Deformation and Mechanical Characteristics of Compacted Binary Mixtures of Plastic (Microcrystalline Cellulose), Elastic (Sodium Starch Glycolate), and Brittle (Lactose Monohydrate) Pharmaceutical Excipients

This work studies the tensile strength, coherence, elastic, and plastic energy of single and bi-component compacted tablets consisting of (i) microcrystalline cellulose (MCC) PH 102 as a plastic material, (ii) (SSG) as an elastic material, and (iii) alpha lactose monohydrate as a brittle material by direct compression. Compacted tablets were studied with various mass ratios formed at an ultimate compaction stress of 150 MPa. The loading and unloading stages of the compaction process for the single and binary tablets were evaluated based on the energies derived from the force-displacement data obtained. The resulting tablet quality was measured in terms of the tensile strength. Material that exhibit predominantly plastic deformation (MCC) shows a dominant property over elastically deforming sodium starch glycolate (SSG) and brittle (lactose) materials during the loading and unloading stages of the compaction process. In conclusion, the tensile strength of the formed tablets depends directly on the plastic energy and indirectly on the elastic energy and is negatively affected by the presence of a brittle material.     

The effect of the wrapped carbon fiber reinforced polymer material on fir and pine woods

The aim of this study is to observe the strength changes of the wood material. The compression and bending strength of the specially wrapped wood materials were investigated. Carbon fiber reinforced polymer (CFRP) material was wrapped onto the wood surface by using a polymer-based glue. The strength ratio of the wrapped and non-wrapped materials was investigated. The specimens were prepared from fir and pine woods that are used widely in buildings. At the same time, two types of woods were compared in terms of strength ratios. As a result of this study, the increase of the compression and three-point bending strength was determined for wrapped CFRP wood materials.     

Determination of Residual Stress in Beams Under Bauschinger Effect Using Surface Strain Measurements

Abstract:  The paper explores the use of surface strain measurements to determine residual stresses induced in plastically bent beams under Bauschinger effect using minimal stress–strain data. The hardening behaviour of some materials in tensile and compressive are dissimilar specially under Bauschinger effect. It is therefore ideally necessary to obtain both tensile and compressive stress–strain data in order to determine residual stresses in such materials. The paper shows that the compression stress–strain data can be implicitly determined from tensile and bending stress–strain results by using equilibrium considerations. This removes the need for separate compression tests to be carried out. The agreement of the derived stress–strain data in compression and of residual stress with experimental results is encouraging.     

Assessment of the mechanical behaviour of glass fibre composites with a tough polydicyclopentadiene (PDCPD) matrix

The use of a tough thermoset polydicyclopentadiene (PDCPD) as a matrix material for composites was explored. A PDCPD–glass fibre composite and an equivalent epoxy composite were compared. Fibre–matrix adhesion quality was assessed by transverse bending tests. The materials were subjected to compression tests, impact tests, static tensile tests and tensile fatigue tests. The results indicate that the tough behaviour of the PDCPD matrix markedly influences the composite damage resistance. The size of the impact damage in the PDCPD composite was half of that in the epoxy composite. The tensile tests indicated no significant difference in tensile strength, but the damage before failure was found to be much more severe in the epoxy samples. The fatigue results showed a much lower variation in fatigue life for the PDCPD material than for the epoxy material, as well as clear differences in damage development for the two materials.     

Tricalcium citrate – a new brittle tableting excipient for direct compression and dry granulation with enormous hardness yield

Objectives: Tricalcium citrate (TCC) was characterized as a tableting excipient for direct compression (DC) and dry granulation (DG).

Significance: Brittle materials usually lead to tablets of inferior mechanical strength compared to plastic deforming materials. A brittle material exhibiting a high tabletability with the ability to retain that behavior during recompression would represent a valuable alternative to the commonly used microcrystalline cellulose.

Methods: Tablets of TCC and other common fillers were directly compressed for the purpose of compression analysis including Heckel analysis, speed dependency, and lubricant sensitivity. DG by roller compaction of TCC was first simulated via briquetting and experiments were subsequently repeated on a roller compactor.

Results: TCC appears as an excellent flowing powder of large agglomerates consisting of lower micron to submicron platelets. Despite the brittle deformation mechanism identified in the Heckel analysis, TCC demonstrated a very high mechanical strength up to 11?MPa in conjunction with an astonishingly low solid fraction of 0.85 at a compression pressure of 400?MPa. This was seen along with hardly any speed and lubricant sensitivity. Nevertheless, disintegration time was very short. TCC tablets suffered only a little from the re-compression: a slight loss in tensile strength of 1–2?MPa was observed for granules produced via roller compaction.

Conclusions: TCC was found to be suitable for DC as a predominantly brittle deforming filler, nevertheless demonstrating an enormous hardness yield while being independent of lubrication and tableting speed. TCC furthermore retained enough bonding capacity after DG to maintain this pronounced tabletability.     

On the identification of kinematic hardening material parameters for accurate springback predictions

An experimental method that frequently has been used for the determination of material hardening parameters is the three-point bending test. The advantage of this test is that it is simple to perform, and standard test equipments can be used. The disadvantage is that the material parameters have to be determined by some kind of inverse approach. The test has then been simulated by means of the Finite Element Method, and the material parameters have been determined by finding a best fit to the experimental results by means of a Response Surface Methodology. An alternative method is the tensile/compression test of a sheet strip. In practice such a test is very difficult to perform, due to the tendency of the strip to buckle in compression. In spite of these difficulties some successful attempts to perform cyclic tension/compression tests have been reported in the literature. However, a few writers have reported that there are substantial differences between hardening parameters determined from bending tests and those determined from tensile/compression tests. The purpose of the present study is to try to understand the background of these differences, to find out the influence on predicted springback, and to determine which of the two methodologies for hardening parameter identification is the most suitable one.     

金属-机织复合材料混合结构的三点弯曲力学性能及失效机理EI北大核心CSCD

为解决传统金属与复合材料混合成形方法中存在的分层失效、纤维破坏等问题,设计一种结合金属增材制造、复合材料机织与缝合等工艺的新型混合结构,将金属骨架与机织复合材料法向缝合后共固化成形,增加异质材料之间的结合强度,实现宏观尺度上金属与复合材料的灵活成形与稳定连接。通过三点弯曲实验研究新型混合结构的面内弯曲性能,采用非接触式图像测量手段分析混合结构样件的损伤形貌及失效机理。结果表明:混合结构失效是多种失效模式的组合,包括纤维层上侧压缩/下侧拉伸断裂、异质材料层间失效及金属塑性损伤等;层间分层是由界面旁侧存在基体裂纹和层间剪应力、相邻层间刚度不相容等多因素造成的;随着样件结构厚度增加,其结构弯曲强度和弯曲弹性模量均增大;开孔处引入缝合纤维可以在一定程度上抑制分层裂纹的扩展,提高结构抗分层断裂性能。     

Bonding Surface area and Bonding Mechanism-Two Important Factors fir the Understanding of Powder Comparability

Abstract

Two factors could be regarded as primary factors for the compactability of powders: the dominating bond mechanism and the surface area over which these bonds are active. Owing to considerable experimental difficulties, these factors have not been evaluated in any detail for pharmaceutical materials. Instead, more indirect, secondary factors are normally studied and used for correlations with tablet strength. Such secondary factors are particle size, shape and surface texture. Also the importance of volume reduction mechanisms, i.e. elastic deformation, plastic deformation and particle fragmentation have been studied in detail.

For the investigation of dominating bond mechanisms and estimation of the magnitude of the surface area of the solids involved in interparticulate attraction in compacts several pharmaceutical excipients representing both plastically deforming materials (sodium chloride, Avicel® PH 101, Sta-Rx 1500®, and sodium bicarbonate) and fragmenting materials (lactose, sucrose, paracetamol and Emcompress®) have been used in a series of publications from our laboratory.

The bonding mechanisms discussed have been solid bridges, representing continous solid bridges between tablet particles, intermolecular forces, representing weaker attraction forces active over distances and mechanical interlocking, representing a bond type dependent on hooking and twisting of irregularly shaped particles. To characterize the dominating bond mechanisms, measurements of compact strength has been performed in media known to reduce bonding with intermolecular forces. The media used were liquids with different dielectric constants and films of magnesium stearate. The results establish that the intermolecular forces constitute the dominating bond mechanism for pharmaceutical materials. Bonding with solid bridges contribute to the compact strength only for coarse plastically deforming materials that can melt during compaction. Only for sodium chloride, of the materials tested, is there substantial evidence for the existence of solid bridges. Bonding with mechanical interlocking is a bonding mechanism of minor importance for most of the investigated materials with the possible exception of Avicel® PH 101.

The results indicate that the surface area utilized for bonding with solid bridges for sodium chloride as measured with gas adsorption is small in relation to the total surface area of the compact. For all the materials bonding with intermolecular forces, only a proportional relation between compact surface area and bonding surface area could be possible. By using permeametry surface area data, the surface specific compact strength was characterized and found similar for all materials bonding primarily with intermolecular forces. For such materials a large bonding surface area will thus be obtained if the surface area of the particles in the tablet is large. This could either be achieved by the use of materials that undergo extensive fragmentation or by the use of very fine paniculate materials or qualities with pronounced surface roughness. It is suggested that most of the so called plastically deforming pharmaceutical materials often possess inadequate plasticity for the development of large zones that could take part in the interparticulate attraction by intermolecular forces.     

Bonding Surface area and Bonding Mechanism-Two Important Factors fir the Understanding of Powder Comparability

Two factors could be regarded as primary factors for the compactability of powders: the dominating bond mechanism and the surface area over which these bonds are active. Owing to considerable experimental difficulties, these factors have not been evaluated in any detail for pharmaceutical materials. Instead, more indirect, secondary factors are normally studied and used for correlations with tablet strength. Such secondary factors are particle size, shape and surface texture. Also the importance of volume reduction mechanisms, i.e. elastic deformation, plastic deformation and particle fragmentation have been studied in detail.

For the investigation of dominating bond mechanisms and estimation of the magnitude of the surface area of the solids involved in interparticulate attraction in compacts several pharmaceutical excipients representing both plastically deforming materials (sodium chloride, Avicel® PH 101, Sta-Rx 1500®, and sodium bicarbonate) and fragmenting materials (lactose, sucrose, paracetamol and Emcompress®) have been used in a series of publications from our laboratory.

The bonding mechanisms discussed have been solid bridges, representing continous solid bridges between tablet particles, intermolecular forces, representing weaker attraction forces active over distances and mechanical interlocking, representing a bond type dependent on hooking and twisting of irregularly shaped particles. To characterize the dominating bond mechanisms, measurements of compact strength has been performed in media known to reduce bonding with intermolecular forces. The media used were liquids with different dielectric constants and films of magnesium stearate. The results establish that the intermolecular forces constitute the dominating bond mechanism for pharmaceutical materials. Bonding with solid bridges contribute to the compact strength only for coarse plastically deforming materials that can melt during compaction. Only for sodium chloride, of the materials tested, is there substantial evidence for the existence of solid bridges. Bonding with mechanical interlocking is a bonding mechanism of minor importance for most of the investigated materials with the possible exception of Avicel® PH 101.

The results indicate that the surface area utilized for bonding with solid bridges for sodium chloride as measured with gas adsorption is small in relation to the total surface area of the compact. For all the materials bonding with intermolecular forces, only a proportional relation between compact surface area and bonding surface area could be possible. By using permeametry surface area data, the surface specific compact strength was characterized and found similar for all materials bonding primarily with intermolecular forces. For such materials a large bonding surface area will thus be obtained if the surface area of the particles in the tablet is large. This could either be achieved by the use of materials that undergo extensive fragmentation or by the use of very fine paniculate materials or qualities with pronounced surface roughness. It is suggested that most of the so called plastically deforming pharmaceutical materials often possess inadequate plasticity for the development of large zones that could take part in the interparticulate attraction by intermolecular forces.     

Mechanical behavior of sandwich panels with hollow Al–Si tubes core construction

A new type of lightweight sandwich panels consisting of vertically aligned hollow Al–Si alloy tubes as core construction and carbon fiber composite face sheets was designed. The hollow Al–Si alloy tubes were fabricated using precision casting and were bonded to the face sheets using an epoxy adhesive. The out-of-plane compression (i.e. core crushing), in-plane compression, and three-point bending response of the panels were tested until failure. The hollow Ai–Si alloy tubes core configuration show superior specific strength under crushing compared to common metallic and stochastic foam cores. Under in-plane compression and three-point bending, the buckling of face sheets and debonding of hollow cores from the face sheets were observed. Simple analytical relationships based on the concepts of mechanics of materials were provided for the compression tests, which estimate the sandwich panels’ strength with high fidelity. For three-point bending, detailed finite element analysis was used to model the response and initial failure of the sandwich panels.     

Versagensverhalten eines Kohlenstoff‐Faserverbundwerkstoffs unter Druckbeanspruchung

In this work the properties of Carbon/Carbon‐material are investigated under quasi‐static compression and model‐like characterized. The investigated material was produced by pyrolysis of a Carbon/Carbon – composite of bidirectionally reinforced fabric layers. For the compression tests, a device to prevent additional bending stress was made. The stress‐strain behaviour of this material has been reproduced in various publications. This will be discussed on the fracture behaviour and compared the experimental results from the compression tests with the characteristics of tensile and shear tests. The different compression and tensile properties of stiffness, poisson and strength were assessed. Differences between the tensile and compression behaviour resulting from on‐axis tests by micro buckling and crack closure and off‐axis experiments by superimposed pressure normal stresses that lead to increased shear friction.     

Diffusion bonding of ceramics: mullite,ZrO2-toughened mullite

Diffusion bonding of fine-grained mullite and ZrO₂-toughened mullite was performed in the temperature range from 1500 to 1550 °C in air. Uniaxial pressure was applied at high temperature during the bonding process. The surface roughness to be bonded (R _max) was about 3 m. Bonding strength was measured by four-point bending tests and the strength of the base material was measured by three-point bending tests. The effects on the bonding strength of bonding conditions such as temperature and applied strain were examined. Bonding strength increased with increasing bonding temperature and applied strain. The bonding strength of mullite and ZrO₂-toughened mullite was about 80% of the strength of the base material before bonding. The bonding strength of mullite was maintained up to 1000 °C.     

Influence of granulating method on physical and mechanical properties, compression behavior, and compactibility of lactose and microcrystalline cellulose granules

The physical and mechanical properties of lactose (LC) and microcrystalline cellulose (MCC) granules prepared by various granulating methods were determined, and their effects on the compression and strength of the tablets were examined. From the force-displacement curve obtained in a crushing test on a single granule, all LC granules appeared brittle, and MCC granules were somewhat plastically deformable. Intergranular porosity ε_inter clearly decreased with greater spherical granule shape for both materials. Decrease in intragranular porosity ε_intra enhanced the crushing force of a single granule F_g. Agitating granulation brought about the most compactness and hardness of granules. In granule compression tests, the initial slope of Heckel plots K₁ appeared closely related to ease of filling voids in a granule bed by the slippage or rolling of granules. The reciprocal of the slope in the succeeding step 1/K₂ in compression of MCC granules indicated positive correlation to F_g, while in LC granules, no such obvious relation was evident. 1/K₂ differed only slightly among granulating methods. Tensile strength of tablets T_t obtained by compression of various LC granules was low as a whole and was little influenced by granulating method. For MCC granules, which are plastically deformable, tablet strength greatly depended on granulation. Granules prepared by extruding or dry granulation gave strong tablets. Tablets prepared from granules made by the agitating method showed particularly low T_t. From stereomicroscopic observation, the contact area between granule particles in a tablet appeared smaller; this would explain the decrease in intergranular bond formation.     

Relationship between static bending and compressive behaviour of particle-reinforced cement composites

Innovative particle-reinforced materials made of alumina particles and cement-based matrix were designed, manufactured and tested to evaluate the potential use of ceramic aggregates in concretes. These particle-reinforced composites were tested in three-point bending and uniaxial compression conditions to determine the influence of the shape and size of the ceramic inclusions, and the addition of silica fume on the mechanical properties. A specific methodology combining post-mortem observations with a statistical analysis of tensile failure stresses (average strength and Weibull modulus) was conducted to deduce the origin of failure for each cement-based composite (porosity or ceramic particles/matrix decohesion). A remarkable correlation is observed between bending failure stress level and the average strength measured under uniaxial compression loading. As main conclusion, addition of alumina particles in a mortar appears to strengthen or to weaken the composite depending on whether silica fume is used in the cementitious matrix.     

Strength evaluations of sinusoidal core for FRP sandwich bridge deck panels

Fiber-reinforced polymer (FRP) sandwich deck panels with sinusoidal core geometry have shown to be successful both in new construction and the rehabilitation of existing bridge decks. This paper is focused on an experimental study of the strength evaluations of a honeycomb sandwich core under out-of-plane compression and transverse shear. The sinusoidal core is made of E-glass Chopped Strand Mat (ChSM) and Polyester resin. The compressive, tensile and shear strengths were first obtained from coupon tests. The out-of-plane compression tests were performed on representative single-cell volume elements of sandwich panels, and the tests included “stabilized” samples to induce compression failure, and “bare” samples to induce local buckling of the core. Finally, four-point bending tests were conducted to study the structural strength behavior under transverse shear. Two types of beam samples were manufactured by orienting the sinusoidal wave either along the length (longitudinal) or along the width (transverse). Both typical shear failure mode of the core material and delamination at the core–facesheet bonding interface were observed for longitudinal samples. The failure for transverse samples was caused by core panel separation. For both single-cell and beam-type specimen tests, the number of bonding layers, i.e., the amount of ChSM contact layer and resin used to embed the core into the facesheet, and the core thickness are varied to study their influence. The experimental results described herein can be subsequently used to develop design guidelines.     

温湿度和紫外老化对纸浆模塑材料性能的影响

目的 研究温度、湿度和紫外老化对脱木素和未脱木素纸浆模塑材料性能的影响,定量地对比不同因素作用下2种材料的力学性能差异。方法 以废纸浆为原料,经打浆、脱木素、湿成型、热压等工艺制得脱木素和未脱木素等2种纸浆模塑材料;模拟不同的温湿度和紫外老化环境,测试2种纸浆模塑材料物理力学性能的变化。结果 在同等条件下,脱木素材料的拉伸强度与弯曲强度均高于未脱木素材料;2种材料的拉伸强度、弹性模量和弯曲强度随着含水率升高而大幅降低;当温度为20 ℃、含水率为0~40%时,脱木素材料的拉伸强度下降了45 MPa,未脱木素材料的拉伸强度下降了35 MPa。当温度为0 ℃、含水率为0~40%时,脱木素材料的弯曲强度下降了70 MPa,未脱木素材料的弯曲强度降低了62 MPa;当含水率低于20%时,脱木素材料的拉伸性能和弯曲性能更易受到温度影响;虽然2种材料的拉伸性能和弯曲性能均随着紫外老化时间的延长而不断降低,但其影响程度远小于温湿度。结论 湿度对材料的力学性能影响最大,其次是温度和紫外老化;脱去木素有利于提高纸浆模塑材料的力学性能和抗紫外老化性能。     

基于弯曲实验的DP980力学性能研究

目的 针对仅通过单向拉伸实验无法准确表征金属板材在弯曲成形过程中的力学性能变化的问题,研究通过弯曲实验获取材料力学性能参数.方法 对高强钢DP980展开力学性能测试研究,主要通过弯曲实验对材料弯曲变形过程中形成的弯矩曲率进行测试,将得到的弯矩曲率转化为应力-应变.分别将弯曲和拉伸得到的应力-应变数据导入到三点弯和辊弯成...     

Study on coexistence of brittle and ductile fractures in nano reinforcement composites under different loading conditions

Experimental study on high volume fraction of metallic matrix nano composites (MMNCs) was conducted, including uniaxial tension, uniaxial compression, and three-point bending. The example materials were two magnesium matrix composites reinforced with 10 and 15% vol. SiC particles (50 nm size). Brittle fracture mode was exhibited under uniaxial tension and three-point bending, while shear dominated ductile fracture mode (up to 12% fracture strain) was observed under uniaxial compression. The original Modified Mohr–Coulomb (MMC) fracture model (Bai and Wierzbicki in Int J Fract 161:1–20, 2010; in a mixed space of stress invariants and equivalent strain) was transferred into a stress based MMC (sMMC) model. This model was demonstrated to be capable of predicting the coexistence of brittle and ductile fracture modes under different loading conditions for MMNCs. A material post-failure softening model was postulated along the damage accumulation to capture the above two different failure modes. This model was implemented to the Abaqus/Explicit as a material subroutine. Numerical simulations using finite element method well duplicated the material strength, fracture initiation sites and crack propagation modes of the Mg/SiC nano composites with a good accuracy. The proposed model has a good potential to predict fracture for a wide range of material with strength asymmetry and coexistence of brittle and ductile fractures modes.     

低成本PVA纤维对超高韧性水泥基复合材料力学性能的影响

超高韧性纤维增强水泥基复合材料（ECC）因其出色的高韧性及多缝开裂特性备受关注,然而一直以来因配比中进口PVA纤维的使用导致高昂的价格限制了其在工程中的大规模应用。为了进一步降低成本及实现原材料的本土化,研究低成本国产PVA纤维对ECC力学性能的影响十分必要。通过单轴拉伸、压缩、三点抗弯及单裂缝拉伸等宏观、细观试验研究两种国产低成本PVA-ECC的力学性能,并借助纤维分散性试验及SEM,探讨纤维的分散等微观特征。结果表明,低成本国产纤维在基体中具有良好的分散性,尽管其纤维桥接余能、最大桥接应力及PSH指数低于进口纤维,但均能满足能量与强度准则,即便相对较差的纤维A试件的3 d、7 d及28 d的极限拉伸应变也可达到2.52%、3.34%及3.08%,可实现良好的应力硬化行为及饱和多缝开裂特性,满足ECC的使用要求。     

Failure initiation and propagation characteristics of honeycomb sandwich composites

The energy absorbed during the failure of a variety of structural shapes is influenced by material, geometry and the failure mode. Failure initiation and propagation of the honeycomb sandwich under loading involves not only non-linear behavior of the constituent materials, but also complex interactions between various failure mechanisms. Therefore, there is a need for an improved understanding of the material characteristics and energy absorption modes to facilitate the design of sandwich performance. In the present study, failure initiation and propagation characteristics of sandwich beams and panels subjected to quasi-static and impact loadings were investigated. Experimental studies involved a series of penetration and perforation tests on 2D beam and 3D panel configurations using a truncated cone impactor with impact velocities up to 10 m/s. Preliminary tests were also performed on the sandwich beams subjected to the three-point bending. Load-carrying, energy-absorbing characteristics and failure mechanisms under quasi-static and impact loading were determined. Dominant deformation modes involved upper skin compression failure in the vicinity of the indenter, core crushing and lower skin tensile failure.