Experimental and Numerical Simulation Studies of RC Beams under the Actions of Equal Energy Impact Loads

In this study, two groups of RC beams were subjected to low-speed drop weight impact test by using the domestic advanced ultrahigh heavy-duty drop weight impact testing machine system. The main aspects studied are the influence of the combination of different impact velocity and mass on the dynamic response and local and global damage change of RC beam under the same impact energy. Next, the numerical model considering material strain rate is established using ABAQUS finite element software to verify and expand the experimental results. The results show the following: (1) under the condition of equal energy, the peak value of impact force measured in this experiment increases with the increase of impact velocity, yet the mid span displacement and rebar strain first increase and then decrease. In addition, when the impact velocity is 2.25 m/s and the impact mass is 400 kg, the beam has the most serious damage; (2) compared with the mass, the impact velocity has more obvious effects on the peak value of cumulative impact force, mid span displacement, and rebar strain; (3) with the decrease of the impact velocity (the increase of the mass), the local damage of the beam is gradually weakened and the overall damage is gradually exacerbated. The failure mode of the beam is transformed from local punching shear failure to overall static failure type

TREM2 deficiency impairs the energy metabolism of Schwann cells and exacerbates peripheral neurological deficits

Abstract Triggering receptor expressed on myeloid cells-2 (TREM2) has been implicated in susceptibility to neurodegenerative disease. Schwann cells (SCs), the predominant glial cell type in the peripheral nervous system (PNS), play a crucial role in myelination, providing trophic support for neurons and nerve regeneration. However, the function of TREM2 in SCs has not been fully elucidated. Here, we found that TREM2 is expressed in SCs but not in neurons in the PNS. TREM2 deficiency leads to disruption of glycolytic flux and oxidative metabolism in SCs, impairing cell proliferation. The energy crisis caused by TREM2 deficiency triggers mitochondrial damage and autophagy by activating AMPK and impairing PI3K-AKT-mTOR signaling. Combined metabolomic analysis demonstrated that energic substrates and energy metabolic pathways were significantly impaired in TREM2-deficient SCs. Moreover, TREM2 deficiency impairs energy metabolism and axonal growth in sciatic nerve, accompanied by exacerbation of neurological deficits and suppression of nerve regeneration in a mouse model of acute motor axonal neuropathy. These results indicate that TREM2 is a critical regulator of energy metabolism in SCs and exerts neuroprotective effects on peripheral neuropathy. TREM2 deficiency impairs glycolysis and oxidative metabolism in Schwann cells, resulting in compromised cell proliferation. The energy crisis caused by TREM2 deficiency induces mitochondrial damage and autophagy by activating AMPK and impairing PI3K-AKT-mTOR signaling. Moreover, TREM2 deficiency disrupts the energy metabolism of the sciatic nerve and impairs support for axonal regeneration, accompanied by exacerbation of neurological deficits and suppression of nerve regeneration in a mouse model of acute motor axonal neuropathy (by FigDraw)

An Experimental Study of the Feasibility of Identifying the Impact Damages of Reinforced Concrete Piers Using a Modal Frequency Method

In this research study, horizontal impact tests were carried out on five reduced scale pier models using China’s most advanced multifunctional ultrahigh heavy drop hammer impact test system and DHDAS dynamic signal acquisition and analysis system. Due to the fact that the traditional measurement method can only be used for local measurement damage, and the volatility is high, this paper proposes a test method for the modal frequency identification of the overall damage of reinforced concrete pier and applies the ultrasonic damage measurement method to verify the results. The tests analyzed the modal frequencies and ultrasonic velocity identifications for the purpose of evaluating the impact damages of bridge piers, as well as the relationship between them. The results showed that the modal frequencies were consistent with the ultrasonic waves in identifying and evaluating the damages to the piers. Also, the modal frequency damage factors were determined to be functions of the ultrasonic wave velocity damage factors. Therefore, the results of this study confirmed that it was feasible to characterize the impact damages of piers using a modal frequency method

Influence of enhanced Li content on the as-cast eutectic phase features and the evolution during homogenization of Al-Cu-Li alloys

The microstructure of Al-Cu-Li alloys is influenced by the alloying contents, which in turn affect the ultimate performance. This study examined the microstructure characteristics of Al-Cu-Li alloys with varying Li contents (1.05, 1.30, and 1.66 wt%) in as-cast state, as well as microstructure evolution during homogenization treatments. The investigation employed a range of analytical techniques, including optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), differential scanning calorimeter (DSC), focused ion beam (FIB), transmission electron microscopy (TEM), and thermodynamic calculation software. The findings indicate that the eutectic phase exhibited significant variations with the Li content changing. Three distinct low-melting phases were identified in 1.05Li alloy, including Ag-containing Al2CuMg, Al7Cu4Li, and Al2Cu. As Li content was elevated to 1.30 wt%, there was a noticeable drop in the quantities of Ag-containing Al2CuMg and Al7Cu4Li phases. Conversely, the Al2Cu phase increased, and a few Al2CuLi phases emerged. When the Li raised to 1.66 wt%, an increased Al2CuLi phase was discovered, which existed along the dendritic edges. However, there were only little Ag-containing Al2CuMg phase, and no Al7Cu4Li phase detected. The initial melting temperatures for the four soluble eutectic phases were systematically arranged in the following order: Ag-containing Al2CuMg < Al7Cu4Li < Al2Cu < Al2CuLi. The elevated Li content resulted in a challenge of dissolution of the eutectic phases. Following 500 °C/12h homogenization process, the containing-Ag Al2CuMg phase dissolved. Additionally, the Al7Cu4Li and Al2Cu phases were eliminated through subsequent 515 °C/12h homogenization. In addition, the Al2CuLi phase was still existing

Machine learning assisted design of aluminum-lithium alloy with high specific modulus and specific strength

Advanced aluminum-lithium alloys are the key structural materials urgently needed for the development of light-weighted aircraft in the aerospace field. In this study, we employ a machine learning approach accompanied by domain knowledge to realize the accelerated design of aluminum-lithium alloy with high specific modulus and specific strength by identifying an optimal combination of key features through a three-step feature filtering of datasets containing 145 alloys. The maximum specific modulus in the experimental alloys that screened from the predicted results increases by 4 % compared with the maximum specific modulus in the comparative dataset. The specific modulus of the designed alloy with the best comprehensive performance increased by 12.6 % compared with the widely used 2195-T8 alloy while maintaining a similar specific strength. Machine learning shows appealing feasibility and reliability in the field of materials design

Near-microscopic grain boundary facilitates fatigue crack propagation in a polycrystalline Al–Zn–Mg–Cu alloy

In present study, grain characteristics with sizes within 10–30 ​μm were fabricated from a same Al–Zn–Mg–Cu alloy, FCP behaviors of the alloys with small grain (SG alloy), medium grain (MG alloy) and large grain (LG alloy) were investigated and related fatigue fracture morphology was analyzed. With the enhancement of stress intensity factor range (ΔK), the alloy with larger grains possessed faster FCP rate, which were successively arranged as SG alloy ​> ​MG alloy ​> ​LG alloy at initial stage while turned to LG alloy ​> ​MG alloy ​> ​SG alloy at final stage for the stable expanding region. Except for conventional characteristics of striations, tearing ridges, secondary cracks, second phases, voids and dimples, more prominent grain boundary features appeared on fracture surface, especially for MG and LG alloy. The calculation of cyclic plastic zone (CPZ) sizes proved that grain boundary participated and promoted FCP behavior when CPZ covered grain and grain boundary together