(yīng)力比最高的1 處要大得多（值17-75和10-20兆帕斯卡），其他要素的梁加載的值</p><p>　　V.A.Kopnov|機械故障分析6（1999）131-141</p><p><b>　　月份</b></p><p>　　圖3 95%

102、的置信區(qū)間運作周期的平均數(shù)</p><p>　　V.A.Kopnov|機械故障分析6（1999）131-141</p><p><b>　　圖4梁的分配計劃</b></p><p>　　不超過絕對值45兆帕斯卡。連接與支持的橋梁起重機加載的時間，也不定期。最大的壓縮應(yīng)力發(fā)生在變形的最大角度，在內(nèi)部看來;最高壓力值將達到到h0MPa和痛苦（計8日