Capacities of Z‐pinning in improving the bending performance of composite T‐joints

This paper studies the influence of z‐pins on the impact resistance and residual tensile properties of composite large curvature components through low‐velocity impact and tension‐after‐impact tests to explore the damage mechanism. Unpinned and z‐pinned specimens with different diameters (0.3 and 0.5 mm) and spacing (3, 4, and 5 mm) were impacted at energies of 28 J and 14 J + 14 J and were stretched until failure. The theoretical models were used to predict impact dent depth and tensile strength, and the effectiveness of z‐pins and damage patterns were characterized by force‐time/displacement curves and through visual observation. The agreement between the experiments and predictions can thus validate the presented approach. Through the low‐velocity impact test, it is found that z‐pins with higher density and smaller diameter make the impact dent shallower and the surface damage less, thus showing better performance. Later, the impacted specimens mainly show delamination, explosion, breakage, and splitting after tension. During the first stage of the force‐displacement curves, since z‐pins mitigate the delamination, tensile strength shows a 29.58%–59.17% increase while in the third stage, a decrease of 3.95%–15.12% occurs due to initial damage caused by z‐pins.Highlights Different impact energies are implemented on large curved CFRP laminates of z‐pins with different diameters and spacing to explore the damage mechanism. Low‐velocity impact and tension‐after‐impact (TAI) tests are used to simulate the centrifugal force of the blade subjected to impact and rotation after impact. Z‐pinned group with a small diameter and high density causes less damage and tensile strength in the first stage increases while decreasing in the third stage compared with the unpinned group.

Section: Analysis Of Damage Pattern In the Tai Testingmentioning

confidence: 99%

Experimental investigations into damage mechanism in the low‐velocity impact and tension‐after‐impact testing of z‐pin reinforced curved CFRP composite

Liu,

Sang,

Jin

et al. 2024

“…[1] The Z-pinning technology offers an efficient method to increase the fracture toughness and damage tolerance of composite laminates. [2,3] The manufacturing process involves the insertion of fine rods made using metallic materials or fiber-reinforced resin matrix composites into the uncured prepreg and the curing of the pinned prepreg. [4,5] So far, most investigations on Z-pin reinforced composite are on the following issues: the bridging mechanisms of Z-pin, [6,7] the improvement of interlaminar fracture toughness, [8][9][10] and the deterioration of in-plane mechanical properties.…”

Section: Introductionmentioning

confidence: 99%

Investigation on insertion mechanism of ultrasound guided insertion process based on numerical simulation

Cheng

Fei

et al. 2022

The insertion of finer Z‐pins is the key factor for increasing the reinforcement effects of Z‐pinned composite laminates. This paper presents a three‐dimensional cohesive zone finite element (FE) model for revealing the insertion mechanism of the ultrasound guided insertion process of fine Z‐pins. The prepreg fracture is modeled based on the cohesive elements, where fracture toughness is obtained from the double insertion method. The contact between the needle and prepreg is simulated by LuGre dynamic friction model. According to model simulation and relevant experiments, compared with nonvibratory insertion, smaller insertion force, earlier surface fracture and slighter ply crimp can be observed in the ultrasound guided insertion process. In addition, the prepreg forms an initial crack firstly after needle insertion, followed by a final crack due to needle extraction and prepreg springback. The effects of needle diameter on the insertion force and crack length are discussed. It can be concluded that larger needle diameter can lead to greater insertion force and initial crack length, but has little effect on the final crack length.

“…[3][4][5] Z-pinning technology, which inserts solid rods with a certain volume density in the thickness direction of composite laminates, has been experimentally evidenced to be an effective method to inhibit delamination growth and increase the fracture toughness. 6,7 Z-pins are needleshaped with diameters of typically 0.1-1.0 mm and made using titanium alloy, aluminum alloy, stainless steel or fiber-reinforced resin matrix composite. 8 The manufacturing process of Z-pinned laminates requires high insertion accuracy to achieve effective throughthickness reinforcements.…”

Section: Introductionmentioning

confidence: 99%

“…Several possible solutions such as Z‐pinning, stitching, or 3D weaving have been investigated to solve the problems 3–5 . Z‐pinning technology, which inserts solid rods with a certain volume density in the thickness direction of composite laminates, has been experimentally evidenced to be an effective method to inhibit delamination growth and increase the fracture toughness 6,7 . Z‐pins are needle‐shaped with diameters of typically 0.1–1.0 mm and made using titanium alloy, aluminum alloy, stainless steel or fiber‐reinforced resin matrix composite 8 .…”

Section: Introductionmentioning

confidence: 99%

Analysis and modeling of the Z‐pin insertion in prepreg based on contact mechanism

Cheng

Fei

et al. 2021

Z-pinning is increasingly applied to improve the fracture toughness in fiberreinforced laminated composites. Force modeling during Z-pin insertion into prepreg is crucial for the manufacturing technology of Z-pinned laminates. In this paper, the effect of lay-up sequence on the Z-pin insertion force is investigated. Experimental testing reveals that the change of ply structure can result in two main force-displacement relationships in the compression phase, namely linear growth and nonlinear growth. Through analyzing the contact mechanism, the force-displacement relationship depends highly on the contact area between Z-pin and prepreg, which is validated by insertion experiments with different conical tipped Z-pins. Two models based on different contact modes of Z-pin insertion are proposed: the analytical model for the unidirectional prepreg and the finite element model for the cross-ply prepreg. The advantage of this approach is its ability to capture the contact behavior during the insertion process, thus predicting the insertion force more accurately. The analysis results are in good agreement with experiments.