Interlaminar properties of polymer laminates containing internal sensor cavities

This research paper presents an experimental investigation into the sensitivity of the interlaminar properties of polymer laminates to long, narrow interlaminar galleries used in comparative vacuum monitoring (CVM). CVM is a structural health monitoring technique for the non-destructive detection of cracks in engineering materials. The paper examines the effect of CVM galleries on the mode I delamination toughness, interlaminar shear strength, and impact damage resistance of a carbon/epoxy laminate. It was found that the galleries improve the mode I delamination toughness by blunting and/or deflecting the crack tip; with the maximum improvement being double the toughness of the laminate free of galleries. The toughness increased with the diameter of the gallery up to a critical size, above which no further improvement was achieved. However, the composite is more prone to unstable delamination cracking in the presence of the galleries. The apparent interlaminar shear strength (ILSS) decreased at a linear rate with an increase in the diameter and volume fraction of galleries. The loss in ILSS is due to the reduction in the effective interlaminar load-bearing area caused by the galleries. Low-energy impact testing revealed that the galleries do not affect the impact damage resistance when below a critical diameter; however, above a threshold gallery size the impact resistance is degraded. This study shows that the incorporation of CVM galleries into laminates can have the added benefit of increased mode I delamination toughness, although the ILSS is degraded and the impact resistance is reduced by large galleries.     

确定轴向冲击下薄壁圆柱壳第二临界速度的新方法

研究薄壁圆柱壳的动态屈曲模式，有助于构造具有高吸能率的抗冲击结构。根据轴向冲击下的薄壁圆柱壳存在使其屈曲模式由轴对称转换为非轴对称的第二临界速度，且当冲击速度大于第二临界速度时薄壁圆柱壳的屈曲模式先呈现轴对称形式，然后随着冲击响应时间逐渐由轴对称形式转化为非轴对称形式这一理论，基于有限元仿真，比较撞击系统动能的时间历程和屈曲变形的时间历程，提出了用以确定第二临界速度的能量迭代法。应用此方法设计薄壁圆柱壳的动力屈曲结构可有效地减少试验次数，降低实验成本。该方法的可行性和正确性利用落锤实验得到了验证。     

The integration of manufacturing and cost information into the engineering design process

In manufacturing systems engaged in the batch manufacture of discrete products, critical decisions on materials and processes are made during the design phase, decisions having significant impact on costs of production. A new computer aided design tool has been developed to enable product designers in small to medium size companies to incorporate manufacturability and cost criteria into their decision making. The paper describes the rationale of the system and its mode of operation. Experiments to validate its practicality and usefulness have yielded encouraging results.     

Experimental investigations on the behaviour of short to long square aluminium tubes subjected to axial loading

The transition between progressive and global buckling of axially loaded aluminium extrusions in alloy AA6060 temper T6 was studied by quasi-static and dynamic tests. The primary variables in the tests were the local (b/h=17.78–40) and global (L/b=5–24) slenderness of the extruded members and the impact velocity. The critical global slenderness is defined as the slenderness where direct global buckling or a transition from progressive to global buckling occurs. In the quasi-static tests and for an impact velocity of 13 m/s, the critical global slenderness was found to be an increasing function of the local slenderness. In contrast, the critical global slenderness was a decreasing function of the local slenderness when the impact velocity was 20 m/s. The energy absorption was found to be very dependent on the collapse mode. Significantly more energy is absorbed in the progressive buckling mode than in the global bending mode. In the case of transition from progressive to global buckling, the energy absorption depends on the time of transition. The difference in energy absorption between the different modes decreases for increasing impact velocity due to inertia forces preventing the direct global buckling mode and the early transition from progressive to global buckling.     

An experimental study on the dynamic axial plastic buckling of cylindrical shells

This paper deals with an experimental study on the dynamic plastic post-buckling behaviour of a stationary AMΓ aluminium alloy cylindrical shell under axial impact. According to current theory, it is believed that within a certain velocity range, the shell will buckle in a uniform axisymmetrical sinusoidal mode. However, we found that when the impact velocity is less than a certain critical value V_c1, the shell will exhibit only uniform plastic deformation in both the axial and radial directions and does not produce the sinusoidal waves. On the other hand, when the impact velocity exceeds another critical value V_c2, the shell will change from the axisymmetric mode into a nonuniform type of large deformation, the number of waves decreases slightly and the shell begins to lose its load-carrying capacity. Experimental results on cylinders with three different thicknesses are presented and discussed. An approximate theoretical formula for estimating V_c2 based on strain rate reversal is also given.     

A Critical Grain Size Concept to Predict the Impact Transition Temperature of Ti-Microalloyed Steels

Based on the assumption that local principal stress remains the same everywhere within a ferrite grain, a critical value of grain size can be determined for a fixed TiN particle size. When the grain size is smaller than the critical size, grain boundary is expected to resist the propagation of a micro-crack that is initiated from a TiN particle. Using this concept, an attempt has been made to predict the local cleavage fracture stress and 27J impact transition temperature (ITT) of different Ti-microalloyed steels, which were subjected to (instrumented) Charpy impact testing.     

Piezoelectric transducer arrangement for the inspection of large composite structures

The aim of the present work is to develop a system of smart devices that could be permanently attached on the surface of the composite structure and monitor the interaction of low-frequency Lamb waves with defects. A linear array of transmitters would generate a relatively uniform wavefront allowing the inspection of large areas with a limited number of sensors. The asymmetric A₀ Lamb mode is generated in carbon fibre reinforced plastic (CFRP) quasi-isotropic laminates using an array of thin piezoceramic transmitters operating in-phase. In this paper, the effect of damage size on the propagation of Lamb waves is presented. Experimental verification is also presented in multidirectional CFRP composite panels. Critical size impact damage is detected. Finally, the technique is applied to a stiffened panel. Damage on the skin or flange is detectable while damage on the web or cap is not detected with the current experimental set up.     

静载和动载下不同龄期混凝土力学特性的试验研究

利用杆径为75mm的SHPB试验装置对5种不同龄期下的混凝土分别进行了冲击压缩试验,系统了解了冲击载荷对不同龄期支护混凝土力学特性的影响。为了进行对比,利用INSTRON系统也进行了相应龄期下的静载压缩试验。试验研究表明:静载下混凝土强度、割线弹性模量随龄期增长而增长,其中强度增长主要集中在龄期7d以前,割线弹性模量增长则集中在龄期14d以后,而峰值应变随龄期增长整体上呈减小的趋势;动载下混凝土强度、峰值应变以及单位体积吸收能随着龄期增长而增长,在各个龄期都表现出对应变率具有一定的敏感性,其中不同龄期混凝土的动态强度随应变率增加呈现指数函数增长趋势。不同龄期的混凝土在动载下以拉伸破坏为主,静载下基本呈现剪切破坏形式。     

On the effect of the geometric shape of abrasive particles on the threshold rate of erosion

The effect of the geometric shape of eroding particles on the threshold rate of failure has been assessed. It has been shown that when the eroding particle size is changed, the failure mode may change from brittle to ductile and vice versa. The paper presents the results of a comparative analysis of the erosion resistance of some metallic materials, using a structural-time criterion of failure, for the impact of a single abrasive particle of cylindrical shape on the surface of an elastic half-space. Hertz’s classical theory of impact is used. __________ Translated from Problemy Prochnosti, No. 1, pp. 69–78, January–February, 2007.     

多轴齿式离心压缩机转子系统耦合振动特性分析

以某五平行轴齿式离心压缩机为研究对象,建立多平行轴齿轮耦合转子系统有限元模型。采用数值方法,在考虑齿轮耦合与不考虑齿轮耦合两种情况下分别对系统运动方程进行求解,得到系统横向及轴向振动的固有频率和振型,在考虑陀螺力矩的情况下计算系统临界转速值并绘制Campbell图,进而详细分析齿轮啮合作用对多平行轴转子系统动力学特性的影响。研究表明齿轮的耦合作用会使系统派生出新的固有频率及耦合振型,整体系统表现为原有单轴的固有特性与耦合特性两种模式,系统出现新的临界转速值,同时分别指出齿轮耦合作用对系统横向振动和轴向振动的不同影响以及派生频率的来源。     

A comparative study on the effects of three commercial Ti–B-based grain refiners on the impact properties of A356 cast aluminium alloy

The effect of three commercial Ti–B-based grain refiners on the impact properties of the A356 cast aluminium alloy was assessed. The impact tests were performed by means of an instrumented Charpy pendulum. During impact testing, the maximum load and the total impact energy, as well as its complementary contributions, the energy at maximum load and the crack propagation energy, were measured. Impact properties were studied as a function of size and shape of the main microstructural features, which were analysed by means of optical microscopy and scanning electron microscopy. The results show that the influence of grain refinement on microstructure involves beneficial and detrimental concurrent effects which strongly affect impact properties. The total impact energy decreases with the addition of all the grain refiners due to a shift from a mixed transgranular–intergranular fracture mode to a more severe transgranular mode. Crack initiation and propagation occur mainly through the fracture of Fe-intermetallics and brittle Si particles, and the mechanism of void coalescence. No direct correlation between grain size and impact properties is found. Moreover, the aspect ratio of eutectic Si particles does not change with grain refinement, implying that there are no mutual poisoning effects between Sr and B. Total impact energy is found to depend on both SDAS and β-platelets size. The concurrent effects of SDAS and β-platelets average maximum length on total impact energy can be taken into account by the multiple regression analysis technique.     

微尺度输流管道考虑热效应的流固耦合振动分析

研究热环境中输送微流体的微尺度管道流固耦合振动问题。根据线性热弹性理论建立系统振动控制方程,并利用复模态法对其进行求解,得到了系统的固有频率和屈曲失稳临界流速,讨论了温度变化、微尺度效应及管道壁厚对系统振动特性的影响。研究结果表明：提高环境温度会降低系统的固有频率和临界流速;管道和流体的微尺度效应分别会使临界流速升高和降低,但微流体的这种影响会随着温度的升高而逐渐减弱并最终消失;管壁较薄（外径接近微尺度特征尺寸）时,壁厚的变化对固有频率的影响很大,而管壁较厚时,温度变化对固有频率的影响更为明显。     

Electrochemical performance of steel in cement extract and bulk matrix properties of cement paste in the presence of Pluronic 123 micelles

The influence of Pluronic P123 (PEO₂₀-PPO₇₀-PEO₂₀) non-stabilized micelles (of 10 nm size) on the corrosion behavior of low-carbon steel in cement extract was studied, using electrochemical impedance spectroscopy (EIS) and potentio-dynamic polarization (PDP). Mercury intrusion porosimetry (MIP) was employed to derive the impact of admixed P123 micelles on porosity and pore-size distribution of cement paste. As far as steel corrosion resistance is concerned, a positive effect was observed, initially denoted to the presence of the polymer itself, rather than the presence of micelles. Further, the P123 micelles were found to result in increased corrosion resistance in the presence of 1 % and 3.5 % NaCl in the alkaline environment of cement extract. There was no significant influence on porosity and pore size distribution of the admixed in cement paste P123 micelles. The observed phenomena are related to self-assembly of the micelles only within higher ionic strength and the presence of chloride, in which case the critical micelle concentration is reduced. At micelles concentration of 0.024 g/l for the chloride-free cement extract (and the solid cement paste specimens, respectively), the medium actually contain unimers that have minimal impact on electrochemical performance and/or microstructural properties. In contrast, with increased ionic strength of the medium (1?3.5 % NaCl and altered ion concentrations resulting from the anodic/cathodic reactions within steel corrosion), the positive effect of 0.024 g/l micelles (and higher of 0.072 g/l) is more pronounced, i.e., increased corrosion resistance and anodic control with external polarization was observed.     

Enhanced crystallization resistance and thermal stability via suppressing the metastable superlattice phase in Ni-(Pd)-P metallic glasses

Virtually,glass formation is to avoid crystallization during solidification,i.e.,a consequence of the competition between the undercooled liquid and primary crystalline phases.It is found that the crystallization resistance of the binary Ni-P system was drastically enhanced with alloying of Pd and correspondingly,the critical size for glass formation increased significantly from the micrometer to millimeter scale.Thermodynamically,the introduction of Pd could effectively increase the atomic size mismatch and heat of mixing,which are beneficial to stabilize the supercooled liquid.Kinetically,the introduction of Pd not only successfully suppresses the formation of metastable superlattice phase,which is prone to nucleation and growth in the supercooled liquid state,but also changes the crystallization mechanism from the primary to eutectic mode.The current finding sheds light on understanding glass formation of the most studied Pd-Ni-P system and the glass-forming ability in general.     

基于能量法研究刚性质量块轴向撞击圆柱壳的屈曲

基于能量法,考虑应力波效应,研究了刚性质量块撞击圆柱壳的屈曲问题。建立拉格朗日函数,将其和计算获得的符合边界条件的准试函数代入第二类拉格朗日方程,得到二阶线性偏微分方程,分析方程解的特性,得到刚性质量块撞击圆柱壳屈曲临界速度的解析表达式。算例分析讨论了临界长度、冲击质量、轴向模态数、环向模态数、径厚比对屈曲的影响。结果表明:应力波效应、初始冲击动能、径厚比对圆柱壳的动力屈曲有明显影响;高速冲击易激发屈曲的高阶模态、也容易在径厚比较小时激发圆柱壳的屈曲。     

Evaluation of the HP 6890/5973 bench-top gas chromatograph/mass selective detector for use in mobile laboratories

Introduced in 1996, the Agilent (Hewlett Packard) HP 6890/5973 GC/MSD system is the latest of the bench-top GC/mass spectrometry (MS) family. Started with the HP 5970 MSD, introduced in the mid-1980s, has provided small/medium size laboratories with the power of a true MS that provides selectively and library-searchable capability. This paper presents study results on instrumental sensitivity achieved with the new MSD, with examples illustrating trace-level analysis of semi-volatile compounds such as PCB and Dioxins. Investigations were carried out to study the effect of some operational parameters such as ionisation energy, dynode voltages and dwell time. In the standard electron impact selected ion monitoring (SIM) mode, the new MSD can provide sub-picogram level sensitivity for chlorinated hydrocarbons. In scan mode, under optimal condition, the system can generate library-searchable spectra from sub-nanogram quantity of analytes. This sensitivity level rivals traditional GC with selective detectors such as electron capture detector but at the same time possesses the advantage of computerised library search against a database of over 100 thousand spectra. The relatively compact size makes the system practical in a mobile laboratory, providing qualitative as well as quantitative data in spill emergencies analyses.     

Rebound behavior of nanoparticle-agglomerates

In general, the rebound behavior of particles depends on the particle/substrate material combination and the particle size. In the present investigation the rebound behavior of nanoparticle agglomerates is investigated in a low pressure impactor and compared to single spherical particles. For agglomerates, their structure and mechanical strength will also affect the rebound behavior. The rebound of openly structured agglomerates (fractal dimension D_f < 2) is determined by the primary particle size and the particle-substrate combination. The impact velocity required for rebound (critical velocity) is independent of the agglomerate size and equal to the critical velocity of single spherical particles having the same size as the primary particles. In case of agglomerate fragmentation no rebound was observed for openly structured agglomerates. For denser agglomerates (D_f > 2), the critical impact velocity decreases with increasing agglomerate size, where the decrease is more accentuated for higher fractal dimensions, finally approaching the behavior of spheres.     

A Comparative Life Cycle Assessment of Disposable and Reusable Packaging for the Distribution of Italian Fruit and Vegetables

Each year in Italy, millions of tons of fruits and vegetables are harvested, packed and transported to national and foreign retail outlets. Packaging is an essential component of this system, but what is its environmental impact? This study takes into consideration the delivery from the field to the retail outlet of 12 types of fruits and vegetables grown and harvested in Italy and sold in Italy and Europe. The study compares two different packaging and distribution systems: one‐way with corrugated boxes and reusable with plastic containers. A number of different scenarios were generated by combining the most diffused packaging sizes with the most important production and selling locations for each type of fruit and vegetable and by considering the specific route required to perform the transportation with each distribution system. The environmental impact of each system in each scenario has then been analysed using the life cycle assessment methodology. Two algorithms and a number of coefficients were derived to simplify data collection and impact analysis for all scenarios. This provides an easy tool to evaluate the potential environmental burden of the two alternative distribution systems in a specific scenario by taking into consideration only a few variables (such as size of packaging and transportation distance). These algorithms and coefficients are presented in the work, along with the process that led to their generation and with considerations about the main critical environmental aspects for both distribution systems. The work aims to suggest possible design solutions that can make each system more sustainable. Copyright © 2011 John Wiley & Sons, Ltd.     

Interaction of laminate damage and adhesive disbonding in composite scarf joints subjected to combined in-plane loading and impact

Impact tests were carried out on composite laminates and composite scarf repairs, while both were subjected to in-plane loading with tensile pre-strain levels up to 5000 microstrain. The results show that pre-straining of the composite laminates has no noticeable influence on the size of the delamination area for the given impact energy of 8 J, which represents a typical barely-visible impact on thin-skin composite structures. For composite scarf joints, however, resulting damage has been found to be a combination of adhesive disbonding and matrix cracking (delamination and intraply cracking) in the composite laminate. The size of this mixed type of damage increases significantly with increasing pre-strain levels. A finite element model was developed to investigate the interaction between adhesive disbonding and composite delamination. The computational results reveal that both delamination and adhesive disbonding are dominated by the mode II fracture. Since the critical mode II fracture energy release rate for composite laminates (G_IIC = 1.08 kJ/m²) is much less than that pertinent to the adhesive (G_IIC = 3.73 kJ/m²), delamination tends to occur first in the composite laminates, which then shield the growth of disbonding in the adhesive.     

Praticle Size Reduction in the Ball Mill

The size distribution produced by the ball milling of various crystalline and non-crystalline materials, showed that initially there was a fairly even distribution over the size range up to 355μm. However, as milling proceeded two distribution modes developed; one at about 90μm (the persistent mode) and one at about 250μm (the transitory mode). Unlike the work of Heywood (1) on coal, further grinding did not produce a gradual elimination of the coarse mode with corresponding increase in the persistent mode at 90μm. Less than 2%w/w of material was always found between the 170-180μm size, indicating that this was a critical dimension in the grinding process. A linear relationship was found between sample weight and milling time required to grind 50% of the sample down to 150μm. The slopes of these lines were steep for rock salt and sucrose (crystalline materials) indicating that milling was rapid, whilst with acacia the rate was half as fast and slower still for the other two non-crystalline materials, cinnamon bark and gentian root. In terms of milling efficiency defined as the amount of material milled to 150μm per minute, it was found that there was no optimum load size; doubling the sample size effectively doubled the milling time. However, the most critical factor affecting the milling process, was the weight and nature of the grinding medium. It was found that heavy porcelain was more efficient than glass spheres and that the optimum weight was 401.8g; the weight required to approximately half fill the ball mill.