Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 21839-2008 Steel for prestressed concrete - Test methods. In addition to a number of editorial changes, the following technical changes have been made with respect to GB/T 21839-2008:
——The normative references are modified (see Clause 2; Clause 2 of Edition 2008);
——Some symbols are modified and added (see Clause 3; Clause 3 of Edition 2008);
——The general provisions concerning test pieces are modified (see Clause 4; Clause 4 of Edition 2008);
——Tensile test is modified; requirements for tensile test pieces are added, parameters A and Z are added for the measurement in tensile test, artificial method is added for the measurement of Agt according to GB/T 228.1; measurement of modulus of elasticity (E) is refined (see 5.3.2);
——Judgment of the bend test result is modified (see 6.4; 6.4 of Edition 2008);
——Equipment for reverse bend test is added (see 7.2);
——Adhesion test of coating is added (see Clause 9);
——Relevant technical requirements of extensometer are modified (see Clause 5 and Annex C; Clause 5 and Annex A of Edition 2008);
——Safety warning for chemical reagents is added at the part of stress corrosion test solution (see 12.3.5);
——Requirements for length of indentation are added (see 15.3.2.4);
——Testing of the content of anti-corrosive grease is added (see Clause 18);
——Measurement of sheath thickness is added (see Clause 19);
——Test for uniformity of coating is added (see Clause 20);
——Test for quality of zinc coating is added (see Clause 21).
This standard has been redrafted and modified in relation to ISO 15630-3:2010 Steel for the reinforcement and prestressing of concrete - Test methods - Part 3: Prestressing steel.
Many structural adjustments have been made with respect to ISO 15630-3:2010, and a comparison table between this standard and ISO 15630-3:2010 in clause/subclause number is listed in Annex A.
This standard includes technical differences with respect to ISO 15630-3:2010. The clauses and subclauses concerned are identified by a vertical single line (|) located in the blank on its external margin of the page. These technical differences and their causes are listed in Annex B.
In addition, the following editorial changes have been made in this standard:
——“Annex A (informative) Comparison between this standard and ISO 15630-3:2010 in clause/subclause number” is added;
——“Annex B (Informative) Technical differences and their causes between this standard and ISO 15630-3: 2010” is added.
——“Annex C (Informative) Methods for tensile test of strand for prestressing concrete” is added.
This standard was proposed by China Iron and Steel Industry Association.
This standard is under the jurisdiction of the National Technical Committee on Iron and Steel of Standardization Administration of China (SAC/TC 183).
The previous edition of this standard is as follows:
—GB/T 21839-2008.
Test methods of steel for prestressing concrete
1 Scope
This standard specifies the methods concerning tensile test, bend test, reverse bend test, torsion test, adhesion test of winding and coating, isothermal relaxation test, axial force fatigue test, stress corrosion test in a solution of thiocyanate, deflected tensile test, determination of chemical composition, measurement of the geometrical dimension, determination of the relative rib area, determination of deviation from nominal weight per metre, testing of the content of anti-corrosive grease, measurement of sheath thickness, test for uniformity of coating and test for quality of galvanized coating, etc. of steel for prestressing concrete.
This standard is applicable to the determination of properties related prestressing steel wire, prestressing steel rod, prestressing steel bar, prestressing steel strand and other products.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 228.1 Metallic materials - Tensile testing - Part 1: Method of test at room temperature (GB/T 228.1-2010, ISO 6892-1:2009, MOD)
GB/T 230.1 Metallic materials - Rockwell hardness test - Part 1: Test method (GB/T 230.1-2018, ISO 6508-1:2016, MOD)
GB/T 232 Metallic materials - Bend test (GB/T 232-2010, ISO 7438:2005, MOD)
GB/T 238 Metallic materials - Wire - Reverse bend test (GB/T 238-2013, ISO 7801:1984, MOD)
GB/T 239.1 Metallic materials - Wire - Part 1: Simple torsion test (GB/T 239.1-2012, ISO 7800:2003, MOD)
GB/T 1839 Test method for gravimetric determination of the mass per unit area of galvanized coatings on steel products (GB/T 1839-2008, ISO 1460:1992, MOD)
GB/T 2972 Test method for uniformity of zinc coating on zinc-coated steel wire by the copper sulphate dip (GB/T 2972-2016, ISO 7989-2:2007, NEQ)
GB/T 2975 Steel and steel products - Location and preparation of samples and test pieces for mechanical testing (GB/T 2975-2018, ISO 377:2017, MOD)
GB/T 2976 Metallic materials - Wire - Wrapping test (GB/T 2976-2004, ISO 7802:1983, IDT)
GB/T 3505 Geometrical product specifications (GPS) - Surface texture: Profile method - Terms definitions and surface texture parameters (GB/T 3505-2009, ISO 4287:1997, IDT)
GB/T 4336 Carbon and low-alloy steel - Determination of multi-element contents - Spark discharge atomic emission spectrometric method (routine method)
GB/T 12160 Calibration of extensometers used in uniaxial testing (GB/T 12160-2002, ISO 9513:1999, IDT)
GB/T 16825.1 Verification of static uniaxial testing machines - Part 1: Tension/compression testing machines - Verification and calibration of the force-measuring system (GB/T 16825.1-2008, ISO 7500-1:2004, IDT)
3 Symbols and definitions
For the purposes of this document, the symbols given in Table 1 apply.
Table 1 Symbols and their description
Symbol Unit Description Reference
am mm Rib height at the mid-point 15.3, 16.2
amax mm Maximum depth of indentation or height of rib 15.3
as,i mm Average height of a rib in unit length ?l 16.2
a1/4 mm Rib height at the quarter-point 15.3, 16.2
a3/4 mm Rib height at the three-quarters point 15.3, 16.2
A % Percentage elongation after fracture 5.3.1
Agt % Percentage total elongation at maximum force 5
At % Total elongation at break 5.3.1
b mm Width of transversal rib 15.3.1.6
c mm Rib or indentation spacing 15.3
C mm Groove width of the mandrel used for the deflected tensile test 13.3.4
d mm Nominal diameter of the rod, wire or strand 11.2, 11.4.6, 12.3.4
da mm Nominal diameter of the mandrel used for the deflected tensile test 13.3.4
db mm Diameter with 2 gauge cylinders in the groove of the mandrel used for the deflected tensile test 13.3.4
de mm Diameter of the gauge cylinder used for the deflected tensile test 13.3.4
dg mm Diameter of guide hole 7.3
di mm Inner diameter of the groove of the mandrel used for the deflected tensile test 13.3.4
D % Average coefficient of reduction of the maximum force in the deflected tensile test 13.2, 13.4
Dc mm Inner diameter of the cell in the stress corrosion test 12.3.4
Di % Individual percentage of reduction of the maximum force in the deflected tensile test 13.4
e mm Average gap between two adjacent ribs or indentation rows 15.3.1.4, 15.3.2.4
E GPa Modulus of elasticity 5.3
f HZ Frequency of force cycles in the axial force fatigue test 11.1, 11.4.2
fR — Relative rib area 16
Fa,i N Individual breaking force in the deflected tensile test 13.4
Fm N Maximum force 5.3
N Mean value of the maximum force 10.2, 12.2, 13.2
Fp0.1 N 0.1% proof force 5.3
Fp0.2 N 0.2% proof force 5.3
Fr N Force range in the axial force fatigue test 11.1, 11.3, 11.4.2
Frt N Residual force in the test piece at time t in the relaxation test 10.1
ΔFrt N Force loss in the test piece at time t in the relaxation test 10.1
FR mm2 Area of longitudinal section of one transverse rib 16.2
Fup N Upper force in the axial force fatigue test 11.1, 11.3, 11.4.2
F0 N Initial force in the stress relaxation test and the stress corrosion test 10.1, 10.3, 10.4, 12.4.2
G mm Depth of the groove of the mandrel used for the deflected tensile test 13.3.4
h mm Distance from the top of cylindrical supports to the bottom of the guide 7.2
hb mm Bow height of the plane of prestressing steel 15.3.4
Lt mm Length of the test piece in the stress corrosion test 12.2
L0 mm Original gauge length in the isothermal relaxation test
Length of the test piece in contact with the solution in the stress corrosion test 10.1, 10.3, 10.4, 12.2, 12.3.4, 12.4.5
ΔL0 mm Elongation of the gauge length, L0, under force, F0, in the isothermal stress relaxation test 10.1, 10.3, 10.4
L'0 mm Determined original gauge length of Agt 5.3
L'u mm Determined gauge length after fracture of Agt 5.3
L1 mm Length of the passive side in the deflected tensile test 13.3.2
L2 mm Length of the active side in the deflected tensile test 13.3.2
m, n — Coefficients or numbers 10.4.9, 15.3, 16.2
P mm Lay length of a strand 15.3.3
R mm Corner radius at the base of the groove of the mandrel used for the deflected tensile test 13.3.4
r mm Radius of cylindrical supports 7.2
Ra μm Surface roughness of the mandrel used for the deflected tensile test 13.3.4
Sn mm2 Nominal cross-sectional area of the test piece 5.3.2
ta h Maximum agreed time for the stress corrosion test 12.4.5
tf,i h Individual lifetime to fracture in the stress corrosion test 12.4.5
h Median lifetime to fracture in the stress corrosion test 12.4.6
t0 s Starting time in the isothermal stress relaxation test and in the stress corrosion test 10.4.2, 12.4
V0 mm3 Volume of test solution to fill the test cell in the stress corrosion test 12.4.3
W g/m Weight of unbonded prestressing steel strand per metre 18.3
W1 g/m Weight of steel strand after removing the sheath and anti-corrosive grease from unbonded prestressing steel strand per metre 18.3
W2 g/m Weight of sheath after removing the anti-corrosive grease from unbonded prestressing steel strand per metre 18.3
W3 g/m Weight of anti-corrosive grease in unbonded prestressing steel strand per metre 18.3
Z % Percentage reduction of area 5.3.1
α (°) Angle of deviation in the deflected tensile test 13.3.2
β (°) Transverse rib or indentation angle to the bar or wire axis 15.3
εx — Value of the strain for a force equal to x 5.3.2
ρ % Relaxation 10.4.8
Σei mm Circumference of transverse rib gap 15.3.1.4, 15.3.2.4, 16.2
Note: 1N/mm2=1MPa
4 General provisions concerning test pieces
Unless otherwise agreed or specified in the product standard, the test pieces shall be taken from the finished product normally before packaging.
Special care should be taken when sampling is made from the packaged product (e.g. coil or bundle), in order to avoid plastic deformation which could change the properties of the samples used to provide the test pieces.
Specific complementary provisions concerning the test pieces may be indicated in the relevant clauses of this standard, if applicable.
5 Tensile test
5.1 Test pieces
?In addition to the general provisions given in Clause 4, the free length of the test piece shall be sufficient for the determination of the percentage total elongation at maximum force (Agt) in accordance with 5.3.1.
If the percentage elongation after fracture is determined manually, the test piece shall be marked in accordance with GB/T 228.1.
If the percentage total elongation at maximum force (Agt) is determined by the manual method for bar or wire, equidistant marks shall be made on the free length of the test piece (see GB/T 228.1). The distance between the marks shall be 20mm, 10mm or 5mm, depending on the test piece diameter.
Foreword i
1 Scope
2 Normative references
3 Symbols and definitions
4 General provisions concerning test pieces
5 Tensile test
6 Bend test
7 Reverse bend test
8 Torsion test
9 Adhesion test of winding and coating
10 Isothermal relaxation test
11 Axial force fatigue test
12 Stress corrosion test in a solution of thiocyanate
13 Deflected tensile test
14 Chemical analysis
15 Measurement of the geometrical dimension
16 Determination of the relative rib area (fR)
17 Determination of deviation from nominal weight per metre
18 Testing of the content of anti-corrosive grease
19 Measurement of sheath thickness
20 Test for uniformity of coating
21 Test for quality of zinc coating
22 Test report
Annex A (Informative) Comparison between this standard and ISO 15630-3: 2010 in clause/subclause number
Annex B (Informative) Technical differences and their causes between this standard and ISO 15630-3:
Annex C (Informative) Methods for tensile test of strand for prestressing concrete
預應力混凝土用鋼材試驗方法
1 范圍
本標準規定了預應力混凝土用鋼材的拉伸、彎曲、反復彎曲、扭轉、纏繞和鍍層附著力、等溫松弛、軸向力疲勞、硫氰酸鹽溶液中的應力腐蝕、偏斜拉伸、化學分析、幾何尺寸測量、相對肋面積確定、每米公稱質量偏差的確定、防腐潤滑脂含量檢測、護套厚度測量、鍍層均勻性、鋅層質量等試驗方法。
本標準適用于預應力鋼絲、預應力鋼棒、預應力鋼筋、預應力鋼絞線等產品相關性能的測定。
2 規范性引用文件
下列文件對于本文件的應用是必不可少的。凡是注日期的引用文件，僅注日期的版本適用于本文件。凡是不注日期的引用文件，其最新版本(包括所有的修改單)適用于本文件。
GB/T 228.1 金屬材料 拉伸試驗 第1部分：室溫試驗方法(GB/T 228.1—2010，ISO 6892-1：2009，MOD)
GB/T 230.1 金屬材料 洛氏硬度試驗 第1部分：試驗方法(GB/T 230.1—2018，ISO 6508-1：2016，MOD)
GB/T 232 金屬材料 彎曲試驗方法(GB/T 232—2010，ISO 7438：2005，MOD)
GB/T 238 金屬材料 線材 反復彎曲試驗方法(GB/T 238—2013，ISO 7801：1984，MOD)
GB/T 239.1 金屬材料 線材 第1部分：單向扭轉試驗方法(GB/T 239.1—2012，ISO 7800：2003，MOD)
GB/T 1839 鋼產品鍍鋅層質量試驗方法(GB/T 1839—2008，ISO 1460：1992，MOD)
GB/T 2972 鍍鋅鋼絲鋅層硫酸銅試驗方法(GB/T 2972—2016，ISO 7989-2：2007，NEQ)
GB/T 2975 鋼及鋼產品 力學性能試驗取樣位置和試樣制備(GB/T 2975—2018，ISO 377：2017，MOD)
GB/T 2976 金屬材料 線材 纏繞試驗方法(GB/T 2976—2004，ISO 7802：1983，IDT)
GB/T 3505 產品幾何技術規范(GPS) 表面結構 輪廓法 術語、定義及表面結構參數(GB/T 3505—2009，ISO 4287：1997，IDT)
GB/T 4336 碳素鋼和中低合金鋼 多元素含量的測定 火花放電原子發射光譜法(常規法)
GB/T 12160 單軸試驗用引伸計的標定(GB/T 12160—2002，ISO 9513：1999，IDT)
GB/T 16825.1 靜力單軸試驗機的檢驗 第1部分：拉力和(或)壓力試驗機測力系統的檢驗與校準(GB/T 16825.1—2008，ISO 7500-1：2004，IDT)
3 符號及說明
表1給出的符號及說明適用于本文件。
表1 符號及說明
符號 單位 說明 涉及章條
am mm 中點肋高 15.3,16.2
amax mm 刻痕深度最大值/最高點肋高 15.3
as,i mm 肋在單位長度Δl上的平均高度 16.2
a1/4 mm 在1/4點處的肋高 15.3,16.2
a3/4 mm 在3/4點處的肋高 15.3,16.2
A % 斷后伸長率 5.3.1
Agt % 最大力總延伸率 5
At % 斷裂總延伸率 5.3.1
b mm 橫肋寬 15.3.1.6
c mm 肋或刻痕距 15.3
C mm 偏斜拉伸試驗用的芯軸凹槽寬度 13.3.4
d mm 預應力鋼棒、鋼絲、鋼絞線的公稱直徑 11.2,11.4.6,12.3.4
da mm 偏斜拉伸試驗用芯軸公稱直徑 13.3.4
db mm 偏斜拉伸試驗用兩量棒放在芯軸凹槽中的直徑 13.3.4
de mm 偏斜拉伸試驗用量棒的直徑 13.3.4
dg mm 導向孔直徑 7.3
di mm 偏斜拉伸試驗用芯軸凹槽的內徑 13.3.4
D % 偏斜拉伸試驗中最大力減少率的平均值 13.2,13.4
Dc mm 應力腐蝕試驗中容器內徑 12.3.4
Di % 偏斜拉伸試驗中單根試樣最大力減少的百分比 13.4
e mm 兩排相鄰的肋或刻痕之間的平均間隙 15.3.1.4,15.3.2.4
E GPa 彈性模量 5.3
f HZ 軸向疲勞試驗中負荷循環頻率 11.1,11.4.2
fR — 相對肋面積 16
Fa,i N 偏斜拉伸試驗中單根試樣破斷力 13.4
Fm N 最大力 5.3
N 最大力平均值 10.2,12.2,13.2
Fp0.1 N 0.1%屈服力 5.3
Fp0.2 N 0.2%屈服力 5.3
Fr N 軸向疲勞試驗中力的范圍 11.1,11.3,11.4.2
Frt N 松弛試驗t時間試樣上的剩余力 10.1
ΔFrt N 松弛試驗t時間試樣松弛損失的力 10.1
FR mm2 橫肋軸向剖面面積 16.2
Fup N 軸向疲勞試驗中的最大力 11.1,11.3,11.4.2
F0 N 應力松弛試驗和應力腐蝕試驗中的初始力 10.1,10.3,10.4,12.4.2
G mm 偏斜拉伸試驗用芯軸凹槽深度 13.3.4
h mm 圓柱支座頂部至撥桿底部距離 7.2
hb mm 預應力鋼材平面矢高 15.3.4
Lt mm 應力腐蝕試驗中試樣的長度 12.2
L0 mm 等溫松弛試驗原始標距，應力腐蝕試驗中試樣在溶液中的浸入長度 10.1,10.3,10.4
12.2,12.3.4,12.4.5
ΔL0 mm 等溫應力松弛試驗中在力F0時標距L0的伸長 10.1,10.3,10.4
L'0 mm 測定Agt的原始標距 5.3
L'u mm 測定Agt的斷后標距 5.3
L1 mm 偏斜拉伸試驗中固定端長度 13.3.2
L2 mm 偏斜拉伸試驗中活動端長度 13.3.2
m,n — 系數或數字 10.4.9,15.3,16.2
P mm 鋼絞線捻距 15.3.3
R mm 偏斜拉伸試驗中芯軸凹槽底部圓角半徑 13.3.4
r mm 圓柱支撐半徑 7.2
Ra μm 偏斜拉伸試驗中芯軸表面粗糙度 13.3.4
Sn mm2 試樣公稱橫截面積 5.3.2
ta h 應力腐蝕試驗中最大規定時間 12.4.5
tf,i h 應力腐蝕試驗中單根試樣的斷裂時間 12.4.5
tf h 應力腐蝕試驗中試樣斷裂時間中值 12.4.6
t0 s 恒溫松弛試驗和應力腐蝕試驗中開始時間 10.4.2,12.4
V0 mm3 應力腐蝕試驗容器中溶液的體積 12.4.3
W g/m 每米長無粘結預應力鋼絞線的質量 18.3
W1 g/m 每米長無粘結預應力鋼絞線中除凈護套和防腐潤滑脂后的鋼絞線的質量 18.3
W2 g/m 每米長無粘結預應力鋼絞線中除凈防腐潤滑脂后的護套的質量 18.3
W3 g/m 每米長無粘結預應力鋼絞線中防腐潤滑脂的質量 18.3
Z % 斷面收縮率 5.3.1
α (°) 偏斜拉伸試驗中偏斜角度 13.3.2
β (°) 鋼棒或鋼絲的橫肋或刻痕與中心線的夾角 15.3
εx — X應變支 5.3.2
ρ % 松弛率 10.4.8
Σei mm 橫肋間隙周長 15.3.1.4,15.3.2.4,16.2
注：1N/mm2=1MPa。
4 試樣的一般規定
除非另有其他協議或產品標準規定，試樣一般在成品包裝前在成品中截取。
當樣品是包裝產品時(例如成卷或成捆)，截取試樣應防止試樣因發生塑性變形而可能改變其性能。
必要時，可對本標準相關條款中試樣的要求進行具體補充。
5 拉伸試驗
5.1 試樣
試樣應符合第4章的規定，測定最大力總延伸率(Agt)時，試樣的自由長度應符合5.3.1的Agt相關要求。
手工法測定斷后伸長率時，按照GB/T 228.1要求劃等距離標記。
用手工法測定鋼絲和鋼棒最大力總延伸率(Agt)時，在試樣自由長度上劃等距離標記(見GB/T 228.1)，標記間的距離根據樣品的直徑確定，可為20mm、10mm 或5mm。
5.2 試驗設備
試驗設備應根據GB/T 16825.1進行校驗和校準，并至少為1級準確度。
測定E、Fp0.1或Fp0.2時，引伸計的準確度應為1級(見GB/T 12160)；用于測定Agt的引伸計可以為2級(見GB/T 12160)。
應使用合適的夾具，避免試樣在夾具內或在夾具附近斷裂。
5.3 試驗程序
5.3.1 概述
5.3.1.1 拉伸試驗應按照GB/T 228.1的要求執行；預應力混凝土用多絲鋼絞線拉伸試驗程序可參照附錄C執行。
5.3.1.2 應該使用引伸計測定彈性模量(E)，0.1%屈服力和0.2%屈服力(Fp0.1和Fp0.2)及最大力總延伸率(Agt)，引伸計的標距按相關產品的標準要求確定。
5.3.1.3 Agt的精確值只能用引伸計來測得。如果試樣上的引伸計不能保持到試樣斷裂時，可按下列方法測定Agt：
——繼續加載直至引伸計記錄的伸長率稍大于Fp0.2時的伸長率，此時取下引伸計，記錄試驗機上下工作臺的距離。繼續加載至試樣斷裂，記錄此時試驗機上下工作臺的最終距離。
——計算出兩次試驗機上下工作臺的距離之差，將此差值與試驗機上下工作臺的初始距離之比和用引伸計測得的百分數相加即為斷裂總延伸率At。
5.3.1.4 對于鋼絲、鋼棒、鋼筋Agt測定，應按照下列方法進行：
測量已拉伸試驗過的試樣最長部分，測量區的范圍應處于距離斷裂處至少5d，距離夾頭至少為2.5d。測量用的原始標距應等于產品標準中規定的值。
按下列式(1)計算：
(1)
式中：
L'u——測定Agt的斷后標距；
L'0——測定Agt的原始標距。
5.3.1.5 在裝引伸計前，宜給試樣預加一負荷，例如該預加負荷為試樣預期最大負荷的約10%。
5.3.1.6 如果Agt不是完全用引伸計測定的，應在試驗報告中注明。
5.3.1.7 拉伸性能值，Fp0.1，Fp0.2，Fm均用力的單位表示。
5.3.1.8 斷后伸長率(A)測定原始標距為試樣公稱直徑的8倍，除非相關產品標準另有規定。在有爭議的情況下，A 的測定采用手工法。
5.3.1.9 當試樣在距夾具3mm 之內發生斷裂，試驗應判為無效，應允許重新試驗。然而，如果所有試驗數據大于等于相應的規定值，其試驗結果有效。
5.3.2 彈性模量的測定
在力-伸長率曲線中，用0.2Fm~0.7Fm范圍內的直線段的斜率除以試樣的公稱橫截面積(Sn)測定彈性模量(E)。
(2)
斜率可以通過對測定數據進行線性回歸得出，也可以用最優擬合目測法得出。
在一些特定情況下，例如預應力鋼筋和鋼棒，上述方法不適用時，可在0.05Fm~0.7Fm范圍內測定彈性模量。
(3)
除5.3.1規定的要求外，測定彈性模量時，在力值范圍內應力速率應保持不變。
6 彎曲試驗
6.1 試樣
試樣應符合第4章規定。
6.2 試驗設備
6.2.1 試驗設備的彎曲原理如圖1所示。
注：圖1為彎曲設備的外形構造，可以是芯軸1和支撐2旋轉，支座3被固定；也可以是支座3旋轉，支撐2或芯軸1被固定。
說明：
1——芯軸；
2——支撐；
3——支座；
D ——芯軸直徑。
圖1 彎曲設備的原理
6.2.2 彎曲試驗也可以按GB/T 232用帶有支撐和芯軸的裝置來進行。
6.3 試驗程序
彎曲試驗應在10℃~35℃的溫度進行，試樣應沿著芯軸進行彎曲。
彎曲角度和芯軸直徑應符合相關產品標準的要求。
6.4 試驗結果的判定
彎曲試驗結果的判定應符合相關產品標準的要求。
當產品標準沒有規定時，若受彎曲部位無目視可見的裂紋，則判定該試樣為合格。
產生在肋的根部或刻痕上的表面裂縫屬于有效試驗。裂縫深度應不大于裂縫寬度。
7 反復彎曲試驗
7.1 試樣
除符合第4章規定外，試樣的制備應符合GB/T 238中的相關規定。
7.2 試驗設備
試驗設備應符合GB/T 238中的相關規定。
公稱直徑10mm
