Fatigue Life Prediction for Carbon-SMC and Carbon-FRP by Considering Elastic Modulus Degradation

In the automotive industry, being lightweight has become an important design factor with the enhancement of environmental regulations. As a result, many studies on the application of composite materials are in progress. Among them, interest in carbon materials, such as carbon sheet molding compound (C-SMC) and carbon-fiber-reinforced plastic (CFRP), which have excellent strength and stiffness, is increasing. However, CFRP is a material that makes it difficult to secure economic feasibility due to its relatively high manufacturing costs and limited mass production, despite its excellent mechanical strength and durability. As a result, many studies have been conducted on C-SMC as an alternative carbon composite material that can be easily mass-produced. In this regard, this study intended to conduct a study on evaluating the fatigue strength of C-SMC and CFRP among mechanical properties due to the lack of clear failure criteria for fatigue design. We investigated the tensile and fatigue strengths of C-SMC and CFRP, respectively. In the case of C-SMC, the mechanical strength tests were conducted for two different width conditions to evaluate the cutting effect and the machining methods to assess the effects of the edge conditions. To evaluate the fatigue failure assessment criteria, the stiffness drop and elastic modulus degradation criteria were applied for each fatigue test result from the C-SMC and CFRP. The results confirmed that the rationality of the failure criteria in terms of the stiffness drop and the application of the fatigue life prediction of C-SMC based on elastic modulus degradation demonstrated promising results.

Fatigue behavior of unbonded prestressed reactive powder concrete beams after creep

Failure modes of two kinds of unbonded prestressed reactive power concrete (UPRPC) beams were studied experimentally under static and fatigue loads, and compared. In the tests, deflections, crack widths, rebar strains, and beam strains were measured and analyzed. The fatigue test results show that the fatigue life of non-creeped beams is more than 2 million loading cycles and the creeped beam is damaged after 1.75 million loading cycles. The compression edge strain, mid-span deflection, and rebar strain are -814 μξ, 7.6 mm, and 484 μξ, respectively, for noncreeped UPRPC beams, and -1110 μξ, 11.2 mm, and 1169 μξ , respectively, for creeped UPRPC beams (μξ represents 1 × 10-6). These values are much smaller than the static load failure values. Considering the fatigue residual strain, fatigue elastic modulus degradation, and fatigue strength degradation, a simplified analysis method for a full fatigue process is proposed, which predicts values in good agreement with the measured results.

Degradation of Dynamic Elastic Modulus of Concrete under Periodic Temperature-Humidity Action

Cracks caused by environmental temperature and humidity variation are generally considered one of the most important factors causing durability deterioration of concrete structures. The seasonal or daily variation of ambient temperature and humidity can be considered periodic. The dynamic modulus of elasticity is an important parameter used to evaluate the performance of structural concrete under periodic loads. Hence, in this paper, the dynamic elastic modulus test of concrete under simulating periodic temperature-humidity variation is carried out according to monthly meteorological data of representative areas (Nanjing, China). The dynamic elastic modulus attenuation pattern and a dynamic elastic modulus degradation model of concrete under periodic temperature-humidity are investigated. The test results show that the dynamic elastic modulus of concrete decreases and tends to be stable under the action of periodic temperature-humidity. Comparative analysis shows that the two-parameter dynamic elastic modulus degradation model is more suitable for describing the dynamic elastic modulus attenuation pattern of concrete under periodic temperature-humidity action than the single-parameter one.

Effects of Elastic Modulus Degradation on Simulation of Stretch-Bend Springback of Dual Phase Steel

The stretch-bend springback of dual phase steel DP590 was studied experimentally and numerically in this paper. The aim of this work is to investigate the effects of elastic modulus degradation on springback prediction. Two anisotropic yield function yld89 and yld2000 were utilized along with isotropic hardening law. The appropriate material parameters characterizing the elastic modulus decrease were identified by response surface modeling. The current work showed that the accuracy of springback simulation improved when considering elastic modulus decreased with plastic strain and yld2000 can predict springback more accurately considering blank orientation in stretch bending.