Solicitation Mode Research Articles

Using FGM concept in fiber-matrix coupling laws to predict the damage in carbon-Epoxy graded composite application in notched plate under thermo-mechanical loading

Reinforcement in composite and notched structures has long been the objective of many researchers. One of the commonly used solutions is hybrid composite. Other recently reemerged solutions are graded materials. These respond, according to their modes of solicitation, to the targeted resistance objectives. However, composites with UD (unidirectional) fiber quality limit the choice of structural grading solely based on their thickness. Using the finite element method and the ABAQUS calculation code, this work presents the embodiment through numerical prediction of an idea based on the concept of material grading by FGM function. The objective of this approach is to introduce the volumetric fraction of the FGM concept into the Fiber-Matrix mixing laws in UD composite. Thickness-graded composites are subjected to a volumetric fraction function raised to the power of a parameter called volumetric fraction index (n). These structures, according to the proposed concepts, are analyzed under thermomechanical loading. The proposed grading of these composites is based on the presence of fibers in the matrix, where the fiber is denser on one side, called the simple concept C-S. The other two symmetrical concepts, named C-2 and C-3, present denser fibers in the middle and on both sides of the plate, respectively. These proposed concepts aim to observe how damage is caused by different responses and levels. The results under the different analyzed parameters are evaluated and compared to the results of the two other non-graded composites, thus showing the limits of those that are graded in terms of properties. According to the thermomechanical loading, the proposed graded composite has demonstrated a resistance overcapacity by the grading index (n) or their locations by concept C1- and C-2 of fibers have played a role in optimizing this capacity. The results also show that damage is caused by deformation overcapacity.

Statistical data for the tensile properties and static fatigue of sic-based bundles.

Due to their high specific strength at elevated temperatures and resistance to oxidative environments, SiC-based fibers are of great interest for the reinforcement of ceramic matrix composites. They are however subjected to a slow crack growth (SCG) phenomenon causing their delayed failure under subcritical conditions. The testing of filaments, other than comprising handling difficulties, requires large sets of data (broadly dispersed), drawback alleviated by multifilament tow testing. The data available in the present paper correspond to a comprehensive mechanical characterization and static fatigue testing of various types of SiC-based fiber bundles. The initial non-linearity of load displacement curves were analyzed to reveal the tow structure originating from filament misalignment. Static fatigue tests were used to assess the lifetime prediction coefficients and its distribution parameters. These data may found interest for the interpretation of dispersion bundle testing can highlight under different solicitation mode. Such data are also prominent for the wealth of composite design and to guaranty long term performances over the broad application field offered.

Modelling of a GFRP adhesive connection by an imperfect soft interface model with initial damage

In this paper a methodology to model a GFRP adhesive connections by using an imperfect soft interface model is presented. The model based on Kachanov’s theory considered a cracked thin adhesive. Within this framework, the mechanical properties and the initial damage (diffuse initial cracks) of the adhesive layer has been experimentally evaluated. With a modified Arcan system, static tests are performed on adhesively bonded assemblies in tensile and shear solicitation mode considering three different adhesive thicknesses. The experimental results highlighted how the thickness of adhesive influences the mechanical strength and stiffness of the bonded connection. CT-scans are performed to measure the porosity rate in the adhesive layer. Furthermore, the excellent comparison of numerical and experimental data of an adhesive GFRP bonded connections allow us to consider the imperfect soft interface model proposed as highly competitive to evaluate complex structure performance in civil engineering context. A parametric analysis has been proposed to provide a formula able to describe the full response of the structure at varying adhesive property.

Experimental investigation of failure mechanisms and evaluation of physical/mechanical properties of unidirectional flax–epoxy composites

Using natural fibers as reinforcement in polymer matrix composites necessitates evaluating the latter under different modes of solicitation. This allows extracting its material properties for engineering design and research purposes. The main objective of the study is preparing a consistent set of material properties for unidirectional flax fiber-reinforced epoxy composite with defined composition and basic configuration. These data are prerequisites for growing researches on flax fiber-reinforced epoxy composites, especially for numerical analysis purposes using the finite element method. In this work, partially green unidirectional-flax fiber-reinforced epoxy composites are tested for physical and mechanical properties and studied for their failure modes. Tension, compression, flexion, and shear properties, as well as physical properties like density, specific heat capacity and thermal diffusivity, are evaluated according to ASTM standard test methods. Flax fibers, which are composites by themselves, come in bundles in the composites and demonstrate a complex behavior. Therefore, a fractographic analysis has been conducted to understand the macro and microscale failure mechanisms to correlate them with the material properties. The results are in good agreement with those of the literature, when available, but they mainly show the specific behavior of unidirectional-flax composites subject to different solicitation modes, especially compression and direct shear modes evaluated this way for the first time for unidirectional-flax fiber-reinforced epoxy composite. They cover most of the data required for engineering design and numerical analysis by methods like finite element method, particularly for simulating the machining process of flax fiber-reinforced epoxy composite in the ongoing works.

Web Versus Other Survey Modes: An Updated and Extended Meta-Analysis Comparing Response Rates

AbstractDo web surveys still yield lower response rates compared with other survey modes? To answer this question, we replicated and extended a meta-analysis done in 2008 which found that, based on 45 experimental comparisons, web surveys had an 11 percentage points lower response rate compared with other survey modes. Fundamental changes in internet accessibility and use since the publication of the original meta-analysis would suggest that people’s propensity to participate in web surveys has changed considerably in the meantime. However, in our replication and extension study, which comprised 114 experimental comparisons between web and other survey modes, we found almost no change: web surveys still yielded lower response rates than other modes (a difference of 12 percentage points in response rates). Furthermore, we found that prenotifications, the sample recruitment strategy, the survey’s solicitation mode, the type of target population, the number of contact attempts, and the country in which the survey was conducted moderated the magnitude of the response rate differences. These findings have substantial implications for web survey methodology and operations.

Mode Effect and Response Rate Issues in Mixed‐Mode Survey Research: Implications for Recreational Fisheries Management

AbstractWhile the social, economic, and ecological impact of recreational fisheries is well established, the inherent diversity of both fisheries resources and resource users, particularly anglers, continues to present a challenge for management agencies. To better understand the diversity of recreational anglers, agencies often utilize survey methods to collect data on angler characteristics and preferences. However, obtaining necessary and representative data is becoming more challenging, exacerbated by declining response rates and an increase in the number of single and mixed‐mode survey designs researchers can choose to collect data. We examined three survey designs—surface mail with a Web push, e‐mail, and mixed mode—each with varying modes of solicitation and response, in the context of a statewide survey of licensed Texas anglers. Our findings illustrated that response rates varied considerably among these three survey designs. We also observed significant variation in terms of anglers’ sociodemographic characteristics based on solicitation and response modes of each survey design. Interestingly, we observed limited variation in terms of anglers’ behaviors, preferences, and motivations. Our results highlight the need for researchers and managers to be aware of the various survey designs available and the variability that particular survey designs can introduce into data.Received August 1, 2014; accepted March 2, 2016 Published online July 13, 2016

New bonded assembly configuration for dynamic mechanical analysis of adhesives

A new sample configuration has been developed in order to study molecular mobility of an adhesive in a bonded assembly configuration by dynamic mechanical analysis. The torsional rectangular mode is used to provide a shear solicitation all along the adherend/adhesive interface. The initial mechanical properties of each assembly's constituent are first investigated as reference. The modulus of aluminum foils used as substrates exhibits a classic elastic component and a slight viscous part due to microstructural changes or stress relaxation. Four relaxation modes are highlighted and identified for epoxy adhesive tested as a bulk material. Its viscoelastic behavior is compared to the one of adhesive tested in assembly configuration. The relaxation modes of the adhesive remain visible in spite of the sample stiffening by aluminum foils. Relaxation modes comparison shows that the temperature of loss modulus associated with the mechanical manifestation of glass transition slightly increases for the assembly configuration. Energy losses during this relaxation are much higher in the assembly configuration. Influence of rigid aluminum substrates is discussed in terms of the adhesively bonded joint solicitation mode.

Criteria for prediction of plastic instabilities for hot working processes (part I: theoretical review)

Hot working processes often induce high levels of strain at high strain rates, and impose very complex multi-axial modes of solicitation. These processes are essentially limited by the apparition and development of plastic instabilities. These may be the direct cause of rapid crack propagation, which lead to a possible final rupture. The complexity of strain modes and the simultaneous intervention of several parameters have led many researchers to develop various criteria, with different approaches, to predict the occurrence of defects and to optimize the process control parameters. The aim of the present paper is to summarize the general characteristics of some instability criteria, widely used in the literature, for the prediction of plastic instabilities during hot working. It was considered appropriate to divide the work into two parts. Part I presents the phenomenological criteria for the prediction of plastic instabilities, based on descriptive observation of the microscopic phenomena of the strain (strain hardening and strain rate sensitivity), and discusses the continuum criteria based on the principle of maximum rate of entropy production of irreversible thermodynamics applied to continuum mechanics of large plastic flow. Also, this part provides a bibliographical discussion among several authors with regard to the physical foundations of the dynamic materials model. In Part II of the work, a comparative study has been carried out to characterize the flow instability during a hot working process of a medium carbon micro-alloyed steel using phenomenological and continuum criteria.

Characterization Microstructural and Mechanical of X-60 Steel Heat-Treated

ABSTRACTIn this paper was study the effect of heat treatment on mechanical properties of an API X-60 steel used for storage and transportation of hydrocarbons.In the first stage evaluation are mechanical properties of steel heat treated by the technique of the three-point test according to ASTM 399-90 was carried out. In the second stage, characterization of the type of failure and microstructure through optical microscopy (OM) was determined; also heat treated samples were then mechanically tested for hardness (HRC) and nano-indentation. The presence of alloying elements by scanning electron microscopy (SEM) and the fracture surfaces generated in the steel with varying times, temperatures and cooling medium generated by different modes of solicitation (Bending), likewise with loading rates were determined. The results revealed a ductile fracture and microstructures (PF) ferrite-pearlite (DP), bainite -ferrite (BF) and martensite-retained and martensite/retained austenite (MA). Finally, this article discusses the effect of heat treatment followed by precipitation hardenable of steel API X-60 on the mechanical properties

Criterios de predicción de inestabilidades plásticas en procesos de conformado en caliente. (Parte I: Revisión teórica)

Hot working processes often induce high levels of deformation at high strain rates, and impose very complex multiaxial modes of solicitation. These processes are essentially limited by apparition and development of plastic instabilities. These may be the direct cause of rapid crack propagation, which lead to a possible final rupture. The complexity of deformation modes and the simultaneous intervention of several parameters have led many researchers to develop various criteria, with different approaches, to predict the occurrence of defects and to optimize process control parameters. The aim of the present paper is to summarize the general characteristics of some instability criteria, widely used in the literature, for the prediction of plastic instabilities during hot working. It was considered appropriate to divide the work into two parts: part I presents the phenomenological criteria for the prediction of plastic instabilities, based on descriptive observation of microscopic phenomena of the deformation (strain hardening and strain rate sensitivity), and discusses the continuum criteria based on the principle of maximum rate of entropy production of irreversible thermodynamics applied to continuum mechanics of large plastic flow. Also, this part provides a bibliographical discussion among several authors with regard to the physical foundations of dynamic materials model. In part II, of the work, a comparative study has been carried out to characterize the flow instability during a hot working process of a medium carbon microalloyed using phenomenological and continuum criteria.

Thermomechanical fatigue of nanostructured Ti–Ni shape memory alloys

A Ø 1.0 mm Ti–50.26 at% Ni wire is cold rolled by varying its true thickness reduction from e = 0.25 to 2.0 and then annealed (400 °C, 1 h) to obtain a nanoscale grain structure or a polygonized dislocation substructure, or a mixture of both. The Ti–Ni alloy is characterized using three complementary fatigue measurement techniques: (a) stress-free recovery, (b) constrained recovery, and (c) assisted two-way shape memory effect (ATWSME). These experiments are used to determine the degradation of the material and the number of cycles to failure during thermomechanical cycling. The optimal cold worked processing is situated between e = 0.75 and 2, followed by the post-deformation annealing at 400 °C, depending on the solicitation mode, the level of stabilization and the required number of cycles to failure. In terms of the degradation of properties, the higher the preliminary cold work intensity, the higher both the recoverable strain ( ɛ r) and the recovery stress ( σ r) during the first cycle and the higher the stability of these values during the repetition of thermomechanical cycles. From the perspective of fatigue life, the number of cycles to failure increases as the cold work increases from quenched to moderate intensity ( e = 0.25), and then reaches a maximum value after high cold working ( e = 0.75 or 1 according to the solicitation mode) and finally decreases after severe cold working ( e = 1.5–2). The formation of the nanostructured material results in higher functional properties, but this important gain is achieved at the expense of the lower fatigue life of the material. Therefore, it can be stated that the optimal cold working intensity increases if high level of stabilization of the functional properties is needed and decreases if a high number of cycles prior to failure is required.

Web Surveys versus other Survey Modes: A Meta-Analysis Comparing Response Rates

One question that arises when discussing the usefulness of web-based surveys is whether they gain the same response rates compared to other modes of collecting survey data. A common perception exists that, in general, web survey response rates are considerably lower. However, such unsystematic anecdotal evidence could be misleading and does not provide any useful quantitative estimate. Metaanalytic procedures synthesising controlled experimental mode comparisons could give accurate answers but, to the best of the authors' knowledge, such research syntheses have so far not been conducted. To overcome this gap, the authors have conducted a meta-analysis of 45 published and unpublished experimental comparisons between web and other survey modes. On average, web surveys yield an 11% lower response rate compared to other modes (the 95% confidence interval is confined by 15% and 6% to the disadvantage of the web mode). This response rate difference to the disadvantage of the web mode is systematically influenced by the sample recruitment base (a smaller difference for panel members as compared to one-time respondents), the solicitation mode chosen for web surveys (a greater difference for postal mail solicitation compared to email) and the number of contacts (the more contacts, the larger the difference in response rates between modes). No significant influence on response rate differences can be revealed for the type of mode web surveys are compared to, the type of target population, the type of sponsorship, whether or not incentives were offered, and the year the studies were conducted. Practical implications are discussed.

Experimental study of torsion behaviour of NiTi alloy

The goal of this paper is to have a better understanding of the parameters which have an influence on torsional response of NiTi shape memory alloys (SMAs). The SMA investigated in this study was a titanium rich NiTi characterized by high transformation temperature (A s of ∼ 95 °C in fully annealed conditions). Resulting from post-forming annealing, two metallurgical conditions were achieved: restored conditions (470 °C-1 h) and recrystallised conditions (600 °C-1 h). The phase transformation temperatures and heat of transformation were measured for both conditions by differential scanning calorimetry. A first set of torsional tests were conducted in isothermal conditions for three different mechanical loading paths. The torque against the angular displacement was measured for each tested temperature. As a comparison, isothermal stress-strain curves obtained in tension and compression were reported which showing the influence of the solicitation mode on mechanical parameters (shear and young moduli, yield strength, critical strain and stress). The second set of tests is designed to measure the amplitude of shape memory effect and the recovery torque during heating. Thermomechanical experiments include the torsion response for thermal cycles under constant applied torque and for specimens deformed in martensitic phase and heated above A f while their displacement was kept constant. The thermo-mechanical cycles were repeated at least three times for each specimen and for one of them the cycling effect (up to 50 cycles) was investigated. We found that the highest recovery torque and the largest level of strain recovery were obtained for restored conditions.

Fatigue Life of Superelastic Springs for an Anterior Cruciate Ligament Prosthesis

The fatigue behavior of NiTi and copper based shape memory springs destined to be integrated into an anterior cruciate ligament prosthesis has been investigated and compared to the fatigue life of NiTi wires of low diameter. The degradation of the superelastic parameters has been evaluated and the number of cycles until rupture has been plotted as a function of the internal strain. The influence of the solicitation mode on the fatigue life of Shape Memory structures is pointed out.

A simple system to measure internal friction and creep

A system is described to measure internal friction and creep of thin materials. The detection is based on the variation in collector current with the capacitance of the tuned circuit of a tuned collector crystal oscillator. The mechanical systems used to realize those measurements are described. A high sensitivity is obtained for the different modes of solicitation.

State Campaign Fund Raising: Targets and Response

The extent to which campaign contributors are solicited by, and respond to, four different fund-raising techniques--direct mail, telephone, personal face-to-face, and group appeal--are reported. Data from contributors in two states indicate that there is significant variation in the use of all four modes of solicitation, and each apparently reaches and motivates somewhat different populations. The data also suggest that many contributors give without being asked while the cadre of new contributors for whom fund-raising solicitations are important is not very large. The study indicates that further research on the use of different fund-raising technologies may provide an important link in understanding the financing of political campaigns.