PSI - Issue 50

V.G. Degtiar et al. / Procedia Structural Integrity 50 (2023) 40–49 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

46

7

k

k

0,0146

at   3,78

4,93;

at     130 1,49

4,93;



s

s

k

k

(7)

3 4



 

  

S

1

k D

;

,

D





a



S

n

l

where s k k , – heights of physical and equivalent roughness elements; n – number of elements of physical roughness (protruding or going inward exposures of reinforcing elements) per unit area in the vicinity to a reference point on the ablated surface;  – correlation argument. In particular, the geometry of the MKU-4M-7 composite frame is similar to the geometry of frames of 4KMS-L, 4KMS-LU composites, except that the diameter of rods is d = 0.7 mm as against d = 1.17 mm. This decreases the height of physical roughness formed as a result of the difference in burning-out of reinforcing elements and the matrix. It also lowers the height of equivalent roughness according to Dirling correlation s k . It follows from (7) that with the similar geometry of frames of 2 composites, if the relation of heights of physical roughness is 1 2 1 2 k k d d  , then 1 2 2 1 k k d d s s  . This decrease is not in direct proportion, rather complies with caused additive terms of roughness that are formed due to the appearance of pores, shells, and other defects. To estimate the real height of physical roughness, comparative fire tests are needed as well as measurements with profilometers-profilographs or methods analog to the presented by Zolotaryov and Plevako (2004). The summary roughness is taken to be equal to a sum of roughness formed by reinforcing elements and defects (pores), meanwhile equivalent roughness for pores of each size is assessed separately and algebraically summed up with others. The perturbation in flow caused by a defect (a pore or a shell) is comparable with the perturbation caused by a protruding element of roughness with the same typical lateral dimension. Consequently, the diameter of an element is calculated using the area of a defect d S by formula  d d S 2  , while the number of elements per unit area d n – using the number of defects of the considered size divided by the area of a zone allocated on the sample surface for study об S =13.0 × 4.0 mm 2 . In particular, the number of defects with area up to 0.001 mm 2 in Fig. 4 is equal to 310. The typical diameter and the number of defects per unit area are equal to 2 2 0,001 3,1415 0,0357 10 m 3 0,001       d S d , 2 6 (310 52) 10 5961539 1 m    d n , correspondingly. Average porosities and their scatter are defined with the use of the results of processing of all micro shots analog to shown in Fig. 5. Corresponding distributions  and scatters of density  are recalculated relative to nominal density with the use of formulas (5), (6) and data of tomographic measurements. The roughness parameters used for the computation of criteria of laminar/turbulent transition in the boundary layer ( ) Ps k and a gain of heat exchange for laminar flow mode in the boundary layer ( ) Ls k , taking into account the influence of the composite frame structure, are calculated by formulas: l a S S , – midsection area and the area of a roughness element seen by the flow;

k k

k k

(8)

;

Ps k k 

Ls k k 





Psn

Lsn

Ts

Ts

Tsn

Tsn

3. Measurements of the extent of graphitation to ensure the computation of ablated shapes An amplification/decay factor

yg k of the ablation due to the extent of graphitation is assessed by formula,

Degtiar, Saveliev et al. (2016),

g

g



4 1 0,06

KMS L 

(9)

k

C C composites 

 

уg

g

g



4

KMS L 

KIMF

where KIMF g , C C composites g  − the extent of graphitation of currently in use 4KMS -L, KIFM composites and a considered new composite. To get the extent of graphitation g , the number of C-C composites passed the X-ray diffraction study with the D8 ADVANCE X-ray diffraction meter of the BRUKER company (filtered CuK  - KMS L g  4 ,