Fail-safe cable and effect of non-frangible wire in cable structures

A synthesis of four (4) factors is applied, through a test approach, to eliminate wire fractures, and fractures and overstressing of other cable components. This approach shows this "crucial flaw" is prevented from occurring amidst other flaws within the "flaw state" of the complex structure of work performing cable. These other flaws prove to be minor during the cable's service life. Non-frangible, ductile aluminum (al) and titanium (ti) wire are used in the cable assembly wherein their high dynamic properties and other attributes prevent wire fractures, and neutralize or reduce wire wear, depending upon load level, to change and improve the cable's "flaw state" so that a "fail-safe" cable may be designed to provide a protracted service life. Steel and copper wire fail to qualify for "fail-safe" cable constructions due to their low dynamic properties and other flaws in the cable structure.

BACKGROUND OF THE INVENTION 
This invention relates to cable wire fractures and fracture-tough wire 
produced from non-frangible aluminum (al) and titanium (ti) base alloys 
that transition from brittle to ductile metallurgical condition in 
processing. More specifically it relates to change in cable flaw state by 
eliminating wire fractures so as to increase reliability and service. Two 
(2) additional patent applications are submitted herewith, (1) Cable 
Stress and Fatigue Control Ser. No. 757,300, and (2) Deep Well Handling 
and Logging System, Ser. No. 757,552. These patent applications are 
related and copending. 
It is found that alloys of al and ti have many attributes for use in cable 
tension members but two (2) attributes are common to selected alloys of 
each, and are crucial to this invention: 
(1) High dynamic properties in the base metals including abnormally high 
spring which are essential to effective energy absorption, storage and 
dissipation in tension systems; and 
(2) Selected alloys are processed through brittle-ductile transition so as 
to embody high energy (in ft.-lbs) and fracture extension resistance, and 
then are non-frangible in cable structures. 
While selected steel alloys may likewise be non-frangible in test specimens 
they fail to qualify because of low dynamic properties and wire fractures, 
crucial to serviceability in steel work performing cable, and in the old 
manners, are extremely limiting in the use of effective design criteria 
for cable constructions. 
In analyzing the significance of fractures in "work performing" cable, it 
should be recognized that the behavior of all structures is derived from 
both the type of mechanical force system and the metallurgical type of 
metal. The mechanical aspects involve the relative compliance 
characteristics which determine the stored energy available for fracture 
propagation (hereinafter called mechanical); the metallurgical aspects 
involve relative ductility characteristics which determine the energy 
absorption and dissipation capacity to fracture initiation and extension 
(hereinafter called metallurgical). These two (2) qualities of any 
structure operate in concert to determine how the structure will respond 
to loading in the presence of flaws, as has been commonly seen in the wire 
fractures and short service of steel cable. Essentially, the flaw state 
design of tension systems is the basis for assessment of these 
interactions as in any structure. In this context cable structures are 
complex, thus placing a premium on non-frangible, ductile wire to overcome 
structural flaws. 
Characteristics cable stresses when performing work are: 
Simple bend stresses are .sigma.b=.delta./D.times.Ec with other bend 
stresses induced depending upon cable constructions 
Surface contact stresses are .sigma.c=K.sqroot.P 
Impact stresses are .sigma.i=Vo.sqroot.Ec.times..rho.c 
Internal stresses are local but may be generally severe as functions of 
relative mass density (.rho.c) and elasticity (Ec). 
These stresses are of course induced and superimposed upon cable tension. 
It may now be seen that frangible wire with low dynamic properties will 
not provide fracture-safe cable structures. Once wire fractures begin, as 
characteristic of structures having flaws, they continue and most often 
accelerate, wherein safety factors grow marginal until reaching a 
catastrophically low strength condition. In view of the complex 
construction of both axially symmetric and contrahelically wrapped 
electrochemical cable for sustaining primary loads and the characteristic 
severity of these dynamic stresses in performing work, three cable 
structures must be considered, (a) mechanically flawed (b) very sensitive 
to both mechanical and physical properties, and (c) metallurgical 
condition. 
SUMMARY OF INVENTION 
This invention embodies four (4) factors which are combined and synthesized 
to result in fracture-tough, non-frangible wire and fracture safe cable. 
The first two (2) factors, mechanical and metallurgical have been outlined 
above. Two other crucial factors are: 
Third factor -- high dynamic properties and high hard spring in wire, such 
as defined (also see FIGS. 1 and 2) above for al and ti, so that dynamic 
stresses superimposed on tension are moderated under passive control 
whereby the physical properties of wear, fatigue and abrasion do not 
result in flaws. 
Fourth factor -- design criteria derived from and synthesized with the 
mechanical and metallurgical factors (above) avoid structural flaws so 
that fail-safe cable may be constructed. These factors combined with lay 
angles, wire sizes and cable constructions, by physical law absorb, store 
and dissipate energy through stress-vibration and counterbalancing wherein 
physical conditions noted above progress at low grade rates, and no single 
dynamic stress, or stress combination, may cause overstressing or 
fracturing of strands or cable. 
This synthesis of factors has been reduced to practice for two (2) ti base 
alloys, one alloy being non-frangible, Ti-6Al-4V, and one frangible alloy, 
Ti-13V-11Cr-3al. The former proved to be fracture and fail-safe during 
protracted cycling. Various flaws developed in shorter cycling periods in 
other type specimens especially including corrosion resistant steel and 
improved plow steel. 
Objects of the invention are: 
First -- Synthesize four (4) cable factors (1--relative mechanical force 
for compliance, 2--relative metallurgical characteristics for ductility, 
3--high dynamic properties, and 4--special design criteria) through a test 
approach to produce fracture-tough and fail-safe cable from al and ti 
alloys. 
Second -- Eliminate "crucial" wire fractions from work performing cable 
during service life. 
Third -- Provide a means to produce and qualify non-frangible, ductile 
wires from the range of al and ti base alloys so that these wires serve as 
models for flaw behavior in the complex cable structure. 
Finally -- Provide a correlated design and test approach to demonstrate 
"fail-safe" cable design that eliminates "crucial" wire fracture flaws 
while further minimizing other flaws of the cable "flaw state." 
Three physical factors operate in concert to sustain the primary load and 
dynamic stresses: 
1. Non frangible wires, having been processed through a brittle-ductile 
transition, then are assembled into work performing cable having a changed 
flaw state 
2. Compliant and ductile wires resist fracture and extension, and are 
permanently lubricated 
3. In service the wires have high resistance to wear, including abrasion, 
and strain-hardening, an uncommon set of attributes. 
The high dynamic properties and soft cable spring for dissipating energy, 
then moderate the attributes outlined above, (1) relative metallurgical 
for storing energy, and (2) relative mechanical for absorbing it, wherein 
each factor has been effectively optimized and the unworkable high tensile 
strength concept has been discarded so that work may be performed on a 
fail-safe, protracted basis. 
Selected alloys of two base metals al and ti, both non-ferrous qualify in 
the two (2) characteristic factors as outlined above, (1) metallurgical 
for storing energy, and (2) mechanical for absorbing energy. Moreover they 
each qualify in the latter characteristic for dissipating energy as well, 
having a high wire hard spring constant. Their alloys each have low 
density and high elasticity for effective high dynamic property ranges: 
Al-density 0.08-0.10 lbs per cu in - E. modulus 16.times.10.sup.6 p.s.i. 
Ti-density 0.15-0.175 lbs per cu in - E modulus 8-9.times.10.sup.6 p.s.i. 
Gap between yield and ultimate strengths, Al 1-15 percent and Ti 2-10 
percent. Although a few steel alloys are non-frangible, their dynamic 
properties are much too low.

It should be convenient to define a range of terms associated with 
fracture-toughness as applied to wire and cable, and explain their 
usefulness in this invention. 
Fracture-toughness is simply defined as a relationship between 
fracture-resistance and strength. In the case of wire it may be determined 
by tensile and torsional strength parameters. Fracture-toughness is 
normally inversely proportional to yield strength. 
Fracture-toughness of metal alloys is determined by standard tests: 
Charpy-V test measures values of fracture initiation, propagation and 
arrest 
Ki is a stress intensity factor denoting the opening mode of crack 
extension, wherein: 
Kic denotes slow-load (static) plane strain fracture-toughness (K.S.I. in) 
Kid denotes dynamic load plane strain fracture-toughness (K.S.I. in.) 
Kq denotes invalid measurements characterizing non-frangible metals. 
Fracture-mechanics of cable recognizes fracture-toughness is controlled by 
mechanical constraint and flaw severity factors, wherein al and ti cable 
may be effectively compared with steel cable as shown in the load 
deflection diagram composite of FIG. 3. 
Ductility is an intrinsic metallurgical characteristic of brittle-ductile 
transition wherein mechanical parameters serve to describe the metal 
response to specific stress states, such as percentage of wire elongation. 
Ductility transition temperature range can only be determined by dynamic 
fracture tests. 
Dynamic tear test represents an advanced engineering test which provides 
accurate indexing of transition in ft.-lb terms as to how fracture 
mechanics apply in plane stress specimen configuration that provides 
sufficient fracture extension to allow plane stress fracture-toughness to 
the degree characteristic of the alloy tested. 
Frangible as applied to metal alloys means breakable and brittle, and in 
wire form, these alloys are susceptible to fracture in cable dynamics 
states. 
Non-frangible is the opposite of frangible, specifically having high 
ductility, fracture-toughness, and fracture extension resistance. 
Fracture extension resistance is a metallurgical condition and index of an 
alloy at a constant load level determined by test; data banks may be 
available to show normalized curves for categories of alloys that 
graphically show load values vs resistance wherein all non-frangible 
alloys would be represented on a steep rising curve. 
Fail-safe design of cable embodies first the use of ductile, non-frangible 
wire assembled into cable which has been designed and tested to eliminate 
fractures, over-stressed components and other flaws when performing work, 
in this invention, by other means than high tensile strength and safety 
factors. 
"Flaw-state" of cable if always a matter of semi-qualitative description, 
and therefore must be described in "rough-cuts" such as "minor" or "major" 
flaws, or "fracture-prone." 
Protracted is specially defined to mean a much longer service period than 
normal for identical steel cable, the common standard perhaps not less 
than four (4) times, and even much greater in many applications. 
The novel factors considered characteristic of the elimination of wire 
fractures and developing fracture-toughness of this invention are set 
forth with particularity in the appended claims. The invention itself 
however, both as to organization and method of operation as well as 
additional objects and advantages will be best understood from the 
following description, starting with a synthesis of the four (4) principle 
factors herewith. 
A synthesis of four (4) factors are essential and is made to prevent wire 
fractures and overstressing in work performing cable in this invention. In 
effect not only the two (2) previously outlined, mechanical and 
metallurgical, are related and interact, but also the following two (2) 
factors interact as further outlined: 
(1) Dynamic stresses are controlled within low regime loading according to 
the data presented above because of the high dynamic properties including 
high hard spring of selected alloys of al and ti wire. These stresses of 
course are a part of mechanical force in cable structures but are 
moderated markedly, compared to steel, so that passive energy control 
embodies not only energy absorption and storage but also distinct cable 
soft spring for dissipating energy. On this basis less energy is absorbed 
and less stored while it is dissipated effectively to improve the cable 
loading characteristic, to the point that tensile stress of the primary 
load is equalized in components rapidly in dynamic states by design, 
compliance, stress vibration and counterbalancing, these factors being 
dynamic interaction characteristics. 
(2) Design criteria become far more effective in the cable structure 
wherein each criterion has far more design scope toward the elimination or 
change of minor flaws, and for that matter, the control of crucial wire 
fractures. The criteria may be confidently used, for example, to reduce 
the number of wires, (or the alternative, increase them) to reduce 
internal stresses, increase compliance in bending cable and 
counterbalancing; apply spring to reduce and dampen torque; and shorten 
lay lengths to increase counterbalancing and flexibility. These options 
may be exercised within limits to prevent wire fractures, or as trade-offs 
to improve performance, efficiency and service wherein the major flaw, 
wire fracture is avoided. These criteria may be used, of course, to 
counteract minor flaws such as wear, fatigue, and to optimize load and 
dynamic stresses. 
Wire fractures in the assembly complex of the cable structure, represent 
catastrophic results of this essential structural component that, in fact 
are crucial to work performance and cable condition. Once wire fractures 
start to occur, they normally accelerate progressively in service wherein 
the cable flaw-state becomes a critical problem in work operations; while 
wire wear and fatigue may be associated, the dominant flaw is wire 
fracturing. 
Eliminating wire fractures, as well as overstressing and fracturing larger 
components and even complete cable-cross sections, is the principle object 
since other flaws are relatively minor. While it is understood that wire 
may always be fractured by overloading and kinking as a part of the 
fracture-mechanics, this requires specially induced plastic flow to 
initiate the fracture process, which is not normally a part of cable flaw 
state. It is also understood that fracture-toughness, as a dual mechanical 
and metallurgical characteristic, is inherently a part of the fracture 
process and the flaw state of cable components. 
The two interrelated factors, outlined above, (1) the mechanical force 
system, and (2) the metallurgy of the wire, operate in concert in the 
behavior of cable structures, wherein by analysis, mechanical and dynamic 
relations involve compliance characteristics for determining stored energy 
available for fracture propagation, whereas the metallurgical and dynamic 
aspects involve the relative ductility characteristics which determine the 
energy absorption capacity (resistance) to fracture initiation and 
extension. These two (2) factors respond to loading in the presence of 
flaws, so that a "fail-safe" design is made by assessing the loading 
interactions. 
A basic requirement of this invention is that test specimens must model the 
behavior of structure that contain flaws. It follows: (1) initial testing 
is performed of suitable metal model specimens to test for (a) 
frangibility and their energy level (ft.-lbs) in a drop tear test to 
resist fracture extension, and (b) brittle-ductile transition at the 
appropriate thermal level, and (2) non-frangible cable specimen testing 
under load is finally performed to determine design suitability in the 
presence of minor flaws, the major flaw of frangibility (fracture) having 
been removed. 
Steel wire often fractures in cables, most often in materials handling 
systems while performing work due to severe bend stresses, and entire 
cables either fracture, or core wires fracture due to impact stresses, 
resulting from starting and stopping and other overload impacts. These two 
stresses combine with other characteristic stresses including wire 
pressure from tension and internal stresses, to induce extremely high 
tension peaks because of low dynamic properties. 
The core strand normally fails first since this strand has less 
constructional stretch than outer strands and greater wire pressure is 
induced into the core strand, compared to the outers. Unfortunately, a 
weakened or overstressed core strand remains unknown, it being covered and 
invisible wherein cables, or their components, are then more susceptible 
to catastrophic failure. FIG. 4 shows two (2) load deflection tests of 
1/4" Ti-6Al-4V cable specimens that produced essentially identical load 
result responses, without evidencing flaws until reaching a plastic state. 
Resulting fracture mechanics were also identical but neither one fractured 
catastrophically. Single wires did not fracture until well into the 
curvalinear part of the load diagram. 
Single fractures of outer wires are especially serious to contrahelically 
armored cable. This cable so damaged becomes very difficult to handle in 
long lengths, its serviceability becoming effectively reduced. Repairs are 
either impractical or are rarely satisfactory. 
These armor fractures are normally due to severe bend stresses in steel 
wire in bending regions when paying out or collecting cable on drums or 
running over sheaves. Bend stresses (.sigma.b) so induced into this wire 
are normally severe due to the high elastic modulus, 29.times.10.sup.6 
p.s.i., and large wire sizes, coupled with tension and wire pressure. 
Moreover, torsional rotation of this cable in long lengths as in oil well 
logging, adds severe fracture and handling complications. 
It will now be understood that cable must have adequate flexibility for 
work handling as in materials handling systems (see FIGS. 1a, b, and c). 
In axially symmetric constructions, individual wires are small enough for 
bending, but the number must be comparatively large to meet the system 
bending requirement. However this construction requirement creates large 
numbers of local internal stresses at wire cross points, arising from 
layer or helical contacts, whih are also severe between non-compliant 
steel wires. As a result, elastic and frictional resistance (FIG. 1) are 
high. 
Further to fractures, relative movement between steel wires causes case 
hardening due to wire pressure and the wear process. The notching effect 
at cross points materially weakens steel wire, which in turn, causes case 
hardening, fatigue and fractures. 
This lack of suitability of steel wire for use in cable should be 
understood as being very high even after many years of development, and in 
fact, the common practice of its use is also expensive. To summarize, it 
has high elastic and frictional resistance, and having low elastic 
compliance, requires a large number of wires to be sufficiently flexible 
wherein internal stresses, fatigue and wear are high regardless, and 
further requires a high D/d ratio to moderate severe bend stresses. Bend 
fatigue with resulting fractures is then characteristic of materials 
handling systems while being contributed to by high surface contact stress 
(.sigma.c), wire pressure (p) and local internal stresses, all 
persistently causing damage while work is being performed, and costly in 
downtime, maintenance and replacement (FIG. 1). 
Al and ti qualify as future, commonly used materials for structural wire 
and cable since a few non-frangible alloys have been produced from each 
metal, while each have high dynamic properties including hard spring as 
noted above, wherein al dynamic properties are superior to ti, whereas ti 
alloys have superior strength to weight ratios and other useful physical 
attributes. Of course, al has already become commonly used as electrical 
wire having a proven conductive capacity on the order of 60 to 64 percent 
that of copper. Neither copper nor steel qualify because of low dynamic 
properties wherein any non-frangible characteristic can not overcome 
stiffness, non-compliance and high tension peaks in performing work 
required by materials handling systems, wherein fracturing flaws are 
dominant. 
Comparison of a frangible and a non-frangible ti base alloy, 
Ti--13V--11Cr--3Al and Ti--6Al--4V, respectively, is of interest in the 
presentation of a detailed description of the invention, hereinbelow, from 
the beginning to the final stage in which the complex, axially symmetric 
cable structure is tested for its "flaw-state"; no fractures occur in the 
"non-frangible" cable in carefully designed cycle testing, the cable test 
specimens persistently modeling "non-fracture" behavior in the presence of 
other minor flaws, but completely without wire fractures. 
First Stage -- Alloy test specimens in laboratory testing 
(a) Brittle-ductile transition. 
Ti--13V--11Cr--3Al -- does not transition from plane strain to plain stress 
and develops unstable fracture extension at elastic stress bends 
Ti--6Al--4V -- transitions from plane strain to plain stress into a high 
energy region 
(b) Fracture extension resistance (R) 
Ti--13V--11Cr--3Al has shown low energy capacity to resist fracture 
extension with unstable extension 
Ti--6Al--4V--Plots at a "high rise" point on the fracture resistance curve 
(developed from data bank) for ductile metals 
(c) Drop tear energy 
Ti--13V--11Cr--3Al is not suited to this test because of its brittle, 
unstable fracture characteristic 
Ti--6Al--4V in a rolled condition having elongation of 18% contains 3050 
ft. lbs energy, the highest energy among the ti base non-frangible alloys 
Second Stage -- wire testing at 0.030" wire size 
(a) Tensile test (ten (10) specimens) 
Ti--13V-11Cr-3Al--248 KPSI 
Ti--6Al-4V--199 KPSI 
(b) Torsional test (ten (10) specimens) 
Ti--13V--11Cr--3Al--8 turns 
Ti--6Al--4V--86 turns 
Note: 
(1) 86 turns is greater than 96 to 105 turns for 0.030" low carbon steel 
wire compared on a strength to weight ratio basis 
(2) Fracture-toughness is generally known to be inversely proportional to 
tensile strength 
Third stage -- Low and high stress regions 
A. Cycle testing in the lower stress region to determine "flaw state" of 
1/4 aircraft control cable for Ti-13V- 11Cr-3A1, Ti-6A1-4V and corrosion 
resistant steel. A D/d ratio of 32 was used. In addition to 150 lb 
tension, a normal load for aircraft control cable, this tension provided a 
long period of cycling to test all physical flaws of the complex 
structure; this long period provided for accumulation of bend (.sigma.b) 
and impact stresses (.sigma.i) together with a low level of surface 
contact stress (.sigma.c) in pulley grooves. Two (2) cable constructions 
7.times.7 and 7.times.19 were used. Steel a/c primary control cable is not 
normally used in the 7.times.7 construction greater than a diameter of 
3/32" because of low elasticity and high stiffness. 
(a) Ti-13V-11Cr-3Al 
1/4 7.times.19 cable -- At 850,000 cycles numerous wire fractures had 
developed, these starting at 750,000. These fractures occurred in bending 
regions and at regions near the end terminals close to the two points of 
impact, in about equal numbers, showing each of these low order stresses 
eventually in this lengthy test had caused local fractures in this brittle 
alloy. However wire wear was very minor showing high abrasion resistance, 
this not being a factor in the fractures. At the conclusion, fractures 
were rapidly increasing. 
(b) Ti-6A1-4V 
First test -- 1/4" 7.times.19 cable was showing excellent results when the 
machine failed at 970,000 cycles. No wire fractures had occurred and wire 
wear was again, in the longer test period, inconsequential on all 133 
wires. 
Second test -- 1/4" 7.times.7 improved cable (49 larger wires) coated with 
solid film lubricant, was continued for 1.5 million cycles (3M reversals) 
without any wire fractures showing that the accumulation of characteristic 
stresses, as induced at bend and impact points had little effect. Wire 
wear again was unmeasurable but wire crowns were bright showing the solid 
film lubricant had been worn through. 
Third test is a load deflection test of two (2) specimens of this improved 
1/4" 7.times.7, thin solid film coated, ti cable. Load deflection diagrams 
were made as shown in FIG. 4(a) and (b). It should be noted these diagrams 
are remarkably identical in load (.sigma.) and strain (.epsilon.), except 
three (3) strands remained unfractured in one, FIG. 4a, whereas 4 strands 
remained unbroken in FIG. 4b, it being surprising that all strands were 
not catastrophically fractured, as occurs in tests of small diam steel 
cable. Also variability in properties had been reduced such as tensile and 
torsional strength, and ductility had been increased in the wire drawing 
process so that wire elongation exceeded fifteen (15) percent. In changing 
from 1/4" 7.times.19 steel cable to 1/4" 7.times.7 Ti-6Al -4V cable, 
efficiency 
##EQU1## 
increased from 80% (CRS) to 92% (Ti-6Al-4V). Moreover, cable breaking 
strength of the first 1/4" 7.times.19 Ti-6Al-4V cable, of five (5) highly 
variable specimens averaged 3750 lbs., compared to 5250 lbs for Ti-6Al-4V 
7.times.7 cable, an increase of forty (40) percent, after variability in 
ductility, uniformity in diameter and hardness were materially reduced. 
(c) Corrosion resistant steel 1/4" 7.times.19 cable was in condition to 
fail catastrophically under 150 lbs tension at less than 1/2 million 
cycles and wire fractures began at 375,000 cycles. Wire crown abrasion was 
sufficiently severe to cause a few fractures as did bend and impact 
stresses, and wire casehardening. It was obvious impacts at each reversal 
were far more severe than the titanium impacts due to the higher noise 
level of the former. 
These tests showed the: 
(1) marked superiority of ti cable, especially the non-frangible Ti-6Al-4V 
(2) non-frangible wire prevented fractures 
(3) fewer cable wires are required when having compliant wire, low density 
and high dynamic properties 
(4) the effect of frangibility and other physical properties upon flaw 
states, and 
(5) the influence of design criteria in complex cable structures in the 
lower stress region. 
B. Cycle test loading in the high stress region, ranged from one-fifth 
(1/5) to one-half (1/2) breaking strength of 1/4" 7.times.19 cable 
assembled from non-frangible Ti-6Al-4V ductile wire having an average 
elongation of fifteen (15) percent. Cycle life was found to be a function 
mainly of two (2) factors, (1) loading and (2) lubrication. At 1/5 
breaking strength (lubricated), cycle life was greatest at 430 K cycles, 
and quite low at 1/2 breaking strength, (lubricated), cycle life being 10 
K cycles. Cycle life was about one-seventh (1/7) with no lubrication 
compared to lubrication at the same loading (1/5). Wire wear was greatest 
on inner wires, especially the core strand. This wear proved to be about 
ten (10) percent at 1/5 loading, and as much as 40-50 percent at 1/3 
loading. Wire fractures found, in a total of eight (8) specimens, to be 
greatest in cores due to a combination of wear, wire pressure & dynamic 
stress. Very few outer strand wires fractured and none fractured due to 
abrasion in pulley grooves. It should now be noted that liquid lubrication 
was used, while effective, was not as effective internally where the 
fractures and greater wear occurred due to being squeezed out under wire 
pressure. Solid film lubrication was concluded to be much more effective, 
when later used, and equally effective in the cable crosssection. 
These conclusions were reached concerning flaw state and fail-safe design: 
(a) The crucial flaw of wire fracture was prevented at one-fifth (1/5) load 
through a long period of work performance and would be substantially 
extended by solid film lubrication to neutralize or reduce wear 
(b) Enlarged core designs would reduce severe core strand wear 
(c) All wire fractures were accompanied by a marked reduction in tensile 
strength due to wear which then caused wire overloading at high stress 
levels, clearly noted in the specimens loaded at one-third and one-half 
breaking strengths 
(d) Greater latitude in applying design criteria improves the fail-safe 
design, and prevents and defers wire fractures in non-frangible wire 
(e) In the high stress region, the combination of (1) unsatisfactory 
lubrication, (2) high primary load (3) high dynamic stresses and (4) wire 
wear caused wire fractures, at 1/2 breaking strength load, wherein wear 
and variability in wire cross sections reduced tensile strength 
(f) Neither wire case hardening nor strain-hardening caused wire fractures 
as occurs in steel wire. 
It will now be understood a process has been developed for changing the 
cable flaw state by analysis of the model behavior of test specimens in 
the three testing stages from metal specimens to complex cable structures, 
which advances cable technology as follows: 
(a) fail-safe cable structures may be designed 
(b) wire fractures as a crucial flaw may now be eliminated 
(c) other flaws such as wear, abrasion, and fatigue may be moderated by 
assessing interactions and advanced cable designs may now be developed 
(d) changing design criteria so as to embody wider criterion latitude and 
improved trade-offs in making fail-safe designs 
Synthesis of the four (4) factors, herein described, provides for 
eliminating wire fractures and the embodiment of superior performance and 
service characteristics. 
Non-frangible al alloys, in the same qualifying manner as outlined for 
testing ti base alloys through three (3) test stages, are suitable for 
work performing cable in both axially symmetric and contrahelical 
constructions. It should be observed that al conductor wire has reached a 
sophisticated and widely accepted state of development, again suitable for 
replacing copper conductor wire on a lower cost basis and at a lower level 
of effectiveness, about 60-64%. 
Structural al wire, however, is of a different character wherein superior 
dynamic properties including medium hard spring may be exploited, as a 
trade off, against the outstanding high strength to weight ratio of ti 
base alloys. 
As a further al attribute, electromechanical cable may be constructed to 
have homogeneous armor and electrical core characteristics, including 
dynamic properties, wherein the mechanical compliance characteristics for 
stored energy would be in concert with the metallurgical relative ductile 
characteristics for absorbing energy to determine how the structure will 
respond to loading in the presence of flaws. Medium hard wire spring would 
be reasonably effective in dissipating energy, and by wide amplitude 
stress vibration, stress propagation and distribution in compliant al 
cables would compare with this same force characteristic in titanium 
cable. The entire complex cross section would function as a tension member 
structural unit, wherein the essence of fail-safe design is the assessment 
of these two (2) interactions. 
Al is our most versatile metal being easily and most economically 
susceptible to all commonly used fabrication processes and techniques, 
including coating for protection. Al wire has been assembled into 
structural cable for static, rigid applications. As noted al also has many 
attributes as does ti. The greatest structural divergence has generally 
been, within the complete range of alloys of both metals, is the lower 
strength-to-weight ratio, together with lower tensile strength of al base 
metal. However the range in al alloy tensile strength is wide, there being 
several accepted alloys just under 100,000 p.s.i. 
Alloying practice is gradually increasing al tensile strength so that it 
may be expected state of the art development should bring tensile strength 
to become considerably greater than at present within two (2) to five (5) 
years in view of very wide commercial usage. Principal elements alloyed 
with al are: 
Copper for improving properties in heat treated conditions 
Manganese for general purposes and improving metal working 
Silicon lowers the melting point without increasing brittleness so that it 
is used in welding wire 
Magnesium produces high strength 
Zinc produces high strength, heat treatable alloys 
In the several categories of alloys it is commonly found that at least one 
alloy will have high tensile strength, low gap between yield and ultimate 
strengths, high elongation and some will have high hardness, while all 
embody superior dynamic properties. Within this large number of alloys, a 
few are non-frangible. 
It should be clear that, for both ti and al base alloys, the superior 
non-frangible alloy should be selected for cable constructions in order to 
produce the maximum effect upon cable flaw-state and fail-safe cable 
design. It was demonstrated in the cable model test (1) for load in the 
high stress region, that wire fractures were prevented until wire wear 
conditions reached a critical point that loading plus dynamic stress 
exceeded breaking strength, and (2), for load in the low stress region 
wherein no flaws developed, especially including fractures and wear so 
that appreciable strength was not lost although wire crown abrasion had 
started. This third stage testing also showed that a (1) fewer number of 
wires could be used to reduce wear and internal stresses, and (2) cable 
efficiency was increased (FIG. 4). Thus the "flaw state" of 1/4" axially 
symmetric cable has been changed and improved, in performing work, by use 
of non-frangible wire having high dynamic properties. At the same time 
"fail-safe" design has been improved and advanced. 
The crucial flaw, wire fractures in cable structures (as well as 
overstressing components) has been overcome and prevented by the novel 
synthesis of four (4) basic factors, as outlined, wherein cable 
"flaw-state" is now reduced to minor flaws which have also been moderated 
in the invention. 
It has now been disclosed that non-frangible wire, together with high 
dynamic properties of al and ti base alloys, when assembled into cable 
improves the "flaw state" and "fail safe" design of work performing cable, 
and eliminates wire fractures as the "crucial flaw" of this cable during 
its service life. Wire fractures will not occur in the lower stress 
region, nor even in the higher stress region until cable breaking strength 
has been reduced at least by twenty-five (25) percent of its nominal 
rating, wherein the weakness caused by mild wear dominates the "flaw 
state." 
These novel test findings upset the high tensile strength approach with 
high factors of safety of massive steel cable constructions in the old 
manner, wherein very redundant breaking strength, accompanied by 
stiffness, wire fractures and dynamic overstressing create early crucial 
flaws which undermine the fail-safe tension system design. The dominance 
of high tensile strength has also been upset in that it is shown to be 
relatively ineffective in classical dynamic states of tension systems for 
performing work. 
The invention and its attendant advantages will be understood from the 
foregoing description and it will be apparent that various changes may be 
made in the form, construction and arrangement of the parts of the 
invention without departing from the spirit and scope thereof and without 
sacrificing its material advantages, the arrangement hereinbefore 
described being by way of example; and I do not wish to be restricted to 
the specific form described, or uses mentioned, except as defined in the 
accompanying claims, wherein various portions have been separated for 
clarity of reading and not for emphasis.