铝合金铸锭铣床翻锭机的改造

通过对铝合金铸锭铣床翻锭机的改造，避免了翻锭机传动轴的断裂。保证了该设备的正常运转。满足了生产的要求。     

Quadratic damage rule in random loading case

The simple mathematical structure of the quadratic damage rule (QDR) enables mathematical expression of the failure condition in the case of random loading. Random loading after modified rainflow analysis is considered as a random marked point process. Moments of the damage distribution can be expressed by use of ensemble averages. A condition for validity of the first damage moment solution is formulated. The QDR damage first moment solution involves failure predictions for both stationary and non‐stationary loadings. In these cases, final fracture conditions suitable for practical use are derived. QDR predicts fatigue lives that are always shorter than the linear damage rule (LDR) in the case of stationary loading with short interval of statistical dependence of random variables. QDR appears to be a suitable additional engineering tool for random loading fatigue life predictions considering loading sequence and loading level interactions.     

Effect of corrosion on mass loss, and high and low cycle fatigue of reinforcing steel

The effect of various levels of corrosion on the mass loss, and the high and low cycle fatigue of BSt500_s steel reinforcement were experimentally investigated. The mass loss, the fatigue limit, and the life expectancy were reduced by 1.5 to 2.9%, 20 to 40%, and 56 to 76%, respectively, according to the corrosion level. Low cycle strain-controlled fatigue testing under a ±1% constant amplitude strain showed that the corroded steel bars exhibit a gradual reduction in the load-bearing ability, the available energy, and the number of cycles to failure. The considerable reduction in the fatigue limit took place because the mass loss led to a reduction of the exterior hard layer of martensite and a drastic drop in the energy density of the corroded specimens, thus developing stress concentration points that are highly localized at imperfections, and especially in the pits and notches of the rib bases of the corroded steel. Because corrosion and cycle fatigue are time-dependent, it seems that steel reliability is also time-dependent.     

CZ70-1型静水压试压机移动车体的Pro/E分析

采用Pro/E软件对CZ70-1型静水压试压机移动车体进行了应力分析,找出了移动车体车箱在最恶劣工况下的应力分布规律,并对车箱进行了优化设计,对车体的易损件滚动轮轴进行了疲劳强度分析。最后对该移动车体的结构设计提出了建议。     

Effects of strain ratio and tensile hold time on low-cycle fatigue of lead-free Sn-3.5Ag-0.5Cu solder

Low-cycle fatigue (LCF) behavior of a lead-free Sn-3.5Ag-0.5Cu solder alloy was investigated at various combinations of strain ratio (R = −1, 0, and 0.5) and tensile hold time (0, 10, and 100 sec). Results showed that the LCF life of the given solder, at each given combination of testing conditions, could be individually described by a Coffin-Manson relationship. An increase of strain ratio from R=−1 to 0 and to 0.5 would cause a significant reduction of LCF life due to a mean strain effect instead of mean stress effect. LCF life was also markedly reduced when the hold time at tensile peak strain was increased from 0 to 100 sec, as a result of additional creep damage generated during LCF loading. With consideration of the effects of strain ratio and tensile hold time, a unified LCF lifetime model was proposed and did an excellent job in describing the LCF lives for all given testing conditions.     

Cyclic Fatigue Fracture of Zr55Al10Ni5Cu30 Bulk Amorphous Alloy with Quenched-in Crystallites

The effects of quenched-in crystallites on the fracture of bulk amorphous alloys under cyclic loading condition were investigated in this paper,For the fully amorphous alloy and specimen with fine crystallites the fatigue crack initiation occurred on the surface,For the specimen with larger cystallites the crack originated from a big broken crystallite near the surface,The average striation spacing on amorphous area is much larger than that on the crystallite Crack initiation occurred at the cystallites is due to that the brittle cyrstallites broke easily under cyclic deformation condition.The fine cystallites seemed to be protruded from the amorphous matrix and some bulges appeared on the surface of specimen with fine crystallites under cyclic loading.     

The effects of loading waveform and microstructure on the fatigue response of titanium aero-engine compressor disk alloys

Microstructural variations produced from manufacturing processes and their influence on fatigue crack growth in titanium disks were investigated. Charpy‐tests on titanium disk material were performed and materials with fracture energy values in the range of 3.8–19.1 J/cm² were selected for tests under cyclic loads. Results of Charpy‐tests were compared with fractographic features related to fatigue crack growth in Ti?6Al?3Mo?0.4Si and Ti?6Al?3Mo?2Cr alloys with a two‐phase (α + β) lamellar structure under various cyclic waveforms using specimens made from compressor disks. The material sensitivity to cyclic load waveform can be seen for in‐service disks using a criteria based on fracture energy values determined in Charpy‐tests. A difference in fatigue crack growth periods of 2.5 times was discovered for specimens made from the disk with a filament type microstructure and the mainly globular two‐phase structure of the Ti?6Al?3Mo?0.4Si alloy. The shorter crack growth period correlated with the mainly facetted pattern formation with local zones of fatigue striations when fatigue crack growth is along the planes of the filaments. Fatigue striations are the major fracture surface relief when crack growth occurs in the perpendicular direction to the plane of the filaments. A quantitative fractographic method for estimating the crack growth period for in‐service failed disks was performed for the case of crack development along planes of such microstructural filaments created during the manufacturing process. Specimen tests involving a hold‐time in the cyclic loads are recommended for in‐service accepted titanium disks using a criteria based on the fracture energy value. Selection of disks based on these criteria can indicate a material sensitivity to cyclic load waveforms.     

Linear elastic fracture mechanics (LEFM) analysis of the effect of residual stress on fatigue crack propagation rate

In this research, both residual and applied stresses are converted to stress intensity factors independently and combined using the superposition principle. The fatigue crack propagation rates are predicted. Experiments using two different loading modes, constant applied stress intensity factor (SIF) range, and constant applied load modes are done for samples with and without initial tensile residual stresses. The samples with initial tensile residual stresses exhibit accelerations of the crack propagation rates. The results show that the weight function method combined with the three-component model provides a good prediction of fatigue crack propagation rates in tensile residual stress fields.     

Investigation of the Relationship between Strains in the Crystallographic Planes and the Fatigue Life of Monocrystals of Molybdenum

The results of fatigue testing of monocrystals of molybdenum with six different crystallographic orientations about the loading axis are studied from the viewpoint of the analysis of the limiting state with regard for the specific features of these monocrystals. It is shown that, in some cases, the limiting state can be described on the basis of well-known approaches modified as applied to the properties of monocrystals and specific features of the deformation and fracture processes in crystallographic planes.