Prediction Of Long-term Strength Research Articles

Flaw characteristics of architectural glass and long-term strength prediction model

Flaw characteristics of architectural glass and long-term strength prediction model

Experimental study of macroscopic and microscopic properties of long-age hydraulic concrete based on high-temperature accelerated curing

Determining the long-term mechanical properties of hydraulic concrete currently requires time-consuming and expensive tests, which has hampered investigations into the mechanical properties of long-age hydraulic concrete. In this study, the indoor macroscopic mechanical property tests of long-age hydraulic concrete with different curing ages (90, 180 days and 1, 2, 3 years) and different fly ash contents (0%, 15%, 35%) were designed and carried out on hydraulic concrete with 0.5 water-to-binder ratio by using a high-temperature accelerated-curing method based on equivalent age theory. Further tests were carried out using SEM, XRD, and MIP tests on long-age hydraulic concrete specimens with different fly ash contents to determine and analyze the long-term evolution of the macroscopic and microscopic properties of hydraulic concrete. The results showed that the fly ash content significantly affects the activation energy Ea of hydraulic concrete and that the curing time required to reach the designed hydration degree increases with increasing fly ash content. The long-age compressive strength and splitting tensile strength of hydraulic concrete with different fly ash contents increased logarithmically with curing age. After hydration for the curing age of 3 years, the overall microscopic structure of the mortar region of the long-age hydraulic concrete becomes dense, and the main XRD peak is due to quartz. The porosity decreases with increasing curing age, and the main pore types transition from multi-harmful pores (>200 nm) to harmless pores (<20 nm) and less harmful pores (20–50 nm). The multiple correlation coefficient of the long-term strength prediction model established by using the combined exponential prediction model ranges from 0.9152 to 0.9765, which indicates that the combined exponential prediction model based on the strength at the curing age of 28 days better replicates the long-term performance of hydraulic concrete.

Study of the Applicability of the Vyalov Long-Term Strength Prediction Equation under Freezing and Thawing Conditions

In order to determine the appropriate utilization conditions of the Vyalov long-term strength prediction equation, this study selected three soil samples from the loess region. These samples were subjected to varying numbers of freeze–thaw cycles, namely 0, 4, 6, 8, 10, 50, and 100 cycles. Subsequently, post-test soil samples underwent spherical template indenter press-in tests and grain size determinations. The experimental outcomes demonstrated that the Vyalov long-term strength prediction equation accurately reflected the long-term strength variations of frozen loess after 10 freeze–thaw cycles. A further analysis revealed that the stability of the soil samples’ grain composition played a vital role in ensuring the accuracy of the prediction equation. Notably, a highly significant positive correlation was observed between the silt content of the soil samples and the prediction equation parameter β. Moreover, employing the Vyalov long-term strength prediction equation after 10 freeze–thaw cycles yielded prediction results consistent with the freeze–thaw cycles–time analogy method for durations of 10, 20, and 30 years. This study is beneficial for the construction and operation of projects in loess areas.

Statistics and Analysis of the Relationship between Strength and Age of Coral Concrete

In this study, based on the experimental results of this study and from the previous research, it is concluded that the compressive strength of coral concrete at 3, 7, 14, 21, 60, and 90 days reaches about 71%, 84%, 92%, 96%, 104%, and 110% of that at 28 days, respectively, indicating that the early strength development of coral concrete is significantly faster than that of ordinary concrete but slower in the later stage. A new model to characterize the strength‐age relationship of coral concrete is proposed in this study, which is in good agreement with the experimental result, but for the long‐term strength prediction of coral concrete in actual engineering, it is recommended to adjust the prediction results according to the environment and working conditions of coral concrete, and the adjustment coefficient could be approximately taken as 0.88. In addition, the effects of water‐binder ratio (w/b), total dosage of cementitious materials (b), supplementary cementitious material (SCM) content, and aggregate properties, on the age strength development of coral concrete are studied.

Determination of Activation Energy and Prediction of Long-Term Strength of Creep Rupture for Alloy Inconel 740/740H: A Method Based on a New Tensile Creep Rupture Model

Determination of Activation Energy and Prediction of Long-Term Strength of Creep Rupture for Alloy Inconel 740/740H: A Method Based on a New Tensile Creep Rupture Model

Long-Term Strength Prediction of Wood Based Composites Using the Kinetic Equations

The existing behaviour models of the structures under constant load (creep) have a fairly wide forecast horizon and low accuracy. As a rule, they consider the transition from an undestroyed state of an element to a destroyed one, in one stage. The purpose of this study is to substantiate and develop a new approach to predicting long-term strength based on kinetic equations, which, in turn, should consider the multistage nature of the process of gradual destruction of structure elements. To achieve this purpose, the study solves the tasks of creating a multistage kinetic transition of individual structure elements from an initially elastic state to a viscoelastic state, and then to a fractured state. When describing this process, the authors employed the methods of formal kinetics and the theory of continuum damage mechanics, including the method of basic diagrams. Wood-based composites were used as the materials under study. Based on the results of the conducted full-scale and computational experiments, the study discovers that a mathematical model based on kinetic equations adequately describes the behaviour of the materials under study for long-term strength; the proposed two-stage model determines the forecast horizon much more accurately than the available one-stage models. The kinetic parameters that determine the rate of transition of a structural element from an elastic state to a viscoelastic state, and then to a destroyed state, were determined based on experimental base chart. The time to fracture was determined at three-point bending at a load equal to 70% of the flexural strength at temperatures of 20°C and 60°C, constant humidity RH 65% and moisture content MC 8%. When building control charts, the load increased by another 15%. The method allows narrowing the forecast horizon and determining the moment of transition of a structure from a stationary state to a blow-up regime with a higher accuracy

Evaluation of controlled low strength materials containing red brick construction waste based on mechanical experiments and BP neural network

In this study, two kinds of controlled low-strength materials (common and rapid-hardening) were designed and prepared by using red brick construction waste fines. Fourteen mixture specimens were prepared with the control parameters of binder to construction waste fine aggregate ratio (α), accelerator to binder ratio (β), and water to solid ratio (γ). The flowability of fresh mixtures, compressive strength of hardened materials were studied. Test results show that it is applicable to use the red brick construction waste fine aggregate to prepare controlled low-strength materials. Increasing α and γ can increase the flowability, however with different the influence mechanisms, where γ has a more significant effect. The 2 hour-strength of rapid-hardening CLSM (controlled low strength material) based on sprayed concrete accelerator can be up to 0.41∼0.79MPa, which meet the needs of emergency backfill engineering. Using on the BP neural network, the long-term strength prediction model of CLSM is established, which can help the civil engineers in the material mix-design.

Prediction of long-term strength of shaped parts of hydro-gas systems by acoustic emission parameters

Prediction of long-term strength of shaped parts of hydro-gas systems by acoustic emission parameters

Correlation between the Compressive, Tensile Strength of Old Concrete under Marine Environment and Prediction of Long-Term Strength

Compressive strength and tensile strength are important mechanical properties of concrete. The long-term strength of concrete under real service environment is an important parameter when evaluating existing buildings, which should also be properly considered in structural design. In this study, the relationship between compressive and splitting tensile strength of old concrete existing for long period under marine environment was investigated. At a deserted harbour, concrete cores samples were drilled by pairs in site. For each pair of samples, the two cores were drilled from the adjacent location and conducted to compressive, splitting tensile test, respectively. 48 compressive and splitting tensile strengths were finally obtained. From the test results, tensile strength presents general uptrend with compressive strength, and the two parameters are well positively correlated. Exponential model generally recommended by building codes or literatures is still capable of describing the relationship between compressive and tensile strength of old deteriorated concrete, when function parameters are properly determined. Based on statistical theory and the experimental result of this study, a method for predicting long-term tensile strength of concrete is developed and an example is given, which may provide a potential way to estimate long-term concrete strength under real marine environment.

ガラス繊維強化PBTの力学特性に及ぼす繊維含有率の影響

Evaluating long-term strength and mechanical properties of composite materials is important in order to use them as construction materials. When the matrix is polymer materials, the composite materials exhibit viscoelasticity. Therefore long-term strength prediction should be based on viscoelasticity. In this study, constant strain rate tests of PBT and short fiber reinforced PBT are performed. As a result, it is confirmed that time-temperature superposition principle can be applied the strength and elastic modulus of each material. And those shift factors coincide regardless of the fiber volume fraction. It is shown that the prediction of time dependence of the elastic modulus by shear lag model cannot be evaluated long-term elastic modulus correctly.

Prediction of Long-Term Compression Strength for Quasi-Isotropic CFRP Laminates

Long-term strength prediction method is developed based on three theories: accelerated testing methodology (ATM), strain invariant failure theory (SIFT) and progressive damage analysis (PDA). It can predict the strength and damage at a given failure time. Net resin 5228A was experimented by dynamic mechanical analysis and static tensile loading under various temperatures to determine the time-temperature shift factors and master curve of Young’s modulus. Unidirectional laminates of CCF300/5228A were tested under different temperatures to calculate the SIFT/ATM critical parameters. Long-term strength of quasi-isotropic composite laminates (QIL) was predicted. Good agreement between numerical results and experiments is observed, which demonstrates the applicability of this method.

Short-Term High-Temperature Tensile Tests and Prediction of Long-Term Strength of Welded Joints of Dissimilar Steels T92/HR3C

The microstructures, surfaces and types of fracture of welded joints of dissimilar steels T92/HR3C are studied after short-term tests at 500 – 650°C. A pioneer equation is obtained for describing the long-term strength of welded joints with the help of data of short-term tensile tests. The values of the long-term strength computed by the equation agree well with experimental data.

Prediction of Long-Term Strength of Concrete Based on Artificial Neural Network

Recently, the safety of existing civil engineering structures attracts more and more attention. The long-term strength of concrete plays a key role during the assessment of safety and durability for civil engineering structures. The strength of concrete will gradually decrease during the service of civil engineering structures. It is significant to accurately predict the strength deterioration of concrete for correctly evaluating the safety of structures. The factors affecting the long-term strength of concrete include environment type, age, climate, water cement ratio, amount of cementing material and so on. In this paper, artificial neural network with powerful mapping ability has been selected to predict the long-term strength of concrete. First, there-layer BP neural network with age, water cement ratio, amount of cementing material as input and long-term strength as output was built. Then, the neural network was trained by the samples measured in real structures and the well-trained neural network was test. From the test results, the trained neural network can accurately predict the long-term strength of concrete with the error less then 9%.

Prediction of long-term strength for frozen soils of the Bolshezemelnaya Tundra

Proposals for selection of equations and assignment of their parameters for prediction of the long-term strength of soils occurring in the area of the route traversed by the Yu. Khyl’chuyu-Varandei 220-volt overhead transmission line are made on the basis of analysis of results of investigations of the strength of frozen soils, which were determined by uniaxial compression and impression of a spherical plate.

Prediction of long term strength of adhesively bonded steel/epoxy joints in sea water

This study is concerned with the development of a tool to predict the long term behaviour of adhesively bonded steel joints aged in sea water. First, diffusion kinetics and the mechanisms governing the degradation of mechanical properties of an epoxy adhesive are described. These two sets of data were used in a coupled finite element (FE) analysis to determine the stress state in double lap shear (DLS) specimens before and after aging. However, subsequent tests on DLS specimens indicated an adhesive and not cohesive failure mode, so this approach could not be used to predict failure in the present case without introducing an interfacial damage parameter. A second approach was therefore employed, in which modified Arcan samples were designed in order to identify directly how the failure envelope changed with aging. Tests were performed on these modified Arcan specimens under shear, tensile/shear and tensile loads before and after aging. The results from these tests have enabled a tension–shear failure envelope to be constructed, which may be used to predict failure in joints with more complex stress states. The application of a coupled diffusion–mechanical property approach is illustrated for the Arcan specimen loaded in tension, and its application to the prediction of failure behaviour after aging is discussed.

Long-term Open-hole Compression Strength of CFRP Laminates based on Strain Invariant Failure Theory

This paper deals with the prediction of long-term strength of CFRP structure components based on the combined method of the strain invariant failure theory (SIFT) developed by Gosse and Christensen and the accelerated testing methodology (ATM) developed by Miyano and Nakada. The time—temperaturedependent master curves of SIFT critical parameters are constructed by tension and compression tests for the longitudinal and transverse directions of unidirectional CFRP under various temperatures based on the time-temperature superposition principle which holds for the viscoelastic modulus of matrix resin. These master curves can be used for predicting the long-term strength of composite structures with multi-directional laminations at any time, temperature. The long-term open-hole compression strength of the quasi-isotropic CFRP laminates is predicted using the master curves of SIFT critical parameters based on SIFT/ATM combined method and structural stress and strain analysis by finite element method. The applicability of SIFT/ATM combined method to predict the long-term strength of CFRP structures is experimentally confirmed.

Accelerated testing for long-term strength of innovative CFRP laminates for marine use

We have proposed the accelerated testing methodology for the long-term durability of polymer composites based on the time–temperature superposition principle (TTSP) to be held for the viscoelasticity of polymer matrix. In this paper, the prediction of long-term strength of CFRP laminates for innovative marine use under water absorption conditions were performed by our developed accelerated testing methodology. Three kinds of CFRP laminates employed were conventional plain fabric T300 carbon fibers/vinylester, flat yarn plain fabric T700 carbon fibers/vinylester and multi-axial knitted T700 carbon fibers/vinylester for innovative marine use as a lightweight CFRP ship structures. These CFRP laminates were prepared under three water absorption conditions of Dry, Wet and Wet + Dry after molding. The three-point bending constant strain rate (CSR) tests for three kinds of CFRP laminates at three conditions of water absorption were carried out at various temperatures and strain rates. As the results, the master curves of CSR strength for these CFRP laminates at three water absorption conditions are constructed by using the test data based on TTSP. Furthermore, the time–temperature–water absorption superposition principle (TTWSP) hold for the flexural CSR strengths for these CFRP laminates. Therefore, it is possible to predict the long-term strength for these CFRP laminates under an arbitrary temperature and water absorption conditions using the master curves. It is cleared from the master curves that the degradation rate of CSR strength of these CFRP laminates is determined only by increasing of time, temperature and water absorption and is independent upon the type and weave of carbon fibers.

Lifetime predictions of polymer matrix composites under constant or monotonic load

A revision of long-term lifetime prediction of composite materials under constant and monotonic load is presented. The main failure criteria revised are energy-based criteria and fracture mechanics. It is shown that they all predict a similar relation between constant stress and constant stress rate failure strength. It is also demonstrated that the methodology proposed by Miyano et al., based on linear damage accumulation law (LCD), produces similar results. Experimental cases published in literature are used to illustrate the theoretical approaches. Finally it is suggested that Monkman–Grant classical equation can be used as a failure criterion for constant strain (or stress) rates. The extrapolation for lower strain rates would permit the long-term strength prediction, based on viscoelastic constitutive law. At last creep strength could be obtained from strength curves by using Miyano et al. methodology.

Long-term strength prediction of concrete with curing temperature

This paper describes a new strength time temperature prediction equation, which utilizes curing temperatures to improve the accuracy of estimates of long-term strength. To develop the model equation, existing data reported in the literature were collected and used. The data were converted into a relative strength ratio based on the strength at 28 days for 8 average curing temperatures in a range of − 0.6∼59.7 °C. The effect of the diffusion shell, which happens during cement hydration, on the long-term strength as a function of the curing temperature was considered using the rate constant model. Temperature influence factors such as rate constant, limiting strength, and reaction coefficient, which are functions of curing temperature, were incorporated in the new equation. Verification of the proposed model was performed by regression analysis. The results of regression analyses showed that the proposed model has higher reliability than existing model equations. The proposed model has higher accuracy at long-term ages the difference with existing models at an early age is not significant.

Application of the Method of Base Diagrams for the Prediction of Long-Term Strength in Notched Specimen Tests

The influence of stress concentrators on long-term strength relationships for heat-resistant steels and alloys is investigated in view of known data on strengthening and weakening effects of these concentrators. The method of base diagrams is substantiated to be appropriate for use to significantly refine their effects. The results of experimental data processing are cited, according to these results, with longer times of loading of notched specimens, hardening mainly gives way to softening.