Fatigue behavior and damage mechanism of aluminum foam sandwich with carbon-fiber face-sheets

Aluminum foam sandwich (AFS) has been used in engineering field, where cyclic loading is in most of the applications. However, limited research has been done on the fatigue behavior of AFS. In the present study, fatigue performance of AFS made of aluminum foam core and carbon-fiber face-sheet was studied experimentally by a high frequency fatigue test machine and the damage mechanisms of the structure were studied by SEM. Results indicated that the fatigue life of AFS decreased with the increasing loading level. The S-N curve of AFS obeys three-parameter lognormal distribution in most of the cases. AFS was sensitive to cyclic loading level and the load capacity after cyclic loading improved significantly when the cyclic loading level was lower. The main life of AFS was its crack initiation stage. Three categories of damage mechanisms were observed. This study is of great significance to the design and application of AFS.

     

Experimental investigation on low energy impact behavior of foam cored sandwich composites

This study focuses on an experimental investigation of damage tolerance of the foam cored sandwich composite subjected to low energy impact. Tests are performed to correlate delamination length with failure loads and loss of damage tolerance of the sandwich composite. The impact force history is used to determine momentum imparted to the specimen, the work done on the specimen, and the kinetic energy in order to gain an understanding of the mechanisms involved in damage due to impact loading.     

An investigation of the markings on wear and fatigue fracture surfaces

The worn surfaces of three polymers sliding against a lapped steel disk were studied by scanning electron microscopy (SEM) and transmission electron microscopy. The surfaces of polymethylmethacrylate and high density polyethylene were covered with bands of arced ripples stretched along the transverse direction. The shape of these ripples is consistent with the distribution of tensile principal stress in the contact zone for a hemispherical indenter sliding on a plane surface. The Polyvinylchloride surface suffered severe plastic deformation during sliding as discerned by the dimples on it. The fatigue fracture surfaces of these materials were also examined by SEM. The polymethylmethacrylate surface exhibited a series of striations whose spacing increased in the direction of crack propagation. The striations on high density polyethylene and Polyvinylchloride surfaces were not observed because fracture was accompanied by considerable plastic deformation. This study shows that the mechanism of the separation of a wear particle from the sliding surface is cumulative damage as encountered in fatigue.     

A study on fracture characteristic of structural adhesive at bonded specimen made by 3D printer

Journal of Mechanical Science and Technology - This study aims at investigating the fracture characteristics of adhesive used at double cantilever beam specimens made by 3D printers. The experiment...     

Effect of a brazing process on mechanical and fatigue behavior of alclad aluminum 3005

Alclad aluminum 3005, intended for use in a radiator tube, was evaluated to identify its tensile strength, fatigue behavior, and microstructure. The material consists of an AA3005 core, an AA4343 clad (outer side), and an AA7072 (inner side). To determine the effect of the brazing process, Al alloys before brazing and after brazing were examined with SEM, EDS and nanoindentation tests. Tensile tests were performed to estimate the fatigue behavior. And fatigue tests were performed under constant load amplitudes with mean loads. The mean stress effect on the fatigue behavior of the brazed aluminum was found to correlate well with the Smith-Watson-Topper relation.     

An investigation into the rapid prototyping of moulds for expanded polystyrene foam

Expanded polystyrene foam, a packaging material, is traditionally injection-moulded by classical moulding techniques. However, the design and fabrication of these moulds is both intricate and time-consuming. In today's manufacturing environment of short time-to-market, the luxury of producing a mould for, often, a first-off article for client approval, is virtually untenable. Rapid prototyping technologies appear to offer an alternative method of fabrication which promises to drastically reduce the time for mould fabrication. When rapid prototyping of the mould is combined with microwave curing of the polystyrene, as an alternative source of energy to traditional steam heating, the benefit of considerably short throughput times can be expected. This paper describes the computer-integrated design and fabrication of both the mould and foam product, and discusses the main issues associated with rapid prototyping the mould, viz. accuracy of the prototype mould and the suitability of acrylic resin used in stereolithography apparatus for fabricating the mould, as well as the parameters for moulding expanded polystyrene using microwave energy. Initial results suggest that both the stereolithography process, and the acrylic resin used to build the stereolithographic model, can be used for rapid prototyping expanded foam products and their associated mould.     

An investigation on sliding wear behavior of PVD coatings

Ti-6Al-4V alloy rubbing against aluminum-bronze 630 was evaluated in this work. High velocity oxygen fuel (HVOF) WC-10%Co-4%Cr thermal sprayed and TiN, CrN and DLC physical vapor deposition (PVD) coatings were applied to increase titanium substrate wear resistance. Pin-on-disk tests were performed with a normal force of 5 N and at a speed of 0.5 m/s, with a quantitative comparison between the five conditions studied. Results showed higher wear resistance for Ti-6Al-4V alloy DLC coated and aluminum-bronze 630 tribological pair and that the presence of graphite carbon structure acting as solid lubricant was the main wear preventing mechanism.     

泡沫铝夹芯结构高速移动工作台研究

为满足高速、超高速加工对机床移动工作台轻质高动态性能的要求,设计了以铸铁为面板、泡沫铝为芯体材料的夹芯结构移动工作台,并利用有限元分析软件研究了该工作台的静、动态特性。研究结果表明与传统铸铁材料工作台相比,泡沫铝夹芯结构移动工作台具有质量轻、固有频率高、谐振响应幅值低等特点,从而证明了泡沫铝夹芯结构工作台在高速、超高速加工中应用的可行性和优越性。     

模数式桥梁伸缩装置疲劳试样尺度研究

为了研究模数式桥梁伸缩装置采用单跨试样代替三跨试样进行疲劳试验的可行性,首先采用力学简化模型对伸缩装置主要构件两种受力情况进行分析,再利用Ansys分析软件分别建立了整体加强320伸缩装置单跨试样与三跨试样的有限元模型,对伸缩装置进行强度对比分析.结果表明:在同种加载情况下,单跨模型中梁最大应力较多跨模型大,而多跨模型...     

Experimental investigation of fatigue behavior of spur gear in altered tooth-sum gearing

This paper deals with the contact stress, power loss, and pitting of spur gear tooth in altered tooth-sum gearing for a tooth-sum of 100 teeth when altered by±4% tooth-sum. Analytical and experimental methods were performed to investigate and compare the altered tooth-sum gearing against the standard tooth-sum gearing. The experiments were performed using a power recirculating type test rig. The tooth loads for the experimental investigations were determined considering the surface durability of gears. A clear picture of the surface damage was obtained using a scanning electron microphotograph. The negative alteration in the tooth-sum performed better than the positive alteration in a tooth-sum operating between specified center distances.     

粉煤灰漂珠/聚氨酯复合泡沫铝材料压缩性能与本构关系研究

采用压力渗透法制备出了铝基复合泡沫材料,填充材料是以粉煤灰漂珠为主要组分、硬质聚氨酯泡沫为粘结剂的复合泡沫材料.通过准静态实验和分离式霍普金森压杆(Split Hopkinson pressure bar,SHPB)动态压缩的方法研究了复合泡沫铝的压缩力学响应,然后建立了动态本构关系.研究表明,复合泡沫铝的压缩应力-应变曲线与其它泡沫材料的应力-应变曲线类似,文中的两种铝基复合泡沫具有应变率效应,复合泡沫铝较密度相近未填充前的泡沫铝基具有更高的压缩强度与能量吸收能力.但由于漂珠尺寸的不同,导致两种复合泡沫铝的动态压缩结果不尽相同,且小颗粒复合泡沫铝在动态冲击下吸能效果最好.在本研究实验的应变率和密度范围内,本文建立的本构模型曲线与实验曲线吻合较好.     

粉煤灰漂珠/聚氨酯复合泡沫铝材料压缩性能与本构关系研究

采用压力渗透法制备出了铝基复合泡沫材料,填充材料是以粉煤灰漂珠为主要组分、硬质聚氨酯泡沫为粘结剂的复合泡沫材料.通过准静态实验和分离式霍普金森压杆(Split Hopkinson pressure bar,SHPB)动态压缩的方法研究了复合泡沫铝的压缩力学响应,然后建立了动态本构关系.研究表明,复合泡沫铝的压缩应力-应变曲线与其它泡沫材料的应力-应变曲线类似,文中的两种铝基复合泡沫具有应变率效应,复合泡沫铝较密度相近未填充前的泡沫铝基具有更高的压缩强度与能量吸收能力.但由于漂珠尺寸的不同,导致两种复合泡沫铝的动态压缩结果不尽相同,且小颗粒复合泡沫铝在动态冲击下吸能效果最好.在本研究实验的应变率和密度范围内,本文建立的本构模型曲线与实验曲线吻合较好.     

A study of the thermal behaviour of a specimen during fatigue

A steel specimen (XC 10), submitted to fatigue by alternating symmetrical torsion, gives rise to heat dissipation, which is a function of the amplitude of the applied forces.The relationship between the amplitude of the applied forces and the quantity of heat dissipated was measured while a specimen underwent fatigue testing (E_n curves).The results appear to show that this relation is not identical for similar specimens at the beginning of the tests, initial state which is assumed to correspond to something like a “virgin state”, but that there is a convergence of the E_n curves as rupture is approached.     

An investigation on the fuel behavior for a PFI type motorcycle engine

Recently, the electrically controlled fuel injection type motorcycle has been emphasized in order to meet regulations for exhaust emissions. However, there are many difficulties in selecting the control parameters because the pulsation phenomenon occurs in the intake port due to the higher speed operating range and the smaller layout than for a passenger car. Therefore, we investigated the injector spray characteristics which are applied to a 4-valve motorcycle gasoline engine. The spray characteristics were visualized by using a CCD camera synchronized with the stroboscope at 6000 rpm. Furthermore, we compared the simulation results using the VECTIS code with experimental results. The results showed that the trajectory of the spray was directed towards the lower wall of the intake port when the fuel was injected at closed valve timing. On the other hand, when the fuel was injected at open valve timing, a large portion of the fuel was lifted towards the upper half of the port. In addition, open valve injection makes fuel evaporation time short; this resulted in better mixture formation than a closed valve injection. From this result, we found that injection timing has a great effect on the mixture formation within a motorcycle cylinder.     

An investigation on collapse behavior of shear localization in elasto-thermo-viscoplastic materials

The stress collapse in the formation of shear bands in elasto-thermo-viscoplatic materials is systematically studied within the framework of one-dimensional formulation via analytical and numerical methods. The elastic energy released in a domain is found to play an important role in the collapse behavior of shear localization. A non-dimensional parameter named the stability indicator is introduced to characterize the collapse behavior, with approximate forms of the incremental governing equations. The stability indicator offers useful information regarding the degree of severity of an abrupt change of deformations during the stress collapse. Numerical experiments are carried out to verify the stability indicator by varying material properties.     

Fretting fatigue behavior of Al7075-T6 at sub-zero temperature

In some fretting fatigue applications, such as aero industry, the temperature may drop well below −50 °C Fretting fatigue behavior of aluminum alloy Al7075-T6 is investigated at temperatures of 24, 0, −25 and −50 °C in this work. The results show that (i) normal fatigue life increases considerably at sub-zero temperatures up to around 85% for low working stresses and reduces to about 40% for higher working stresses; (ii) fretting fatigue life at sub-zero temperatures rises significantly up to around 220% for low working stresses and reduces to about 50% for higher working stresses; (iii) ultimate strength of material changes from −15% to 15% under the fretting fatigue test conditions; and finally (iv) some parameters such as mechanical properties and fatigue behavior of material at low temperatures, contact load relaxation, crack closure, oxidation and some unknown sources can be thought to be responsible for fretting fatigue behavior of Al7075-T6 at sub-zero temperatures.     

An experimental investigation into the micro-electrodischarge machining behavior of p-type silicon

The present study aims to investigate the feasibility of micro-structuring in p-type silicon, using conventional die-sinking electrodischarge machining (EDM). The EDM behavior of the silicon material is studied in terms of the effect of major operating parameters on the performance characteristics during the micro-hole machining. In addition, microelectrodes are fabricated successfully on the conventional EDM machine for machining different micro-structures in silicon. Three different types of micro-structures??micro-hole, blind slots, and through slots??are fabricated in p-type silicon successfully by using optimum parameters setting. It has been observed that p-type silicon is machinable by EDM using both the polarities. Moreover, like other electrodischarge machinable materials, the selection of optimum operating parameters is very important for improved performance, as those parameters are found to influence the EDM performance of silicon significantly. Finally, it has been concluded that p-type silicon is machinable into different forms of micro-structures by understanding its electrodischarge machining behavior and by careful selection of optimum parameters.     

Viscoplastic behavior of AA7075 aluminum alloy at high strain rate

Journal of Mechanical Science and Technology - The flow stress increases with the increase in strain rate. This phenomenon is the strain rate effect of plastic deformation. Hopkinson experiment...     

多晶硅薄膜离面疲劳特性研究

多晶硅薄膜材料为微电子机械系统(MEMS)器件最重要的材料之一,对其疲劳特性的研究是现阶段失效分析研究的热点和重点.利用表面加工的多晶硅矩形微悬臂梁结构对该问题展开实验研究.通过干法刻蚀在微悬臂梁根部制作纵向应力集中区,利用静电激励激励微悬臂梁进行离面振动,谐振频率检振方法跟踪微悬臂梁机械性能的变化.结果证明在1010～1011次循环振动载荷作用后,微悬臂梁结构刚度下降,谐振频率减小,频率最大绝对偏移量达到1.544 kHz,相对偏移量达到结构本征频率的1.3%.这些结果首次验证了MEMS结构在离面振动方向上也存在显著疲劳现象.和已有文献相比,实验中结构所受应力幅度较其小2个数量级(约1～10 MPa量级),而频率偏移量却高于其数十倍.这很可能是因为纵向干法刻蚀引入了较大的粗糙度,显著加速了多晶硅结构的晶界分离速度,因而也加速了疲劳.