Experimental study on mechanical property and stone-chip resistance of automotive coatings

The damage of automotive coatings caused by stone impact is a problem that has attracted great attention from automotive companies and users. In this work, experiments were conducted to investigate the dynamic tensile properties and stone-chip resistance of automotive coatings. Four kinds of paint films and three typical coatings (single-layer electrocoat coating, single-layer primer coating, and multilayered coating) were used. Under dynamic tensile load using split Hopkinson tension bar (SHTB), the engineering stress-strain curves of the paint films at medium and high strain rates (from 50 to 600 s ^−1 ) were obtained. Results indicated that the mechanical properties of the paint films exhibited strong nonlinearity and strain-rate correlation. A modified anti-impact tester was used to complete repeatable single impact tests. The effects of some key parameters, i.e., impact velocity, impact angle, and paint film thickness, on the stone-chip resistance of coatings were systematically investigated. The influence of contact type under high-speed impact conditions was investigated as well. The surface morphologies of the coatings after impact were examined by scanning electron microscopy (SEM), and the failure mechanism of the coatings under normal/oblique impact was discussed. In all experiments, the paint films showed brittle fracture behavior

Single-Impact Failure of Multi-Layered Automotive Coatings: A Finite Element-Based Study

Automotive coatings are a multi-layered polymer composite structure whose impact resistance is closely related to the appearance and safety of a vehicle. Since experimental methods are of high cost and poor repeatability, in our work, a finite element model is developed for the single-impact failure of automotive coatings. In this model, a multi-mechanism damage model and a large deformation cohesive zone model are employed to account for the polymer-ply and interlaminar failures of the coating, and some rate-dependent material models are adopted to capture the effect of impact velocity. The simulated results indicate that the proposed model can reproduce the failure patterns of automotive coatings well. In addition, the impact failure mechanisms of the coating are revealed. Numerical findings show that both brittle and ductile failures are found in the coating and there are three stages for the propagation of the delamination crack. Finally, we numerically investigate the effects of primer mechanical properties, i.e., Young’s modulus, yield strength, and re-hardening modulus, on the impact resistance of automotive coatings. Our work is helpful to the design of coating, which can improve the impact resistance of automotive coatings

Effects of Interlaminar Failure on the Scratch Damage of Automotive Coatings: Cohesive Zone Modeling

Interlaminar failure caused by scratches is a common damage mode in automotive coatings and is considered the potential trigger for irreversible destruction, i.e., plowing. This work strives to numerically investigate the mechanisms responsible for the complex scratch behavior of an automotive coating system, considering the interfacial failure. A finite element model is developed by incorporating a large deformation cohesive zone model for scratch-induced debonding simulation, where the mass scaling technique is utilized to minimize computational burden while ensuring accuracy. The delamination phenomenon of the automotive coating is reproduced, and its effects on scratch damage behavior are analyzed. Accordingly, it is revealed that the interlaminar delamination would produce significant stress redistribution, which leads to brittle and ductile damage of the coating and consequently affects the formation of plowing. Eventually, parametric studies on the effects of interfacial properties are performed. They demonstrate that the shear strength and shear fracture energy dominate scratch-induced delamination

Adverse effects of low serum lipoprotein cholesterol on the immune microenvironment in gastric cancer: a case‒control study

Abstract Background Cholesterol is crucial for tumor immune microenvironment (TIME) remodeling. Serum lipoprotein cholesterol is closely associated with gastric cancer (GC) progression, but whether it affects TIME remodeling is unknown. Methods GC patients with differential serum high-density lipoprotein (HDL) or low-density lipoprotein (LDL) cholesterol levels were collected. After balancing the baseline, immunohistochemical staining was performed on serial whole-tissue sections to detect B-cell and T-cell subsets, macrophages, and PD-L1. Features of tertiary lymphoid structures (TLSs) and the extra-TLS zone, including TLS distribution and maturation, immune cell density, and PD-L1 expression, were measured by annotating TLSs or regions of interest (ROIs) in the extra-TLS zone. Results A total of 9,192 TLSs and over 300 ROIs from 61 patients were measured. Compared to HDL-normal patients, HDL-low patients had a decreased secondary-TLS fraction or density but an elevated NK-cell density in the extra-TLS zone. Compared to LDL-normal patients, LDL-low patients had a higher ratio of PD-1 + T follicular helper cells to CD20 + B cells in TLSs, a higher ratio of PD-1 + T cells to CD8 + T cells and increased PD-1 + T-cell density in the extra-TLS zone. Different correlations were found in groups with differential HDL or LDL levels. Cell dynamics in the immune response were weaker in patients with low lipoprotein cholesterol. TLS parameters reached their peak earlier than those of the extra-TLS zone along with tumor progression. Conclusion Low serum lipoprotein cholesterol caused adverse effects on antitumor immunity in GC. Lipid management or immunometabolic drugs deserve more attention