Unaged Specimens Research Articles

Properties of Porous Asphalt Mixture Made with Styrene Butadiene Styrene under Long Term Oven Ageing

Oven ageing is a set of procedure to simulate the accelerated effects of ageing on pavements structures. In this study, the effect of long-term oven ageing on porous asphalt mixture made with SBS modified binder was investigated. The resilient modulus, water permeability and air voids test results were the performance indicators used to evaluate the effects of ageing. The test results showed that, the resilient modulus of long term aged specimens was higher than those of unaged specimens. From the permeability test results, unaged SBS mixes exhibit lower coefficient permeability compared to the corresponding long-term oven age specimens. Most likely, ageing caused binder hardening, making the mix more difficult to compact and hence exhibited more continuous voids which in turn lead to higher permeability. In addition, the coefficient of permeability decreases as the binder content increased.

Effect of Moisture Absorption on the Bending Strength of CFRP

The effects of moisture content on the bending strength of T300/914 composite laminates that immersed in water for 7 days and 14 days was discussed in this paper. The three-point bending tests were conducted on the composite laminates. Experimental results reveal that the moisture content in the laminates increased with immersion time and that moisture absorption accelerated damage propagation in the composite laminates. The bending strength of the unaged, aged specimens were characterized and analyzed. Compared to the unaged specimens, the bending strength of the composite laminates immersed for 7 and 14 days decreased by 6.62% and 16.98%, respectively. The results revealed that the bending strength of the aged specimens decreased with the increasing immersion time.

Effect of Moisture Absorption on the Residual Strength after Bending Fatigue of CFRP

This study investigates the effect of moisture content on the residual bending strength after bending fatigue of T300/914 composite laminates immersed in water for 7 days and 14 days. Displacement-controlled three-point bending fatigue tests were conducted on specimens. After 40,000 cycles the fatigue test was stopped and the residual properties were measured on the tested specimens. Reduction in material strength was found to depend on the level of moisture content. Experimental results reveal that the moisture content in the laminates increased with immersion time. Compared to the unaged specimens, the residual bending strength after bending fatigue decreased by 6.67% and 37.04%, respectively. The residual bending strength and strength retention decreased with increased immersion time.

Effect of Moisture Absorption on the Bending Strength of Carbon/Epoxy Composites with Voids

The effects of voids on the bending strength of T300/914 laminates that exposed to room temperature, hygrothermal and drying environment was discussed in this paper. The experimental results revealed that the saturated moisture content and the rate of water uptake increased with porosity increasing from 0.71% to 1.50%, which proved that voids facilitate moisture absorption. The bending strength of the unaged, aged and dried specimens were characterized and analyzed. The results revealed that the bending strength of the aged specimens decreased with the increasing void contents and immersion time. Compared to the unaged specimens, the bending strength of the aged specimens decreased 13.33% and 18.78% with porosity of 0.71% and 1.50%, respectively. The bending strength of the dried specimens was higher than that of the aged specimens and lower than that of the unaged specimens in the case of similar porosity.

Qualitative separation of the effect of voids on the static mechanical properties of hygrothermally conditioned carbon/epoxy composites

The paper investigates the effect of voids and hygrothermal conditions on bending, compressive, and interlami- nar shear strength (ILSS) of T300/914 composite laminates. By adopting different autoclave pressures during a cure cycle, specimens with three different void contents ranging from 0.33% to 1.50% were obtained. Experimental results reveal that compressive, bending strength, and ILSS decrease with increasing void contents and immersion time. The most significant decrease in strength of aged specimens is in the ILSS and compressive strength, followed by the bending strength. The effect of voids on the absorption/desorption behavior is also discussed. For a similar porosity, the compressive strength and ILSS of dried specimens are higher than that of the aged specimens, while they are lower than that of the unaged specimens. The bending strength of the dried specimens is higher than that of the unaged specimens. The experimental results are explained by the supportive micrographs that illustrate different types of voids and their morphology before and after mois- ture absorption/desorption.

The Effect of Thermal Aging on Tensile Strength of Three-Dimension and Five-Direction Braided Carbon Fiber/BMI Composites

This work aims at investigating the effect of thermal aging on tensile properties of three-dimension (3D) and five-direction braided carbon fiber/BMI resin composites prepared by resin transfer molding (RTM) process. The influence of high temperature on the tensile strength and the failure mechanisms of un-aged and aged composites were studied, respectively. As for the thermal aging condition, 180 for 24h was selected. The tensile strength of both un-aged and aged specimens were tested by SHIMADZU universal material testing machine at room temperature. The fracture modes of specimens were observed by scanning electron microscopy (SEM). It was found that the tensile load at break and tensile strength decreased after ageing. From the SEM views of the failed samples, the fracture surface presented hackles which were specific to the debonding of the interface between fibers and matrix. A lot of fibers were pulled-out in the aged state specimen. It can be confirmed that the failure occurred at the fiber/matrix interface and the fiber/matrix interface seemed to be weak in aged carbon fabrics reinforced BMI composites.

Evaluation of fatigue properties for aged 9Cr-1Mo steel

Low cycle fatigue tests of 9Cr-1Mo steel aged at 600°C for 5000 h and 10000 h were conducted at RT-600°C. Fatigue life was not decreased with aging. Cyclic softening was seen with cycles in both unaged and aged specimens. Aging decreased the amount of softening at RT and 400°C but increased it at 600°C. The precipitate species were not changed with aging upto 5000 h but Laves phase was precipitated after 10000 h aging. Fatigue life of 9Cr-1Mo steel aged to 10000 h is dependent on dislocation slip behavior rather than the amount and coarsening of precipitate.

Durability by Design: New Results on Load-Carrying Silicone Bonding

Abstract In the year 2000, the Herz-Jesu church in Munich, Germany was finalized featuring a glass façade with advanced bonded load-carrying structures. The façade was stiffened in such a way that wind- and dead-loaded glass elements were joined to stainless steel channels by a two-component silicone adhesive for load transfer. Durability aspects related to this type of bonding were already presented by the author at the previous symposium in 2003. The technical questions raised by the design of the Herz-Jesu church initiated detailed research investigations within Germany concerning the application of complex bonding geometries for structural engineering purposes. These studies comprised experimental and theoretical activities which were focused on the mechanical properties of two-component silicone adhesives as well as on the behavior of various bonding geometries resulting from the use of L- and T-type steel elements. In the context of these research activities, attention was also paid to different aspects directly or indirectly related to durability issues. Regarding adhesive material behavior, tensile, compression, and shear tests were performed on aged and unaged specimens in order to analyze the impact of an aggressive environment. Several degradation modes were induced into the specimens in a systematic manner in order to evaluate the load-bearing capacities and failure mechanisms of the different bonding geometries and in order to assess the behavior in the view of partial failure. This paper presents an overview of the obtained experimental results complemented by detailed finite element analysis results. Former results obtained for the U-type bonding geometry are reviewed in the light of new experimental findings. Furthermore, bonding geometries like the T-type bonding are assessed in a similar way as previously done for the U-type bonding geometry. Finally, the paper concludes by directly comparing all investigated bonding geometries with respect to durability aspects.

Influence of cyclic fatigue in water on the load-bearing capacity of dental bridges made of zirconia

The humid atmosphere and permanent occurrence of chewing forces in the oral environment lead to degradation of ceramics used for prosthetic restorations. The aim of this in vitro study was to evaluate the influence of artificial aging on the load-bearing capacity of four-unit bridges, with both undamaged and predamaged zirconia frameworks. Additionally, different parameters for chewing simulation have been investigated and a finite element analysis was made to predict the location of highest tensile stresses within the bridges. A total of 60 frameworks were milled from presintered zirconia and divided into six homogeneous groups. Prior to veneering, frameworks of two groups were “damaged” by a defined saw cut similar to an accidental flaw generated during shape cutting. After veneering, FPDs were subjected to thermal and mechanical cycling – with the exception of control groups. The load-bearing capacity of tested FPDs was significantly reduced by artificial aging. In comparison to unaged specimens, fracture resistance decreased by about 40%, whereas preliminary damage did not have a significant effect. Increasing number of cycles and increasing upper load limit failed to show any additional effect on fracture force. To predict the progression of degradation under the terms of in vitro simulation for even longer periods, further aging experiments are required.

Influence of Step Aging on Creep Behavior and Microstructural Evolution of Fine-Grained Fully Lamellar XD TiAl Alloys

Fine-grained fully lamellar (FGFL) structures of XD TiAl alloys (Ti-45 and 47Al-2Nb-2Mn+0.8vol.%TiB2) (at.%) were stabilized to varying degrees by different aging treatments. Specimens with and without aging were creep tested at 760°C and 207 MPa. It was found that during creep deformation, degradation of the lamellar structure involving coarsening within the colonies and spheroidization at colony boundaries occurred, forming fine globular structures at the colony boundaries and increasing the creep rate. Aging treatments stabilized the lamellar structure and retarded the coarsening and spheroidization processes during creep deformation. As a result, the aged specimens exhibited lower minimum creep rates and longer creep lives than the unaged specimens. A multiple step aging stabilized the lamellar structure to the greatest extent and suppressed other degradation processes during aging, resulting in the best creep resistance. These results demonstrate that the multiple step aging is the optimal aging condition for stabilizing FGFL XD TiAl alloys.

Characterization of Adhesion Interlayer Between Rubber and Brass by a Novel Method of Sample Preparation

Abstract Instrumental characterization of an adhesion interface in a rubber-brass system often faces a difficulty in exposing a clean surface due to a stick of rubber residue on a brass surface. We have succeeded in isolating an interface from the rubber matrix by inserting a filter paper between rubber and brass during the vulcanization. Clean interface was obtained by removing the filter paper after the vulcanization, enabling a detailed characterization of the interface by XPS and SEM-EDX from a practical rubber formulation. Formulation of cobalt naphthenate did not contribute to a formation of adhesion interlayer in an initial stage of cure, but greatly affected the composition of copper sulfide during the vulcanization. It was found that a dosage of cobalt improved a growth of interface at aging. Copper sulfide particles were found to be spherical at the interface for unaged specimens. It was revealed that excess growth of copper sulfide was a main feature at a humidity aging, while the growth of zinc oxide was eminent under a hot water aging. Scheme of an aging reaction was considered to depend on an interaction between brass and external factors such as heat, water, and oxygen.

Physical and water aging of glass fiber-reinforced plastic pipes

Physical and water aging of glass/epoxy composite — GFRE — pipes used for oil transport were investigated with special emphasis on their effect on the flexural and impact behavior. Different aging conditions were selected in order to simulate in-service environments trying to obtain reliable results from accelerated laboratory tests. In water uptake experiments at 80°C, the mass increases continuously, suggesting that an irreversible process occurs. In addition, samples aged in air at 80°C exhibit a DSC endothermic peak that can be related to physical aging. The calorimetric curve for specimens water aged at 80°C shows combined effects of water absorption and physical aging. On the other hand, while the independent effect of temperature and water aging on the composites mechanical response is only moderate, their combined effect seems to be dramatic. This result is mostly attributed to the weakening of the fiber–matrix interface induced by the water ging at high temperature, which consequently affects flexural and impact properties. SEM observations confirm the irreversible damage observed in water uptake experiments. Good interfacial adhesion between fiber glass and epoxy resin is observed for unaged specimens, whereas completely clean fibers are seen for specimens water aged at 80°C, indicating that the fiber–matrix interface is completely removed as a result of this aging condition.

Influence of hydrolytic ageing on the acoustic emission signatures of damage mechanisms occurring during tensile tests on a polyester composite: Application of a Kohonen’s map

The effects of hydrolytic ageing on the acoustic emission signature of damage mechanisms occurring during tensile tests on a glass fibre reinforced polyester composite are investigated. These results are used to test the validity of a Kohonen’s map established with AE data collected from an unaged specimen. This method enabled identification and classification of AE signals belonging to two different failure modes. The Kohonen self-organising map, trained on unaged specimens, is a valuable tool in assessment of damage type on the aged specimens.

界面はく離法により作製したゴムと黄銅接着界面のＳＥＭ‐ＥＤＸによる解析

We have previously succeeded in analyzing a clean adhesion interface by XPS utilizing a specific sample preparation of composite in which a filter paper was inserted between rubber and brass during the vulcanization. In this study, morphology of the interlayer was examined by SEM-EDX, in addition to the characterization of elemental distribution.Cu2S was found to be spherical at the interface for unaged specimens. Since Cu2S tended to corrupt gradually by an emission of electron beam during the SEM analysis, Cu2S was assumed to be amorphous.From the specimen aged under a humid environment, morphology of the Cu2S was found to be ragged crystalline. SEM image revealed that Cu2S did not corrupt during the emission of electron beam, which suggests the change in morphology from soft amorphous to rigid crystalline during the aging under humid conditions. Crystallization of Cu2S may lower the adhesion strength owing to decreased surface area and increased brittleness of the interfacial structure.ZnO tended to grow at the interface in the specimen aged with hot water. ZnO was found to occur during the aging in hot water by dezincification with moisture along with the migration from rubber matrix.

Martensitic Transformation and Shape Memory Effect in Ausaged Fe-Ni-Si Alloys.

Martensitic transformations in the Fe-(24-30)Ni-(5-8)Si (mass%) alloys have been investigated by means of optical and transmission electron microscopy, differential scanning calorimetry and hardness-testing. The Ms temperature is decreased by Si addition and the morphology of martensite is mainly lenticular in the unaged specimens. However, a pronounced decrease in the Ms temperature and a change in the martensite morphology from the lenticular to the thin plate type are observed on ausaging at 400°C. The increase in austenite hardness, the decrease in the Ms temperature and the increase in the tetragonality of martensite after ausaging at 400°C are clarified as due to the formation of nanoscale particles of γ'-(Ni,Fe) 3 Si with the L12 structure during ausaging at 400°C. The Fe-Ni-Si alloys that form thin plate martensite show the shape memory effect, which arises from the reverse transformation of stress-induced martensite to austenite. Precipitation hardening of the austenite phase by fine y' particles during ausaging improves the degree of shape recovery.

A comparative study of the stress relaxation in aged and un-aged high-purity aluminium polycrystals

Stress relaxation in 99.996% aluminium polycrystals of average grain-diameter 0.30, 0.42 and 0.51 mm, annealed at 500°C and aged for six months at room temperature, has been studied as a function of initial stress level from which relaxation at constant strain was allowed to start. Data were also obtained with annealed but un-aged aluminium specimens of the same purity and grain size for comparison. The grain size has no notable effect on the strength parameters and stress-relaxation rate in both aged and un-aged aluminium. The room-temperature ageing causes significant increase in the yield stress, while tensile strength and fracture stress remain un-effected. The intrinsic height of the thermally-activable energy barrier (1.64 eV) evaluated for aged aluminium is comparable with that (1.94 eV) for un-aged aluminium, and is of the order of magnitude for recovery processes. In aged specimens, the relaxation rate at a given stress level is 30% larger and associated activation volume is accordingly smaller than that in un-aged specimens. This is most probably due to the diffusion of vacancies and/or residual gaseous and metallic impurity atoms to the cores of edge dislocations in aged specimens.

Effect of Natural Ageing on the Strain-Rate Sensitivity of Flow Stress in High-Purity Aluminium Polycrystals

Strain-rate-cycling experiments between 4.6 × 10 -3 s -1 and 4.6 × 10 -4 s -1 were performed with 99.996% aluminium polycrystals of mean grain-diameter 0.25, 0.36, and 0.47 mm, which had been annealed at 500°C and aged for six months at room temperature prior to deformation. Similar studies were also carried out with 500 °C annealed but unaged aluminium specimens of the same purity and grain size for comparison. It is observed that yield stress, ultimate tensile stress, fracture stress, and strain-rate sensitivity Δσ of a given flow stress σ in the range 30 to 70 MPa are not influenced by the grain size in both aged and unaged aluminium. However, natural ageing significantly enhances the yield stress as well as the strain-rate sensitivity Δσ of a given flow stress σ by 30% while ultimate tensile stress and fracture stress remain unaffected. Migration of point defects, e.g. vacancies, residual gaseous and metallic impurity atorns etc., to the cores of edge dislocations during ageing seems to be responsible for the increase in yield stress and strain-rate sensitivity of the flow stress. The analysis of the Δσ/σ data in terms of Feltham's single barrier model of plastic flow shows that the intrinsic height of the thermally activable energy barrier (3.4 eV) evaluated for aged aluminium is comparable with that (4.2 eV) for unaged aluminium, and dislocation-dislocation intersection is the rate process of plastic flow.

The effect of thermal aging on the Mode-I interlaminar fracture behavior of a high-temperature IM7/LaRC-RP46 composite

High-temperature Mode-I interlaminar fracture tests have been conducted to evaluate the effect of thermal aging at various temperatures on the fracture behavior of IM7/LaRC-RP46 composites. Double cantilever beam specimens made of unidirectional laminates were used in the test program. The specimens were aged at high temperatures for times up to and including 6000 h. Changes in fracture behavior that occurred over periods of aging time and aging temperature have been measured and determined for variations of test temperature and loading rate. As expected, the crack growth at high temperature showed non-linear load–displacement response as a result of the rate-dependent nature of behaviour of the matrix. Present loading rates had no measurable effect on G IC values for unaged and aged specimens. High temperature increased G IC values of aged and unaged specimens at temperature near T g and decreased at temperatures above T g. Thermal aging for longer times also significantly reduced G IC initiation values for aged specimens. In contrast, thermal aging increased G IC propagation values as a result of the occurrence of increased fiber bridging, fiber breakage and microcracks, as deduced from SEM studies. Results also indicated that high temperatures slowed crack-growth rates. However, thermal aging and higher loading rates accelerated crack-growth rates. The effect of thermal aging and temperature on the crack growth rate, d a/d t, can be correlated with the C * parameter in the power-law relationship.

Micromechanical properties of cementitious composites

Micromechanical properties of cement matrices in cementitious composites were investigated by means of the microindentation method. The research focused on the correlation between micromechanical properties such as modulus of elasticity and creep, and distance of the indentation from the aggregate-matrix interface. Composites based on ordinary Portland cement (OPC) matrix were examined after exposure to two types of ageing procedures. The sub-micron accuracy of the positioning system of the microindentation apparatus provided means for a meaningful investigation of cement matrix in close vicinity to the aggregate-matrix interface. For the purpose of statistical analyses, the data were divided into two groups with respect to the distance of the indent from the aggregatematrix interface. While the tests performed within a 30 μm distance from the interface were classified as indents within the interfacial transition zone (ITZ), indents outside this distance were considered to describe properties of the ‘bulk matrix’. The results provide quantitative comparison of the microstructural properties of the interfacial transition zone (ITZ) with those of the bulk cement matrix assessed by well understood characteristics such as elastic modulus and creep. It was shown that, for unaged specimens, the elastic modulus measured within the interfacial transition zone was about 25% lower than that of the bulk matrix. Such results have significant consequences for improvement in modelling of cementitious composites.

Effect of Mode-mixity on the Fracture Toughness of Ti-6al-4v/fm-5 Adhesive Joints

Using several different fracture tests, the fracture toughness of a chromic acid anodized titanium (Ti-6A-4V)/polyimide (FM-5) adhesive system was evaluated. Mode I, mode II, and mixed mode (I and II) tests were conducted using double cantilever beam (DCB), end notch flexure (ENF), and mixed mode flexure (MMF) geometries. Interfacial type failures were observed in the ENF and MMF specimens as a result of the mode II loading inherent in these tests. Pure mode I loading, as is the case with symmetric DCB specimens, resulted in cohesive failures with a fracture energy around 2500 J/m2 on as-received specimens. The asymmetric DCB specimens had fracture energy values around 2000 J/m2, the MMF specimens close to 1970 J/m2, and ENF specimens around 1300 J/m2. All the above measurements were made on as-bonded (unaged) specimens. Titanium/FM-5 bonds supplied by the Boeing Company were then aged in one of three different environments for 2 and 6 months respectively. The environments included: 177degC in air and 2 psia, and 204degC in air. Following the aging, DCB, ENF, and MMF tests were conducted on the specimens. The results showed that aging in all three environments resulted in decreases in fracture energy for the above specimen testing configurations. The largest drop (20 percent) in fracture toughness was noted in specimens aged for 6 months in air at 204degC. An unusual finding from this study, in contrast to what other researchers have seen on other systems, was that increasing mode II loading resulted in significant reductions in toughness. Crack path selection and interaction with the woven glass scrim within the bonded specimens may be responsible for the lower mode II fracture energies. From the tests conducted, failure envelopes were developed to predict failure energy and type for use in designing structural joints.