Compression properties of cost-efficient porous expanded clay reinforced AA7075 syntactic foams fabricated by industrial-oriented die casting technology

In today’s manufacturing industries,hard competition between rival firms makes it compulsory for researchers to design lighter and cheaper machine components due to the megatrends of cost-effectiveness and anti-pollution.At this point,aluminum syntactic foams(ASFs)are new-generation engineering composites and come into the upfront as a problem-solver.Owing to their features like low density,sufficient elongation,and perfect energy absorption ability,these advanced foams have been considerably seductive for many industrial sectors nowadays.In this study,an industrial-oriented automatic die casting technology was used for the first time to manufacture the combination of AA7075/porous expanded clay(PEC).Micro evaluations(optical and FESEM)reveal that there is a homogenous particle distribution in the foam samples,and inspections are compatible with the other ASF studies.Additionally,T6 aging heat treatment was operated on one half of the produced foams to explore the probable impact of aging on the compressive responses.Attained results show that PEC particles can be an alternative to expensive hollow spheres used in the previous works.Besides,a favorable relationship is ascertained between the aging treatment and mechanical properties such as compression strength and plateau strength.

Microstructure comparison of ZK60 alloy under casting,twin roll casting and hot compression

The microstructures of ZK60 alloy under conventional direct as-casting (DC),twin roll casting (TRC) and twin roll casting followed by hot compression (TRC-HC) were analyzed by optical morphology (OM),electron backscatter diffraction (EBSD) and X-ray diffraction (XRD).The deformation condition of hot compression is 350 ℃,0.1 s?1.The microstructural evolution under TRC-HC deformation followed by annealing at different temperatures and time was discussed.The results show that TRC provides more modified microstructure compared with DC.Twins are found in TRC processing;dynamic recrystallization (DRX),shear bands and twins are found in TRC-HC.A short annealing time has little effect on hardness,while during a long time annealing,it is found that low annealing temperatures increase the micro-hardness and high temperature decreases it.

Dynamic modeling of twin roll casting AZ41 magnesium alloy during hot compression processing

A dynamic material model of Mg-4.51Al-1.19Zn-0.5Mn-0.5Ca(AZ41,mass fraction,%)magnesium alloy was put forward.The results show that the dynamic material model can characterize the deformation behavior and microstructure evolution and describe the relations among flow stress,strain,strain rates and deformation temperatures.Statistical analysis shows the validity of the proposed model.The model predicts that lower deformation temperature and higher strain rate cause the sharp strain hardening. Meanwhile,the flow stress curve turns into a steady state at high temperature and lower strain rate.The moderate temperature of 350 ℃and strain rate of 0.01 s-1 are appropriate to this alloy.

Microstructure and hot compression behavior of twin-roll-casting AZ41M magnesium alloy

The relationship of true stress and true strain of AZ41M magnesium alloy under twin-roll-cast （TRC） and hot compression was analyzed us- ing a Gleeble 1500 machine. Microstructural evolutions of the TRC magnesium alloy under different deformation conditions （strain, sWain rate and deformation temperature） were examined using optical microscopy and discussed. The relationship of true stress and true sWain pre- dicted that lower deformation temperature and higher sWain rate caused sharp strain hardening. Meanwhile, the flow stress curve turned into a steady state at high temperature and lower strain rate. The intermediate temperature and strain rate （623 K and 0.01 s^-1） is appropriate.

Non-dendritic structural 7075 aluminum alloy by liquidus cast and its semi-solid compression behavior

Fine, equiaxed, non dendritic structure needed by semi solid processing was obtained by liquidus cast, i.e. 7075 wrought aluminum alloy cast from liquidus temperature. The microstructures after heat treatment at different temperatures and time in the semi solid range were observed, and the compression deformation behavior at different temperatures (490～600 ℃) and strain rates (5×10 -3 ～5s -1 ) was investigated by means of Gleeble 1500 thermal mechanical simulator. The results show that the deformation resistance of the non dendritic structure attained by liquidus cast in semi solid is remarkably lower than that of conventional dendritic structure. The formability of non dendritic structure is better than that of dendritic structure.

EFFECTS OF STRAIN RATE & TEMPERATURE ON HOT COMPRESSION FLOW BEHAVIOR OF A HYDROGENATED CAST Ti-25Al-10Nb-3V-1Mo ALLOY

The flow behavior of a cast Ti-25Al-10Nb-3V-1Mo alloy based onTi3Al, with and without hydrogen content, was investigated under isothermal compression test at strain rates of 0.1s-1 to 0.001s -1 in the temperature range of 900℃ to1000 ℃. The hot compression peak stress (or the maximum flow stress) of the alloy withand without hydrogen decreases with the increasing temperature and the decreasingstrain rate. Hydrogenation makes the hot compression peak stress decrease by 37%～53%, which corresponds to lowering the deformation temperature by about 50℃.Strain rate does not change the favorable effect of hydrogenation on hot compressionflow behavior at all three deformation temperatures. The microstructure of the alloywith 0.2% H (mass %) deformed at a fixed temperature exhibits the same feature asthat of the alloys without hydrogenation deformed at higher temperatures for bothstrain rates. Hydrogenation has the same effect on microstructure as strain rate andtemperature.

Compressive behavior of NiAl/(Cr,Mo)Hf alloy prepared by high-pressure die casting and hot isostatic pressing

The NiAl-28Cr-5.85Mo-0.15Hf alloy was prepared by high-pressure die casting (HPDC) and subsequent hot isostatic pressing(HIP), and tested for compressible strength and fracture behavior at 300-1 373 K. The results show that the elevated temperature 0.2% compressible yield strength as well as the room-temperature compressible fracture strain of as-HIP alloy are larger than those of the same alloy prepared by directional solidification (DS). It suggests that the fine structures with a homogeneous distribution of fine Cr (Mo) and Hf-rich phase created by high-pressure die casting lead to these improvements.

Sea Urchin Spines as a Model-System for Permeable,Light-Weight Ceramics with Graceful Failure Behavior.Part Ⅱ.Mechanical Behavior of Sea Urchin Spine Inspired Porous Aluminum Oxide Ceramics under Compression

Sea urchin spines were chosen as a model system for biomimetic ceramics obtained using starch-blended slip casting. Porous alumina ceramics with cap-shaped layers with different alternating porosities were found to have superior fracture behavior under bulk compression compared to ceramics with uniform porosity.They fail in a cascading manner,absorbing high amounts of energy during extended compression paths.The porosity variation in an otherwise single phase material mimicks the architectural microstructure design of sea urchin spines of Heterocentrotus mammillatus,which are promising model materials for impact protection.

Compression behavior of 316L lattice structures produced by indirect additive manufacturing

As a new type of lightweight structure,metallic lattice structure has higher stiffness and strength to weight ratio.To freely obtain 316L lattice structures with designed cell structure and adjustable porosity,additive manufacturing combined with investment casting was conducted to fabricate the 316L lattice structures with Kelvin cell.The compression simulation of 316L lattice structures with different porosities was carried out by using the finite element method.The numerical simulation results were verified by compression experiment,and the simulated results were consistent with the compression tests.The compressive mechanical properties of 316L lattice structures are directly related to porosity and independent of strut diameters.The 316L lattice structures with Kelvin cell have a smooth stress-strain curve and obvious plastic platform,and the hump stress-strain curves are avoided.

Effect of Zr on behavior of compressive creep in as cast ZA27 alloy

The effect of Zr on the behavior of compressive creep in as cast ZA27 alloy was investigated in the temperature range of 20160 ℃ and under different compressive stresses in the range of 50137.5 MPa with special apparatus. The results show that the primary compressive creep strains and steady creep rates of ZA27 Zr alloy and ZA27 alloy increase with increasing temperature and stress. However, the primary compressive creep strain and steady creep rate of the ZA27 Zr alloy are lower than that of the ZA27 alloy below 100 ℃, but higher at 160 ℃. The compressive creep behaviors in both ZA27 Zr alloy and ZA27 alloy obey an empirical equation ln t=C-n ln σ+ Q/RT , and the exponent stress n is 3.63 for ZA27 Zr alloy and 3.46 for ZA27 alloy, respectively, the activation energy Q is 87.32 kJ/mol for ZA27 Zr alloy and 81.09 kJ/mol for ZA27 alloy. Different material structural constants are associated with different compressive creep behaviors in the alloy. The compressive creep rate in the alloy is controlled by the lattice diffusion of zinc and dislocation limb.

Preparation and properties of gradient Al_2O_3-ZrO_2 ceramic foam by centrifugal slip casting method

The aim of the present research is to provide a novel technique for preparing gradient Al 2 O 3-ZrO 2 ceramic foams.This technique used epispastic polystyrene spheres to array templates and centrifugal slip casting to obtain cell struts with gradient distribution of Al 2 O 3 and ZrO 2 particles and high packing density.Aqueous Al 2 O 3-20vol.% ZrO 2 slurries with 20vol.% solid contents were prepared and the dispersion and rheological characteristics of the slurries were investigated.The settling velocity and mass segregation of Al 2 O 3 and ZrO 2 particles at different centrifugal accelerations were calculated and studied.The drying behavior,macrostructure,microstructure,compressive property and resistance to thermal shock of the sintered products were also investigated.The results show that the difference of settling velocity of Al 2 O 3 and ZrO 2 particles increases and mass segregation becomes acute with an increase in centrifugal acceleration.The cell struts prepared at a centrifugal acceleration of 1,690 g have high sintered density(99.0% TD) and continuous gradient distribution of Al 2 O 3 and ZrO 2 particles.When sintered at 1,550 o C for 2 h,the cell size of gradient Al 2 O 3-ZrO 2 foam is approximately uniform,about 1.1 mm.With the porosity of gradient Al 2 O 3-ZrO 2 ceramic foams increasing from 75.3% to 83.0%,the compressive strength decreases from 4.4 to 2.4 MPa,and the ceramic foams can resist 8-11 repeated thermal shock from 1,100 o C to room temperature.

Rapid preparation of ceramic moulds for medium-sized superalloy castings with magnesia-phosphate-bonded bauxite-mullite investments

Phosphate-bonded investments have already been widely utilized in dental restoration and micro-casting of artistic products for its outstanding rapid setting and high strength. However, the rapid setting rate of investment slurry has up to now been a barrier to extend the use of such slurry in preparation of medium-sized ceramic moulds. This paper proposes a new process of rapid fabrication of magnesia-phosphate-bonded investment ceramic moulds for medium-sized superalloy castings utilizing bauxite and mullite as refractory aggregates. In order to determine the properties of magnesia-phosphate-bonded bauxite-mullite investments (MPBBMI), a series of experiments were conducted, including modifciation of the workable time of slurry by liquid(mL)/powder(g)(L/P) ratio and addition of boric acid as retard agent and sodium tri-polyphosphate (STP) as strengthening agent, and adjustment of bauxite (g)/mullite(g)(B/M) ratio for mechanical strength. Mechanical vibration was applied to improve initial setting time and fluidity when pouring investment slurry; then an intermediate size ceramic mould for superalloy castings was manufactured by means of this rapid preparing process with MPBBMI material. The results showed that the MPBBMI slurry exhibits proper initial setting time and excellent fluidity when the L/P ratio is 0.64 and the boric acid content is 0.88wt.%. The fired specimens made from the MPBBMI material demonstrated adequate compression strength to withstand impact force of molten metal when the B/M ratio is 0.89 and the STP content is 0.92wt.%. The experimental results confirmed the feasibility of the proposed rapid fabricating process for medium-sized ceramic moulds with MPBBMI material by appropriate measures.

Influence of Boron Fiber Powder and Graphite Reinforcements on Physical and Mechanical Properties of Aluminum 2024 Alloy Fabricated by Stir Casting

In this study, boron fiber powder and graphite is reinforced to Al 2024 alloy to develop hybrid metal matrix composite by stir casting process. Hybrid MMCs developed with different weight fraction for 4%, 6%, 8% and 10% of boron fiber and 2% of graphite. Stirring parameters are optimized to obtain solid casting. Reinforcements are poured into molten aluminium at 15 g/min and stirrer is rotated for 5 minutes at 250 rpm with two stages stirring. 1% of magnesium was added to improve the wettability of Al 2024. Cast samples are machined as per the standards to investigate the microstructure, physical and mechanical properties. Optical and SEM analysis was carried out on machined sample to study the uniform distribution of particles. XRD and EDAX analysis is carried out to confirm the dispersion of particles into the matrix. Uniform distribution of the particles is found in optical and SEM images for these stirring parameters. The peak representation of boron and graphite particles is also observed in XRD and EDAX analysis. Theoretical and experimental density of the cast sample is determined by rule of mixture and Archimedes principle. Result shows the density of the composite decreases by increasing percentage of reinforcements. Micro Vickers hardness was tested on the cast composites and the result showed Al 2024 alloy hardness was increased by 31.25% by reinforcing boron and graphite. Similarly, tensile and compression strength increased by increasing the percentage of reinforcement. Tensile and compression strength of Al 2024 alloy increased by 45.23% and 29.18% respectively. The ductility of the composites decreased by increasing the percentage of reinforcements.

Predicting model on ultimate compressive strength of Al_2O_3-ZrO_2 ceramic foam filter based on BP neural network

In present study, BP neural network model was proposed for the prediction of ultimate compressive strength of Al2O3-ZrO2 ceramic foam filter prepared by centrifugal slip casting. The inputs of the BP neural network model were the applied load on the epispastic polystyrene template （F）, centrifugal acceleration （v） and sintering temperature （T）, while the only output was the ultimate compressive strength （（7）. According to the registered BP model, the effects of F, v, T on 0 were analyzed. The predicted results agree with the actual data within reasonable experimental error, indicating that the BP model is practically a very useful tool in property prediction and process parameter design of the Al2O3-ZrO2 ceramic foam filter prepared by centrifugal slip casting.

改性铸造废砂对混凝土力学及耐磨性能的影响

用水玻璃对铸造废砂进行了改性处理,研究了改性铸造废砂的掺量(0、10%、30%、50%、70%)对混凝土力学性能和耐磨性能的影响。结果表明:随着改性铸造废砂掺量的增加,试件的28 d抗压强度先增大后减小,最佳掺量为10%;随着改性铸造废砂掺量的增加,试件的28 d弹性模量和磨耗量降低,说明弹性变形能力变大,耐磨性能提高。

大直径嵌岩灌注桩承载特性试验与有限元模拟

基于青岛某工程的4根大直径嵌岩灌注桩,在现场开展了单桩竖向抗压静载试验和桩身完整性测试,以明确大直径嵌岩灌注桩在竖向荷载下的承载特征,拟揭示不同荷载水平下嵌岩灌注桩的承载力发挥机制。结合不同嵌岩深度的单桩承载性能有限元模拟,重点分析了单桩在不同嵌岩深度下的竖向抗压承载特性和桩土位移分布特征。研究表明:在笔者试验条件下,大直径嵌岩灌注桩单桩竖向抗压承载力具有一定离散性,桩头部位的损坏会极大影响单桩承载力的有效发挥;加载完成后,数值模拟得到的桩顶沉降量为31.56 mm,约为现场实测值的1.1倍,模拟结果与实测结果较为吻合;通过不同嵌岩比的模拟结果对比发现,嵌岩深度越大桩端阻力占桩顶荷载的比例越小,且桩端阻力占比的变化速率随着嵌岩比的增加逐渐减缓;嵌岩深度取2.5倍桩径为宜。

浇注PBX替代材料的准静态压缩力学行为及本构模型标定

为研究高聚物粘结炸药(PBX)的准静态压缩行为,对两种典型配方(含铝粉与否)的浇注PBX替代材料在不同应变率下进行单轴准静态压缩试验,并对其力学性能进行了对比分析。同时基于朱‑王‑唐(ZWT)模型提出一种新模型来描述材料的准静态压缩行为,通过遗传算法获取本构模型参数,并使用Fortran语言在Abaqus有限元软件的用户材料子程序(UMAT)接口中进行本构模型的建立。结果表明:浇注PBX替代材料的准静态压缩过程可分为弹性压缩、应力衰减以及失稳破坏3个阶段;准静态压缩力学行为与应变率有明显的相关性,随着应变率的提高,材料的有效压缩应变基本不变,而压缩模量、屈服强度和压缩强度的对数与应变率对数近似呈现出线性关系;铝粉的加入使浇注PBX替代材料压缩模量、屈服强度和压缩强度均有所提升。新构建的本构模型能较好描述浇注PBX替代材料的准静态压缩行为,使用有限元软件对本构模型普适性进行验证,得到仿真计算结果与试验结果间可决系数R^(2)均大于0.98,吻合程度较高。

具有贯穿结构的铜/铝复合材料的强化及热导率

为了在提高铝合金强度的同时避免降低其热导率,设计了一种具有单向贯穿结构的新型铜/铝双金属复合材料,并采用增材制造结合挤压铸造的工艺实现制备成形。该复合材料表现出较好的强度(约340 MPa)和热导率(200 W/(m·K))匹配性,综合性能超过传统铝合金。这种良好的导热性能归因于单向贯穿的Cu骨架增强体结构能够为电子传导提供快速通道。同时,界面处生成Al2Cu共晶相,实现良好的界面冶金结合,有效改善复合材料的力学性能。

压缩浇筑混凝土的应力-应变关系

压缩浇筑可以显著提高混凝土的强度和耐久性,无需添加任何化学添加剂和矿物掺料.采用压缩浇筑方法制作压缩浇筑混凝土试件,并开展单轴受压试验.试验结果表明,相比于普通混凝土,压缩浇筑混凝土的抗压强度和弹性模量显著提高,而峰值应力对应的应变稍有减小.基于现有混凝土应力-应变模型对试验结果进行回归分析,得到压缩浇筑混凝土的应力-应变关系模型.在此基础上,利用受弯定理推导了压缩浇筑混凝土受弯构件的等效矩形应力块参数模型.研究成果可为压缩浇筑混凝土构件的抗弯设计和分析提供理论依据.

连续刚构桥悬臂现浇施工菱形挂篮荷载试验控制要点分析

大跨径桥梁悬臂挂篮施工技术要求高,安全管控压力大。以云南宣会高速公路牛栏江特大桥为例,主要对菱形挂篮拼装、荷载试验、测量观测、变形观测、数据分析5个方面进行讨论。进行分级预压试验,加载至箱梁施工荷载状态的120%,支架变形量小于1 mm/h时,挂篮预压沉降趋于稳定,挂篮结构安全。加载试验为类似菱形挂篮悬臂现浇施工提供技术支持和参考。