YIELD POINT AND STRESS RELAXATION BEHAVIOR OF PLY-PLY INTERACTION OF THERMOSET PREPREGS

The forming of continuous-fiber composites is an automated manufacturing process capable of high production rates. Its greatest weakness lies in the tendency to develop wrinkle defects. The formation of wrinkle defects is the effect of a combination of multiple material deformation mechanisms. This paper investigates possible improvements for current manufacturing techniques by studying the interply properties of continuous-fiber thermoset prepreg. In this research, the inter-ply slip deformation behavior is tested via double lap shear tests. The results show that pressure, deformation rate, and moisture have a strong effect on the ply-ply interaction response. The multi-stage nature of the loaddisplacement response suggests the complex nature of the deformation. To better understand each stage of deformation, the total amount of slip deformation of the double lap shear test is measured. The total slip versus displacement profile indicates the presence of a yield point in the ply-ply interface. The yield point indicates both the softening of the ply-ply interface and the initiation of plastic deformation. The plastic deformation past the yield point can be further increased if the preform is held in a deformed state for some time before removing the external load. A new manufacturing process is proposed based on these results. One can take advantage of the yield point of the ply-ply interface and conform a preform onto an intermediate tool before conforming it onto the final tool. As deformation can be preserved once the material deforms past the yield point, this sequential forming approach can reduce the risk of wrinkling by reducing the slip required to complete the forming operation.

Performance assessment of gaussian process regression to predict the bond strength of FRP sheets to concrete

A Gaussian process regression (GPR) model for predicting the bond strength of FRP-to-concrete is proposed in this study. Published single-lap shear test specimens are used to predict the bond strength of externally bonded FRP systems adhered to concrete prisms. A database of 150 experimental results collected from published works is used for the training and testing phases of the proposed GPR model, containing 6 input parameters (width of concrete prism, concrete compressive strength, FRP thickness, FRP width, FRP length, and FRP modulus of elasticity). The output parameter of the prediction problem is bond strength. Three statistical indicators, namely the coefficient of determination, root mean square error (RMSE), and mean absolute error (MAE) are used to evaluate the performance of the proposed GPR model over 500 simulations. The results of this study indicate that the GPR provides an efficient alternative method for predicting the bond strength of FRP-to-concrete when compared to experimental results.

In Situ Computed Tomography—Analysis of a Single-Lap Shear Test with Clinch Points

As lightweight design gains more and more attention, time and cost-efficient joining methods such as clinching are becoming more popular. A clinch point’s quality is usually determined by ex situ destructive analyses such as microsectioning. However, these methods do not yield the detection of phenomena occurring during loading such as elastic deformations and cracks that close after unloading. Alternatively, in situ computed tomography (in situ CT) can be used to investigate the loading process of clinch points. In this paper, a method for in situ CT analysis of a single-lap shear test with clinched metal sheets is presented at the example of a clinched joint with two 2 mm thick aluminum sheets. Furthermore, the potential of this method to validate numerical simulations is shown. Since the sheets’ surfaces are locally in contact with each other, the interface between both aluminum sheets and therefore the exact contour of the joining partners is difficult to identify in CT analyses. To compensate for this, the application of copper varnish between the sheets is investigated. The best in situ CT results are achieved with both sheets treated. It showed that with this treatment, in situ CT is suitable to properly observe the three-dimensional deformation behavior and to identify the failure modes.

The adhesion of clots in wounds contributes to hemostasis and can be enhanced by coagulation factor XIII

The adhesion of blood clots to wounds is necessary to seal injured vasculature and achieve hemostasis. However, it has not been specifically tested if adhesive failure of clots is a major contributor to rebleeding and what mechanisms prevent clot delamination. Here, we quantified the contribution of adhesive and cohesive failure to rebleeding in a rat model of femoral artery injury, and identified mechanisms that contribute to the adhesive strength of bulk clots in a lap-shear test in vitro. In the rat bleeding model, the frequency of clot failures correlated positively with blood loss (R = 0.81, p = 0.014) and negatively with survival time (R = − 0.89, p = 0.0030), with adhesive failures accounting for 51 ± 14% of rebleeds. In vitro, adhesion depended on fibrinogen and coagulation factor XIII (FXIII), and supraphysiological FXIII improved adhesive strength. Furthermore, when exogenous FXIII was topically applied into the wound pocket of rats, eleven adhesive failures occurred between eight rats, compared to seventeen adhesive failures between eight untreated rats, whereas the number of cohesive failures remained the same at sixteen in both groups. In conclusion, rebleeding from both adhesive and cohesive failure of clots decreases survival from hemorrhage in vivo. Both endogenous and exogenous FXIII improves the adhesive strength of clots.