ICS 17.617
ROMANIAN STANDARD TESTS OF METALS TENSION TESTING OF REINFORCING STEEL, WIRE AND WIRE PRODUCTS FOR PRESTRESSED CONCRETE
Încerc!rile metalelor – Încercarea la trac "iune a o"elului beton, a sârmei #i a produselor din sârm ! pentru beton precomprimat Essais des metaux – Essai de traction de l’acier pour beton arme, fil et produits en fil pour beton beton precontraint 1 1.1
STAS 6605-78 Classification index B 03 Supersedes:
STAS 6605-67 Previous editions: 1967; 1977
Validation date: 1978-12-01
GENERAL
This standard establishes the method and the conditions for performing the tension test of reinforcing steel, wire and wire products for prestressed concrete, in view of determining, under the ambient atmosphere conditions according to STAS 6300-64, the following mechanical characteristics: - apparent yield strength; - conventional yield strength; - remanent yield strength; - conventional elongation limit; - ultimate strength; - breaking strain; - remanent uniform elongation; - total elongation under maximum force; - conventional perfect elasticity; - sectional conventional elasticity modulus.
1.2
The mechanical characteristics being determined are to be specified in the standard or other normative technical documents of the product.
1.3
Terms and symbols, according to the table.
Point
Term
Symbol
Definition
Measuring unit
1.3.1
Initial section area
S0
The cross-section surface of the test piece, determined before testing
mm2
1.3.2
Rated section area
S
The cross-section surface corresponding to the rated diameter
mm2
1.3.3
Rated diameter
d
The diameter specified in the product standard
mm
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© ASRO
Entire or partial multiplication or use of t his standard in any kind of publications and by any m eans (electronically, (electronically, mechanically, photocopy, micromedia etc.) is strictly forbidden without a prior written consent of ASRO
STAS 6605-78 Point
-2 Term
Symbol
Definition
Measuring unit
1.3.4
Initial length
L0
The length between the guiding marks traced on the test piece, considered before testing
mm
1.3.5
Length before breaking
Ln
The length between the guiding marks that delimit the initial length, measured after applying a certain tensile force, but before the test piece breaks
mm
1.3.6
Final length
Lu
The length between the guiding marks that delimit the initial length, measured after the test piece breaks
mm
1.3.7
Prolongation
! L
The difference between the final length and the initial length
mm
! L = Lu – L0
1.3.8
Elongation
A
The ratio of the prolongation to the initial length of the test piece !L 100 A " L0
%
total
At
The elongation determined during testing
%
total at maximum force
Amax
The total elongation corresponding to the breaking force
%
non-proportional
A p
The part of the total elongation, determined on the tension test diagram, with a deviation from the linear variation (considered to be proportional)
%
remanent
Ar
The elongation determined after the discharge of the test piece
%
remanent uniform
Au
The remanent elongation determined after the test piece breaks, the measuring being done without including the area influenced by constriction
%
upon breaking
An
The remanent elongation determined after the test piece breaks, including the area influenced by constriction
%
NOTE – The n dimensional factor is indicated only when it is different from 5. For any section, the n factor is determined by using the formula: n=
L 0
1 . 13 S 0
and for circular sections, through the following formula: L 0 n=
1.3.9
Force
F
d 0
The load applied to the test piece during tension test NOTE – In STAS 200-75, F is called stress
N
STAS 6605-78
-3Point
Term
Symbol
Definition
Measuring unit
F e
The force upon which the prolongation grows without increasing the load
N
1.3.11 Conventional yield force
F p 0.2
The force corresponding to a non-proportional elongation of 0.2%
N
1.3.12
F r 0.2
The force corresponding to a remanent elongation f 0.2%
N
F p 0.01
The force corresponding to a non-proportional elongation of 0.01%
N
F t
The force corresponding to a total specified elongation
N
F max
The maximum force to which the test piece resists during the tension test
N
1.3.10 Apparent yield force
Remanent yield force
1.3.13 Conventional elasticity force 1.3.14 Conventional tensile force 1.3.15 Maximum force
NOTE – In the product standards the maximum force is also called breaking force
1.3.16 Apparent yield strength
Re
The ratio of the apparent yield force to the initial area of the test piece cross-section (effective or rated) F Re = e S 0
N/mm2
NOTE – The determination of the upper ReH and the lower ReL yield strength is performed according to STAS 200-75. The upper yield strength is considered as the apparent yield strength
1.3.17 Conventional yield strength
R p 0.2
The ratio of the conventional yield strength to the initial cross-section area of the test piece (effective or rated) F p 0.2 R p 0.2 =
1.3.18
Remanent yield strength
Rr 0.2
1.3.19 Conventional tension limit (for a specified total elongation)
Rt
R p 0.01
N/mm2
F t S 0
The ratio of the conventional elasticity force to the initial cross-section area of the test piece (effective or rated) F p 0.01 R p 0.01 =
N/mm2
S 0
The ratio of the force corresponding to a specified total elongation to the initial cross-section area of the test piece (effective or rated) Rt =
1.3.20 Conventional elasticity limit
S 0
The ratio of the remanent yield strength to the initial cross-section area of the test piece (effective or rated) F r 0.2 Rr 0.2 =
N/mm2
S 0
N/mm2
STAS 6605-78 Point
-4 Term
1.3.21 Ultimate strength
Symbol
Definition
Measuring unit
Rm
The ratio of the maximum force to the initial crosssection area of the test piece (effective or rated)
N/mm2
Rm =
1.3.22 Conventional sectional elasticity modulus
E s
---
2
S 0
The ratio of the F t conventional tension force to the product between the initial cross-section area and the corresponding At total elongation E s =
1.3.23 Tension test diagram
F max N/mm2
F t S 0 # At
The representation by using rectangular coordinates of the variation recorded by the force-area ratio depending on the total elongation or the variation of the force depending on prolongation
---
THE METHOD PRINCIPLE
The test consists in applying a tension force – usually until breaking – on the test piece’s longitudinal axis direction. 3 3.1
EQUIPMENT
The current tests are performed on testing machines within the 1% accuracy class, according to STAS 1510-66.
The assembly of the test piece on the testing machine must provide the axiality of applying the force and respectively the uniform prolongation of the test piece. For forces of up to 0.5 Rm, the acceptable difference between the prolongations measured on the test piece outside fibers shall be of maximum 5% of the prolongation maximum value. 3.2
NOTE - The deviation from the axial application of the force is determined by measuring the prolongations on two antipodal fibers, respectively on two parallel faces of the test piece, placed in the columns axis plane of the testing machine and in a plane perpendicular to the first.
The prolongation is measured with extensometers, attached to the test pieces. The extensometer has to provide the simultaneous measurement of prolongations on two fibers respectively on two opposed faces of the test piece, with an accuracy of: 0.001% for the determination of the conventional elasticity limit and the sectional conventional elasticity modulus; 0.01% for the determination of the conventional yield strength; 0.1% for the determination of elongation. The devices for length measurement must provide a 1% accuracy. 3.3
The recording of the tension test diagram must provide the conditions for measuring the force and prolongation, in order to be used for the determination of the yield strengths. 3.4
The diagrams in which is recorded an increase of force based on the removal of the machine wedges are allowed for the determination of the mechanical characteristics only if the difference between the wedge displacement and the length of the calibrated part is less than 10% of the to be determined length value. The testing machines can also make use of test piece fastening devices, specific to that product, that must not cause cuts, notches or flexions of the test piece. 3.5
4 4.1
TEST PIECES
The length of the test piece between the testing machine wedges, before testing, must be of: 350 … 450 mm, for wires and bars (STAS 438/1-73; STAS 438/2-73; STAS 438/3-75 and STAS 6482/2-73; STAS 6482/3-73); 450 ... 600 mm, for stranded wires; 600 … 800 mm, for strands (STAS 6482/4-74);
STAS 6605-78
-54.2
The initial length is marked on the test pieces with guiding marks that must not influence the test results.
The measurement of the test piece cross-sectional dimensions is made with an accuracy of at least 0.01 mm for wire and wire products and at least 0.1 mm for reinforcing steel. The measuring is performed in two perpendicular planes, placed in the middle third part of the test piece length. The test piece dimensions are determined as an arithmetical mean of the obtained values, provided that the differences between them do not exceed the admissible deviations. 4.3
4.4
4.4.1 4.4.2
The initial cross-section area is determined: for smooth steel by considering the mean of the two diameters measured according to subclause 4.3; in periodical profile steel (STAS 438/1-74 and STAS 6482/3-73) according to the formula: S o =
m L. $
( mm2 )
where: weighed mass of the test piece in g; given length of the test piece in mm; 3 wire density, $ = 0.00785 g/mm . The method can be applied also to other products if it is stipulated by the product standard.
m L "
4.4.3 In stranded wires and strands as the sum of the initial cross-sectional areas of the composing wires, according to paragraph 4.4.1. 4.5
The sampling is made according to the instructions given in the product standard.
The test pieces are sampled directly from samples, with no other processing. The layer of oxides or dross is cleaned with a wire brush. The ends of the periodical profile steel test pieces are mechanically cut, perpendicular to the test piece’s longitudinal axis. 4.6
4.7
In case it has to be straightened, this operation can be performed: - by hand; - with a wooden or copper hammer, on a wooden or copper anvil; - with a straightening machine that does not affect the surface status and the test piece section.
For the reinforced steel products, the possible ridges from cutting the test pieces is recommended to be polished and the ends of the stranded wires and strands to be wrapped with thin and soft binding wire. 4.8
5 5.1
PERFORMING THE TEST
The initial elastic stressing speed is chosen as follows: 8 … 10 N/mm2 * s 25 … 30 N/mm2 * s 80 … 100 N/mm2 * s
for the determination of the apparent yield strength; for the determination of the conventional yield strength, the remanent yield strength, the conventional prolongation limit, the conventional elasticity limit and the sectional conventional elasticity modulus; for the determination of the ultimate strength only.
In case of tension test when only the ultimate strength and the ultimate elongation are to be determined, the use of wedge removing speed is accepted instead of the elastic stressing speed. The admitted wedge movement speed is established according to STAS 200-75. The extensometer assembly initial force shall be of: Maximum 50N/mm2 for the determination of the conventional yield strength, of the conventional tension limit, of the conventional elasticity limit and the conventional sectional elasticity modulus; 10% of the minimum breaking force, specified in the respective product standard, for the determination of the total elongation under maximum force. 5.2
The tension test diagram can be obtained by recording, under the conditions stipulated by subclause 3.4 or by representing the individual measurements. The tension test diagram is represented for the values of the corresponding forces and prolongations measured in a progressive loading with forces equal to: 10%; 25%; 50%; 75%; 90%; 100%; 110%; 120%; 130% of the force corresponding to the specified yield strength from the product standard. 5.3
NOTE – The values of the stages above can be rounded in the minus, depending on the initially established force, meaning: for multiples of 250 N for forces under 10 kN; for multiples of 500 N for forces between 10 and 100 kN; for multiples of 1000 N for forces over 100 kN; 5.4
5.4.1 (fig. 1).
The determination of the Re apparent yield strength; The test piece is continuously and progressively loaded visually observing the force and prolongation variation
STAS 6605-78
-6 -
Fig. 1
The F e apparent yield force is determined by observing the position of the carried pointer on the stopping or lowering of the dial pointer on the force measuring device from the testing machine. 5.4.2 In case of the recorded diagram, the Re apparent yield strength (the apparent yield force) is determined according to the diagram. 5.5
The determination of the conventional yield strength R p 0.2.
Fig. 2
On the tension test diagram (figure 2) a straight line parallel to the initial linear portion is traced at a distance (measured on a parallel direction with the abscise axis) equal to an A p = 0.2% non-proportional elongation. NOTE - The R p 0.2 conventional yield strength can be equaled based on statistical studies with the Rt tension strength. 5.6
The determination of the Rr 0.2 remanent yield strength.
5.6.1
The extensometer is assembled under the conditions stipulated by subclause 5.2.
The testing is performed continuously in cycles with increasing amplitude. The interlaced discharges have to reach the extensometer initial assembly force. The first charging stage is chosen to be of 85 … 90% of the force corresponding to the specified yield strength, after which a discharge to the initial force is performed and then it is continued with loading stages of 50 N/mm 2. After each cycle the total prolongation under maximum force and remanent prolongation under initial force are measured. Based on the results of the measurements the tension test diagram is realized, with a separate tracing of the total elongation curve and the remanent elongation curve (fig. 3).
STAS 6605-78
-7-
Fig. 3
5.6.2 From the remanent elongation curve, in the point of the 0.2% elongation results the Rr 0.2 remanent yield strength. The determination of the Rt conventional elongation limit. The extensometer is assembled under the conditions stipulated by subcaluse 5.2. The test piece is further loaded, with the speed stipulated by subclause 5.1, until the total elongation specified in th e product standard is reached. The value of the total elongation is specified as an index of the conventional yield limit symbol. 5.7
The determination of the Rm ultimate strength. The loading is performed continuously and progressively until the test piece breaking under the conditions stipulated by subclause 5.1. 5.8
5.9
5.9.1
The determination of the An breaking elongation. The breaking elongation is determined for the products within STAS 438/1-74; STAS 438/2-74 and STAS 438/3-75 after the test piece breaks. The initial length is: Lo = 5 d , according to STAS 438/1-74; Lo = 10 d , according to STAS 438/2-75 and 438/3-75. The values of Lo are rounded higher, to a N full number of 10 mm divisions (figure 4 a). Holding end
Holding end
Fig. 4 a
5.9.2 The Lu final length must frame the breaking section in its middle third part, after the test piece is coaxially reconstructed and without any gap between the broken parts (figures 4 b, c). NOTE - The determination is considered also in case breaking occurred outside the middle third part, if the minimum specified value of the elongation is obtained. N=odd
Fig. 4 b
N=even
Fig. 4 c
STAS 6605-78
-8 -
The determination of the Au remanent uniform elongation. 5.10.1 The Au remanent uniform elongation is determined for SBP and SBPA (STAS 6482/2-73; STAS 6482/3-73) after test piece breaking. 5.10.2 The marking of the test pieces for the determination of the remanent uniform elongation is made every 10 mm, on a minimum 240 mm portion, at a distance of minimum 2 d from the machine holding wedges. 5.10.3 The Lo initial length is of 100 mm, corresponding to 10 divisions. The Lu final length is measured outside the breaking area, starting with the third visible marking point from the breaking section, in the test piece part that remains with the highest number of divisions (fig. 5). 5.10
10 divisions Fig. 5
The determination of the total elongation to the Amax maximum force. 5.11.1 The total elongation to the maximum force is determined for stranded wires and strands for the effective breaking force. 5.11.2 The test piece is loaded with 10% of the minimum breaking force specified in the product standard (with rounding according to the provisions of subclause 5.3) and fitted with an extensometer or another appropriate device providing the 3% accuracy. 5.11.3 The test piece is loaded up to the maximum force observing the increase of the total elongation up to that moment. 5.11
NOTE - It is admitted that the elongation is measured only until the minimum value of this characteristic, stipulated in the product standard is reached.
The determination of the R p 0.01 conventional elasticity limit. On the tension test diagram (figure 6) a line parallel to the initial linear part is traced, at a distance (measured on a direction that is parallel to the abscise axis) equal to the A p = 0.01% non-proportional elongation. The ordinate of the point where this straight line meets the diagram is the F p 0.01 conventional elasticity force, respectively the R p 0.01 conventional elasticity limit. 5.12
Fig. 6
5.13
The determination of the E 8 conventional sectional elasticity modulus.
On the tension test diagram (fig. 7) is traced a straight line that connects the axes origin with the points on the diagram that correspond to the prolongations and tension forces, equal to 10%; 20%; 30% and 40% of the force corresponding to the minimum yield strength specified in the product standard.
STAS 6605-78 -9The appropriate conventional sectional elasticity modulus is determined for each of these tension forces by using the formula indicated in subclause 1.3.22. The result of the determination is taken as an arithmetical mean of t he four determinations.
Fig. 7
6
MENTIONS IN THE TEST BULLETIN
The following shall be indicated in the test bulletin: -
the product type (quality, rated diameter);
-
the product origin;
-
the laboratory performing the test;
-
the test piece shape and size;
-
the straightening method (if performed);
-
the determined characteristics, by indicating the considered section (initial S o or rated S);
-
the possible identified flaws(informative).
__________________
STAS 6605-78
-10 -
Drafted by: The Ministry of Metallurgical Industry-
Co-workers:
Metallurgical plant-Cîmpia Turzii Project Manager: physicist Mihai Goia
-The Central Institute for Research, Design and Management in Constructions -The Institute of Research and Economy in Constructions The Institute for Welding and Material Testing Timi#oara -The „Laminorul-Br !ila” Factory
Final draft: Romanian Standards Institute , The
Metallurgy and General Standards Bureau eng. Rimma Stroescu
