The flat grid structure consisting of a number of tension and compression bars connected at the joints has been widely used to construct industrial buildings, airplane hangar facilities, and public buildings due to its simple construction and better performance of the comprising members[1].Due to the intended purpose of this type of structures, suspended cranes are often used.These cranes generate repeated loading to the joints of the grid structure, especially those at the bottom chord.The fatigue failure at a joint can result in a structural collapse.For example, the grid structure of a plant in Datong City in Shanxi Province, China, collapsed locally on May 20, 2015 and the investigation shows that joint fatigue failure was the main cause.Either a welded or bolted joint at the hollow sphere was used in practice with the former accounting for about 70%[2-3].Therefore, the fatigue behavior of welded hollow spherical joints (WHSJs)under repetitive loads warrants a further study.

小波阈值去噪中应用得最为广泛的是硬阈值函数以及软阈值函数 [2].硬阈值函数的计算简单，但是具有不连续性，导致在处理后的信号中可能会存在伪吉布斯现象.软阈值函数在时域内是连续的，但是经过其处理后的信号与未带噪前相比会出现偏差问题.为了解决硬、软阈值函数上述的问题，文献[3]中对阈值函数进行改进，克服了软、硬阈值函数已有的问题，但该文献提出的改进阈值函数适用于重叠峰很少的标记荧光蛋白信号.

The WHSJs[4] were developed by Liu in 1965, which have been applied in space frame structures successfully since then, and they were adopted for technical specification for space frame structures (JGJ7—2010)[5] as a common joint type.Previous studies related to WHSJs focused on the static behavior and ultimate bearing capacity of WHSJs under axial loading and in-plane bending.Han et al.[5] conducted experimental and numerical studies to investigate the ultimate bearing capacity of WHSJs with the sphere diameter of 160 to 900 mm under axial loads.Han et al.[6]performed a full-scale joint test and nonlinear finite element analysis (FEA)to study the strength performance of the large spherical joint under multi-axial loads.Based on the experimental and FEA results, Dong et al.[7] obtained the load-carrying capacity and proposed a practical calculation method for the WHSJs connecting square steel tubes under the axial load, in-plane bending moment.Hu et al.[8-9] discussed the bearing capacity formula of WHSJs.Jiang et al.[10] studied the influence of different factors on the carrying capacity of WHSJs analytically and numerically.Xiong et al.[11-12] conducted the experimental study and FEA on full-scale large spherical joints under multi-axial loading.Ding et al.[13] found that the usual assumption of rigid connection for WHSJs was inadequate and proposed an improved computational model for WHSJs.Zhang et al.[14] studied the effects of outer rib stiffeners on WHSJ’s carrying capacity numerically.Chen et al.[15] did a parametric study using the finite element method and established an empirical formula for calculating the tensile capacity of a large WHSJ with a diameter exceeding 1 m.

Very limited research has been conducted on the fatigue performance of the WHSJs in a grid structure, mostly carried out in China.Lei[2] conducted experiments and FEAs to investigate the stress distribution on the surface of WHSJs under multi-directional tension loads and proposed a calculation formula for bearing capacity, S-N fatigue curves, and a theoretical formula for determining the stress concentration factor kf of a WPSJ.Xiao et al.[16] utilized the test and FEA results to discuss the stress distribution and fatigue performance of welded cross plate-hollow spherical joints (WCPHSJs)and concluded that the decisive factors for the joint stress were the width of the plate and the thickness of sphere.They also stated that, when the width of the cross plate is greater than a coefficient times the outside diameter of the tube, the fatigue resistance of the WCPHSJ is greater than that of the welded tube-hollow spherical joint.Xu et al.[17] presented a method for calculating the fatigue life of a WHSJ, based on the fracture mechanics field survey results of more than twenty factories with suspended cranes.Zhang et al.[18] discussed the key factors affecting the fatigue of large-scale welded structures through fatigue experiments.Jiao[19] collected and investigated 86 practical projects with suspended cranes and concluded that the fatigue issue should be considered for a grid structure with suspended cranes.Liu et al.[20] conducted a fatigue study on 16Mn base steel metal and its welded joints, and concluded that the fatigue strength of the joint was about 40% to 45% of the base metal and the fatigue crack mainly initiated at the welded toe or geometrically discontinuous location.

Part 1.9 in the current EuroCode3[21] states that no provisions contained in Table 8.5 can be used exactly for WCPHSJs and the fatigue tests should be carried out to determine the fatigue strength for details not included in the code.The current Chinese steel design code GB 50017—2003[22] states that fatigue should be assessed for a steel member and its connections under a repeated dynamic loading of 5×104 cycles.The current Chinese technical specification for space frame structures JGJ7—2010[5] also states that the fatigue of a flat space with suspended cranes should be evaluated when the number of stress cycles exceeds 5×104.The relevant allowable stress value and construction should be determined by a special fatigue test.

The Swiss made AMSLER fatigue test machine was used to simulate the constant amplitude fatigue loads on fatigue specimens during the test.The heaviest load was as high as 1 000 kN.The 1 000 kN hydraulic pressure servo fatigue machine was used to load the specimen at the frequency of 6.67 Hz.The loading cycle was represented by a strictly-controlled, smooth sine wave.

鉴于我国绝大多数AMI患者直接就诊于基层医院，而基层医院的诊治现状又极不规范，因此，规范化胸痛中心建设应该立足于建立区域协同救治模式。

1　Static Analysis of WCPHSJs

The static characteristics of the joint are essential for fatigue behavior.The WCPHSJs were statically analyzed by the software ANSYS to obtain the stress and deformation distributions on the hollow sphere under uniform tension loadings.KQ-4 as the typical specimen was chosen and analyzed, which has the following dimensions: a φ400 mm×10 mm welded hollow sphere, 2-160 mm×10 mm crossed plates, and the welded height hf of 8 mm.The material is Q235B.

The literature study[16] reveals that the crossed plate-half sphere can be used as the calculated model by assuming the fixed condition at the end of the sphere (see Fig.1(a)).Realizing that the interaction among the free ends of the four outstanding plates is relatively little, the above model may be simplified by considering only a single plate on a half sphere, the so-called single plate-half model (see Fig.1(b))[19].

(a)

(b)

Fig.1　Calculation model of the joints.(a)Cross plate; (b)Single plate

1.1　Foundation of FE model

In the FE analysis, the welding hollow sphere, cross plate, and the welding were assumed in the linear-elastic phase.The elastic modulus E of Q235B steel is 206 GPa and the Poisson ratio υ is 0.3.Linear elastic analyses were performed.The mapping division was adopted and the element type was SOLID95 (see Fig.2).The FE model consists of 1 970 elements and 12 811 nodes.The welding deficiency and residual stress caused by the joint welding process was ignored.The connection welding was considered based on the base metal material, but only the configuration size of the welding was considered.

(a)

(b)

Fig.2　The FE model.(a)Configuration model; (b)Connection of the plate and the sphere

1.2　The FEA results

The conducted tests include five types of details designed to imitate the actual fatigue details of a grid structure with suspended cranes.They are labeled as KQ-4, KQ-5, KQ-6, KQ-7, and KQ-8, as shown in Fig.4.The fatigue design principle is that the load capacity of a WCPHSJ is less than that of welded circular tube-hollow sphere.Butt welds were used at either joint type for specimens KQ-4, KQ-5, and KQ-6, while fillet welds with the root height hf of 8 mm were used at either joint type for specimens KQ-7 and KQ-8 (see Tab.1).

With the established FE model representing the joint, the stress and deformation distributions of the welded hollow sphere under uniform axial tension loading were obtained and analyzed (see Figs.3(a)and (b)).For the hot spot at the joint, the stress distribution along the radial, circumferential and the thickness directions of the hollow sphere were discussed in order to present the real stress state there (see Figs.3(c)to (e)).

1.3　Discussion of the analysis results

Figs.3(a)and (b)show that the Von-Mises stress and deformation at the free end of the connection between the crossed plate and welded hollow sphere are the greatest.

r=-0.763 3,　[Δσ]2×106=18.38 MPa

Figs.3(c)to (e)also show that:1)The normal stresses in the three directions (i.e., σθ,σφ,σR)at the hot spot are all greater than zero, indicating all tension and the worst stress condition; 2)The radial stress σθ decreases rapidly with the distance from the hot spot (the stress at 10 mm location being only 33.7% of that at the hot spot); 3)The circumferential stress σφ also decreases rapidly and is reversed at 28.6 mm location(σφmin≈10.5% of σφmax); 4)The stress along the sphere thickness σR reverses sign across the thickness with tensile stress prevailing over 64% of the thickness (σRmin≈36.0% of σRmax).

In conclusion, the weld toe location at the free end of the plate of a WCPHSJ is most critical, where fatigue failure will initiate.

2　Experimental Program

The main purpose of the fatigue tests is to develop the stress-loading cycle curves (i.e., S-N curves)for WCPHSJs.According to the Chinese standard[23], at least 14 sets of fatigue data are required to derive an S-N curve, in which about 8 sets will be used to develop the inclined portion of the curve and the remaining 6 sets will be used to achieve the horizontal part.Gurney[24] also reported that 8 to 12 similar specimens are needed to be tested to obtain the fatigue strength of a connection under random repeated loading conditions.EuroCode3[21] also specifies that a number of data points no less than 10 should be considered in the statistical analysis.

(a)

(b)

(c)

(d)

(e)

Fig.3　The FEA results.(a)The Von-Mises stress diagram; (b)The deformation diagram; (c)The radial stress distribution diagram; (d)The circumferential stress distribution diagram; (e)The stress distribution along the sphere thickness diagram

2.1　Specimen design

The main task of the FE model for the specimen was to determine the location of the hot-spot and its stress condition.As such, the initial location of fatigue cracks can be determined.For the static linear-elastic analysis using the single plate-half model, the interaction effect between the cross plates was found to be negligible.Hence, for simplification, this model was adopted in the subsequent analyses.All analysis results were found to be reasonably accurate.Fatigue failure analysis for the specimens was not conducted.

The initial crack sources in KQ-7-6 fatigue fracture were magnified 60 times (see Fig.10(a))to observe more clearly that some small black voids exist in the bottom right region of fatigue sources and the developed fatigue zone is flat and smooth with radial shell-like lines.The initial defects found were due to the heat treatment during the test process.The crack source magnified 2 000 times (see Figs.10(b)and (c))shows more clearly that apparent fatigue source appears and tiny grain-size defects show up on the left side of the central region.In addition, Fig.10(c)also indicates that fatigue propagation is obvious and the interval of bay ridges becomes increasingly constant with the fatigue crack propagation after the initiation of the fatigue cracks.Fig.10(d)clearly shows each fatigue striation in the fatigue stripe in the fatigue propagation region that was magnified 5 000 times.

(a)

(b)

(c)

(d)

(e)

Fig.4　Fatigue details of the specimens (unit: mm).(a)KQ-4;(b)KQ-5;(c)KQ-6;(d)KQ-7;(e)KQ-8

Tab.1　Geometrical characteristics of the specimen

SpecimenlabelTestednumberD×t/(mm×mm)d×t1，b×t2/(mm×mm)αConnectiontypeKQ⁃43ϕ400×10ϕ159×10，2⁃160×101．47ButtweldKQ⁃56ϕ400×10ϕ159×10，2⁃210×101．08ButtweldKQ⁃62ϕ400×10ϕ159×10，2⁃260×100．84ButtweldKQ⁃77ϕ400×10ϕ159×10，2⁃160×101．95FilletweldKQ⁃81ϕ400×10ϕ159×10，2⁃210×101．40Filletweld

Notes:D is the diameter of the welded hollow sphere; t is the thickness of the sphere; d is the diameter of the steel tube; t1 is the thickness of the steel tube; b is the width of the crossed plate; t2 is the thickness of the crossed plate; α is the limit strength ratio of the steel tube welded sphere and the cross plate welded sphere.

2.2　Test rig

The test rig (see Fig.5)is intended to test the specimens to study the fatigue behavior of WCPHSJs under the constant amplitude load.It was designed to be self-reacting and situated on the floor and the setup was relatively simple.Preliminary fatigue tests demonstrate that the test rig is efficient, stable, reliable, time saving, and cost effective.

(a)

(b)

Fig.5　Load program.(a)Central loading condition; (b)Bilateral loading condition

2.2.1　Load program

Two specimens were fixed on the steel beam in the test rig under the central loading condition (see Fig.5(a)), with its bottom connected with a pair of M33 high strength bolts and the top pinned to the rig by studs.The advantage of central loading is that the loads can be applied to two similar specimens at the same time.In addition, if one of the specimens fails in fatigue, then one of the following two alternatives may be considered: 1)Replace the damaged specimen with a new one and impose the load; 2)Apply a further increasing load to the undamaged specimen.The disadvantage of central loading is that the maximum load is limited to 50 t for each specimen as the fatigue machine can only accommodate 100 t of load capacity.

One specimen was fixed in the middle of the steel beam in the test rig under the bilateral loading condition (see Fig.5(b)), with its bottom connected by two pairs of M33 high strength bolts and its top also pinned to the rig by studs.The advantage of bilateral loading is that the maximum load stretches to 200 t, twice as large as the load capacity of the fatigue machine.

与成人重度窒息所致脑灰质弥漫性受损表现不同，HIBD对新生儿脑组织损伤位置具有很强选择性，且不同成熟度的新生儿脑损伤位置也呈不同的特点。这与新生儿脑组织各部位对能量需求强弱、缺氧缺血发生时间、性质及脑血管解剖生理等有很强相关性[6-7]。Logitharajah等[8]研究表明机体发生急性缺氧缺血性窒息时，脑内血流再分布代偿机制会失效，常易发生在代谢能量需求最旺盛基底节、丘脑等部位脑损伤。本研究发现新生儿窒息的病例MRI双侧苍白球区呈稍短T1WI异常信号，考虑为缺氧缺血性脑损伤和高胆红素血症脑损伤所致[9]。这也是本研究将轻度缺氧缺血性脑损伤病例的感兴趣区放置于双侧基底节的苍白球区原因。

2.2.2　Test equipment

To this date, fatigue study for WHSJs is rather limited, relative to the study of static behavior.Consequently, the current design specifications do not have a specific fatigue provision for WHSJs in a grid structure.Designers have thus been forced to design such joints solely based on past experiences, raising concerns on structural reliability and safety.It is therefore warranted to study further the fatigue of the joints in a grid structure.Current construction practice of the suspension joints in a grid structure consists of two common kinds of joints: a welded steel tube-hollow sphere joint and a welded cross-plate hollow sphere joint (WCPHSJ).In this paper, both experimental and theoretical analyses on constant fatigue behaviors of WCPHSJs in a grid structure under repeated loads are presented, as well as the constant amplitude fatigue calculating method.

在油井生产过程中，石油在地层压力的驱动下流入井底，在井底压力作用下又沿井筒向上流动。随着流动压力的逐步降低，溶解在石油中的天然气在低于饱和压力下伴生、分离出来，进入套管与油管之间的环形空间，就形成了套管气。套管气在套管环形空间内积聚所形成的压力，称为套压。套压的变化将直接影响油井的工况。主要表现在以下几个方面：

2.3　Fatigue test results and fatigue failure modes

2.3.1　Test results

Based on the test rig and pre-determined load program, five types of total 19 specimens were tested under various constant amplitude loads in ascending load order.The test results are summarized in Tab.2.

2.3.2　Fatigue failure modes

Based on the analysis of broken specimens, all 5 different specimen types appear to display a similar fatigue failure mode, namely the fatigue crack initiated on the edge of the weld toe at the joint between the cross plate and the sphere and then propagating circumferentially around the sphere with the diameter equaling the width of the entire cross plate.Typical failure modes of the specimens are shown in Fig.6.

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(b)

(c)

(d)

Fig.6　Failure mode of fatigue specimens.(a)KQ-4-1;(b)KQ-5-13;(c)KQ-6-17; (d)KQ-7-3

2.3.3　Metallographic analysis of fatigue fracture

Metallographic analysis is a very important tool to detect material or a member fatigue fracture from the fracture form and presents some details of fatigue fracture.It can also provide important information of crack nucleation, crack initiation, crack propagation, and final fracture etc.An electron scanning microscope (TESCAN Mira3 LMH)was used to observe the precise fatigue fracture form and features.Through the constant amplitude fatigue tests on specimens KQ-4, KQ-5, KQ-6, KQ-7, and KQ-8, macroscopic and microscopic metallographic analyses were made to determine the fatigue fracture mechanism of WCPHSJs.

Tab.2　Test results of welded cross plate-hollow sphere joints under constant amplitude load

Specimenlabelσmax/MPaσmin/MPaΔσ/MPalg(Δσ)N/104lg(N)ρKQ⁃4⁃235．313．9731．341．50100．476．000．113KQ⁃4⁃425．382．9922．391．35104．036．020．118KQ⁃4⁃623．392．7920．601．312006．300．119KQ⁃5⁃126．923．0323．891．3890．275．960．113KQ⁃5⁃2∗48．9614．6934．271．5365．415．820．300KQ⁃5⁃3∗43．5213．0530．471．4862．715．800．300KQ⁃5⁃8∗46．544．6541．881．6246．115．660．100KQ⁃5⁃13∗95．647．847．81．6815．725．200．500KQ⁃5⁃18∗49．084．9144．171．6523．705．370．100KQ⁃6⁃14∗57．728．828．81．46106．376．030．500KQ⁃6⁃17∗65．332．732．71．5172．85．860．500KQ⁃7⁃132．353．6828．661．4687．275．940．114KQ⁃7⁃223．392．7920．601．31196．446．290．119KQ⁃7⁃431．353．5827．771．44131．606．120．114KQ⁃7⁃630．363．4926．871．4347．595．680．115KQ⁃7⁃1128．373．2925．081．4030．105．480．116KQ⁃7⁃1328．373．2925．081．4077．275．890．116KQ⁃7⁃1426．383．0923．291．3794．545．980．117KQ⁃8⁃1∗54．4016．3338．081．5830．945．490．300

Note: Specimens with * are subjected to the bilateral loading condition, and other specimens are subjected to the central loading condition; F is the axial load of fatigue specimens, kN; b is the width of crossed plate; t is the thickness of sphere; σ=F/πbt is the nominal stress of fatigue specimens; Δσ=σmax-σmin is the stress range; ρ=σmin/σmax is the stress ratio.

Some typical fatigue fractures surfaces for specimens KQ-7-4/6 are described as follows.Fig.7 show that the initial defects induced from manufacturing, pores and inclusions are the main source contributing to the fatigue problem.

高压氧(hyperbaric oxygen，HBO)在外科的一些领域已经证实可以促进伤口恢复，减轻瘢痕增生。本研究通过动物实验研究HBO对减轻鼻腔黏膜术后恢复过程中产生的瘢痕粘连是否有效。

(a)

(b)

Fig.7　Macro-fracture surface of fatigue specimen.(a)KQ-7-4; (b)KQ-7-6

Fig.7(a)also shows that the tiny vertical cracks in specimen KQ-7-4 lie in the sunken fracture zone where two bright blocks are noted.This implies that two fatigue sources exist in the fatigue fracture and both are in the initial stage of fatigue cracking.Each fatigue source propagates separately at first, then combines into a bigger crack source, and continues to propagate until broken.Fig.7(b)also shows the bright semi-circular region exists in the middle sunken fracture zone of specimen KQ-7-6.It has been determined as the fatigue source of the specimen.

审查该产品的专家这样评论：“Calyxt公司将其豆油作为‘非转基因’食品销售给食品制造商，给出的解释是，该产品不含有任何外源遗传物质。”

The two initial crack sourcesⅠ and Ⅱ in KQ-7-4 fatigue fracture were magnified 60 times (see Figs.8(a)and 9(a))to observe more clearly that some small voids exist in the middle region of fatigue sources.These initial defects detected were caused by the pores or inclusions during the test process, which led to fatigue source initiation.The first crack source magnified 2 000 times shows more clearly the propagated direction of the fatigue cracks (see Figs.8(b)and 9(b)).

The circular tube, welded hollow sphere, cross plate, and cover plate were fabricated from Q235B steel.The sphere meets the requirement of JG/T 11—2009[25] and all welded hollow sphere joints were not stiffened.

2.4　Constant amplitude fatigue design method

Nineteen effective fatigue test results listed in Tab.2 are taken to perform the regression analysis to obtain constant amplitude S-N curves of WCPHSJs in a grid structure, as shown in Fig.11, where Δσ is the stress constant amplitude and N is the number of loading cycles.

Based on the discrete fatigue test data shown in Fig.11, the following S-N equation is derived:

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(b)

Fig.8　Micro-fracture surface of KQ-7-4(Ⅰ).(a)Magnified 60 times; (b)Magnified 2 000 times

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(b)

Fig.9　Micro-fracture surface of KQ-7-4(Ⅱ).(a)Magnified 60 times; (b)Magnified 2 000 times

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(b)

(c)

(d)

Fig.10　Micro-fracture surface of KQ-7-6.(a)Magnified 60 times; (b)Magnified 2 000 times (overall region); (c)Magnified 2 000 times (partial region); (d)Magnified 5 000 times

The constant amplitude fatigue design method for WCPHSJs (Eq.(1))assumes Δσ as the design variable.The conventional fatigue design criterion can be described by

企业存在对HSE管理体系运行监督不严格、不系统、不全面的实际问题，难以实现对HSE管理体系运行的有效调控，出现了监督缺位、工作缺失等一系列问题。代表性的问题有：一是，企业没有对HSE管理体系运行的重点监督体系，出现对HSE管理体系实际运行的控制不良、监督不系统等问题，特别是对于HSE管理体系运行的细节难以达到全面控制，被表面性的日常工作所困扰而造成监督效果和功能不良等问题。二是，监督体系中没有将预防思想作为监督工作的第一原则，“以罚代管”、“以查代管”的问题频繁出现，难以确保HSE管理体系全面、系统地运行，产生了HSE管理体系运行的危害性和危险性。

(1)

各个子模型可以准确的表达非线性系统在各个建模工况点附近的动态信息，由此构成的多模型集完全包含了被控对象的动态信息。取得被控对象的阶跃响应模型ai后，假设控制器的输出保持不变，未来N个时刻的对象输出有初始预测值系统在稳态启动时便可取其中k+i|k表示在k时刻对k+i时刻的输出预测。Δu(k)表示k时刻控制器的控制增量值。由此，可利用线性系统叠加性质计算出在控制增量作用下被控对象未来时刻的输出值，如式(2)所示：

(2)

where r is the correlation coefficient and [Δσ]2×106 is the allowable maximum nominal stress amplitude corresponding to 2×106 loading cycles.

lgN=10.980 0-3.507 3lg(Δσ)±0.245 6

Fig.11　Constant amplitude S-N curves

Δσ≤[Δσ]

(3)

(4)

where Δσ=σmax-σmin, σmax is the maximum radial stress at the intersection of a joint and Δσh is the minimum radial stress; C and β are the two relevant coefficients, and their values are 0.955×1011 and 3.507 3, respectively.

3　Fatigue Design Method Based on Hot-Spot Stress Amplitudes

To assess the fatigue strength of a WCPHSJ, the hot spot stress is more suitable than the nominal stress[16].Considering the complex configuration of the joint and taking the advantage of the conventional fatigue design, a fatigue design method using the hot spot stress amplitude as a design variable is feasible, which is capable of indicating the actual stress state in the fatigue crack resource.

但是，这种建立在私人银行信贷业务基础上的自由开放的金融秩序并没有坚持很长时间。随着1929年美国股市的崩溃以及随之而来的世界范围的大萧条的出现，国家间债务及清偿问题再次成为人们关注的焦点。危机之初，发达国家试图通过去政治化的中央银行的合作以及建立国际清算银行等手段来挽救自由开放的国际金融秩序，但是这些努力都没能阻挡住国内、外金融市场信心的崩溃。1931年，随着投机资本的泛滥，美国终止对欧洲的长期贷款，德国和奥地利又恢复了外汇管制，而英国则在危机中放弃了金本位制度。自由主义所建立的国际金融秩序轰然倒塌。

3.1　Stress concentration factor kf at the hot spot location

A total of 25 finite element analyses (FEAs)were performed to analyze the WCPHSJs, which considered five parameters (sphere out-diameter, sphere thickness, cross plate width, cross plate thickness, and filled weld height), with each parameter varying 5 times.

In addition, a static test was conducted for one representative specimen to verify the FEA results[19].Both the FEA and test results indicate that the critical point or hot spot occurs at the weld toe of the free end intersection between the plate and sphere, and that the radial stress in the sphere at the hot spot location is very significant compared to the circumferential stress and the stress along the sphere thickness.This is in line with what has been reported[16].Based on the linear regression analysis, a kf formula for the plate end at the plate-sphere intersection may be derived.For the different specimens investigated, the kf values at the hot spots range from 3.176 to 5.365[19].

3.2　Fatigue design formula

Considering the stress distribution on the surface of a WCPHSJ, spherical radial stress at the weld toe at the end plate-sphere intersection was chosen as the main variable for the fatigue design method.For safer designs, the kf value of 3.176 is recommended to be multiplied to both sides of Eq.(3).The fatigue strength corresponding to N of 2×106 cycles is viewed as an international unified standard, which yields the allowable hot-spot stress amplitude of 62.44 MPa.The following fatigue design formula is suggested:

Δσh=kfhΔσ≤[Δσh]2×106

(5)

where Δσh is the hot spot stress amplitude and kfh is the stress concentration factor at the hot spot.

4　Conclusions

1)Fatigue failure is likely for welded cross plate-hollow sphere joints in a grid structure under repeated crane loads.Attention to the fatigue behavior of such suspension joints should be taken in design and erection.

解析：(1)这种解释合理,它体现了铝热反应的特点之一,即放热较多,并且解释时结合了表中提供的熔点数据。(2)证明某固体是不是含有铝,只要取少量块状熔融物,加入足量NaOH溶液即可,若含有铝,则固体部分溶解,有气泡产生,反应的离子方程式为(3)铝、铁熔融物在一定条件下与浓硫酸或稀硝酸反应,会产生有毒气体,而且消耗的两种酸量又多,熔融物中铁不能与NaOH溶液反应,故最好选用稀硫酸溶解该熔融物。

此外，《人民法院办理刑事案件排除非法证据规程（试行）》规定，法庭对证据收集的合法性进行调查的，应当重视对讯问录音录像的审查。据此，如果被告人在审判阶段提出非法证据排除的申请并且提供了相应的材料，法庭认为现有证据无法排除非法取证可能性的，应有权调取监察机关取证时的录音录像。因此，如果监察机关认为录音录像不适合移送司法机关的，应当由监察机关调查人员出庭就证据收集的情况进行说明，如果仍然无法排除非法取证可能性的，相关证据不能作为定案的依据。

2)Fatigue failure generally occurs at the weld toe location where severe stress is concentrated, as evidenced by the test and FEA results.For welded cross plate-hollow sphere joints, fatigue cracks initiate at the weld toe and then propagate circumferentially around the sphere with a diameter equivalent to the width of the cross plate until fatigue fracture.

3)The metallographic analysis shows that unavoidable initial welding defects caused by the surface processing may lead to a fatigue failure at the joint.

4)A better fatigue design method based on hot-spot stress amplitudes (Eq.(5))and the relevant S-N curves (Fig.11)for the welded cross plate-hollow sphere joints are suggested.

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