Issue 78

V. Pisarev et alii, Fracture and Structural Integrity, 78 (2026) 96-117; DOI: 10.3221/IGF-ESIS.78.06

  9 0/90 S . Milling technological process is used for this purpose. Generalized mechanical properties of orthotropic composite material are the following: Longitudinal modulus 1 E = 73100 MPa; Transverse modulus. 2 E = 73100 MPa; Shear modulus 12 G = 5300 MPa; Poisson’s ratio 12 21     0.25 [1, 2]. Each coupon contains two contact dimples caused by low-velocity impact with different energy as it is shown in Fig. 1 and Tab.1. Details of experimental methodology and characteristics of testing machine used for low-velocity impact are presented in Ref. [1, 2]. Nomenclature of coupons, impact energy and diameter of contact dimple are listed in Tab. 1. The CFRP laminate used has a designation ACM1412C200UD. This material is characterized by the following properties. Fiber type is UMT400-12K-EP/VE {unidirectional carbon fiber: tensile strength 4.9 GPa; elasticity modulus 400 GPa). Surface density equals to 200 g/m 2 . Producer is: rosatom-composites.ru/company/alabugavolokno/. Matrix system consists of ASM1412 structural epoxy binder developed for parts operating under high loads. Fiber volume fraction equals to 67%. UMATEX prepreg technology is used during manufacturing process. The fiber is impregnated with an uncured epoxy binder (ACM1412), then dried and cut into sheets (tapes). Next, a package of the required thickness is assembled and molded. Vacuum influence and pressing in an autoclave, while the polymerization process takes place at temperatures up to 180 ° C, is applied to harden the matrix and form the part. Laminate quality is high enough to be used in aerospace structures. UMATEX prepregs are produced by impregnating a reinforcing fiber base with evenly distributed polymer resin systems. The melt method used ensures the achievement of maximum mechanical properties of the reinforced material. Fiber impregnation improves the quality of the material by 30%. Void content is less than 2.5% with a warranty.

Figure 1: Two contact dimple positions on impact side and two contours referred to dimple edges on back side.

Nomenclature Impact energy, J Dimple diameter 2 0 R , mm

Sp_55

Sp_65

Sp_75

Sp_75-Back

55

65

75

75

8.2

9.0

9.6

9.6

Drill entrance surface Back side Table 1: Nomenclature of coupons, dimple diameter values for different impact energy and drill entrance surface. Impact side Impact side Impact side

98