Compaction pressure,wall friction and surface roughness upon compaction strength of Andrographis paniculata tablets

A well-known Malaysian herb, Andrographis paniculata was used in this study. This herb is famous at reducing sugar levels for diabetic patients. In this study, the herb was compressed into tablets. A compressed tablet, which is a universal form in modern medicine, needs to meet certain mechanical strength criteria in order to withstand post-compaction loading such as coating, handling, packaging and storage. The objectives of this work were to investigate the effects of compaction pressure, wall friction and surface roughness upon compaction strength of A. paniculata herb during compression. A universal testing machine with pressures ranging from 15 to 30 MPa was used to compact the herb using a 20-mm-diameter cylindrical stainless steel uniaxial die. The tensile strength of the tablet increased as the compaction pressure increased. During compression, as the amount of powder being compressed increased, the tensile strength increased, and from the surface roughness test, the coefficient of wall friction and angle of wall friction decreased. In general, the compaction pressure, the wall friction and surface roughness plays a significant role in tabletting; hence, in producing a tough and coherent tablet.     

Theoretical study of mechanical behavior of thin circular film adhered to a flat punch

In this paper we present a theoretical study of the cylindrical punch test where a thin circular film clamped at the periphery is adhered to the planar surface of a rigid cylindrical punch, and an external tensile load is applied to the punch causing the film to delaminate from the substrate. We obtain analytical solutions to the deflection of the membrane in the asymptotic limit of large or small loads, and then combine the bending and stretching effects using a lumped parameter force-deflection model. An equilibrium theory of delamination mechanics is derived based on energy balance. The cases of initially stress-free and prestressed film are analyzed, which ought to have significant implications in many technological situations.     

Numerical simulation on the local stress and local deformation in multi-point stretch forming process

Multi-point stretch forming (MPSF) is a new flexible forming technique to form aircraft outer skin parts. The multi-point stretching die (MPSD) replaces the traditional fixed shape stretching die, and the sheet metal is formed over a MPSD composed by the punch element. The MPSD is a discontinuous surface of discrete stretching die, and the stress concentration and local strain occur on formed parts. These lead to generate dimples on the surface of formed part. In this paper, a series of numerical simulations on MPSF processes for stretching parabolic cylindrical, spherical, and saddle-shaped parts were carried out. The local stress and local strain in thickness distribution of MPSF part were analyzed by dispersed the blank into solid elements. The forming results of MPSF were compared with those that use traditional stretch forming, and the influences of thickness of elastic cushion and the size of punch element on the stress concentration and local strain were surveyed. The simulation results show the distribution of local stress and local deformation in different layers, and the elastic cushion and the small size of punch element can reduce the stress concentration and local deformation. The results may understand the stress distribution on the sheet and prevent the defect of dimple.     

Cold compaction of an array of cylindrical fibres

The biaxial compaction of a square array of circular cylinders is studied using slip-line field, upper bound and finite element methods. Densification is assumed to occur by plastic deformation at the contacts. It is found that contact–contact interaction has a softening effect on the local indentation pressure at each contact. The yield surfaces resulting from hydrostatic and closed-die compaction are constructed at various stages of densification: the size and shape of the yield surface depend upon the loading history and upon the relative density of the compact. The finite element predictions suggest the formation of a vertex at the loading point for the entire densification process in the case of isostatic compaction. On the other hand, a vertex at the loading point is formed only for a relative density D0.85 in the case of closed-die compaction.     

Estimating the surface density of fissures in clay soil from deterministic parallel sections

In much clay soil the pore space consists of 3-D networks of narrow, approximately planar fissures. The density of the interface between fissures and solid soil is important; a method for its estimation from the horizontal and vertical cuboid samples that are taken conventionally is described here. Undisturbed samples are impregnated with resin containing a fluorescent dye. Parallel plane faces are cut, and the exposed surfaces are photographed under u.v. light. Pairs of superimposed photographic negatives are projected onto a screen, and the lateral displacement of each interface from one section to the next is measured at points of intersection of the interface with linear probes through the soil. These distances are used to infer the local orientation of the interfaces, which are then used with the point counts to estimate the interface areas. The method was applied to subsoil of the Windsor series. The interface density was estimated to be 9.69cm²/cm³ from one horizontal and one vertical sample. Point-counting with isotropic uniform random linear probes applied to five randomly orientated samples from the same site gave an estimate of 8.78cm²/cm³. It seems probable that the error associated with the new method is no greater than that associated with the standard method.     

Characterization of Frictional Behavior in Cold Forging

In the present investigation, tip test was utilized to characterize the effects of surface roughness of the specimen and forming tools, rate of deformation, and type of lubricants on friction in solid and solid contact under high contact pressure at room temperature. For the test, a cylindrical specimen made of aluminum alloy of 6061-O was used and grease, corn oil, VG100, and VG32 were applied as lubricants. Single punch and two counter punch sets with different surface roughness of R _a = 0.08 and 0.63 μm were manufactured in order to investigate a frictional behavior during the test. In addition, two different deformation speeds of 0.1 and 5.0 mm/s were used for the test to check their effect on friction as well. Load levels and tip distances obtained from the test were compared to find out any correlation between the two. The change of surface topology of the specimen was monitored by optical measurement technique to better understand a frictional behavior at the punch and counter punch interfaces. Present investigation clearly shows that tip test is easy to apply to experimentally characterize the frictional behavior in cold forging under various processing conditions considered.     

Deep drawing with internal air-pressing to increase the limit drawing ratio of aluminum sheet

The effects of internal air-pressing on deep drawability are investigated in this study to increase the deep drawability of aluminum sheet. The conventional deep drawing process is limited to a certain limit drawing ratio(LDR) beyong which failure will occur. The intention of this work is to examine the possibilities of relaxing the above limitation through the deep drawing with internal air-pressing, aiming towards a process with an increased drawing ratio. The idea which may lead to this goal is the use of special punch that can exert high pressure on the internal surface of deforming sheet during the deep drawing process. Over the ranges of conditions investigated for Al-1050, the local strain concentration at punch nose radius area was decreased by internal air-pressing of punch, and the deep drawing with internal air-pressing was proved to be very effective process for obtaining higher LDR.     

Determining coefficients of friction in compaction of refractory metal powders

Knowing the coefficients of friction in tool compaction of powders of metals and alloys allows one to rationally design technological equipment for manufacturing powder semifinished products experiencing minimal warping under vacuum or hydrogen sintering. This is of particular significance when consumable electrodes are produced from powders of refractory metals being compacted as rather long fillets that are curved in sintering if any irregularities in the density in the cross section and in the fillet bulk are present. Both well-known and new methods are analyzed for finding the coefficients of friction in powder compaction, in particular in cylindrical containers. Stable and valid measurement results are shown to be unachievable. A new method for experimental determination of the coefficients of friction under powder compaction is described. It consists in comparing the force parameters of one- and two-sided compaction. This method allows finding the coefficient of side pressure and contact friction (on the cylindrical surface of the container) during the formation of briquettes of TsM-2A alloy with different concentrations of plasticizer and solvent. A positive effect of a plasticizer and negative one of a solvent on the coefficient of friction is stated.     

Development of magnetorheological fluid-based process for finishing of ferromagnetic cylindrical workpiece

A magnetorheological fluid-based process is developed for the internal surface finishing of ferromagnetic cylindrical workpiece. The existing finishing processes based on magnetorheological fluid are not equipped to finish the internal ferromagnetic cylindrical surface significantly as it obtained higher magnetic flux density than the MR polishing fluid. At present, magnetorheological fluid-based finishing tools are designed to ensure the maximum magnetic flux density always present on the outer finishing tool core surface as compared to internal surface of ferromagnetic cylindrical workpiece surface. To validate this present principal idea, the magnetostatic finite element analysis has been performed on the newly designed finishing tools. The preliminary experiments have also been conducted to evaluate the finishing performance with the two newly designed finishing tools. The percentage reduction in surface roughness (R_a) values with I-shaped tool core is found as 65–78% after 150 min of finishing, whereas, with rectangular shaped tool core is found as 78–81% after 90 min of finishing. The results clearly revealed that the present finishing tool with rectangular shaped core is more suitable for uniform significant finishing of ferromagnetic cylindrical internal workpiece than the I-shaped core. The developed process can be useful in finishing of cylindrical mold and dies, hydraulic cylinder, barrel for injection molding, etc.     

Friction and Wear Properties of 3D Carbon/Silicon Carbide Composites Prepared by Liquid Silicon Infiltration

Carbon/silicon carbide (C/SiC) composites were prepared by a liquid silicon infiltration (LSI) process and their microstructure and friction and wear properties studied. The matrices of the C/C green bodies were found to be reinforced with dense carbon fiber bundles hanging together. The density of the composites before and after the LSI process was 1.25 and 1.94 g/cm³, respectively. However, the open porosity of C/SiC composites was about 16% due to the opening of closed pores during the machining process. The C/SiC composites exhibited excellent tribological properties in the dry condition, with an average coefficient of friction (COF) and wear rate of about 0.29 and 16.15 μg/m MPa, respectively. In comparison, the average COF was about 0.13 in the moist condition, with a wear rate of 5.87 μg/m MPa. The main wear mechanism of the C/SiC composites was worn particles and debris with a high degree of hardness, producing a plough effect on the friction surface in the dry condition and an adhesive effect in the moist condition.     

An Analytical Approach for Backward-Extrusion Forging of Regular Polygonal Hollow Components

An upper-bound formula was developed to analyze the backward-extrusion forging of regular polygon cup-shaped components. An admissible spherical velocity field has been suggested for the early stage of the extrusion process. This stage was facilitated by substitution of a nosed punch with cylindrical surface instead of a flat one. The optimum nose contour was determined by the minimization technique. On the other hand, by this method the semi-prism angle of dead zone was calculated.For the final stage of the process, an admissible cylindrical velocity field has been applied. In any stage of the process, by increasing the number of polygonal sides, the upper-bound results approaches that of circular cups which was obtained by other investigators. The comparison of analytical results to that of experimental investigations showed excellent agreement.     

车身复杂结构大规模问题的缩减计算

针对车身设计中复杂结构多参数大规模问题,提出了一种基于减基法和有限元的混合算法来进行缩减计算。该方法首先通过计算系统在有限个样本下的响应构造近似解空间,然后基于有限元方法分离出刚度矩阵中的设计参数,接着将矩阵向解空间进行投影,最后构建减缩计算系统。在新参数条件下,通过减缩系统得到大规模问题的响应,极大地提高了结构响应的计算效率。     

A laser spectrometer of field-asymmetric ion mobility

A method for analyzing a substance has been experimentally tested. The method combines the field-asymmetric ion mobility spectrometry and laser ionization of molecules under atmospheric pressure. Pulsed radiation of the fourth harmonic of an YAG: Nd³⁺ laser (λ = 266 nm) and a spectrometer with a cylindrical analysis camera were used. The results of detecting nitrocompounds—trinitrotoluene, cyclotrimethylenetrinitramine (hexogen, RDX), etc.—are presented. The experimental detection limits of the spectrometer are 5 × 10⁻¹⁵ g/cm³ (cyclotrimethylenetrinitramine) and ≤3 × 10⁻¹⁵ g/cm³ (trinitrotoluene).     

高性能铁基预混合粉的温压工艺性能研究

简要介绍温压工艺,着重从工艺稳定性、生坯密度、生坯强度以及拉伸强度等方面研究自制高性能铁基预混合粉的温压工艺性能。研究结果表明,自制高强度铁基粉末具有良好的温压工艺性能。     

Impression creep: Effects of slip, stick and cavity depth

The impression creep of a power-law material by pushing a rigid cylindrical punch into an existing cavity of the same diameter as the punch located in the surface of a half-space was studied by using finite element method. For both the slip and stick conditions at the interface of the punch and the half-space, there is a well-defined steady punch penetration velocity after a transient stage. The steady penetration velocity is a power function of the applied load, which has the same stress exponent as by conventional creep tests. It increases with the stress exponent but decreases with increasing cavity depth, and is the largest for all slip condition and the smallest for both stick condition on the circular interface between the punch and the cavity and all stick condition.     

Effect of Er:YAG laser irradiation on deciduous enamel roughness and bacterial adhesion: An in vitro study

Laser irradiation has been proposed as a preventive method against dental caries since it is capable to inhibit enamel demineralization by reducing carbonate and modifying organic matter, yet it can produce significant morphological changes. The purpose of this study was to evaluate the influence of Er:YAG laser irradiation on superficial roughness of deciduous dental enamel and bacterial adhesion. Fifty‐four samples of deciduous enamel were divided into three groups (n = 18 each). G1_control (nonirradiated); G2_100 (7.5 J/cm²) and G3_100 (12.7 J/cm²) were irradiated with Er:YAG laser at 7.5 and 12.7 J/cm², respectively, under water irrigation. Surface roughness was measured before and after irradiation using a profilometer. Afterwards, six samples per group were used to measure bacterial growth by XTT cell viability assay. Adhered bacteria were observed using confocal laser scanning microscopy (CLSM) and a scanning electron microscopy (SEM). Paired t‐, one‐way analysis of variance (ANOVA), Kruskal‐Wallis and pairwise Mann–Whitney U tests were performed to analyze statistical differences (p < .05). Before treatment, samples showed homogenous surface roughness, and after Er:YAG laser irradiation, the surfaces showed a significant increase in roughness values (p < .05). G3_100 (12.7 J/cm²) showed the highest amount of Streptococcus mutans adhered (p < .05). The increase in the roughness of the tooth enamel surfaces was proportional to the energy density used; the increase in surface roughness caused by laser irradiation did not augment the adhesion of Streptococcus sanguinis; only the use of the energy density of 12.7 J/cm² favored significantly the adhesion of S. mutans.     

Isostatic compaction of bimodal powder mixtures and composites

We study the effect of using a mixture of particles of two different sizes for the compaction of spherical metallic powders by discrete element method simulations (DEM). The study focuses on large size ratios (4 and 8) for which a wide range of volume fractions of large particles is investigated (from 0% to 80% volume). The bimodality of the powder is shown to affect all stages of powder compaction. The relative density of the powder when no significant load is applied (tap density) is a function of both the size ratio and the volume fraction of large particles. Furthermore, we show that bimodal compacts exhibit a stiffer response during isostatic plastic compaction compared to the monomodal case. The important practical application of a mixture of soft deformable particles (metallic) with hard particles (ceramic) is also studied. Following compaction, the unloading of the compact and the resulting tensile strength (green strength) are also shown to depend on the bimodality of the compact.     

Measurement of Mobility of Radioactive Air Ions in Atmosphere

A method for measuring the mobility of radon daughter products, ²¹⁸Po, in gas medium is described. The mobility of the daughter products was measured using the flow-through technique of air ion detection. The flow-through technique is based on precipitation of ions from Rn-containing air flow on the surface of a semiconductor detector. Precipitation occurs in an electrostatic field of a plane capacitor. Upon precipitation, alpha radiation of ²¹⁸Po is detected. The dependence of ion mobility on the absolute humidity of air was determined (the age of ions was about 1 s). It was shown that, within a range of humidity from 3.4 to 13.6 g/m³, this dependence is negligible. The mean mobility of ²¹⁸Po was found to be 1.05 ± 0.05 cm²/(sV).     

On cropping and related processes

Two distinct aspects of cropping and related processes are considered, (i) the maximum in punch force caused by plastic instability and (ii) the initiation and propagation of cracks after the onset of plastic flow.An expression for punch travel at the peak load is derived in terms of the work hardening index of the workpiece, its thickness and state of prestrain. Good agreement is found with experimental results from a variety of sources. The expression is also modified to include cases where cracks appear before the peak in load.A re-examination of experimental autographic punch load-punch penetration traces shows that it is possible, within the limitations of a single shear plane model, to partition the total work of deformation into flow and fracture components. It would seem that crack propagation in cropping or blanking starts when the incremental energy consumed by cracking plus flow is smaller than the alternative process of carrying on flowing over a larger plastic volume with no cracking. Estimates for fracture toughness are possible by this method, e.g. 500–600 lbf-in/in² for brass and aluminium and 170 lbf-in/in² for lead from the results of Chang and Swift[1]. A criterion for the occurrence of multiple cracking on the cropped faces is derived in terms of toughness, flow stress and workpiece/punch geometry and is shown to agree with experimental observations.An appendix highlights some more general aspects of the area of combined flow and fracture, and discusses how cracks in plastic flow fields may be identified and dealt with analytically.     

Die compaction of copper powder designed for material parameter identification

This article presents uniaxial compaction experiments of a fine copper powder in a cylindrical die. The compaction process consists of monotonic loading and of loading paths with inserted unloading and reloading cycles. An experimental setup that has been developed for determining the axial and radial stresses during the compaction is described and the calibration of the new device using highly accurate p-finite element simulations of the dies response to internal pressure is shown. The experimental results were subsequently used for the identification of the material parameters of a constitutive model for granular materials recently proposed by Bier and Hartmann [A finite strain constitutive model for metal powder compaction using a unique and convex single surface yield function. accepted for publication by European Journal of Mechanics, Series A/Solids 2006.]. The identification of the elasticity parameters was treated with special attention.